Tyre max speed rating?

[TTM]

Hello everyone,

Anyone heard of issues when driving "much faster" than the speed for which a tyre is guaranteed for?

 

[GlennS]

I'm not sure how that circumstance would come about as it will be an insurance requirement that tyres meet the vehicle manufacturers specifications and those are rated to the maximum speed of your car. An exception MIGHT be winter tyres as those are sometimes specified at lower v-max than the car is capable of. As an example, my Merc handbook specifies "H" rated winter tyres and recommends that I set the car's speed limiter to avoid inadvertently exceeding 130mph (summer tyre requirement is "W" as the car is limited to 155).

Whilst there might be some "wriggle room" in the tyre manufacturer's speed ratings exceeding them sounds like a bad idea.

 

[TTM]

I don't think anyone said it was a good idea, I was just asking if there was documented cases of things having "gone wrong" in such circumstances.

 

[JamesO]

If you had asked the question a day earlier, I could have asked a physicist chap I know who used be involved in the design of car tyres who strangely moved into weather prediction/forecast. Won't see him for a while now unfortunately.

 

[Mark Elder]

This is a while ago now but might indicate the type of problem: I was driving a girl friend's car up the M6 without knowing it had re-molds (remember them?!) on it. After I while I realised there was a worsening "wheels out of balance" wobble developing. Stopped on hard shoulder to check the tyres and one had developed a nice bulge about 6" long in middle of tread. Appeared the layers of thread had separated so the tread could come away from the tyre.

 

[Indi9xx]

This is one of the worries I have about tyres, Z is rated for 150MPH Plus, but what is its limit?

If it had no limit, then Bugatti would not have developed special tyres for the veyron.

I have been up to 175 on Z rated tyres, without issues.

Then you have Y rated tyres, which are limited to 186 MPH..

So for the 200 MPH club, what tyres to use?

 

[JamesO]

I will try and get hold of Ben but I fear the answer will, from past conversations over beer about tyre testing and design, be far from simple and definitive involving many different parameters and calculations.

 

[TTM]

James, would be nice to hear what this guy has to say about it.

I suppose the speed rating relates to how hot a tyre can get before "going wrong".

Maybe it's ok to push tyres to a speed that's higher than their rating, but certainly not stay there for any extended time?

 

[TTM]

ORIGINAL: Indi9xx
Then you have Y rated tyres, which are limited to 186 MPH..

So for the 200 MPH club, what tyres to use?

I spotted a (Y) rating for 186+ mph.

 

[Indi9xx]

Are you thinking of seeing how the 944 copes at over 200mph then TTM?

 

[George Elliott]

[] my thoughts exactly Jon

 

[TTM]

... [] ...

On a side note, any clue on what's the biggest and lightest brake caliper one can fit under 17" Cup wheels? Aren't 996 calipers lighter than big blacks while using the same pads?

 

[George Elliott]

Was unaware of that TTM, but unsprung weight is the enemy

I see "Carbon Revolution" rims have continued where Dymag failed.........

You got a front splitter...they go slightly floaty in 5th (or 6th) eventually
George
944t

 

[TTM]

I agree about unsprung weight, but I think having a fully secure set up is more important, especially considering that past a certain speed on a straight line, (unsprung) weight should not be that relevant, and the issue here is there does not seem to be any 245/45 16" tyre rated for 186+ mph speeds.

I agree that a front splitter is obligatory, as the front end gets uncomfortably light well past 120 mph. Not a problem on the car in question.

 

[Hilux]

Any tyre with a rating should be used only for 10 minutes or so at that speed - if you need to do that speed continuously you should be on the next rating (or two) upwards as they can overheat disastrously - just like anything on its limit.