Safe Speed Forums

With my car I got a 3 year servicing and tyres deal ... so as long as I don't kerb / egg the tyres, or drive in glass yards, my tyres are replaced when they reach the end of their life.

Problem is, it does not define end of life.

I've done 24,000 or so miles on them, as part of usual checks tonight I measured them with the tread depth gauge and the fronts are down to between 2 and 3mm. I would usually replace at this point, if not sooner ... any idea what VAG's tyre replacement policy would be? I'd rather pay for new tyres than let them go much further than this, to be honest.

On another, side issue, when I replaced the front pair of my wife's car in December, the tyre place told me that it was their (or possibly Michelin) policy not to replace fronts, but to switch the rear to the front and put new tyres on the rear. The rears still had 7mm or so left, so I wasn't overly worried, and I had them change the rears over "cross corners" (recommended in the car manual, as the tyres were non-directional). Anyone else heard of this approach, is it a good / bad / indifferent one to adopt?

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COAST Not just somewhere to keep a beach.

A young loner on a crusade to champion the cause of the innocent, the helpless, the powerless, in a world of criminals who operate above the law.

My local tyre shop has the opposite policy. They always put the new tyres on the front axle (assuming it's an FWD car) as that is where you need the most grip.

No idea on VAGs policy. If it's done by accountants, it will probably be right when it's at 1.6mm, same as with most company car fleet managers.

If you press the point at 2 - 3 mm I'm sure they'll swap them. I've never had a problem at below 3mm on my company car - and was all prepared to ask them to order me a taxi and leave it there pending a decision from the depot. Claim you don't feel safe at that tread depth and they'll not chance the lawsuit following a crash.

As for whether new tyres should go on front or rear, having experienced a blowout on both axles over the years, I'd sooner have the new ones on the back, particularly if the tread pattern is different and the more modern one offers better lateral grip. Mind you, I'm a timid so-and-so and do not want to experience FWD tail-out slides. I had this years ago when I had worn Michelin XZXs on the back and new MXs on the front. The only way to correct a "power slide" was to stick your toe down and cautiously pay off the steering unti everything was straight ahead. With a car coming toward you on a fairly narrow road, that was quite an experience

Finally, I am wondering why the corner-to-corner swap? I had been led to believe that changing the running direction of steel-braced radial (irrespective of tread pattern) is a recipie for poor handling until the tyre is bedded in again in the new rolling direction (and that that process gives a sharp wear rate, scrubbing a fair part of a mm off in a few hundred miles).

Kwik-fit have the same policy - and some manufacturers (at least) agree. HTH,

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Will

They sell more tyres that way

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Ross

Yes I'm a hoon, but only on the track!!!!

This is DEFINITELY wrong, at least in part. Aquaplaning almost always starts at the front, because before aquaplaning the rears run on drier road squeegeed by the front.

If you know you're about to hit surface water - for example where there's a flow across a motorway - lifting off for a bit of forwards weight transfer before you hit it is AMAZINGLY effective in preserving proper grip.

So for aquaplaning prevention having more tread depth on the front is surely the way to go.

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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

Yes, sounds like bullsh1t to me! As Paul says, the rears tend to run in the bit of road already cleared by the fronts. I was always told that the reasons for putting the new ones on the back (of a front wheel drive car were twofold:

1. The rear tyres (on a front whele drive) car tend to wear much more slowly than the fronts. Tyres loose grip though age as the rubber gets harder. It's better to put the part-worn ones on the front so that they are killed off sooner and replaced. That way, the car spends more of its time with relatively evenly matched tyres at both ends.

2. Most modern front-wheel drives tend to understeer at the limit. Apparently "Joe public" can handle understeer better than oversteer so it makes sense to loose grip at the front first. In any case, almost all cars are better at protecting the occupants in a frontal crash than any other sort, so if you ARE going to "fall off" it makes sense to do it going forwards!

I don't know about swapping tyres diagonally being a bad thing but it's impossible on many newer cars because the tyres are directional anyway.

It's not only Cooper who say that - I just quoted them because they were the first my search returned. Kwik-Fit have the same explanation on their depot wall and a quick search of the 'net reveals that Michelin, Dunlop, Bridgestone, Firestone, and several tyre fitting centres give the same advice - if you're going to fit only two tyres, fit them to the rear axle because new tyres on the front and worn ones on the rear is dangerous.

For example, BTW, it's worth following the link above because their FAQ page includes a short film that dramatically shows this point.

HTH,

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Will

the wear limit quoted by the lady I spoke to yesterday was 2mm, apparently this is what VAG recommend as the replacement point. I said I had between 2 and 3mm, she said that would be OK - as it covered by the replacement policy, not OK to drive on.

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COAST Not just somewhere to keep a beach.

A young loner on a crusade to champion the cause of the innocent, the helpless, the powerless, in a world of criminals who operate above the law.

Hmmn, I guess it depends.


If you are driving powerfull RWD (?) sports cars at high speeds on wet roads then I guess new on rear is better.

OTOH

If you are driving a 55HP VW transporter with a top speed of 65MPH Stopping quickly is likly to be more important than high speed cornering! So wouldnt "New on front" be better in this case?

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"The road to a police state is paved with public safety legislation"

I agree with the 'general advice' to arrange for more grip at the rear for a typical driver. It's harder to get into big trouble with a little bit of understeer than a little bit of oversteer. Personally, however, I'd much rather have a little bit of oversteer.

But the bit about aquaplaning is definitely wrong, because the lion's share of the risk must start with the front.

I'm no fan of moving tyres around either. I believe that they wear to suit the suspension characteristics (especially camber) and have to be wastefully 'worn to suit' if you move them.

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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 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.

Even if the speed of onset of aquaplaning is higher with new tyres at the front, in the vast majority of situations you will have felt a little understeer well before the onset of aquaplaning and so reduced speed to suit the conditions. Personally, I'd rather have a car that I can't drive quite so quickly but which reacts predictably and gives plenty of warning, than one that can potentially be driven faster but gives no warning and can "bite your head off" when things go wrong.

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Will

Thats correct, but only really in a straight line. Loss of grip on the rear of a vehicle while cornering is much more important than loss at the front.

Once grip is lost at the rear, its pretty much unrecoverable for most drivers. Loose grip at the front, and its pretty easy to get it back.

Thats why rear-tyre blowouts are much worse than front-tyre blowouts.

It's not that I disagree with the notice but I don't think that it's true for the reasons they say it's true. Looking at the spelling, I guess it's an American notice? IF so, I think that a much greater proportion of their cars are rear wheel drive. I therefore agree that loss of traction is more likely to occur on the rear wheels but NOT as a result of aquaplaning - more as a result of poor grip on the older tyres due to the plasticisers leaching out of the rubber and making them go harder.

I'd prefer to have my older tyres on the front because under cornering forces, it would just understeer a bit more (which I find easier to cope with). Under braking, it's true that I wouldn't get QUITE as much grip as if I'd put the new ones on the front but on the other hand, I'd sooner lock a front wheel than a rear one. Finally, driving through standing water, the front tyres are the ones that "see" the most water so I'd rather have the deeper tread on them than the rears.

Also, I've never had a "blow out" on a rear wheel drive car but I've had a couple on front wheel drive cars at motorway speeds and they were no big deal. I've never had a front wheel blow out on anything but I would imagine this to be potentially MUCH worse.

Rear wheel blowouts are potentially much more dangerous than front wheel blowouts.

Ahh. So it wouldn't be anything at all to do with truth or best practice then. It'd just be the position of 'least liability'.

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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 had the same issue about 3 years ago when I had 2 new tyres fitted to a BMW 328 by a national chain of tyre fitters. Despite my protestations they insisted on putting the new tyres on the back and putting the old rears onto the front, which had about 4mm tread remaining.

The net effect was that a fine handling car was turned into a bag of nerves, with the front twitching about and having to be coaxed into corners and ploughing on in a frighteningly straight line under braking. A day later I swapped the tyres back and normality was restored - pin sharp steering with the worn rears giving fairly progressive oversteer under heavy throttle.

Contrary to modern thinking, I still believe that oversteer is actually safer than understeer. At least with oversteer the car basically goes where you point it, and recovery is fairly intuitive (ie steer where you want to go). With unexpected understeer the car doesn't go where you point it, and the intuitive reaction (ie applying more lock to steer where you want to go) actually makes the situation worse.

I admit that snap oversteer at high speed is damn near uncontrollable to most mere mortals, but I'd also argue that snap understeer at high speeds is if anything worse (think tightening left hander with oncoming traffic!!!). But in any case, variations in (legal levels of) front to rear tread depth don't generally lead to sudden loss of grip balance, rather to a more progressive loss of traction.

So on balance I'll go with the traditional school of thought and have the new rubber at the front please, on the basis that if I can get the front of the car round the corner there is at least a fighting chance that the back will follow; and that if I have to stop in a hurry I want the tread where all the weight is - ie at the front.

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I believe a substantial part of that effect was due to the former rears not matching the front suspension geometry.

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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

Could you expand a bit on that please? It hasn't ben my experience so far and I'd always been taught the opposite so I'm curious!

When I worked for a sport car manufacturer, we'd never send a press car out with less than 500 miles on a set of tyres to make sure they were "scrubbed-in" to the geometry of their particular corner of car! These represented an "extreme" case because the cars were very light and the tyres were pretty wide (and low profile). Also, they used to run a fair bit of negative camber too. All this could combine to create a situation where, on brand new tyres, you could almost see daylight between the outermost line of tread blocks and the steel ramp the car was standing on! Certainly, with the racing cars, (which obviously had slicks on and even more camber), it was interesting to send one out for a couple of laps on brand new tyres and then put the temperature probe across the width of the tyre surface. They would always be colder on their outside edges and warmer on their inside edges.