Tyre Width Advice without rubbing
- Thread starter sumotan
- Start date
CheersI think your post here shows you understand as much as you need to. Wider profile gives more contact area, a greater wheel diameter does the same but only very very marginally.Nictrix said:Oooohh you made yourself look all clever by trying to spell it out but really it just looks the same with no explanation. :thumbsdown:mr wilks said:Nictrix said:
I'l tryhere we go nice and slow
a 2 4 5 - 4 0 - 1 8 tyre fitted to a 8.5j rim will have a greater contact area on the tarmac than a 2 5 5 - 3 5 - 1 8 tyre .
It was a simple question that I thought you might have been able to explain.
Surely a 255 tyre has 10mm more tread across the width of the tyre in contact with the road than a 245, so how does increasing the sidewall by 5% increase the contact area of the tyre?
The fact remains that BMW know best when it comes to tyres. More rubber will lower your aqua planing speed and reduce grip in the wet generally.
May be better in the dry but I am not a tyre/suspension etc engineer or developer.
mcbutler said:I think your post here shows you understand as much as you need to. Wider profile gives more contact area, a greater wheel diameter does the same but only very very marginally.Nictrix said:Oooohh you made yourself look all clever by trying to spell it out but really it just looks the same with no explanation. :thumbsdown:mr wilks said:I'l try
a 2 4 5 - 4 0 - 1 8 tyre fitted to a 8.5j rim will have a greater contact area on the tarmac than a 2 5 5 - 3 5 - 1 8 tyre .
It was a simple question that I thought you might have been able to explain.
Surely a 255 tyre has 10mm more tread across the width of the tyre in contact with the road than a 245, so how does increasing the sidewall by 5% increase the contact area of the tyre?
The fact remains that BMW know best when it comes to tyres. More rubber will lower your aqua planing speed and reduce grip in the wet generally.
May be better in the dry but I am not a tyre/suspension etc engineer or developer.
Actually that's incorrect. ANY PROFILE OF TIRE will have, by definition, the same contact area for a given level of inflation. That last bit is important.
So, lets do the math. For convenience lets say theres a 2000 pound car. Each tire by definition has about 500 pounds on it (assuming 50/50, etc etc). If you air the tire up to 50psi (again convenience of numbers) thats 50 pounds per square inch. The math show us that we have 10 square inches of contact area. Period.
A wider tire at the same inflation will have a different geometry to the contact path. Wider side to side, and shorter front to back, but still 10 square inches in my example. However, with a wider tire you CAN deflate a bit, giving you a wider contact area, without having the tire deform as much. I think thats where the myth of "wider tire means more contact area" comes from. You also change whether you have more traction front to back or side to side depending on how you change the geometry of the contact area.
Now, there may be some differences brought upon by the fact that at the very edge of the contact area you dont get the full pressure, it feathers out. And that region will be larger on a wider tire. So a wider tire probably does have SLIGHTLY more contact area as a result, but its pretty close to negligible in the grand scheme of things.
