2 new tyres

[Sticks.]

This interesting thread came up on the Audi page of this forum http://www.pistonheads.com/gassing/topic.asp?h=0&a... 2 new tyres, front or rear?

The gist is that on a front wd car if you have one pair of new tyres they should go on the back, not the front.

Interesting arguments, and with respect to those who've commented, but I can't get past the concept that in wet weather you'd want the best ones at the front because a) fwd cars are designed to understeer and b)less tread = less water dispersal = longer braking distance.

Setting aside a set of four tyres being best, I don't mind being wrong (you'd want to get it right in real life), but what's the view of those who've had additional training?

[Sticks.]

Thanks for that. I do see the argument for 'rear' in terms of balance, oversteer limits etc but isn't that about driving beyond the safe conditions of the road? Surely we should aim to be well within them.

But in this scenario, where would you want your best tyres?

At a safe speed but on a wet road a child runs out right in front of you and you have to brake very hard.

In the wet, what difference will tread depth make to your stopping distance?

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StressedDave said:

Here's Michelin's take on the subject:

http://www.michelin.co.uk/michelinuk/en/car-4x4-va...

If you only ever drive in a straight line then you might just be able to make a case for having the grippier tyres at the front, but as you don't (and depending on the imbalance having grippier tyres on the front can make your car dynamically unstable even in a straight line), they go on the rear. Michelin had a video where they put new tyres on the front and then put the car on a relatively low grip surface with a group of motorway driving reps - it was effectively uncontrollable. With the tyres reversed it was the exact opposite.

I guess what I'm saying is, if that's the case, but also the Top Gear video and this http://www.rospa.com/roadsafety/advice/motorvehicl... then it'd have to be four good ones then?

Btw, remember when TG was for grown ups? lol

[Sticks.]

NBirkitt, wasn't ignoring your post, it just crossed, well, in the post, as it were.

Interesting, thanks.

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heebeegeetee said:

If, in wet or slippery conditions, you have the best tyres on the front you will be exacerbating the imbalance further.

There simply is no need to put the new tyres on the front.

Except that most of the braking is done through the fronts, so in wet conditions, less tread depth = less water dispersal = longer stopping distance. For all the other arguments about balance etc, is there one to show I'm incorrect about that? If so, I just want to know. Thanks.

[Sticks.]

Thanks for that. I had a quick look at the Auto Express one and it makes the pointhat the 'theory' had changed because, it says, most people can cope with a front wheel skid better than a back wheel one. Possibly so.

But isn't it the case that in the wet, a front wheel skid is more likely to happen under heavy braking and end with you hitting someone?

I'm stuggling to see how the chance of a back wheel skid (which I've never experienced in a fwd car - been driving 30 years) outweighs lengthening my wet weather stopping distance (which I've had to call on before now) which directly increases my risk of hitting someone.

Interesting discussion, thanks for your input.

[Sticks.]

As I've said, I see the logic of the 'rears' argument, though even having had a 205cti which was alledgedly famous for LOOS, probably driven at a time when my enthusiasm was greater than my skill or experience, I've still not encountered it.

I have had to brake very hard in the wet to avoid an accident a good number of times and been glad of maxium water displacement (= grip) where all the braking is going on, ie front.

Some intersting numbers here http://www.youtube.com/watch?v=zA6MUlVNkLM

[Sticks.]

Ok possibly, but if I've made an emergency stop on the wet motorway, say from 70, if you're behind me with used fronts on, from the video you'll still be doing 40mph when you reach me.

[Sticks.]

heebeegeetee said:

Are two rotating tyres better than 4?

Sorry, don't understand that.

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heebeegeetee said:

driversdomainuk said:

1. I was driving at the absolute limits where you would never drive on road, and possibly not even on a track day.....(fire proof overalls and all that LOL!!)

When I put worn tyres on the rear of my Golf GTi many moons ago, and was hooning round my favourite roundabout late one night, i doubt that in reality i was anywhere near the limits of the car, but by gum i exceeded the limits of the back tyres when the car just swapped ends on me without warning...

No harm done. I remember coming round a bend with enthusiasm in modeately wet conditions in the 205 with very-soon-afterwards-changed front tyres and finding an unexpected queue of traffic.......very close Could have been serious, lesson learned.

I guess our experiences shape our opinions.

[Sticks.]

Yep, but still there's the issue of shorter wet weather braking distance. I think it's unlikely you'd spin like that, and if you did, you'd not spin and continue in the same direction. But if the fronts lose grip when braking, yu just keep going in the direction of what you're trying to miss.

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heebeegeetee said:

Ultimately you can choose braking distances and you can choose gaps to the car in front, but i had no choice when those rears let go on me. (Apart from the choice of driving sensibly, i guess ).

Yes, usually, by driving sensibly, agreed. But when someone's stupid kid runs out or someone pulls out without looking? I guess my thinking is that, as you say, you can control the rear wheels more, by driving sensibly, but sometimes braking distance is controlled by someone else by their lack of care/awareness.

g2g

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heebeegeetee said:

I guess just going by my own circumstances, it's very rare indeed that i ever have to slam the brakes on, and tbh, i can't remember ever having to so in the rain, in over 30 years of driving.

However, i do like to pedal on as often as possible, so i guess it's fair to say that i have spent time cornering quickly infinitely more times than emergency stopping.

That's the difference for me. You control your cornering speed, but you can't control someone else's stupidity which requires an emergency stop. Why is an emergency stop part of the test? Because it happens.

From the Youtube link I posted earlier if I stop in the wet from 70 with my good tires, you'll still be doing 40 when you go into me on medium-worn ones. Not good. (Winter's approaching so there'll soon be a M way pile up to demsonstrate this.) But if you have to brake at 30 in the wet you'll still be moving when you reach granny/kid crossing the road when you might not have been.

I appreciate the current thinking is about handling etc, but I'm surprised, with a similar 30 years behind me I've never exerienced it.

Years ago I was in a bad accident. Tyre tread depth was loked at by the insurance company to see if they could reduce their liability on the grounds that more tread = shorter stopping distance = less impact speed = lesser injuries. Ie if your tyres had been better you'd not have got so badly hurt so why should we pay? For me it wasn't an issue.

Sorry, this sounds a bit bullish, not meant to, I'm grateful for your input but suspect we'll have to agree to differ. Food for thought though

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heebeegeetee said:

1.The chances of you needing a life saving stop occurring in the wet when your tyres are brand new are so remote that it's not worth worrying about, so i think it's best to follow official advice and be done with.

2.Michelin will have all the emergency stopping figures under the sun i imagine, in every different type of vehicle and road condition and weather condition and absolutely everything, and they still tell us to put new tyres on the back. I for one am not going to overide that degree of knowledge based on one youtube clip of film.

(my numbers)

1. It's more outcome than just probability.

2. They did - see para on driving on wet roads
'On a wet road stopping distances increase, and this is even more the case with worn tyres. '

http://www.michelin.co.uk/connected/tyres/learn-sh...

They seem quite taken with the idea http://join-the-fight.michelin.co.uk/#/home

Goodyear even designed a tyre spcifically with this in mind. http://eu.goodyear.com/uk_en/tires/repository/opti...

Bridgestone....... http://www.bridgestone.co.uk/press/press-releases/...

Rospa thought braking distance was important enough to test it http://www.rospa.com/RoadSafety/info/tyre_tread_de...

I could go on but I don't think we're likely to agree

[Sticks.]

Whatever you say

if stopping distance isn't as important to you as max speed round a roundabout we're unlikely to agree. Btw every authority apart from the ones I quoted

Thanks for your imput.

Edited by Sticks. on Tuesday 14th September 19:25