race tyres coefficient of friction
Discussion
I'm doing a university project around vehicle braking and wanted to put some reasonably accurate data in. Does anybody have a rough idea of the coefficient of friction of a general racing slick (GT3 sort of spec.) and that of a semi slick track day tyre (toyo R888 etc.) At a guess I would put the slick at 0.90 - 1.0 and the R888 at 0.75-0.85 but wondered if anyone could enlighten me with any data they may have.
Thanks
Thanks
No, tyre adhesion doesn't follow classic physics. I don't know specific numbers but a good road tyre probably has a CF around 1.0. I think I am right in saying that the Dunlop Historic race tyres that I have on my Formula Ford have a CF around 1.3. I have seen numbers greater than 1.7 for modern racing tyres probably higher.
You also need to know that the CF of a tyre typically drops off as load increases. So, if you corner hard and transfer and extra 50% load to the outer tyres their grip does not increase by 50%. This is why light cars with low CG's corner better then heavy cars with a high CG.
Tyres not only rely on friction, they also "bond" to the track surface, (track tyres get sticky when hot) and then there is a mechanical component where the rubber conforms to the track surface and achieves some mechanical keying.
Also, remember that the track surface has a lot to do with the amount of friction (grip) that you can achieve from any given tyre. When I was first driving the local council started to apply Shell Grip on bends etc, awesome amount of grip even from my Morris Marina on battery casing tyres.
Tyres are a complex subject, there will be others here that know much more than I.
You also need to know that the CF of a tyre typically drops off as load increases. So, if you corner hard and transfer and extra 50% load to the outer tyres their grip does not increase by 50%. This is why light cars with low CG's corner better then heavy cars with a high CG.
Tyres not only rely on friction, they also "bond" to the track surface, (track tyres get sticky when hot) and then there is a mechanical component where the rubber conforms to the track surface and achieves some mechanical keying.
Also, remember that the track surface has a lot to do with the amount of friction (grip) that you can achieve from any given tyre. When I was first driving the local council started to apply Shell Grip on bends etc, awesome amount of grip even from my Morris Marina on battery casing tyres.
Tyres are a complex subject, there will be others here that know much more than I.
The best way is to look at what sort of acceleration is being achieved. This would give you a rough estimate of the average Cf. If a car is achieving a maximum of 1.8g with no aero effect then the average Cf is 1.8.
Although I suspect that you're trying to do it the other way round which isn't really possible (too many other effects as previously explained). You can look at tyre data on the Avon website for a reasonable comparison of tyre characteristics (http://www.avonmotorsport.com/resource-centre/downloads) but you won't get an absolute number out.
Although I suspect that you're trying to do it the other way round which isn't really possible (too many other effects as previously explained). You can look at tyre data on the Avon website for a reasonable comparison of tyre characteristics (http://www.avonmotorsport.com/resource-centre/downloads) but you won't get an absolute number out.
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