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Post by north200 on Mar 29, 2024 7:34:54 GMT 10
How does the tow hitch height effect the caravan axle weights on a twin axle caravan.
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Post by arewelost on Mar 29, 2024 9:21:58 GMT 10
It depends on the type of van suspension. If it is load sharing, then the weights on each axle will be equalised. So a nose up or down attitude matters little. With a non load sharing suspension, a nose down attitude will increase weight on the front axle while reducing weight on the rear.
This will reduce the amount of travel on the front suspension, so it bottoms sooner, and requires slightly higher tyre pressure. It may cause that axle to be overloaded. On the road, the handling may feel a little twitchy. So the goal is to be level or very slightly nose down.
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Post by yobarr on Mar 29, 2024 12:45:24 GMT 10
It depends on the type of van suspension. If it is load sharing, then the weights on each axle will be equalised. So a nose up or down attitude matters little. With a non load sharing suspension, a nose down attitude will increase weight on the front axle while reducing weight on the rear. This will reduce the amount of travel on the front suspension, so it bottoms sooner, and requires slightly higher tyre pressure. It may cause that axle to be overloaded. On the road, the handling may feel a little twitchy. So the goal is to be level or very slightly nose down. No, no, no. Details later.
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Post by arewelost on Mar 29, 2024 13:00:39 GMT 10
Yobarr, did you see the message I sent you a few days ago?
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Post by yobarr on Mar 29, 2024 13:45:09 GMT 10
Yobarr, did you see the message I sent you a few days ago? Hi Stephen, not sure which email you're referring to, but our last correspondence was Feb 27th last when we discussed my video that shows the stupidity of this Green Energy rubbish. If there has been further communication, then "No" I have not received it! Cheers
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Post by yobarr on Mar 29, 2024 14:16:05 GMT 10
It depends on the type of van suspension. If it is load sharing, then the weights on each axle will be equalised. So a nose up or down attitude matters little. With a non load sharing suspension, a nose down attitude will increase weight on the front axle while reducing weight on the rear. This will reduce the amount of travel on the front suspension, so it bottoms sooner, and requires slightly higher tyre pressure. It may cause that axle to be overloaded. On the road, the handling may feel a little twitchy. So the goal is to be level or very slightly nose down. No, no, no. Details later. OK, here we go. Much of what Stephen has written is correct, except for the comment on tyre pressure. When you're running nose-down on non-loadsharing suspension then obviously there will be more weight on the front axle of the van. IF you increase the tyre pressure in the wheels on that front axle you will take even morevweight off the van's rear axle and shift the rear axis forward. Dangerous. This is a definite "No No" as there now will be an increase in rear overhang, automatically increasing the risk of yaw, a major cause of caravan accidents. The pressures in the tyres on the front axle should be lower than than the pressures in the rear axle's tyres to the extent that the rear axle becomes the effective pivot point on turns, with the front axle being the one to "scuff" sideways. Usually around 3-4psi works, but this is dependent on weights etc as lowering the pressure in that axle will put more weight onto the van's rear axle. Obviously the pressure difference will be dependent on how far the van is nose-down, but it is FAR BETTER to adjust your car's towbar height to get the van level, or slightly nose-down. Maybe 25mm? However, raising towball height will also increase towball weight. DO NOT be tempted to increase pressures in tyres on front axle of van to compensate as to do so is asking for trouble. With load-sharing suspension it matters little, but even so, being only slightly nose-down seems to work best. Also, be aware that just because a suspension system is marketed as "independent" does NOT mean that it is load-sharing.
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Post by arewelost on Mar 29, 2024 17:54:53 GMT 10
Hi Stephen, not sure which email you're referring to, Message on this forum. Home, Messages, Inbox. Will get to your post later.
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Post by north200 on Mar 29, 2024 18:18:31 GMT 10
Ok, I understand what you have said, the thing I am struggling to understand is how adjusting the pressure in the shocks in independent suspension affects the balance.
Thanks for the information.
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Post by yobarr on Mar 29, 2024 19:01:08 GMT 10
Ok, I understand what you have said, the thing I am struggling to understand is how adjusting the pressure in the shocks in independent suspension affects the balance. Thanks for the information. Hmmmm. Interesting. Never have I heard of adjusting pressure in shocks of a caravan. There is no mention of this in your first post in this thread, where you sought help with how towball height affects axle weights. Have I missed something? Happy to help if you can advise exactly what you would like help with. Cheers
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Post by arewelost on Mar 29, 2024 23:42:42 GMT 10
Ok, I understand what you have said, the thing I am struggling to understand is how adjusting the pressure in the shocks in independent suspension affects the balance. Thanks for the information. Two clarifications on your post. We were referring to tyre pressures, not shock absorbers. And as Yobarr said, independent suspension does not mean load sharing or non load sharing. It could be either. As Yobarr said, what is the background to your question?
To address Yobarr's comments (and talking about non load sharing suspension): I agree with the issue on handling. The dilemma is that there is no good solution. If the van has a nose down attitude the front tyres will have a greater loading. So they will get hotter. If you reduce the pressure in those tyres that heat will further increase.
So while lower pressures may help to address the handling, there are other flow on effects. Apart from getting hotter, underinflated tyres have less grip (reduced handling and braking), more rolling resistance (higher fuel consumption), and irregular wear pattern.
You may compensate somewhat by increasing rear tyre pressures but that is not ideal either.
It really depends on the amount of nose down attitude. At 25mm I would not worry about it.
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Post by north200 on Mar 30, 2024 8:05:44 GMT 10
Auto levelling air suspension on the caravan, not load sharing King adjustable shocks on the caravan. Auto levelling air suspension on rear axle of the tug.
Adjustable shocks on the caravan are very helpful on corrugated roads.
I have a small problem with tyre ware on the front axle of the caravan.
Always looking for ways to improve the way it handles on remote outback roads
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Post by Mike Harding on Mar 30, 2024 12:07:39 GMT 10
My caravan has AlKo rubber torsion suspension for each axel which, I assume, is not load sharing?
What sort of suspensions are load sharing and how do they work?
I'm a bit sceptical about adjusting hitch height via 3 or 4psi difference in axel pressures: given caravans generally run around 50psi that is only about 6% difference and I doubt given, measurement variations and temperature differences this could be reliably maintained - but I'm open to correction.
I've often thought my hitch looked lower than I'd prefer but I seem to get away with it and I'm am regularly off the bitumen. And on the bitumen with a usual tow speed of 90kph and no sway control, WDH etc the car/van combination seems stable.
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Post by yobarr on Mar 30, 2024 12:55:24 GMT 10
My caravan has AlKo rubber torsion suspension for each axel which, I assume, is not load sharing? What sort of suspensions are load sharing and how do they work? I'm a bit sceptical about adjusting hitch height via 3 or 4psi difference in axel pressures: given caravans generally run around 50psi that is only about 6% difference and I doubt given, measurement variations and temperature differences this could be reliably maintained - but I'm open to correction. I've often thought my hitch looked lower than I'd prefer but I seem to get away with it and I'm am regularly off the bitumen. And on the bitumen with a usual tow speed of 90kph and no sway control, WDH etc the car/van combination seems stable. Hi Mike, Sorry to say this, but it seems that I've completely confused you here! The 3-4 psi I threw into the topic, simply as a start point, has NOTHING to do with towball height, but is used only in an effort to minimise the negative effects of that too-low towball height. My tyres are 265/75 R16 which I ran at 38-40psi with GTM of 3200kg on bitumen, lower on dirt. As a percentage, running 3-4psi lower is thus around 10% lower pressure. This reduction in tyre pressure obviously is variable, depending on tyre size, type and weights carried. VERY briefly, load- sharing suspension is designed so that if one wheel drops into a hole it still carries the same weight as it did before it dropped into that hole. In theory, each wheel should always carry a constant weight. Non-loadsharing suspension is where the load on wheels changes as the wheels ride over bumps, or into holes in the road. For example, if you tow your caravan over a speed-bump, when the wheels on the front axle reach the top of that speed-bump there may be NO weight on the wheels on the van's rear axle, but as the van moves forward so that the wheels on the rear axle are on top of that speed-bump there may be NO weight on the wheels on the van's front axle. Please note that as I am short of time, this is a VERY BRIEF description of how things work, and there are many variables, but this may give you a basic idea of how things work. Cheers
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Post by Mike Harding on Mar 31, 2024 11:34:11 GMT 10
All noted Yobarr.
So the towball height of a twin axel trailer is set by the height of the receiver on the towing vehicle thus, other than adjusting that, is fixed. Is that correct?
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Post by yobarr on Mar 31, 2024 14:46:31 GMT 10
All noted Yobarr. So the towball height of a twin axel trailer is set by the height of the receiver on the towing vehicle thus, other than adjusting that, is fixed. Is that correct? Hi Mike, without getting pedantic what you've written is correct. Messing around with things like adjustable shocks etc is a waste of time and money, in my opinion. After breaking spring packs on the Suttor Development Road I fitted EFS XTR shocks, one of the best things I've done to the van, but I can not see how making them "adjustable" would be any sort of an improvement. To maintain a relatively constant towball weight all my 5 water tanks have their own taps, but are plumbed into a commom feedline to the water pumps. This way I can control how much weight is ahead of the axle group and how much is behind. My grey-water tank is over the axles so has no effect on towball weight. Cheers
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