A lot has been made of not exceeding Rear Axle Load.
I am seeking information on this topic
Firstly what are the mechanical & perhaps safety consequences of exceeding Rear Axle Load?
Perhaps what I am really after ... What determines Rear Axle load rating?
eg .. Wheel bearing construction? - spring assembly limitations? - Wheel & tyre limitations? - chassis construction?
Lastly Is there anything that can be done to raise Rear Axle Load rating?
montie said
10:32 AM May 28, 2022
The lowest denominator determines the rating......that could be tyres, springs, bearings etc., The rating is set by the tug manufacturer's engineers and the sum of your axle ratings usually exceed the GVM. As for an upgrade, I have never heard of it being done on a one out basis. A GVM upgrade raises the ratings but I would suggest you talk to somebody more qualified than me on the subject.
-- Edited by montie on Saturday 28th of May 2022 10:36:20 AM
Cupie said
11:10 AM May 28, 2022
Montie Thanks for that.
As I expected, the manufactures' engineers have some sort of black magic formulae, kept secret from we the great unwashed. Cynical me!
yobarr said
11:20 AM May 28, 2022
Cupie wrote:
A lot has been made of not exceeding Rear Axle Load.
I am seeking information on this topic
Firstly what are the mechanical & perhaps safety consequences of exceeding Rear Axle Load?
Perhaps what I am really after ... What determines Rear Axle load rating?
eg .. Wheel bearing construction? - spring assembly limitations? - Wheel & tyre limitations? - chassis construction?
Lastly Is there anything that can be done to raise Rear Axle Load rating?
Hi Cupie. Although I know that you live in Brisbane I've forgotten what model your car is. Long story short, Carroll Springs in Wacol can increase rear axle capacity on certain models at a price that is a lot lower than the over-the-top rates charged by some of the well known suppliers. Contact is/was Doug Butler. Happy to offer more help if you wish. Cheers
Cupie said
08:44 PM May 28, 2022
Thanks for the offer, but I am only seeking understanding. I have no problems with my 1996 4.2EFI GQ Patrol.
shakey55 said
07:48 AM Jul 9, 2022
Cupie wrote:
Thanks for the offer, but I am only seeking understanding. I have no problems with my 1996 4.2EFI GQ Patrol.
I needed a GVM upgrade for my 2005 4.2TD wagon. Took GVM from 3080 to 3505. I was shocked when I put truck over weigh bridge.
Not cheap - in excess of $5000, but now confident I can attach caravan, add a little cargo and be satisfied that if I was to have a dingle insurance would cover me.
(Also had ATM upgrade to 2011 New Age Big Red 19)
-- Edited by shakey55 on Saturday 9th of July 2022 07:49:38 AM
Ivan 01 said
08:56 AM Jul 9, 2022
The most common manufacturer upgrade in rear axle weight capacity occurs on some of the more modern variations of the large American utes.
They tend to convert the housing to dual wheels and quite often a heavier design of outer bearings.
The old model designation was a little clue with Fords
F100 was rated at 1 tonne F150 was 1.5 tonne then you got into the F250s which could be either single or dual wheel rear with different ratings in the USA.
This may or may not have applied in our country.
For example, with the well reported new Dodge Ram or just Ram as it is now known,it could probably be easily upgraded with a wheel and tyre modification or to really push it they might even have available a heavier rear axle option that might fit. In the USA they have gear that we might only dream about when our wallet is so full it becomes painful.
In the USA they dont muck around with this sort of modification because you would just by a Ram 250 for example or the next model up the weight tree.
With the correct engineering certificate and a pocket full of folding stuff almost anything is possible.
In days gone by we had in Aus a plethora of F100 fords which consisted of differing mechanical components.
Some people used to think they were indestructible and quit often would overload the rear axle.
As a result the rear axle housing would fail, generally around the area where the axle tube joined the centre housing,
I have seen all types of abominations of bits of steel welded along the axle tubes and various other add ons to support the weak structure of the tube.
Of course the axle tubes were fine if you only loaded to the specified weight and if you were tempting an overload then drive very carefully on our less than adequate roads if we compare our road infrastructure to the USA.
Many F 100s had heavier diffs and springs etc fitted for what we might call off highway work. Some fire authorities used those utes with some modifications as well for extra weight, I believe.
With many of our mid size utes and SUV wagons the weight restriction is for the reason of vehicle stability rather than the axle housing snapping in half.
We see this when the vehicle modification companies upgrade springs and shock absorbers to gain an upgrade.
The argument would be that the handbook of vehicle specifications states the rear axle load as standard and this will be the base of the argument of the modification that doesnt give you any increase,
I dont want to get into an argument as when towing a conventional caravan the ball weight specification of the vehicle comes very importantly into play.
If we look at the vehicle modification without considering towing then the popular SUV once modified can carry the mining personnel in the back and still have the bars and spare wheel etc and can and does comply with the law and with insurance company requirements.
I dont think welding a couple of pieces of heavy angle iron along the diff axle tubes will pass the test today. Having said that I have read adverts somewhere where companies do build or supply heavier housings for special purposes.
I have seen claims of some of the rear track widening kits for the very off road and industrial farmers and mining utes, do increase the load capability. Again this modification is sought after by the likes of some fire authorities when using these vehicles for off road fire control.
Montie has covered how these figures and specifications are met but with the correct engineering there are lots more possibilities.
A great example of this comes from the Street Rod fraternity who can build and have registered almost anything BUT, these car builders and their cars modifications must pass the scrutiny of engineers qualified to assess these vehicles.
I hope this covers it Cupie
Cupie said
11:18 AM Jul 9, 2022
Thanks all for your replies & expertise.
As I previously indicated, I have no need/desire to increase Axel load rating for my ageing tug. It has 288,000km travelled, around 95% towing the van, all on bitumen.
It is extremely difficult to get the numbers for a 1996 GQ TB42 efi (Petrol) Patrol. It seems that according to several sources that it has a higher tow capacity than the TD42 GQ (2.8t v 2.5t). In any case my Jayco is comfortably under both but it has a high towball weight of 271kg (hitch capacity 350kg - perhaps due to in part to the gas bottles on the A frame & a front boot as well as a front kitchen) & ATM 2334. Haven't bothered to measure the rear axel weight as I have no reference figure.
BTW .. I have had continuing problems with my passenger side rear axel bearing weeping. I have had various 'experts' look at it over the years including both inner & outer seals replaced several times & the bearing replaced on two occasions .. the bearing is destroyed in getting to the outer seal. The latest try seems to have fixed it.
The latest Patrol specialist diagnosed it as having had the axel 'skimmed' to just below specifications (I think that this happened when it was first looked at, at 80,000km). The solution was to install a selected second hand axel, bearing etc. and grease the sealed bearing using a special needle nib on the grease gun. No sign of a weep after 15,000km.
I did from time to time wonder if the cause was an overloaded rear axel.
Once again, thanks for your input.
Ivan 01 said
11:32 AM Jul 9, 2022
Cupie wrote:
Thanks all for your replies & expertise.
As I previously indicated, I have no need/desire to increase Axel load rating for my ageing tug. It has 288,000km travelled, around 95% towing the van, all on bitumen.
It is extremely difficult to get the numbers for a 1996 GQ TB42 efi (Petrol) Patrol. It seems that according to several sources that it has a higher tow capacity than the TD42 GQ (2.8t v 2.5t). In any case my Jayco is comfortably under both but it has a high towball weight of 271kg (hitch capacity 350kg - perhaps due to in part to the gas bottles on the A frame & a front boot as well as a front kitchen) & ATM 2334. Haven't bothered to measure the rear axel weight as I have no reference figure.
BTW .. I have had continuing problems with my passenger side rear axel bearing weeping. I have had various 'experts' look at it over the years including both inner & outer seals replaced several times & the bearing replaced on two occasions .. the bearing is destroyed in getting to the outer seal. The latest try seems to have fixed it.
The latest Patrol specialist diagnosed it as having had the axel 'skimmed' to just below specifications (I think that this happened when it was first looked at, at 80,000km). The solution was to install a selected second hand axel, bearing etc. and grease the sealed bearing using a special needle nib on the grease gun. No sign of a weep after 15,000km.
I did from time to time wonder if the cause was an overloaded rear axel.
Once again, thanks for your input.
If we knew your problem was a leaking axle seal then someone may have suggested a *speedy sleeve*.
The left hand side often is the axle that leaks first because it is in a lower position due to the camber of the road.
Sometimes just lowering the oil level in the diff by a tiny bit will fix it.
Many servicemen fill the diff and then it becomes a contest to get the level plug back in before the oil has actually found its true level thus resulting in a slightly overfill.
Leaking sealed bearings are usually the cause of the Chinese factory where they are made.
Also heat can damage the seal in a sealed bearing.
Heat may be generated with something as simple as a dragging brake or it may be a symptom or overloading or high loading of the rear axle.
The weight will transfer a larger proportion of itself to the left hub due to the roads camber again generating more heat in that bearing,
You seem to be on top of it and that is a good thing.
yobarr said
03:58 AM Jul 17, 2022
Cupie wrote:
Thanks all for your replies & expertise.
As I previously indicated, I have no need/desire to increase Axel load rating for my ageing tug. It has 288,000km travelled, around 95% towing the van, all on bitumen.
It is extremely difficult to get the numbers for a 1996 GQ TB42 efi (Petrol) Patrol. It seems that according to several sources that it has a higher tow capacity than the TD42 GQ (2.8t v 2.5t). In any case my Jayco is comfortably under both but it has a high towball weight of 271kg (hitch capacity 350kg - perhaps due to in part to the gas bottles on the A frame & a front boot as well as a front kitchen) & ATM 2334. Haven't bothered to measure the rear axle weight as I have no reference figure.
Hi Cupie. Rear axle capacity is 1800kg for your car. Your 271kg ball weight will put around 400kg onto your car's rear axle. Cheers
Cupie said
09:56 AM Jul 17, 2022
Chris ..Thanks for that.
Where do you get your figures from?
Some time back I did lots of searching with no success.
What are the factors that cause a 271kg ball weight result in 400g on the rear axel?
I assume it is something related to 'lever action' & distance from ball to 'fulcrum point' of rear axel.
BTW, I have always used a HR WDH that has the effect of correcting the rear end sag when the van is connected. It was fitted by the people that purchased the van from.
cheers
Are We Lost said
12:04 PM Jul 17, 2022
I think Yobarr just uses approximations based on experience. To accurately calculate what load the van adds to the rear axle load you need three things:
TBL = Towball load WB = Wheelbase (use mm for accuracy) OVH = Towball overhang (distance from rear axle to towball)
Rear axle load added by van = TBL x (WB + OVH) / WB
For your Patrol, I found a figure of 2970 for wheelbase. You will need to measure your towball overhang. I did a calculation and tried a few different figures to arrive at Yobarr's estimate of 400kg. I suspect that may be close enough, but marginally overstated because it would mean a towball overhang of 1420mm. I thought the Patrol would be less than that. Anyway, using that hypothetical figure here is the calculation:
Rear axle load (400) = 271 x (2970 + 1420) / 2970
If you change OVH to 1200mm it comes out to 380kg, so not a huge difference.
Because this only looks at the difference when connecting the van, not the actual axle load, the formula works regardless of how your load is distributed in the tow vehicle. To deternine how much weight is lifted off the front wheels, just subtract the towball weight from the rear axle loading calculation ... in your case it works out to 110-130kg.
-- Edited by Are We Lost on Sunday 17th of July 2022 12:11:53 PM
Cupie said
12:29 PM Jul 17, 2022
Thanks Stephen..
Mike Harding said
12:59 PM Jul 17, 2022
Are We Lost:
Excellent explanation, thank you, it accords with how I thought it all worked.
Next: would you to care to explain weight distribution hitches in words of one syllable for mechanically challenged electronics engineers? :)
Ivan 01 said
01:29 PM Jul 17, 2022
Easy to demonstrate on a weigh bridge.
Compare connected and disconnected axle weights with the WDH on the same vehicle.
Mike Harding said
02:03 PM Jul 17, 2022
Ivan 01 wrote:
Easy to demonstrate on a weigh bridge.
But can you explain it without the aid of a weighbridge?
Cupie said
02:31 PM Jul 17, 2022
Are We Lost wrote:
I think Yobarr just uses approximations based on experience. To accurately calculate what load the van adds to the rear axle load you need three things:
TBL = Towball load WB = Wheelbase (use mm for accuracy) OVH = Towball overhang (distance from rear axle to towball)
Rear axle load added by van = TBL x (WB + OVH) / WB
For your Patrol, I found a figure of 2970 for wheelbase. You will need to measure your towball overhang. I did a calculation and tried a few different figures to arrive at Yobarr's estimate of 400kg. I suspect that may be close enough, but marginally overstated because it would mean a towball overhang of 1420mm. I thought the Patrol would be less than that. Anyway, using that hypothetical figure here is the calculation:
Rear axle load (400) = 271 x (2970 + 1420) / 2970
If you change OVH to 1200mm it comes out to 380kg, so not a huge difference.
Because this only looks at the difference when connecting the van, not the actual axle load, the formula works regardless of how your load is distributed in the tow vehicle. To determine how much weight is lifted off the front wheels, just subtract the towball weight from the rear axle loading calculation ... in your case it works out to 110-130kg.
-- Edited by Are We Lost on Sunday 17th of July 2022 12:11:53 PM
Just measured the OVH and it is 1200
Thanks again to all.
-- Edited by Cupie on Sunday 17th of July 2022 02:32:21 PM
yobarr said
03:10 PM Jul 17, 2022
Mike Harding wrote:
Are We Lost:
Excellent explanation, thank you, it accords with how I thought it all worked.
Next: would you to care to explain weight distribution hitches in words of one syllable for mechanically challenged electronics engineers? :)
Certainly I will explain, Mike! First I would like to thank Stephen for explaining my figures for Cupie. Now, a WDH increases TBO (towball overhang, or distance from rear axle to hitchpoint) thus increasing the extra load applied to the car's rear axle by towball weight. Obviously more weight is removed from the car's front axle and transferred to the car's rear axle. Because the TBO is increased the effects of YAW also are increased, meaning it is easier to have the "Tail wagging the Dog" which is the biggest cause of caravans going RSup. When a van starts flicking from side to side it is actually travelling faster than the car and trying to overtake! Physics that few understand. A WDH also increases the weight on a van's wheels (GTM) which can result in the van's ATM being exceeded because a WDH DOES NOT change towball weight EVER. Another negative for a WDH is that it is even MORE weight hanging off the end of your towbar shank so that as well as increasing TBO it is increasing the weight on the car's rear axle before you even hook-up the van! SO we've got the weight of the actual WDH which can be way more than 20kg with bars, chains and tensioners, plus extra weight caused by extra TBO, maybe 30kg, for a total of 50kg(+/-) EXTRA weight on car's rear axle. A McHitch increases TBO even more, increasing the weight transfer. Then you tension the cure-it-all WDH to transfer some weight from the car's rear axle back onto the car's front axle, and some weight onto the van's axle group. Using Stephen's example, you will have taken 110-130kg off the car's front axle when you applied the van's towball weight to the car. The more you tension the WDH the greater are the risks of oversteer in the car, which is not much fun with a van in tow! When all calculations are done you're messing around with less than 100kg and if that relatively insignificant weight is the difference between being safe and being unsafe then there is something wrong with the whole setup. VERY few people understand the workings of a WDH, but if they did they would understand that it is not the universal cure-it-all that many people conside it to be. Many times I have written that a WDH is used only by those who are trying to make a car do things for which it was not designed. Get a smaller van or a more suitable car, and make sure that ALWAYS the weight on the wheels of the car is at least 10% more than the weight on the wheels of the van. Happy travels! Cheers
Some time back I did lots of searching with no success.
What are the factors that cause a 271kg ball weight result in 400g on the rear axel?
I assume it is something related to 'lever action' & distance from ball to 'fulcrum point' of rear axel.
BTW, I have always used a HR WDH that has the effect of correcting the rear end sag when the van is connected. It was fitted by the people that purchased the van from.
cheers
Hi Cupie. The axle ratings are among my records, and as Stephen suggested, the 400kg added to your rear axle was simply an estimate, intended to illustrate a point. There is actually one greatly over rated vehicle that has TBO of better than 50% so a 350kg towball weight puts over 520kg onto its lightweight rear axle, but we won't go there! Cheers
Ivan 01 said
03:29 PM Jul 17, 2022
Mike Harding wrote:
Ivan 01 wrote:
Easy to demonstrate on a weigh bridge.
But can you explain it without the aid of a weighbridge?
Without complicating the procedure if a vehicle and a pig trailer are connected together at a hitch with a tow ball then the weight of the trailer portion of the tow ball weight is applied as an increase to the towing vehicles weight.
This increased mass is applied to the rear of the vehicle via the tow bar which means that extra weight is carried onto the road via the rear axle ( wheels and tyres)
When a WDH is installed correctly the torsion affect of the bars provide a more rigid transfer of this extra weight along the length of the combination of vehicle and trailer.
This weight transfer results in a slight increase in the weight on the front axle of the tow vehicle and again a slight increase on the axle or axles of the pig trailer while at the same time removing that weight by the sum of the increase of the steer and trailer axles from the rear axle of the tow vehicle.
I dont intend to go any further into the whys and why nots if we should use one. They are recommended for some vehicles when towing and some manufacturer's suggest that they arent to be used which is generally dependent on the vehicles construction.
So,
How was that Mike.?
Mike Harding said
04:21 PM Jul 17, 2022
Ivan 01 wrote:
How was that Mike.?
Poor, no better than Yobarr's - I don't think either of you properly understand what's happening with a weight distribution hitch.
>provide a more rigid transfer of this extra weight
Whatever is "a more rigid transfer" of weight? and what units is it measured in?!
Is there a proper mechanical engineer in the house?
Ivan 01 said
04:40 PM Jul 17, 2022
Mike Harding wrote:
Ivan 01 wrote:
How was that Mike.?
Poor, no better than Yobarr's - I don't think either of you properly understand what's happening with a weight distribution hitch.
>provide a more rigid transfer of this extra weight
Whatever is "a more rigid transfer" of weight? and what units is it measured in?!
Is there a proper mechanical engineer in the house?
I made no claim of being a proper or an improper mechanical engineer myself but I am happy to take on board any detailed description from a qualified person if we have one.
It is difficult to explain a rigid transfer of weight but I am sure there will be a technical term for it.
Oh just one thing Mike, I fully understand what happens with a WDH. No one has to be a Mechanical Engineer to know how they work.
In hindsight I should have said *no* to your question, had I known you were looking for a description from a proper Engineer I would have.
Mike Harding said
04:56 PM Jul 17, 2022
Ivan 01 wrote:
Oh just one thing Mike, I fully understand what happens with a WDH. No one has to be a Mechanical Engineer to know how they work.
Ivan: there is a very, very old adage in engineering and it is:
If you can't explain it then you don't understand it.
yobarr said
05:12 PM Jul 17, 2022
A WDH applies what is effectively a solid bar, or stiffarm, from the front axle of the car, through the hitch point, to the axle group of the caravan. This means that as a car and van are driven through a table drain, for example, almost all weight is carried at only two points. Can you imagine the stresses on the chassis and drawbar when this happens. Wound up to extremes a WDH can keep the rear wheels of the car suspended in mid- air. WDHs are used only by people who are trying to make a car do things for which it never was designed, and a WDH can cause more problems than it 'solves'. Get a smaller van or a better car. This has all been explained many, many times before, in great detail, and help can be found if the 'search' function is used. Cheers
yobarr said
05:38 PM Jul 17, 2022
Mike Harding wrote:
Ivan 01 wrote:
Oh just one thing Mike, I fully understand what happens with a WDH. No one has to be a Mechanical Engineer to know how they work.
Ivan: there is a very, very old adage in engineering and it is:
If you can't explain it then you don't understand it.
The problem we have, Mike, is that trying to explain it in a way that most readers can understand is an impossibility. Different levels of comprehension by readers, along with very little understanding of basic physics by some, make the task very difficult, which is why I have to generalise. When I first joined the forum and posted that a WDH increased a van's weight I was criticised and shouted down left, right and centre by many 'senior' members, but I stuck to my guns and continued explaining, on a regular basis, how a WDH actually does work until now it is generally understood that a WDH takes weight off the rear axle (NOT the towball) and puts some of that weight back onto the car's front axle, from where it came, and also it puts some weight onto the van's axle group, thus increasing the weight of the van. Total weight of car has decreased, Total weight of van has increased, Total weight (GCM if you like) stays the same. Believe me, I can sit here for hours and explain in great detail how a WDH works, but unless the reader actually WANTS to learn, rather than argue, I'm wasting my time. However, rote learning does seem to work eventually. Slowly but surely many members are realising that, with weights, I know what I'm talking about, but because of continual interference by others who who know little, understand less, and have no interest in learning, several members have chosen to contact me by PM to get help with their weights. Indeed, I have also visited them to help. Cheers
-- Edited by yobarr on Sunday 17th of July 2022 05:41:02 PM
Ivan 01 said
05:50 PM Jul 17, 2022
Mike Harding wrote:
Ivan 01 wrote:
Oh just one thing Mike, I fully understand what happens with a WDH. No one has to be a Mechanical Engineer to know how they work.
Ivan: there is a very, very old adage in engineering and it is:
If you can't explain it then you don't understand it.
Well it will be interesting next time someone might offer help with a fridge problem. Where is a refrigeration engineer when you need one.
Do we wait until our mechanical engineer comes on to help someone with a wheel alignment problem or will a mechanic suffice.
I have worked along side quite a few mechanical and civil engineers during my career and I have never heard that said however I take it on board.
I will wait to hear the explanation from a mechanical engineer if only to check myself on knowing how a WDH works.
I wonder if someone who has the title of associate (degree or Diploma) of mechanical engineers will qualify to explain.
-- Edited by Ivan 01 on Sunday 17th of July 2022 05:53:37 PM
-- Edited by Ivan 01 on Sunday 17th of July 2022 06:10:45 PM
yobarr said
06:48 PM Jul 17, 2022
Ivan 01 wrote:
Mike Harding wrote:
Ivan 01 wrote:
Oh just one thing Mike, I fully understand what happens with a WDH. No one has to be a Mechanical Engineer to know how they work.
Ivan: there is a very, very old adage in engineering and it is:
If you can't explain it then you don't understand it.
Well it will be interesting next time someone might offer help with a fridge problem. Where is a refrigeration engineer when you need one.
Do we wait until our mechanical engineer comes on to help someone with a wheel alignment problem or will a mechanic suffice.
I have worked along side quite a few mechanical and civil engineers during my career and I have never heard that said however I take it on board.
I will wait to hear the explanation from a mechanical engineer if only to check myself on knowing how a WDH works.
I wonder if someone who has the title of associate (degree or Diploma) of mechanical engineers will qualify to explain.
Hi Ivan. I'm surprised that after all the explanations that have been given regarding how a WDH works, along with actual weighbridge test results etc, you still seem hesitant to accept the simple facts. The fact that many retailers of these pieces of equipment have little idea dies not help. Perhaps you could Google "John Cadogan. How a WDH works" or similar and if, after watching the video you still do not understand there is little more that can be done to help you. John is, as explained in the video, an engineer with much experience. Cheers
P.S "Weight distribution and load levelling hitches for heavy towing" John Cadogan is the video you need to find!
If you're pressed for time the important stuff is between 13th and 14th minute and between 17th and 19th minute. He explains only the basics so as to make it as easy as possible for it to be understood by many.
-- Edited by yobarr on Sunday 17th of July 2022 07:36:27 PM
I have little time for Cadogan and I dont agree with your views on WDH use.
I will just leave it at that if that is OK with you.
Are We Lost said
01:38 AM Jul 18, 2022
I see there are a few posts with explanations on how a WDH works, and interspersed in those are the opinions on whether they are good or bad. But they are mostly on what they do, and not a lot on how, which is what Mike was asking. Like Ivan, I will skip the discussion on the pros and cons .... for now. But I have taken a different tack to the explanation method, and kept in mind Mike's request for simplicity. I hope I haven't gone too far.
But first, I believe that a sagging rear end is just an easy visual signal that something is wrong, and it is weight on the wheels that need attention. Its the weight that matters, not the level. But for simplicity I have focused mainly on levelling in this explanation. Also I have not tried to use the correct physics terminology ... weight, mass, torque, force, load. My high school physics is now forgotten.
Imagine you are standing at the back of your tow vehicle with van attached, looking at sagging rear end. One of these days you will do something about it. You happen to see a couple of bars made from spring steel lying there at the campsite.
Being a fit muscular fellow, you think one of these bars might come in handy for a workout. At the back of the car, you find there is a spot you can push it in from the rear and it seems to lock in place. It feels rock solid and has effectively become an extension of the car. Onto your workout, and with some effort lifting the bar you can see that the car body lifts up a bit at the rear and the whole rig becomes closer to level. If you had scales you would see the weight on the front wheels is now slightly more, and the weight on the back wheels is less.
Also, if you used a tape measure you would see that the end of the bar you are holding was raised more than the body of the car. Or to put it a different way, the leverage enabled you to lift the rear end further than if you had tried at the rear bumper. I will come back to this point.
You note that there is a bracket on the caravan drawbar you can attach this bar to. Being an innovative fellow, an idea starts to form in your mind. Maybe this will help with the levelling. So with a supreme effort you manage to lift the bar a little more and hook the end of it onto the bracket. While you are recovering, you check and notice that the sag has returned a bit, but not as much as before. Just for fun you stand on the drawbar and bounce a bit. You realise that it feels a lot firmer than you expected it to. It's a bit puzzling. The bar is still lifting up the back of the car, but the end of that bar is resting on the drawbar bracket and is pulling the drawbar down harder onto the towball.
Why does this work? Surely if the bar is lifting the rear end up, but that very same bar is pulling the drawbar down, they will cancel each other out and you will achieve nothing.
Well, its late now so I think I will call this the first instalment and write the rest in the morning. If someone wants to have a go, please do.
-- Edited by Are We Lost on Monday 18th of July 2022 01:58:52 AM
yobarr said
02:56 PM Jul 18, 2022
i
-- Edited by yobarr on Monday 18th of July 2022 03:10:09 PM
A lot has been made of not exceeding Rear Axle Load.
I am seeking information on this topic
Firstly what are the mechanical & perhaps safety consequences of exceeding Rear Axle Load?
Perhaps what I am really after ... What determines Rear Axle load rating?
eg .. Wheel bearing construction? - spring assembly limitations? - Wheel & tyre limitations? - chassis construction?
Lastly Is there anything that can be done to raise Rear Axle Load rating?
The lowest denominator determines the rating......that could be tyres, springs, bearings etc.,
The rating is set by the tug manufacturer's engineers and the sum of your axle ratings usually exceed the GVM.
As for an upgrade, I have never heard of it being done on a one out basis. A GVM upgrade raises the ratings but I would suggest you talk to somebody more qualified than me on the subject.
-- Edited by montie on Saturday 28th of May 2022 10:36:20 AM
Montie Thanks for that.
As I expected, the manufactures' engineers have some sort of black magic formulae, kept secret from we the great unwashed. Cynical me!
Hi Cupie. Although I know that you live in Brisbane I've forgotten what model your car is. Long story short, Carroll Springs in Wacol can increase rear axle capacity on certain models at a price that is a lot lower than the over-the-top rates charged by some of the well known suppliers. Contact is/was Doug Butler. Happy to offer more help if you wish. Cheers
Thanks for the offer, but I am only seeking understanding. I have no problems with my 1996 4.2EFI GQ Patrol.
I needed a GVM upgrade for my 2005 4.2TD wagon. Took GVM from 3080 to 3505. I was shocked when I put truck over weigh bridge.
Not cheap - in excess of $5000, but now confident I can attach caravan, add a little cargo and be satisfied that if I was to have a dingle insurance would cover me.
(Also had ATM upgrade to 2011 New Age Big Red 19)
-- Edited by shakey55 on Saturday 9th of July 2022 07:49:38 AM
They tend to convert the housing to dual wheels and quite often a heavier design of outer bearings.
The old model designation was a little clue with Fords
F100 was rated at 1 tonne F150 was 1.5 tonne then you got into the F250s which could be either single or dual wheel rear with different ratings in the USA.
This may or may not have applied in our country.
For example, with the well reported new Dodge Ram or just Ram as it is now known,it could probably be easily upgraded with a wheel and tyre modification or to really push it they might even have available a heavier rear axle option that might fit. In the USA they have gear that we might only dream about when our wallet is so full it becomes painful.
In the USA they dont muck around with this sort of modification because you would just by a Ram 250 for example or the next model up the weight tree.
With the correct engineering certificate and a pocket full of folding stuff almost anything is possible.
In days gone by we had in Aus a plethora of F100 fords which consisted of differing mechanical components.
Some people used to think they were indestructible and quit often would overload the rear axle.
As a result the rear axle housing would fail, generally around the area where the axle tube joined the centre housing,
I have seen all types of abominations of bits of steel welded along the axle tubes and various other add ons to support the weak structure of the tube.
Of course the axle tubes were fine if you only loaded to the specified weight and if you were tempting an overload then drive very carefully on our less than adequate roads if we compare our road infrastructure to the USA.
Many F 100s had heavier diffs and springs etc fitted for what we might call off highway work. Some fire authorities used those utes with some modifications as well for extra weight, I believe.
With many of our mid size utes and SUV wagons the weight restriction is for the reason of vehicle stability rather than the axle housing snapping in half.
We see this when the vehicle modification companies upgrade springs and shock absorbers to gain an upgrade.
The argument would be that the handbook of vehicle specifications states the rear axle load as standard and this will be the base of the argument of the modification that doesnt give you any increase,
I dont want to get into an argument as when towing a conventional caravan the ball weight specification of the vehicle comes very importantly into play.
If we look at the vehicle modification without considering towing then the popular SUV once modified can carry the mining personnel in the back and still have the bars and spare wheel etc and can and does comply with the law and with insurance company requirements.
I dont think welding a couple of pieces of heavy angle iron along the diff axle tubes will pass the test today. Having said that I have read adverts somewhere where companies do build or supply heavier housings for special purposes.
I have seen claims of some of the rear track widening kits for the very off road and industrial farmers and mining utes, do increase the load capability. Again this modification is sought after by the likes of some fire authorities when using these vehicles for off road fire control.
Montie has covered how these figures and specifications are met but with the correct engineering there are lots more possibilities.
A great example of this comes from the Street Rod fraternity who can build and have registered almost anything BUT, these car builders and their cars modifications must pass the scrutiny of engineers qualified to assess these vehicles.
I hope this covers it Cupie
Thanks all for your replies & expertise.
As I previously indicated, I have no need/desire to increase Axel load rating for my ageing tug. It has 288,000km travelled, around 95% towing the van, all on bitumen.
It is extremely difficult to get the numbers for a 1996 GQ TB42 efi (Petrol) Patrol. It seems that according to several sources that it has a higher tow capacity than the TD42 GQ (2.8t v 2.5t). In any case my Jayco is comfortably under both but it has a high towball weight of 271kg (hitch capacity 350kg - perhaps due to in part to the gas bottles on the A frame & a front boot as well as a front kitchen) & ATM 2334. Haven't bothered to measure the rear axel weight as I have no reference figure.
BTW .. I have had continuing problems with my passenger side rear axel bearing weeping. I have had various 'experts' look at it over the years including both inner & outer seals replaced several times & the bearing replaced on two occasions .. the bearing is destroyed in getting to the outer seal. The latest try seems to have fixed it.
The latest Patrol specialist diagnosed it as having had the axel 'skimmed' to just below specifications (I think that this happened when it was first looked at, at 80,000km). The solution was to install a selected second hand axel, bearing etc. and grease the sealed bearing using a special needle nib on the grease gun. No sign of a weep after 15,000km.
I did from time to time wonder if the cause was an overloaded rear axel.
Once again, thanks for your input.
If we knew your problem was a leaking axle seal then someone may have suggested a *speedy sleeve*.
The left hand side often is the axle that leaks first because it is in a lower position due to the camber of the road.
Sometimes just lowering the oil level in the diff by a tiny bit will fix it.
Many servicemen fill the diff and then it becomes a contest to get the level plug back in before the oil has actually found its true level thus resulting in a slightly overfill.
Leaking sealed bearings are usually the cause of the Chinese factory where they are made.
Also heat can damage the seal in a sealed bearing.
Heat may be generated with something as simple as a dragging brake or it may be a symptom or overloading or high loading of the rear axle.
The weight will transfer a larger proportion of itself to the left hub due to the roads camber again generating more heat in that bearing,
You seem to be on top of it and that is a good thing.
Hi Cupie. Rear axle capacity is 1800kg for your car. Your 271kg ball weight will put around 400kg onto your car's rear axle. Cheers
Chris ..Thanks for that.
Where do you get your figures from?
Some time back I did lots of searching with no success.
What are the factors that cause a 271kg ball weight result in 400g on the rear axel?
I assume it is something related to 'lever action' & distance from ball to 'fulcrum point' of rear axel.
BTW, I have always used a HR WDH that has the effect of correcting the rear end sag when the van is connected. It was fitted by the people that purchased the van from.
cheers
I think Yobarr just uses approximations based on experience. To accurately calculate what load the van adds to the rear axle load you need three things:
TBL = Towball load
WB = Wheelbase (use mm for accuracy)
OVH = Towball overhang (distance from rear axle to towball)
Rear axle load added by van = TBL x (WB + OVH) / WB
For your Patrol, I found a figure of 2970 for wheelbase. You will need to measure your towball overhang. I did a calculation and tried a few different figures to arrive at Yobarr's estimate of 400kg. I suspect that may be close enough, but marginally overstated because it would mean a towball overhang of 1420mm. I thought the Patrol would be less than that. Anyway, using that hypothetical figure here is the calculation:
Rear axle load (400) = 271 x (2970 + 1420) / 2970
If you change OVH to 1200mm it comes out to 380kg, so not a huge difference.
Because this only looks at the difference when connecting the van, not the actual axle load, the formula works regardless of how your load is distributed in the tow vehicle. To deternine how much weight is lifted off the front wheels, just subtract the towball weight from the rear axle loading calculation ... in your case it works out to 110-130kg.
-- Edited by Are We Lost on Sunday 17th of July 2022 12:11:53 PM
Thanks Stephen..
Are We Lost:
Excellent explanation, thank you, it accords with how I thought it all worked.
Next: would you to care to explain weight distribution hitches in words of one syllable for mechanically challenged electronics engineers? :)
Compare connected and disconnected axle weights with the WDH on the same vehicle.
But can you explain it without the aid of a weighbridge?
Just measured the OVH and it is 1200
Thanks again to all.
-- Edited by Cupie on Sunday 17th of July 2022 02:32:21 PM
Certainly I will explain, Mike! First I would like to thank Stephen for explaining my figures for Cupie. Now, a WDH increases TBO (towball overhang, or distance from rear axle to hitchpoint) thus increasing the extra load applied to the car's rear axle by towball weight. Obviously more weight is removed from the car's front axle and transferred to the car's rear axle. Because the TBO is increased the effects of YAW also are increased, meaning it is easier to have the "Tail wagging the Dog" which is the biggest cause of caravans going RSup. When a van starts flicking from side to side it is actually travelling faster than the car and trying to overtake! Physics that few understand. A WDH also increases the weight on a van's wheels (GTM) which can result in the van's ATM being exceeded because a WDH DOES NOT change towball weight EVER. Another negative for a WDH is that it is even MORE weight hanging off the end of your towbar shank so that as well as increasing TBO it is increasing the weight on the car's rear axle before you even hook-up the van! SO we've got the weight of the actual WDH which can be way more than 20kg with bars, chains and tensioners, plus extra weight caused by extra TBO, maybe 30kg, for a total of 50kg(+/-) EXTRA weight on car's rear axle. A McHitch increases TBO even more, increasing the weight transfer. Then you tension the cure-it-all WDH to transfer some weight from the car's rear axle back onto the car's front axle, and some weight onto the van's axle group. Using Stephen's example, you will have taken 110-130kg off the car's front axle when you applied the van's towball weight to the car. The more you tension the WDH the greater are the risks of oversteer in the car, which is not much fun with a van in tow! When all calculations are done you're messing around with less than 100kg and if that relatively insignificant weight is the difference between being safe and being unsafe then there is something wrong with the whole setup. VERY few people understand the workings of a WDH, but if they did they would understand that it is not the universal cure-it-all that many people conside it to be. Many times I have written that a WDH is used only by those who are trying to make a car do things for which it was not designed. Get a smaller van or a more suitable car, and make sure that ALWAYS the weight on the wheels of the car is at least 10% more than the weight on the wheels of the van. Happy travels! Cheers
Hi Cupie. The axle ratings are among my records, and as Stephen suggested, the 400kg added to your rear axle was simply an estimate, intended to illustrate a point. There is actually one greatly over rated vehicle that has TBO of better than 50% so a 350kg towball weight puts over 520kg onto its lightweight rear axle, but we won't go there! Cheers
Without complicating the procedure if a vehicle and a pig trailer are connected together at a hitch with a tow ball then the weight of the trailer portion of the tow ball weight is applied as an increase to the towing vehicles weight.
This increased mass is applied to the rear of the vehicle via the tow bar which means that extra weight is carried onto the road via the rear axle ( wheels and tyres)
When a WDH is installed correctly the torsion affect of the bars provide a more rigid transfer of this extra weight along the length of the combination of vehicle and trailer.
This weight transfer results in a slight increase in the weight on the front axle of the tow vehicle and again a slight increase on the axle or axles of the pig trailer while at the same time removing that weight by the sum of the increase of the steer and trailer axles from the rear axle of the tow vehicle.
I dont intend to go any further into the whys and why nots if we should use one. They are recommended for some vehicles when towing and some manufacturer's suggest that they arent to be used which is generally dependent on the vehicles construction.
So,
How was that Mike.?
Poor, no better than Yobarr's - I don't think either of you properly understand what's happening with a weight distribution hitch.
>provide a more rigid transfer of this extra weight
Whatever is "a more rigid transfer" of weight? and what units is it measured in?!
Is there a proper mechanical engineer in the house?
I made no claim of being a proper or an improper mechanical engineer myself but I am happy to take on board any detailed description from a qualified person if we have one.
It is difficult to explain a rigid transfer of weight but I am sure there will be a technical term for it.
Oh just one thing Mike, I fully understand what happens with a WDH. No one has to be a Mechanical Engineer to know how they work.
In hindsight I should have said *no* to your question, had I known you were looking for a description from a proper Engineer I would have.
Ivan: there is a very, very old adage in engineering and it is:
If you can't explain it then you don't understand it.
A WDH applies what is effectively a solid bar, or stiffarm, from the front axle of the car, through the hitch point, to the axle group of the caravan. This means that as a car and van are driven through a table drain, for example, almost all weight is carried at only two points. Can you imagine the stresses on the chassis and drawbar when this happens. Wound up to extremes a WDH can keep the rear wheels of the car suspended in mid- air. WDHs are used only by people who are trying to make a car do things for which it never was designed, and a WDH can cause more problems than it 'solves'. Get a smaller van or a better car. This has all been explained many, many times before, in great detail, and help can be found if the 'search' function is used. Cheers
The problem we have, Mike, is that trying to explain it in a way that most readers can understand is an impossibility. Different levels of comprehension by readers, along with very little understanding of basic physics by some, make the task very difficult, which is why I have to generalise. When I first joined the forum and posted that a WDH increased a van's weight I was criticised and shouted down left, right and centre by many 'senior' members, but I stuck to my guns and continued explaining, on a regular basis, how a WDH actually does work until now it is generally understood that a WDH takes weight off the rear axle (NOT the towball) and puts some of that weight back onto the car's front axle, from where it came, and also it puts some weight onto the van's axle group, thus increasing the weight of the van. Total weight of car has decreased, Total weight of van has increased, Total weight (GCM if you like) stays the same. Believe me, I can sit here for hours and explain in great detail how a WDH works, but unless the reader actually WANTS to learn, rather than argue, I'm wasting my time. However, rote learning does seem to work eventually. Slowly but surely many members are realising that, with weights, I know what I'm talking about, but because of continual interference by others who who know little, understand less, and have no interest in learning, several members have chosen to contact me by PM to get help with their weights. Indeed, I have also visited them to help. Cheers
-- Edited by yobarr on Sunday 17th of July 2022 05:41:02 PM
Well it will be interesting next time someone might offer help with a fridge problem. Where is a refrigeration engineer when you need one.
Do we wait until our mechanical engineer comes on to help someone with a wheel alignment problem or will a mechanic suffice.
I have worked along side quite a few mechanical and civil engineers during my career and I have never heard that said however I take it on board.
I will wait to hear the explanation from a mechanical engineer if only to check myself on knowing how a WDH works.
I wonder if someone who has the title of associate (degree or Diploma) of mechanical engineers will qualify to explain.
-- Edited by Ivan 01 on Sunday 17th of July 2022 05:53:37 PM
-- Edited by Ivan 01 on Sunday 17th of July 2022 06:10:45 PM
Hi Ivan. I'm surprised that after all the explanations that have been given regarding how a WDH works, along with actual weighbridge test results etc, you still seem hesitant to accept the simple facts. The fact that many retailers of these pieces of equipment have little idea dies not help. Perhaps you could Google "John Cadogan. How a WDH works" or similar and if, after watching the video you still do not understand there is little more that can be done to help you. John is, as explained in the video, an engineer with much experience. Cheers
P.S "Weight distribution and load levelling hitches for heavy towing" John Cadogan is the video you need to find!
If you're pressed for time the important stuff is between 13th and 14th minute and between 17th and 19th minute. He explains only the basics so as to make it as easy as possible for it to be understood by many.
-- Edited by yobarr on Sunday 17th of July 2022 07:36:27 PM
I have little time for Cadogan and I dont agree with your views on WDH use.
I will just leave it at that if that is OK with you.
I see there are a few posts with explanations on how a WDH works, and interspersed in those are the opinions on whether they are good or bad. But they are mostly on what they do, and not a lot on how, which is what Mike was asking. Like Ivan, I will skip the discussion on the pros and cons .... for now. But I have taken a different tack to the explanation method, and kept in mind Mike's request for simplicity. I hope I haven't gone too far.
But first, I believe that a sagging rear end is just an easy visual signal that something is wrong, and it is weight on the wheels that need attention. Its the weight that matters, not the level. But for simplicity I have focused mainly on levelling in this explanation. Also I have not tried to use the correct physics terminology ... weight, mass, torque, force, load. My high school physics is now forgotten.
Imagine you are standing at the back of your tow vehicle with van attached, looking at sagging rear end. One of these days you will do something about it. You happen to see a couple of bars made from spring steel lying there at the campsite.
Being a fit muscular fellow, you think one of these bars might come in handy for a workout. At the back of the car, you find there is a spot you can push it in from the rear and it seems to lock in place. It feels rock solid and has effectively become an extension of the car. Onto your workout, and with some effort lifting the bar you can see that the car body lifts up a bit at the rear and the whole rig becomes closer to level. If you had scales you would see the weight on the front wheels is now slightly more, and the weight on the back wheels is less.
Also, if you used a tape measure you would see that the end of the bar you are holding was raised more than the body of the car. Or to put it a different way, the leverage enabled you to lift the rear end further than if you had tried at the rear bumper. I will come back to this point.
You note that there is a bracket on the caravan drawbar you can attach this bar to. Being an innovative fellow, an idea starts to form in your mind. Maybe this will help with the levelling. So with a supreme effort you manage to lift the bar a little more and hook the end of it onto the bracket. While you are recovering, you check and notice that the sag has returned a bit, but not as much as before. Just for fun you stand on the drawbar and bounce a bit. You realise that it feels a lot firmer than you expected it to. It's a bit puzzling. The bar is still lifting up the back of the car, but the end of that bar is resting on the drawbar bracket and is pulling the drawbar down harder onto the towball.
Why does this work? Surely if the bar is lifting the rear end up, but that very same bar is pulling the drawbar down, they will cancel each other out and you will achieve nothing.
Well, its late now so I think I will call this the first instalment and write the rest in the morning. If someone wants to have a go, please do.
-- Edited by Are We Lost on Monday 18th of July 2022 01:58:52 AM
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-- Edited by yobarr on Monday 18th of July 2022 03:10:09 PM