Ball weight, a static measurement, who knows for sure what it should be, but I have never read any article that relates to dynamic measurement. Once a trailer, but more so a caravan is moving other forces come into play, the size and length, the position (includes height) of the center of gravity. The pull of the drag generated, the leverage of air pressure at the front and the lift generated from the profile.
Then there is the change in position of the center of gravity when going up or down a slope. The effects of different suspension system's etc. Its all like QI and know body knows. My guess is that a caravan doing 100kph, the weight parameters will be quite different from the static measurements.
Who mentioned wind tunnel tests ? no manufacturer would want those figures let out the box.
When a vehicle manufacturer sets a tow ball weight limit on a vehicle or a towbar, the dynamic forces are taken into consideration.
This is usually worked out these days by computer modeling
There are programs to do this available to the public if you want to do it but you will need a degree in mechanical engineering.
Yep, if ball weight is 270kg, when driving probably varies from 200 to 350kg.
Now yobarr will correct me. Lol
There is no disputing that ball weight varies when driving,quite possibly in the range you suggest,but probably impossible to measure? However,it still is important to get the car and van correctly balanced before travelling,thus minimising the chances of the tail wagging the dog,which can result in the whole unit going base over apex,or R Sup.Cheers
Yep, if ball weight is 270kg, when driving probably varies from 200 to 350kg.
Now yobarr will correct me. Lol
Indeed Yobarr did but added nothing of value in the process :)
Tony
Bit bored are we? After 2 months we finally get an obviously well considered response.You seem to have not READ my post,so I will highlight the salient point for you. "There is no disputing that towball weight varies when driving?" This would indicate concurrence with Neil's comment that towball weight varies when driving,surely? My post then refers to the importance of having the car and van properly balanced,and explains the likely results of not doing so,such as the "Tail wagging the Dog",and the whole lot going R Sup. What more "of value" do you think I should have added? As you no doubt are well aware,I have a reasonable understanding of weights and dynamics,and could have posted all sorts of figures,but this was not deemed necessary in this case.However,I would be happy to hear how you believe my post could have contained more "of value".Cheers
Can someone please explain to me, why there is there so much discussion about ball weight?
IMHO ball weight is measured with the caravan unattached to the towing vehicle, the only reason this is required is to ensure that the tow ball weight dose not exceed the TBW rating of the towbar.
Eg my towbar has a rated towing capacity of 3000kg and a rated TBW of 250kg.
After you establish your TBW as soon as you hitch you caravan up to the towing vehicle it becomes irrelevant, because it becomes unmeasurable.
Can someone please explain to me, why there is there so much discussion about ball weight?
IMHO ball weight is measured with the caravan unattached to the towing vehicle, the only reason this is required is to ensure that the tow ball weight dose not exceed the TBW rating of the towbar.
Eg my towbar has a rated towing capacity of 3000kg and a rated TBW of 250kg.
After you establish your TBW as soon as you hitch you caravan up to the towing vehicle it becomes irrelevant, because it becomes unmeasurable.
You got it Gundog.
Just make sure the measured weight unhitched does not exceed the tug or towbar rating and for safe towing is around 10% of the loaded van.
I did some calculations to determine how the tow ball weight effected the weight over the rear axle of the tow vehicle, for a ball weight of 250kg, the weight over the rear axle became 352kg, and for a weight of 350kg, the weight over the rear axle became 493kg.
As I understand it, zero ball weight means the center of gravity is right over the pivot point of the wheels, and the van is very twitchy, negative ball weight, the van is unstable, and positive ball weight, the center of gravity is ahead of the pivot point of the wheels and the van is stable.
I did some calculations to determine how the tow ball weight effected the weight over the rear axle of the tow vehicle, for a ball weight of 250kg, the weight over the rear axle became 352kg, and for a weight of 350kg, the weight over the rear axle became 493kg. As I understand it, zero ball weight means the center of gravity is right over the pivot point of the wheels, and the van is very twitchy, negative ball weight, the van is unstable, and positive ball weight, the center of gravity is ahead of the pivot point of the wheels and the van is stable.
Hi Ian.Your calculated figures would be for a car with relatively short TBO compared with wheelbase.Cheers
Nope, BT50, tow ball 1317mm from center of rear axle.
"Relatively short TBO,compared with wheelbase"
Yep.Most BT50s have wheelbase around 3200mm,although seems the later models are only 3125mm?? This is a good wheelbase with a relatively short TBO,but when you get a car like the McHitch and WDH equipped LC200,you have TBO of around 1500mm on a car with a miserable 2850mm wheelbase. With this all too common setup,as well as massive problems with yaw,the 350kg towball weight would put 534kg onto the lightweight 1950kg rear axle,which is rated at only 100kg more than the rear axle on your car.And then there's the massive difference in tare,around 600kg.But we won't go there.BT50 is a good car for safely towing up to about a 3100kg ATM van.Cheers
For general interest, I have done some measuring. the distance from the center of the diff to the tow ball on our vehicle is 1317mm, the same measurement with a RH fitted is 1415mm, an increase of 98 mm. An increase in weight of the tow ball and hitch assembly of 17.25 kg, but there was the top rod of a stone guard fitted.
Calculations for the weight over the rear axle for our vehicle with a standard ball and tongue assembly fitted :- 3200 + 1317= 4517 (distance tow ball the front axle point)
Calculation of leverage :- 4517 * 350 = 1580950 (using max ball weight allowed)
Weight over the rear axle :- 1580950/3200 = 494 kg (moments divided by wheel base)
Increase in weight over the rear axle at max ball weight :- 144kg
Calculations for the weight over the rear axle for our vehicle with a Reece ball and receiver assembly fitted :- 3200 + 1415 = 4615 mm
Calculation of leverage :- 4615 * 350 + 17.25kg = 1694858.75 (using max ball weight allowed plus the weight of the hitch)
Weight over the rear axle :- 1694858.75 /3200 = 529.5 kg
Increase in weight over the rear axle at max ball weight : 179.5 kg ( 529.5 - 350 i.e. nothing hitched up to being hitched up)
so with a Reece Hitch receiver fitted to our vehicle at max 350 kg tow ball weight, there is an increase of 17kg weight in the receiver assy. And an increase of 179.5 kg on the rear axle, and an increase of 35kg over our standard setup.
What I haven't included is the weight of the RH levers and chains.
For general interest, I have done some measuring. the distance from the center of the diff to the tow ball on our vehicle is 1317mm, the same measurement with a RH fitted is 1415mm, an increase of 98 mm. An increase in weight of the tow ball and hitch assembly of 17.25 kg, but there was the top rod of a stone guard fitted.
Calculations for the weight over the rear axle for our vehicle with a standard ball and tongue assembly fitted :- 3200 + 1317= 4517 (distance tow ball the front axle point) Calculation of leverage :- 4517 * 350 = 1580950 (using max ball weight allowed) Weight over the rear axle :- 1580950/3200 = 494 kg (moments divided by wheel base) Increase in weight over the rear axle at max ball weight :- 144kg
Calculations for the weight over the rear axle for our vehicle with a Reece ball and receiver assembly fitted :- 3200 + 1415 = 4615 mm Calculation of leverage :- 4615 * 350 + 17.25kg = 1694858.75 (using max ball weight allowed plus the weight of the hitch) Weight over the rear axle :- 1694858.75 /3200 = 529.5 kg Increase in weight over the rear axle at max ball weight : 179.5 kg ( 529.5 - 350 i.e. nothing hitched up to being hitched up)
so with a Reece Hitch receiver fitted to our vehicle at max 350 kg tow ball weight, there is an increase of 17kg weight in the receiver assy. And an increase of 179.5 kg on the rear axle, and an increase of 35kg over our standard setup.
What I haven't included is the weight of the RH levers and chains.
For general interest, I have done some measuring. the distance from the center of the diff to the tow ball on our vehicle is 1317mm, the same measurement with a RH fitted is 1415mm, an increase of 98 mm. An increase in weight of the tow ball and hitch assembly of 17.25 kg, but there was the top rod of a stone guard fitted.
Calculations for the weight over the rear axle for our vehicle with a standard ball and tongue assembly fitted :- 3200 + 1317= 4517 (distance tow ball the front axle point) Calculation of leverage :- 4517 * 350 = 1580950 (using max ball weight allowed) Weight over the rear axle :- 1580950/3200 = 494 kg (moments divided by wheel base) Increase in weight over the rear axle at max ball weight :- 144kg
Calculations for the weight over the rear axle for our vehicle with a Reece ball and receiver assembly fitted :- 3200 + 1415 = 4615 mm Calculation of leverage :- 4615 * 350 + 17.25kg = 1694858.75 (using max ball weight allowed plus the weight of the hitch) Weight over the rear axle :- 1694858.75 /3200 = 529.5 kg Increase in weight over the rear axle at max ball weight : 179.5 kg ( 529.5 - 350 i.e. nothing hitched up to being hitched up)
so with a Reece Hitch receiver fitted to our vehicle at max 350 kg tow ball weight, there is an increase of 17kg weight in the receiver assy. And an increase of 179.5 kg on the rear axle, and an increase of 35kg over our standard setup.
What I haven't included is the weight of the RH levers and chains.
Blxxdy hell!
Just measure the ball weight.....
Not that this situation effects my towing of my lightweight 400kg camper( and yes I did have it weighed to varify), but on the new towbars on my model Suzuki 2012, the the towball sits out and extra 6 inches, to get away from the spare wheel, so that would add more weight to the tow ball weight and would be a problem possibly if I were to put a light weight c.van or even a Avan. that weighs anywhere near my max weight of trailer at 1850kg. As my actually tow ball weight is only 140kg. I will have to take this into consideration if I ever go back to a van.
