Hi ..im a Newbie havent done much traveling to date (small Matilda Motorhome )recently had experienced were over taking trucks seamed to pull my small motorhome towards them as they passed ...spooked me a bit am I imagine this or has any one eles experienced simalor ...thinking maybe wind direction was a factor....
Cheers john
Bryan said
09:05 AM May 25, 2016
This is normal, some sort of venturi effect. I read a long time ago that train tracks had to be laid a certain minimum distance apart for the same reason that the coaches would lean towards each other in similar circumstances.
Yuglamron said
09:51 AM May 25, 2016
Brian is correct Venturi effect.
If you notice large trucks generally (Not All) move left on narrow roads to reduce the effect. happens with water too When ships 'RAS' replenish at sea, they have to be a set distance apart when they use cables to transfer good and pipelines at sea otherwise they get drawn together.
Worst time on the road is when two rigs pass on passing places and the lanes are narrow. Just another thing to watch on the highways and byways.
Bruce and Bev said
09:58 AM May 25, 2016
it also depends on the "type" of truck eg cattle truck, solid side truck etc.
I had ESC fitted to the 'van we have now and you don't get this effect at all......
The Phantom said
10:10 AM May 25, 2016
You should experience this effect while sitting on the Maglev train in Shanghai and another passes it going in the opposite direction. With both doing 411Km/h.
It is similar to an explosion.
The Phantom
Liventhedream said
10:13 AM May 25, 2016
Hi thank for replies. ..how much is ESC cost what does it do
Cheers john
Bryan said
10:38 AM May 25, 2016
Liventhedream wrote:
Hi thank for replies. ..how much is ESC cost what does it do Cheers john
The ESC Bruce is talking about is an caravan specific Alko product. In your motorhome it's best to just slow down as this will lessen and even eliminate the problem.
Happywanderer said
12:19 PM May 25, 2016
It happened to me once when I had Myrtle. I was on a bridge when an overtaking truck went flying past.
I could feel the van being pulled in, it was a struggle to keep it straight especially with the concrete of the bridge on the other side.
Frightened the bejesus out of me.
Tony Bev said
02:31 PM May 25, 2016
Hello liventhedream
What Bryan said is correct, Venturi/Vacuum effect
What you described is a normal situation, between trucks and motorhomes, and you will get use to it
I keep to the left as far as possible, (without slipping off the bitumen, or falling into crumbling edges), and find that there is less Venturi/Vacuum pulling me towards the overtaking truck, as well as less wind buffeting from the approaching trucks
When there are no trucks around, I keep away from the crumbling edges
gumpybsc said
04:12 PM May 25, 2016
I'm agreeing with all of the below. Pressure is reduced in the space between the RV and the truck as the air speeds up in the gap as the truck passes. Big tall solid-sided trucks such as panteknicans (?spelling) are the worst. The Alko ESC on our van really helps, however my simple strategy is to just keep calm, drive straight, and back off the speed a little before the vehicles pass.
Vince said
04:23 PM May 25, 2016
I feel it most when a truck of size is coming along side same direction and passing us
it just draws us back on speed from the air rush hitting the front of the van.
Don't suffer from vacuum passing opposite directions though.
Bruce and Bev said
07:24 PM May 25, 2016
Hey Phantom - yep - fast trains passing each other can be startling the first time - to say the least.
Have been on several "bullet" type trains in various countries and when your train leans over away from the other passing train is "interesting".
Also standing on a train platform when one of these trains go through the station at full speed and you feel it sucking you towards it is frightening
The Phantom said
10:24 PM May 25, 2016
The first time I rode the Maglev, we pulled into Longyang Road Station and a Chinese guy, in full uniform, was saluting the train. It made me feel a bit special, but, mind you, I had been in China for a full hour before that ride.
It was so high on my bucket list that I came out of Pudong Airport and straight onto the train. I just had to do it. Edit: The 25km journey took about 8 minutes.
Once I got to Longyang Station, I had to backtrack in a taxi to my hotel.
Sitting on the train watching the speedo is riveting stuff.
The Phantom
-- Edited by The Phantom on Wednesday 25th of May 2016 10:25:54 PM
Hylife said
11:22 PM May 25, 2016
Actually it is neither venturi nor a vacuum.
The speed difference between you and the semi is little more than jogging pace. You at 90 them at 100 is 10kph and does not create a vacuum or venturi.
The effect you feel is the removal of the headwind drag on YOUR tug/van/motorhome/combination.
When YOU are (excuse the pun) breaking the wind, the headwind drag keeps your vehicle/combination inline. Should your van move sideways the headwind on its side pushes it right back. Now, during that passing move, when the semi cab is in line with you your van, you will feel a push AWAY from the semi as his headwind flows sideways from his cab. You will naturally self correct on your steering wheel.
When the semi cab has moved in front of your van or vehicle that push is removed, requiring you to remove the correction and you mistake it for a vacuum. In addition, he is now breaking your headwind and now you have no drag to keep you on the straight and narrow. As a consequence of you correcting for the removal of the sideways push as it coincides with the drop in the headwind drag, you get that eerie feeling of being sucked towards the semi and an inexperienced driver can easily over-correct and get the wobbles.
It is only a reverse sensation that is no different to getting an unexpected sideways gust. No vacuum, no venturi, just a removal of drag.
Relax, hold the wheel steady, do NOT lift your foot off the accelerator, do not over-correct, do not panic, just drive on straight as normal.
The general term is called slipstreaming and racing cars use it to great effect in order to pass rivals who may in fact be faster than them. Truckies used to slipstream each other on the Hume Hwy to save on fuel. Two trucks close together use less fuel and can go faster than one. Thankfully the practice has been banned, because when it does go wrong, two trucks make a h3ll of a mess and usually someone dies.
Liventhedream said
02:08 AM May 26, 2016
Thanks Hylife ....will take your advise ...but No nite driving for me ..cant see who's overtaking ...to prepare for the ...sway .
Cheers john
rockylizard said
08:24 AM May 26, 2016
Gday...
Here's some information to explain the venturi effect caused by an overtaking/passing truck on a caravan.
Hi ..im a Newbie havent done much traveling to date (small Matilda Motorhome )recently had experienced were over taking trucks seamed to pull my small motorhome towards them as they passed ...spooked me a bit am I imagine this or has any one eles experienced simalor ...thinking maybe wind direction was a factor....
Cheers john
This is normal, some sort of venturi effect. I read a long time ago that train tracks had to be laid a certain minimum distance apart for the same reason that the coaches would lean towards each other in similar circumstances.
Brian is correct Venturi effect.
If you notice large trucks generally (Not All) move left on narrow roads to reduce the effect. happens with water too When ships 'RAS' replenish at sea, they have to be a set distance apart when they use cables to transfer good and pipelines at sea otherwise they get drawn together.
Worst time on the road is when two rigs pass on passing places and the lanes are narrow. Just another thing to watch on the highways and byways.
I had ESC fitted to the 'van we have now and you don't get this effect at all......
You should experience this effect while sitting on the Maglev train in Shanghai and another passes it going in the opposite direction. With both doing 411Km/h.
It is similar to an explosion.
The Phantom
Cheers john
The ESC Bruce is talking about is an caravan specific Alko product. In your motorhome it's best to just slow down as this will lessen and even eliminate the problem.
I could feel the van being pulled in, it was a struggle to keep it straight especially with the concrete of the bridge on the other side.
Frightened the bejesus out of me.
What Bryan said is correct, Venturi/Vacuum effect
What you described is a normal situation, between trucks and motorhomes, and you will get use to it
I keep to the left as far as possible, (without slipping off the bitumen, or falling into crumbling edges), and find that there is less Venturi/Vacuum pulling me towards the overtaking truck, as well as less wind buffeting from the approaching trucks
When there are no trucks around, I keep away from the crumbling edges
I'm agreeing with all of the below. Pressure is reduced in the space between the RV and the truck as the air speeds up in the gap as the truck passes. Big tall solid-sided trucks such as panteknicans (?spelling) are the worst. The Alko ESC on our van really helps, however my simple strategy is to just keep calm, drive straight, and back off the speed a little before the vehicles pass.
it just draws us back on speed from the air rush hitting the front of the van.
Don't suffer from vacuum passing opposite directions though.
Have been on several "bullet" type trains in various countries and when your train leans over away from the other passing train is "interesting".
Also standing on a train platform when one of these trains go through the station at full speed and you feel it sucking you towards it is frightening
The first time I rode the Maglev, we pulled into Longyang Road Station and a Chinese guy, in full uniform, was saluting the train. It made me feel a bit special, but, mind you, I had been in China for a full hour before that ride.
It was so high on my bucket list that I came out of Pudong Airport and straight onto the train. I just had to do it. Edit: The 25km journey took about 8 minutes.
Once I got to Longyang Station, I had to backtrack in a taxi to my hotel.
Sitting on the train watching the speedo is riveting stuff.
The Phantom
-- Edited by The Phantom on Wednesday 25th of May 2016 10:25:54 PM
Actually it is neither venturi nor a vacuum.
The speed difference between you and the semi is little more than jogging pace. You at 90 them at 100 is 10kph and does not create a vacuum or venturi.
The effect you feel is the removal of the headwind drag on YOUR tug/van/motorhome/combination.
When YOU are (excuse the pun) breaking the wind, the headwind drag keeps your vehicle/combination inline. Should your van move sideways the headwind on its side pushes it right back.
Now, during that passing move, when the semi cab is in line with you your van, you will feel a push AWAY from the semi as his headwind flows sideways from his cab. You will naturally self correct on your steering wheel.
When the semi cab has moved in front of your van or vehicle that push is removed, requiring you to remove the correction and you mistake it for a vacuum.
In addition, he is now breaking your headwind and now you have no drag to keep you on the straight and narrow.
As a consequence of you correcting for the removal of the sideways push as it coincides with the drop in the headwind drag, you get that eerie feeling of being sucked towards the semi and an inexperienced driver can easily over-correct and get the wobbles.
It is only a reverse sensation that is no different to getting an unexpected sideways gust. No vacuum, no venturi, just a removal of drag.
Relax, hold the wheel steady, do NOT lift your foot off the accelerator, do not over-correct, do not panic, just drive on straight as normal.
The general term is called slipstreaming and racing cars use it to great effect in order to pass rivals who may in fact be faster than them.
Truckies used to slipstream each other on the Hume Hwy to save on fuel. Two trucks close together use less fuel and can go faster than one. Thankfully the practice has been banned, because when it does go wrong, two trucks make a h3ll of a mess and usually someone dies.
Cheers john
Gday...
Here's some information to explain the venturi effect caused by an overtaking/passing truck on a caravan.
https://caravanchronicles.com/guides/understanding-the-dynamics-of-towing-being-overtaken/
Cheers - John