Optimum Tyre Width
Discussion
Hi Guys
I was wondering last night what is the optimum tyre width for a given wheel size? How do you know? If for example you're running a FWD car on 18 inch rims do you put 235 on the front and 245 or 255 on the rear etc.
Surely the wider the tyre the more grip in all conditions yes? So why not fit the widest possible like 355 front and rear LOL. Of course I just know there must be a trade off but I dont know what it is?
Mark.
I was wondering last night what is the optimum tyre width for a given wheel size? How do you know? If for example you're running a FWD car on 18 inch rims do you put 235 on the front and 245 or 255 on the rear etc.
Surely the wider the tyre the more grip in all conditions yes? So why not fit the widest possible like 355 front and rear LOL. Of course I just know there must be a trade off but I dont know what it is?
Mark.
In the racing world (which I presume you're talking about in the Motorsport section), the way to get the most traction it to buy the softest compound you possibly can, then go wide enough to control the temperatures. There are obvious limitations of regs and bodywork.
With road tyres you can keep going wider, but you will sacrifice wet weather ability, noise, comfort etc, but you will reach a point where the suspension's geometry control means most of the tyre isn't doing anything anyway.
With road tyres you can keep going wider, but you will sacrifice wet weather ability, noise, comfort etc, but you will reach a point where the suspension's geometry control means most of the tyre isn't doing anything anyway.
Soul Reaver said:
Hi Guys
I was wondering last night what is the optimum tyre width for a given wheel size? How do you know? If for example you're running a FWD car on 18 inch rims do you put 235 on the front and 245 or 255 on the rear etc.
Why would A: The diameter of the tyre have any bearing on it's width, and B: why would you put wider tyres on the rear of a FWD?I was wondering last night what is the optimum tyre width for a given wheel size? How do you know? If for example you're running a FWD car on 18 inch rims do you put 235 on the front and 245 or 255 on the rear etc.
If this is to increase grip for competition, then fit the widest tyres that will safely fit on your wheels, that you can fit without either fouling suspension components or the wheel arches, and without significantly affecting the scrub radius with low offset wheels. Then buy the softest compound that you are either allowed to by regulation, or can afford in terms of wear.
Edited by Kozy on Thursday 15th November 10:10
It depends where you're approaching it from.
If the regs specify a maximum wheel width (lets say 7.5") you would obviously refer to your preferred (or perhaps specified) tyre manufacturer for a recommended tyre size.
But then it can get interesting, because the tyre manufacturer may say you can use anything from a 185 to a 215 section on that rim - so do you always go for the biggest?
IMHO not necessarily, because a smaller tyre slightly stretched on the rim will give better response to steering inputs than a larger section with a relatively squashy sidewall. This is not just my opinion btw but advice offered to me (and anyone else who asked, I guess) by the motorsport department at Toyo, specifically about their R888 tyre.
In the end, you've got to test any setup to see whats best for you, in your car, at that track, on that day - so not many variables there, then
Kim
If the regs specify a maximum wheel width (lets say 7.5") you would obviously refer to your preferred (or perhaps specified) tyre manufacturer for a recommended tyre size.
But then it can get interesting, because the tyre manufacturer may say you can use anything from a 185 to a 215 section on that rim - so do you always go for the biggest?
IMHO not necessarily, because a smaller tyre slightly stretched on the rim will give better response to steering inputs than a larger section with a relatively squashy sidewall. This is not just my opinion btw but advice offered to me (and anyone else who asked, I guess) by the motorsport department at Toyo, specifically about their R888 tyre.
In the end, you've got to test any setup to see whats best for you, in your car, at that track, on that day - so not many variables there, then
Kim
Count Johnny said:
Surely, in the racing world, you should attempt to align the contact patches with the weight distribution of the car. In other words, if the weight ratio of your car is 45/55 (front to rear) then it is desirable to have contact patches that are also 45/55 (front to rear).
This is extremely tyre specific. Your contact patch size is generally a function of tyre width, tyre pressure and applied load. The equation that dictates this varies massively from tyre to tyre. An ideal tyre's contact patch is actually independent of tyre width (supposedly, although its been a while since I did the sums), however tyre carcass stiffness screws this up.So essentially, a 10% load difference does not mean you need 10% width difference, the fact that the load is greater on one axle by itself will increase contact patch size.
Tyre width is a lot more to do with temperature control.
Just speculation, as I have no real knowledge of the subject, but I do suspect that you can have too much tyre for a given vehicle/tyre compound combination. If you have a very large contact patch the amount of work per unit area will be reduced - possibly to the level where the tyre never gets up to its optimum working temperature? Then of course, there's the suspension geometry to consider - seems to me the wider the tyre the more susceptible it is to camber changes.
andylaurence said:
In sprinting, a tyre never gets up to temperature in my experience. I'd say go soft and go wide, in that order.
In some situations I would agree, but hot weather and longer distances can cause soft tyres to overheat.1 & 3/4 laps of Llandow on a hot day for example will have your sticky 888's, etc, turning to putty.
Adam205 said:
This is extremely tyre specific.
Kinda my point. If you are free to choose your tyre, then I'm suggesting you choose one that matches the static weight distribution of your car. In the case of my Speads, this means using Hoosiers (for which my car was originally designed) in preference to the (much easier to obtain and a little cheaper) Avons that I had to run when we had a brief foray into the SPEED Series.Adam205 said:
So essentially, a 10% load difference does not mean you need 10% width difference, the fact that the load is greater on one axle by itself will increase contact patch size.
Not, surely (and I stand to be corrrected) by 10%?Adam205 said:
Really? My A15 avons were going off at Pembrey and Llandow!
Perhaps it's just me then. My Avons were going off after two back-to-back 1.75 lap runs at Llandow on a hot day earlier this year. Llandow is particularly abrasive though. I tend to get the tyres up to temperature on longer sprints and the only time they've been too hot on a sprint was at Silverstone last year on a 1.75 lap run around the Stowe circuit. It was really quite hot that day. Generally, I'm struggling to get heat into the tyres in the 35-80 seconds of a sprint. For reference, the car weighs about 510kg with me in it on the starting line and the tyres are 210 width, although I previously ran the softest compound Yokohamas in a 200 width and the results were similar. The engine is a standard K8 GSXR1000.chris_w said:
You can overtyre a car too - a friend who races MX-5's swears the extra drag on the straights (of fitting wider tyres) negated the benefits in the corners.
This was very obvious at Spa the other year. Two of the cars with us were a Class A and a Class B Mg Midgets.the class A runs more power, less weight, and wider tyres. the class A was quicker through the twisties but on the long kemel straight the class b car on its narrower slicks would overhaul it and go past.
Many many good pointers here.
The optimum width is related to (a) weight of the car (b) power of the car (c) downforce [which is co-related to (a), (d) rolling radius of the wheel/tyre combination.
If you can't get heat into the tyre, it won't work.
If your tyre is too wide it'll cause too much drag and you'll be a sitting duck on the straight.
If your car has an excess of grin inducing horsepower, ie: high power to weight, then you can get away with bigger boots as you can use that horsepower to wear them out/heat them up to working temp easily.
If you're running a stock MX5, then 145/13's are probably plenty
I've been working on a plan to take one of my old FWD cars and make it the "ultimate" that it can be, and looked at wheel/tyre size. To get the best rubber, I need to be looking at GT rubber, as that's where the development is, and that means 18". The car is light, or will be, aiming for around the 500-550Kg FWD, so realistically I don't want to go beyond 9" wide which is pretty well as narrow as I can go to get that GT rubber. With that in mind, the little varmit should be a limpet and having about 400hp/tonne it ought to be quite quick!
The optimum width is related to (a) weight of the car (b) power of the car (c) downforce [which is co-related to (a), (d) rolling radius of the wheel/tyre combination.
If you can't get heat into the tyre, it won't work.
If your tyre is too wide it'll cause too much drag and you'll be a sitting duck on the straight.
If your car has an excess of grin inducing horsepower, ie: high power to weight, then you can get away with bigger boots as you can use that horsepower to wear them out/heat them up to working temp easily.
If you're running a stock MX5, then 145/13's are probably plenty
I've been working on a plan to take one of my old FWD cars and make it the "ultimate" that it can be, and looked at wheel/tyre size. To get the best rubber, I need to be looking at GT rubber, as that's where the development is, and that means 18". The car is light, or will be, aiming for around the 500-550Kg FWD, so realistically I don't want to go beyond 9" wide which is pretty well as narrow as I can go to get that GT rubber. With that in mind, the little varmit should be a limpet and having about 400hp/tonne it ought to be quite quick!
Gassing Station | UK Club Motorsport | Top of Page | What's New | My Stuff