Some years ago we had a 2009 Vauxhall Zafira 1.8 Auto and we towed a caravan we put Spring Assisters in the dealer did it for us 
This is the logic as explained to me by Michelin at that time, around 1990. I was towing with a Citroen BX. Only 65 bhp but it went all over Europe and a great tow car in the end. But at first it was very unstable. A lot of this was due to a back heavy new caravan. This was so bad the ministry tested it and said it should not be on the road. However, strangely they did not have the power to have it taken off the road. Also the Caravan Club refused to get involved!
It came to a point that I needed new tyres, I had non premium tyres fitted and the stability improved beyond recognition.
I made the enquiry with Michelin who told me that premium tyres have supple walls in order to keep more tread on the road. But this had the result of making the rear end of the car move about a bit more both in pitch and yaw. This in turn is enlarged by the caravan and might lead towards the caravan controlling the car.
Having said that, I have used Michelin on other cars, including my present one, without any problem. But still worth bearing in mind when trying to work out why an outfit may not be as stable as you might expect.
John
I had a Citroen BX 16 estate after a Volvo 245 decided to self destroy from the rust bug. The Citroen attracted me due to its ability to drive on three wheels are at least stay level and steer. It was very reliable, quite fast for its day but the fit and finish of its plastic internal bodywork left something to be desired. I sold it to my neighbour who used it for two years doing nothing at all to it. Said he couldn’t find the oil filler. No wonder then that when I showed him it was terminal.
The old chestnut again, as in the song when will they ever learn?
Spot on as usual Prof. If you are going to start towing with a used car it is essential to establish ALL mechanical aspects are upto standard as when new.
The rubber blocks that fit between part of the coil springs are flawed imo. In essence they place more stress than originally designed on the rest of the coil spring. Not good and could lead to premature failure.
As Clive says many manufacturers offer stiffer suspension for given models. Worth a look.
I suggest it is equally important to consider more efficient shock absorbers, better damping under higher loads.
Essential the vehicles stability programmes etc are compatible.
be safe.
Spot on as usual Prof. If you are going to start towing with a used car it is essential to establish ALL mechanical aspects are upto standard as when new.
The rubber blocks that fit between part of the coil springs are flawed imo. In essence they place more stress than originally designed on the rest of the coil spring. Not good and could lead to premature failure.
As Clive says many manufacturers offer stiffer suspension for given models. Worth a look.
I suggest it is equally important to consider more efficient shock absorbers, better damping under higher loads.
Essential the vehicles stability programmes etc are compatible.
be safe.
So that again vindicates the car manufacturers. So why do people think they should modify the car when the problem is actually with something else?
Don't "cure" the symptom, find and sort out the cause.
Some people use spring assisters to make an outfit "look" right, even though there was nothing technically wrong.
Spring assisters are a bit like tyre bands. They are a solutions looking for a problems.
But where Spring assisters do have one advantage over tyre bands is they have a discernible effect. Tyre bands just sit there doing nothing and even when a tyre blow out occurs there's no definitive evidence they improve outcomes.
Spring assisters are a bit like tyre bands. They are a solutions looking for a problems.
But where Spring assisters do have one advantage over tyre bands is they have a discernible effect. Tyre bands just sit there doing nothing and even when a tyre blow out occurs there's no definitive evidence they improve outcomes.
I’m not that sure that advice given by Michelin for a 1990 Citroen BX has a lot of bearing on today’s vehicles as in those days all French cars came out in Michelins. And Michelin didn’t make the car, but would have worked with Citroen.
Certainly not disagreeing with PJL that any tow vehicle should be in a serviceable condition but there will always be this occasions when even in a perfect world a little extra assistance is required. The OP was asking about the Grayson assisters. My take was to fit the MAD springs as they behave like a normal spring unladen but provide extra support when laden.
I totally fail to understand your reasoning. So far I have 100% agreed with you that the tow vehicle should be mechanicallycorrect before looking as modifications.
Or, as you say, Don't "cure" the symptom, find and sort out the cause.
However, it is has been, and continually will be, that modifications specific for the job can, and do improve safety, They can make the towing experience better and with a smoother more balanced outfit must reduce wear and tear.
But if they are not needed then don’t do it, simple.
John
The Michelin advice was nothing to do with Citroen nor can it be out of date. It concerns the fundamental difference between premium and non premium tyres.
John
Yes but advice given in 1990; how relevant is it to today’s tyres where the buyer has a far larger range of choice with most majors also making tyres that span a wider range than of yore and under different brand labels.
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The 1990 Citroen / Michelin point is relevant. Both Companies are French.The French look after themselves😃. In 1990
The Uniroyal-Goodrich Tire Company became part of the Michelin Group which had now reached the critical size to secure its future in North America.
The Uniroyal-Goodrich Tire Company became part of the Michelin Group which had now reached the critical size to secure its future in North America.
I'm with the Prof on this one. If the car feels unsafe or uneasy when towing then it would also feel the same if the boot is fully loaded, but that is a condition that the car manufacturer should have taken into account in the design.
Hello John,
When an accessory manufacturer who sells modifications spends a realistic sum on proving their products "improve" safety compared the sums spent by the vehicle manufacturer then I might believe them implicitly.
Unfortunately some off the shelf modifications may apparently improve one aspect of a vehicle, but without proper testing they will not know it the mod actually compromises some other aspect of the vehicle. It is also possible that some parts may not even enhance the function they've been bought to improve.
When someone want's to modify a vehicle it's because the vehicle doesn't do what they want it to do. Basically they have chosen the wrong vehicle.
Spring assisters won't stop pitching. By increasing the spring rate they can only make the back end harder, thereby redung the amplitude of the pitching movement. To reduce the pitching frequency one would have to fit harder dampers (shock absorbers).
Lutz, you are not correct, dampers are not shock absorbers, the dampers slow down the rate of amplitude of the rebound, the shock absorbers take the load weither they be coil springs or leaf springs. Some vehicles now have them combined in one unit with magnetic control. For the dampening rate.
But dampers are commonly and colloquially referred to as shock absorbers. Springs aren't.
Shock absorbers are a common, but incorrect, alternative name for dampers - not sure what the combined units you're referring to unless they're "self-energising self-levelling" dampers which are fitted to some cars.
My Kia Sorento had self energising self levelling system by Sach. At standstill the car when being loaded would drop slightly. Then when driven the movement of the suspension would pump up the system and level the ride height. Worked really well
In the mid 1980s I worked on electro rheological fluids which would change their viscosity dependant on the electrical potential applied. These made for very rapid changes in damping characteristics and could be used in multi degree of freedom mounting raft systems for attenuating transmitted vibrations. Suitably programmed they would self adjust to suit the changes in driving frequency as the machinery varied load and speed. The major issue was that computing power and processor sizes had not quite caught up with the technology. But it has now and such dampers are installed in many applications including automotive.
Variable dynamic dampers working on the above principles are available on a number of premium models - my Touareg included it as part of the air suspension package - I generally leave it set in Comfort but when towing or on motorways I use the Sport setting.
Even my 1995 SWB Pajero had electrically adjustable dampers. But after around 20 years one failed and they were quite expensive. So I removed them and fitted a set of Pedders variable rate longer springs and their foam “shocks”. Made such a difference to the car plus the suspension lift aided off road jaunts. Almost as good as spring assisters, but best not go there 😱
The towing dynamics are totally different than just loading the boot. The load that requires controlling is exerting live forces which need controlling.
I agree totally. But in reality.
People do buy tow cars in good faith in the expectation that they will do the job. And on paper they should.
Most people cannot afford to keep changing there tow car until they find one that suits.
Different outfits have differing characteristics, often these can’t be isolated or proven.
Manufacturers by enlarge have little interest in designing for towing.
Most purchase a tow car as a compromise so it can be used as an everyday car aswell.
Assisters are accepted for MOT’s (but testers are advised to check if they are fitted to mask a fault).
A little research shows that suspension mods have been successful for many years. I have not come across any that have failed or caused a danger. Though I feel sure there must have been. Donuts reputedly can cause a spring failure. But has anyone heard of that actually happening. The MAD assisters are designed to only come into operation when under load.
In the ideal world, with a little research we should reliably be ably to buy a tow car which makes a good stable outfit. But so many time this ends as a mismatch. We could try sueing the car manufacture, good luck with that. Or keep changing the car. Or fit a reliable tried and tested modification.
John
Agreed, the towing dynamics are somewhat different, but spring assisters are not going to solve a pitching problem. Spring assisters can only prevent the suspension bottoming out if the vehicle is regularly used at maximum rear axle load, but to prevent pitching, one has to increase the damping effect and springs don't do that.
While I agree that dampening would be best. In my opinion stiffening the rear end certainly does affect pitching. You said so yourself in post 40.
“Spring assisters won't stop pitching. By increasing the spring rate they can only make the back end harder, thereby redung the amplitude of the pitching movement. To reduce the pitching frequency one would have to fit harder dampers (shock absorbers).“
Just reducing the amplitude has to have a beneficial affect.
I have used donuts with success on about 3 vehicles over the years and MAD springs on 1, which were so much better. But lots of other cars have needed nothing. But not one of them had the “bottoming out” problem before or after.
John
Note that stiffening up the rear suspension will tend to make the car oversteer in the solo condition and oversteer is more difficult for the average driver to master. That's why manufacturers tune their suspension setups to make the car predominantly understeer. It's not something that one would necessarily notice under normal driving conditions, but it can make all the difference in emergency evasive action.
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