Just wondering how strict tyre ratings are?!

I would never push them on the road, but I am looking at tiddly rear wheels/tyre combos for use on the back axle when doing straight line drag racing. A tempting tyre at the moment is the Toyo E60, but it's an M rated tyre which means 81mph.... I will be aiming for 1/4 mile passes at around 105mph (hopefully soon....)

So, the question is whether the speed rating perhaps can be "inflated" a bit for straight line use only, and not on driven wheels?

It would be the ideal tyre size at 125/70 R14.

The safest next option is using 155/65 R14 which are generally all T rated tyres, up to 118mph.

they generally do have a safety factor for speed ratings, but they will wear out really quickly too if you push them

I personally would never take a tyre past it's speed rating to the extent that 105mph is over 81mph. That is pretty much a 20% difference, which is quite high....

Not speaking from experience though so I'm sure someone else with more knowledge will be able to help more

Aye - I just thought perhaps speed ratings were more to do with the forces a tyre is put under whilst cornering at, say 81mph, whereas I would hope to be putting them under very little stress in a straight line.

I'm not sure, hence the question.

Got some 12" wheels?

YOKOHAMA TYRES / TRACKDAY TRACK DAY / YOKOHAMA A048 R ADVAN YOKOHAMA AO48 R - 165/55R12 (M-MEDIUM) :: :: Track Day Tyres - Trackday Tyres - Motorsport Tyres :: R12" - 165/55/12, 165/55 R12 ::

I'm wanting 14" really just so I continue to use furby steel wheels.

And I know a 125 wide space saver will look quite odd on a fabia steel, with the steel being I think 5.5J (so roughly 14cm) and the tyre actually being narrower. "Stretch" on a steel....

You can get those in 14" too and the come in S M and I think H for soft, medium and hard compound.

Of course you could always use a more normal tyre, and put the pressure up to the limit, if you're trying to reduce rolling resistance.

Speed ratings are based on a 10 minute "endurance test" rather than an instantaneous speed, so if you are only doing 1/4 mile passes there should be some factor of safety there - although I have no idea how much.

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I'd concur with Andy here, speed rating isn't likely to be based on an instantaneous thing, 1/4 miles should be fine surely...?

Speed ratings are based on a 10 minute "endurance test" rather than an instantaneous speed, so if you are only doing 1/4 mile passes there should be some factor of safety there - although I have no idea how much.

This is kind of what I was hoping, and what would be verified. Thanks for the link - kind of confirms this in a vague way. Any "pressure" would be straight line only and I would not use them on the road.

I know the mongrel isn't quite a drag racer - but here is some super-slo-mo video footage showing what happens to the tyres on those things...

YouTube - Drag racing - super slow motion camera

I'm sure similar forces are involved with your car - even if not quite the same magnitude

Bearing mind these are for the back wheels only which are just trailing in a Fabia, I'd not be too concerned.

I can't use Youtube from work. Is that footage of a drag racing slick? If so, it's designed to wrinkle when still, distort on launch, and actually grows to about twice its resting radius at 200mph!

Hmm - 125 wheels on the front, and 215 alloys on the rear. Now THAT would be a fun 1/4 mile

I can't use Youtube from work. Is that footage of a drag racing slick? If so, it's designed to wrinkle when still, distort on launch, and actually grows to about twice its resting radius at 200mph!

Yes - its been around on youtube for a while - but still impresses me

Since it's for the track and not the road could you buy part worn tyres of a higher rating?

Would a tyre dealer sell you cast offs with a few mm of tread?

I don't know if they are allowed to.

However, you will look like this:

with the steel being I think 5.5J

Thought the 14'' steel wheels only came in 2 width's and 5.5J is not one of them. IIRC they came in 5J and 6J

Call me crazy but I thought the main thing with speed ratings was the heat.

At the recommended pressure the tyre will be sightly flatter at the bottom where it touches the ground.

As the tyre turns the whole circumference will be flattened in turn and the sidewalls flex and then heat up.

It is the heat that is the problem.

If you only do a short run there won't be long enough for the tyres to heat up (since they aren't the driven wheels).

I think you'll be fine, esp. if you turn up the tyre pressures a bit to reduce the flexing a bit.

*disclaimer*

I don't know what I'm talking about.

I don't know what I'm talking about.

Neither do I but.....

Your post seems to explain why the ratings are given based on a 10 minute "endurance test".

Anyway - its only Jason - I'm sure he's expendable in the name of scientific research for the benefit of the Briskoda masses.

And if it does all go horribly wrong its not like he's a stranger to being upside down

Interesting read, as like Jason, I am going to do something similar me thinkies.

Anyone got any links to some 'thin' steelies to purchase for the rear of ours?