Got a burst tyre yesterday , a large nail.

Anyway, the bloke at the tyre garage
(Charlie Brown), said I have to have
the other three changed as well or the
handling will be effected.

At £150 a pop, this could be expensive.

Is he right?

Any quick advice is appreciate as I'm having
the tyre(s) fitted at 1700 hours today.

Thanks

JR

Sorry I meant £135 per tyre.

JR

yeap he's right, when you have a 4wd car you should replace all 4 tyres at the same time!
what type of tyres do you have, i'd shop around for a better deal!

Depends how much tread is on the other tyres.

If your skint at the moment you could have your new tyre scrubbed by someone like demon tweeks to the same tread depth of the other 3 tyres.

that will save you 400 quid for now but will obviosly mean your new tyre will wear out at the same time as the other 3.

I did not know that you had to replace all 4 at the same time. I replaced my two fronts and the handling is supreme (still).

But then that is road driving where an Impreza on bald slicks on snow will probably still be better than a normal car in the dry.

KRS,

An impreza with bald slicks on snow would NOT be anywhere near as safe as a "normal" car in the dry.

An impreza with standard road tyres (205/50R16) is overshod for ice/snow driving, so standard novas and fiestas with thin width tyres are likely to corner better in these conditions. Fit proper snow/ice tyres on an impreza and the balance changes back into the scooby's favour.

Moray

I got a burst tyre the other day. Turned out to be a 12mm spanner! I took it to guy that fixed it too! Don't really know how safe it is but it is holding air and is not out of balance.

There`s no way I `m ever forking out for 4 new tires if one gets a puncture.

Handling differences might be noticeable on a track in an F1 car if you don`t change all four, but otherwise it sounds like a tyre-industry inspired sellling ploy.

Maybe if I had more money than sense.....

This is nothing to do with handling.

It is all to do with blowing up your transmission.

In a 4 wheel drive car there are no trailing, free running wheels. If there is a large difference in the tread depth the wheels at each revolution will be travelling different distances. This will lead to transmission / diff windup and if enough can cause failure.

Keep att tread depths within 2mm and replace all tyres togeter if necessary to achieve this. Or expect expensive repairs!

Differentials allow for different rotational speeds of the wheels. I haven't done the calculations, but I would guess that the differencr between rotational speeds of left and right side wheels when a car goes around a corner would be ccomparable to the difference between a new and old tyre. Has anyone calculated it? The donut spare on my Evo is a different diameter to the rest of the wheels. You are not supposed to drive on a donut for more than 50 miles or so, but I would think that the manufacturers would try to keep it pretty close to the rest of the wheels if it were that much of a problem.

Don't let the tread depth range go over 2mm on any of the 4 tyres. This could otherwise damage the transmission & would void the warranty.

Also keep to the same make tyre on all 4 wheels otherwise you could affect the "at the limit" handling.

The issue is the centre diff, not the front/rear diffs.

The centre diff is not designed to have any difference in wheel speed front/rear.

To be acurate it is actually front/rear propshaft speed. It is the viscous centre diff which would suffer.

I remember hearing or reading a few months back about a chap who had bought four brand new tyre. Popped them on his car and it handled like a dog. Turns out that there were 3 tyres from one batch and one from another. If different batches of the same tyre from the same company can do this to a car, just think what different sizes and/or tyre type combinations can do!

Cheers,

Pat.

Where does it say in the owner's manual about different tyre wear damaging the transmission? I'm only a 'trainee' Subaru owner, but am soon to change to my third set of tyres after 28K miles in the ten months I've had by MY99 car. What I've had to do is swop the front tyres to the back after about 7.5K miles and then change all four at around 15K miles. Am I doing the right thing?
On the subject of tyres, I'm currently running Yoko 520's which seem great, even though they are a bit noisy and lively in the wet, at £100 each fitted they don't seem bad. Can anyone tell me what the Pirelli P-Zero's are like?

If the centre diff can't handle different speeds of the front and rear wheels, how does that sit with the 4WD system transferring power to the slipping wheels when you get wheelspin? Doesn't that actively encourage it or I am missing something fundamental?

A few rough calculations have come up with the following numbers.

difference in rolling radius due to 2mm tread depth difference= 0.6%

difference in turn radius of left and right wheels for 10m inside wheel radius= 15%

difference in front to rear proshaft speeds for same 10m rear inside radius= 3%


Sounds to me like any suggestion that a 2mm front to rear tread difference will damage the transmission or spoil the handling has no basis in fact. This agrees with Richards comments above.

Alan

I blew a tyre last year and replaced only 2. However, I made the big mistake of putting 2 different tyres onto the front. You need to read

alanp: thank god someone is talking sense.
If a diff cannot cope with differences in speed what is it there for?

The difference in tyre diameters is miniscual compared to the other differences these components are meant to deal with.

I am shortly to be needing 4 new tyres and am therefore reading all these tyre threads with vigor!

Winter tyres/best wet tyres/2 sets of tyres etc. etc. - it's fascinating.