Things about tyres

[barks944]

I don't intend for this to be the usual which tyres should I by thread but more of a collection of information that would help people select a tyre. This is partially inspired by the clever chap who designed the GTR, I was interested to see how he designed the car around the tyres. I would like to know what people thing about some of the ideas that have been bouncing around in my head.

• For any given tyre there is a point where the rate of increase in grip per unit area due to additional force pushing down on the tyre is at a maximum.
• Adding weight to a car increases overall grip but also increase the forces required to accelerate the car, requiring more grip. There is an optimum weight for a tyre where the grip generated best matches the grip required to accelerate the car. Therefore there is an optimum tyre contact patch for any given weight of car/compound/tread pattern that will give the highest accelerations.
• Fitting wider tyres of the same compound/tread increases the area over which the weight of the car is applied to the road reducing the overall grip per unit area. You could end up with less grip doing this if the increase in contact area from the increased tyre width does not compensate for the overall reduction in grip per unit area.
• The weight considered on the tyre should be the weight on the tyre when accelerating e.g during cornering there is weight transfer onto the tyre.

 

[BlackMagic]

Just remember that the traction delivered by a tyre is a function of the friction coefficient between the tyre compound and the road surface. Total friction is friction coefficient multiplied by weigt. Hence, in theory at least, type width has little effect on friction. However, there are considerations such as soft tyres (ie high grip) can only take so much force per unit area before the rubber is just torn away, tall sidewalls flex too much and the tyre rolls onto its side, etc.

The real challenge is to find a tyre in the right size for the car that has a compound that suits the driving conditions that you experience most of the time. Too soft and you will have fantastic grip but no life, too hard and they will last but less grip, and then you have to deal with road temperature, wet or dry, etc. etc.

Hence there are so many view on what the 'right' tyre is.

 

[zcacogp]

Here is the most informative (bar none) stuff I have ever read about wheels and tyres.

http://www.carbibles.com/tyre_bible.html

A couple of pages of good reading, with some excellent stuff on contact patches on the second page.

Well worth taking half-an-hour or so to read.


Oli.

 

[barks944]

That's a good read thanks for the info. Going to stick with the conti sport contact 2' that are on the car now I think.

 

[ChasR]

I'm not entirely convinced by the treadwear ratings on the side of tyres and it is always something that I will take with a pinch of salt. As an example, Pirelli tyres have a treadwear rating of 180, and Michelin Pilots (in general) are around 280 with others being above that (I think the Falkens are). On two cars I have owned, P6000s seem to last an eternity (on my Pug 306 GTi-6 it was still on it's second set of P6000s with plenty of tread after the car covering 117,000 miles with the tyres being at least 5 years old according to the DOT codes). Again, the Michelin Pilots on my sister's car seem to be wearing very well, far better than the Hankook's or Continentals that were on the car.

 

[Neil Haughey]

I agree with ChasR, that is certainly my experience as well. The wear rating seems to bare little resemblance to actual mileage. As an example I have Hankook RS-2s on the 968 at the moment, previously I had gone off them as a not very good track tyre due to being so hard and taking so long to warm up. I take that back now as I have done several thousand road miles on em now and they still have a good 5 mm of tread. It seems that anything less then 10/10ths seems to not touch them. Not a great track tyre perhaps but a surprisingly good road tyre if a bit dodgy in the wet. Yokohama tyres seem to be the complete opposite, no matter how gently one drives they wear away in a few thousand miles. Best tyres I have where Michelin pilots on my old Saab 9-5, great grip cold wet or dry and they seemed to last really well.