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I had a couple of new tyres on my campervan at the end of last week. I had them on the front by choice (more tread depth to clear water, less understeer, front most important for braking).

But now I have a subtle but annoying handling characteristic. Turn in bite is improved 'too much'. I'll wind on a tiny bit of steering lock, get more steering than I expected and have to unwind a little. This happens with very low cornering loads, so I don't think it's genuine oversteer.

I'm finding it quite hard to describe, but it feels like an 'over centre' mechanism. I put in little steering and the chassis responds by giving me more than I asked for.

I've now done over 700 miles on the new tyres and it's still the same. All the ball joints and so on were checked last week during servicing.

I'm adapting to it of course, but I'm absolutely positive that it's not a case of learning to wind on less lock - I'm winding on the right amount and the chassis is 'over-responding'. I should also point out that the effect is pretty much tiny, but I'm sensitive to it.

I'm thinking: tracking, but I can't figure out why the new tyres seem to have made the condition appear.

Any ideas?

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Paul Smith
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Hi Paul, this indicates to me at least that there may be a little excess compliance in some of the suspension components, rubbers perhaps or some excess clearances in these components stacking up and changing the geometry when you dial in an amount of lock.
Did you change tyre brands maybe?
Its possible you may need to readjust the tyre pressures to eliminate this "feature" youve developed. Im thinking that maybe this trait was already present and the new tyre has exposed it due to different characteristics etc.
The tyre fitter did get them on the correct rotations i presume?
More investigation required.

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Back in the days when I had a FWD car (had 3, 1995 1.1 Fiesta, 1999 Audi A3 1.8, 2001 Audi A4 1.9 TDI before getting a 2003 Audi A4 1.9 TDI Quattro in 2005) I used to do exactly what that article says, new tyres on the back. If the fronts were needing replacement I'd put the part-worn rears on the front and the new tyres on the rear.

However my last 2 cars have been 4WD (the 2003 A4 Quattro and now a 2006 A4 2.0 TDI Quattro 170), and generally all 4 tyres need replacing at once. There is slightly more wear to the front tyres as they're driving and steering so I usually swap front and rear mid-life to make sure the wear is even across all 4 tyres.

With the Torsen centre diff you can't have more than 3mm difference in tread depth between the front and rears otherwise you get diff wind-up. The A3 and TT use a Haldex centre diff (multiplate clutch) so are primarily FWD, switching to 4WD if the front wheels slip. The Torsen stops wheel slip from happening in the first place.

What's quite interesting is the 4Motion Passat (based on the B7 platform, same as the current A4) uses a Haldex centre diff rather than Torsen, as the Passat's engine is transverse rather than longitudinal as on the A4.

I should bloody coco!

That's an arse-covering publicity-generating bit of rubbish.

On water clearing, they REALLY should know that the back wheels run in the squeeged track of the front wheels, so aquaplaning almost always starts at the front.

They should know that tread depth affects braking distance and probably over 70% of braking effort comes from the front.

And they should know that I'd much rather have oversteer than understeer, thanks very much!

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Paul Smith
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The back wheels only run in the path cleared by the front wheels when the vehicle is travelling in the absolute straight ahead and the front and rear track widths are the same



Yes it does. One a dry road, zero tread depth will give maximum grip and braking



This is a personal choice. Most cars are manufactured to understeer as this is believed to be safer due to the predicatablity and inherently more natural correction

Not sure that is true, slicks are designed for grip with no tread but I seem to remember some tests that show treaded tyres grip deteriorates even in the dry when heavily worn. Something to do with the compound being designed to work with the way the tread blocks 'walk' across the surface of the road iirc. Hopefully someone else on here may be able to confirm or deny this from real knowledge.

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True, except you need speed for a aquaplane risk, which tends to preclude much in the way of steering. And there are very few vehicle with different track widths front and back.

So in all normal aquaplane risk situations the front squeege effect is by far the most important.

And that's before I've straightened the steering because of the standing water.



Agreed, and obviously I was talking about wet grip. But I'm more than happy to trade a tiny bit of dry grip for quite a lot of wet grip.



Or possibly because most drivers haven't bothered to get the training and experience required to enjoy oversteer.

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Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
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Interested to hear of your experience. I have Evo7 and the fronts wear soonest. Replaced worn Bridgestone with Falkens and PEC tyres of Corwen who are knowledgeable about tyre technology and competition matters offered that Falken had similar grip to Bridgestone due to harder compound but loaded with mica.

I had exactly the same experience; turn in significantly increased and back more ready to step out. I suspect that new tyres gave some slightly higher friction improvement over part worns and that ones driving prior to fitment unconciously took into account the tyre condition so one drove to achieve a neutral to oversteer response. Changing friction/grip levels meant that ones 'progrma was unsettled for about 30-40 miles until it re-compensated and the difference vanished.

I too prefer an inherently oversteering car - far far safer under all conditions but understand that the average driver could be caught out hence the general preference for understeer. ( 'natural' my ass)

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Richard Ceen
We live in a time where emotions and feelings count far more than the truth, and there is a vast ignorance of science (James Lovelock 2005)

I am sure that Top Gear or Fifth Gear did an article on this. Their conclusion (after some track/skidpan tests) was that you should fit a new pair of tyres to the rear.

This was because it tended to cause understeer, which for the average motorist is a safer characteristic, and in extreme situations would also help prevent oversteer ('cos the rears were grippier).

However, bear in mind that this information was targeted at the "average motorist", who probably doesn't have a clue what understeer, oversteer, slip-angles etc. are!

mb

I can confirm that when I let the rear tyre on my modded Z1 starts to get close to the wear limit, there is no way I can even come close to scraping the pegs.

By contrast, with a reasonable amount of tread on the tyre I can have the pegs pushed firmly against their stops (hell, I could probably grind the cases off the engine) and the bike doesn't even show the slightest sign of letting go.

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I'm sorry you thought the url of no use.
However, the preferred fitment for two new tyres in the trade is new on the rear. Worn on the front. So, is your oversteer caused by faulty steering components ? Or by the back coming round ?
The same way I always re-new both tyres on the bike at the same time. Even if the front has useable tread, it gets changed at the same time as the rear. Expensive, but the bike never handles the same with one new and one old tyre.

Not sure if this is of any use or relevance, but here is a brief synopsis of a fairly scary handling issue I had a couple of years ago:

Car was a BMW 328 (E36 model) which IIRC was running tyres of about 205 x 16" with an aspect ratio of 55 or thereabouts. When I bought it it had Michelin Pilots all round, which were phenomenally good in dry or wet, but also pretty damned expensive.

A year or two (and several expensive tyre changes) later I reached a stage where the rear tyres were approaching wear limit yet I knew I was getting rid of the car in a month or two, so didn't really want to put £120 tyres on for someone else.

So I went to a well trusted local supplier and asked if he could advise of a reasonable quality tyre that might be a bit cheaper. He recommended some German ones which were about £70 (no names no pack drill) and said he'd had good reports about them, though obviously they weren't going to be right up there with the premium tyres I was using.

This seemed a good compromise - even when selling the car on I had sufficient social responsibility not to fit £40 "Teflon Non-Sticks" to a car of reasonable performance.

So these were duly fitted to the rear wheels and off we went. At low speeds all was fine, with a reasonable amount of grip and everything reasonably in balance. But at motorway speeds the car became pretty damned scary. When making (say) a lane change the car would have no initial turn in but then turn in savagely when you applied more lock; then you'd actually have to wind the lock back off and counter-steer a bit to get the car to straighten up in the new lane - it was like steering a boat!

As per Paul's post you wouldn't actually call it oversteer, as the car seemed to have full grip, but the effect was pretty much the same, and the faster you went the worse it got. Going faster still you'd get two or three such osciallations that you had to work quite hard to damp out again.

After some thought I came up with a theory, which was that the cheaper tyres basically had softer sidewalls. Thus the front turned in positively but the back didn't initially respond, leading to the lack of initial steering response. Then when the car did turn the rear sidewalls would flex more than the front, allowing the car to turn in more than it should, and so on.I partially proved this by deliberately over-inflating the rear tyres by about 15psi. This more or less cured the problem - though of course I then ended up with real oversteer, as you might expect.

In the end I swapped the new tyres onto the front, and this seemed to bear out my theory, as this handling problem now stopped completely, just leaving me with a car that was now very vague and mushy as the front tyres flexed around; where previously the steering had been pin-sharp.

It's a funny thing to relate, but I have read myriads of posts on various BMW fora about cars with mysterious handling "shimmys" and so on, usually leading to mega bills as suspension and steering components are systematically replaced; and I often wonder how many might simply be due to mis-matched tyres. And of course, the more finely tuned the suspension and steering is, the more susceptible it will be to issues such as this.

[edited to add]
On re-reading the original post, whilst this might appear to be the exact opposite situation, could it be that the tyres Paul has fitted to the front of the SS "Mini-Winnie" have stiffer sidewalls than the ones that were already on the back, thus indirectly replicating the situation I described.

I have to say Paul's description of the symptoms exactly sums up my memory of the effect my car exhibited.

Easy test anyway - swap the tyres front to back and try it out...

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We had this discussion a little while ago: link

Paul is of course, 100% correct in all things, and as Willcove pointed out at the time:



Paul must be correct, as the very idea of a multi million pound industry being right when he says they are wrong is inconceivable.

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willcove wrote:
I suppose that it is conceivable that every major tyre manufacturer who disagrees with you (which is all from who I've so far been able to find recommendations) could be wrong, or that the Michelin film to demonstrate the effect could be rigged, but I can't (particularly with a litigious society like the USA) understand why they'd want to spread disinformation that could (if you're correct) have potentially lethal results.

Could they possibly want to sell twice as many tyres?

Paul, it could be a whole load of things. One thing that springs to mind is that you have one or more "tired" (but not knackered) front suspension bushes and that with the older tyres on the front, they simply didn't have the levels of "bite" to show the problem up. It could also be that you just got a brand of tyre that isn't well suited to the vehicle. I once replaced the Goodyears on Mrs. Mole's Peugeot 405 with some Bridgestones because I could get a good deal on them at the time. It felt AWFUL! They had loads of give in the sidewalls and you could drive down the motorway flicking the steering right and left and having the car respond completely 180 degrees out of phase (i.e. it was yawing left when the wheel was being turned right). I put the same tyres on my car (lucky we used the same size at the time) and the effect wasn't noticeable at all! Some tyres just don't go well with some cars. It's not that the BRidgestones were bad, just not suitable for that car.

As for aquaplaning, does your campervan have double back wheels? If so, it might not quite be true that they are running in the dry bit of road but I guess it weighs well over 2 tons and doesn't go that fast so I would have thought you'd have to try quite hard to get it to aquaplane in most normal circumstances!

Finally, it's not just because "joe public" can correct understeer easier than oversteer that manufacturers tend to opt for understeer. They also build most of the crashworthiness into the front end so if you "fall off", it's best done going forwards!

P.S. You must be the only person in the whole world who prefers OVERSTEER in a CAMPER VAN

IMO Paul, "JT" mentioned the solution...... "Sidewall Stiffness".

I once had a MK5 Cortina with gas struts which understeered like crazy until I changed the tyres. Sidewall stiffness is a VERY overlooked feature and decreases of course with age and agressive use.

Once the sidewall stiffness (or strength) is gone, the tyre begins to roll on corners and the tread starts to wear.

Put on a new set on the other axle and................?

The old ones roll................the new ones don't!

A multi-million pound industry you say? And what do multi-million pound industries do? They act in their own interests. In this case they know where potential legal liability lies. It lies in loss of control through oversteer, and not in understeer or extended braking distances.

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Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

Yeah, I think that's a good guess.



Single rear wheels. I have no idea what it weighs! I probably ought to find out.



Yeah, but you're assuming 'loss of control', which is way down on my list of likely things. To me, understeer represents 'loss of steering' and oversteer doesn't.



I've never been anywhere near the grip limits in it - I'd be throwing things around in the back long before I started losing grip - so you adapt and drive with less 'g'. Nevertheless If I can't have neutral handling balance, I'll take oversteer every time.

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Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

I have to agree with you there. While you may lose the backend while bombing around a skidpan (as in the michelin video), in the real world I've only ever had aquaplaning while driving along a motorway and it's always the front end that goes first.

Your tyres would have to be completely crap or you'd have to be doing something monumentally stupid to lose the rear end at 45mph on a public road due simply to a bit of water on the road.