Best/Worst OEM Wheels
Discussion
Tigger2050 said:
It's not a suggestion, it is an absolute physical fact.
Go read this thread:https://www.pistonheads.com/gassing/topic.asp?h=0&...
"For the same pressure a wider tyre could easily have a larger area because contact patch is affected more by tyre construction than by pressure. Pressure has an effect, but it's a non-linear effect with maximum and minimum values dictated by tyre construction. The fact that there are tyres that function perfectly well without air in them at all shows the relative significance of of tyre construction."
Olivera said:
Go read this thread:
https://www.pistonheads.com/gassing/topic.asp?h=0&...
"For the same pressure a wider tyre could easily have a larger area because contact patch is affected more by tyre construction than by pressure. Pressure has an effect, but it's a non-linear effect with maximum and minimum values dictated by tyre construction. The fact that there are tyres that function perfectly well without air in them at all shows the relative significance of of tyre construction."
If you take a completely differently constructed tyre then the patch might be different. A solid rubber tyre would be different.https://www.pistonheads.com/gassing/topic.asp?h=0&...
"For the same pressure a wider tyre could easily have a larger area because contact patch is affected more by tyre construction than by pressure. Pressure has an effect, but it's a non-linear effect with maximum and minimum values dictated by tyre construction. The fact that there are tyres that function perfectly well without air in them at all shows the relative significance of of tyre construction."
We are talking road cars here and different sizes of very similarly made tyres. Tyre manufacturers may use slightly different rubber compounds, will have different tread patterns but they are very similar in construction. Put 15" Michelens against 20" Michelen's on the same car and the contact patch will be the same. The difference between Michelen, Pirelli or Bridgestone's will be absolutely minimal.
I don't know why people are so upset about the basic physics that control the contact patch on pneumatic tyres.
Perhaps they don't like to accept that their 'garden roller' tyres are putting no more rubber down than the basic model's tyres.
Olivera said:
Go read this thread:
https://www.pistonheads.com/gassing/topic.asp?h=0&...
"For the same pressure a wider tyre could easily have a larger area because contact patch is affected more by tyre construction than by pressure. Pressure has an effect, but it's a non-linear effect with maximum and minimum values dictated by tyre construction. The fact that there are tyres that function perfectly well without air in them at all shows the relative significance of of tyre construction."
I'd also question that statement. Pretty sure pressure has a larger effect. https://www.pistonheads.com/gassing/topic.asp?h=0&...
"For the same pressure a wider tyre could easily have a larger area because contact patch is affected more by tyre construction than by pressure. Pressure has an effect, but it's a non-linear effect with maximum and minimum values dictated by tyre construction. The fact that there are tyres that function perfectly well without air in them at all shows the relative significance of of tyre construction."
DoubleD said:
Has anyone got a link to a proper study on this contact patch thing? And no im not upset because my 22inch spinners have no more grip than a smaller tyre.
Lots on line about the subject. It is a pretty straightforward application of physical laws though.As I said before, a wider, lower profile tyre will have more traction on a smooth track surface.
On handling with the smaller tyre, the contact area is the same size as on the wider tyre as this is decided by weight and tyre pressure. The contact patch is a different shape though, being longer and thinner.
Given a perfectly smooth road surface this tyre should start to lose grip earlier due to the bigger slip angle of the higher profile tyre and the fact the tyre will start to slide from the slimmer front of the contact patch. The wider contact patch of the bigger lower profile tyre will therefore hang on longer but will break away less progressively as it is a shorter contact patch. The driver gets more warning about reducing traction with the slimmer tyre.
It all presupposes a smooth surface though, on a bumpy ridged surface, the suspension will be able to keep the lighter wheels in contact with the road surface more readily, so through any particular corner you might well have an overall higher average traction than with the heavier more bouncy wheel.
DoubleD said:
So a bigger but lighter wheel is best overall?
Well yes, for wider lighter wheels, traction and handling would be better. Low profile tyres would be bad for ride though.Hard to make bigger wheels lighter than smaller wheels though, unless you are going to sacrifice strength or come up with some fancy and expensive materials, not very realistic for road cars.
Tigger2050 said:
DoubleD said:
So a bigger but lighter wheel is best overall?
Well yes, for wider lighter wheels, traction and handling would be better. Low profile tyres would be bad for ride though.Hard to make bigger wheels lighter than smaller wheels though, unless you are going to sacrifice strength or come up with some fancy and expensive materials, not very realistic for road cars.
DoubleD said:
Obviously this depends on the weight of the wheels that you start with, but you can easily get inexpensive light alloys for road cars.
You also have to bear in mind that it's the total unsprung weight which matters more than the wheel weight - so wheels, brakes, hubs, uprights, bits of the damper and wishbones... reducing the weight of the wheels by 50% will probably reduce the overall unsprung mass by no more than 20% so you will still need a significant degree of suspension compliance between the rim and the road in order to maintain grip on bumpy surfaces. I recently read an interview of an F1 designer who was claiming that the increase in wheel size from 13 to 18 inch next year will significantly reduce overall grip levels simply because of the loss of sidewall compliance and that's on relatively smooth circuits with very light wheels.
kambites said:
I recently read an interview of an F1 designer who was claiming that the increase in wheel size from 13 to 18 inch next year will significantly reduce overall grip levels simply because of the loss of sidewall compliance and that's on relatively smooth circuits with very light wheels.
Maybe they'll come here for some advice and change to narrower wheels and tyres, on the front at least. Tigger2050 said:
On handling with the smaller tyre, the contact area is the same size as on the wider tyre as this is decided by weight and tyre pressure.
No. No it's not. Because the rigid structure of the tyre doesn't deform like a balloon.http://www.enginebasics.com/Chassis%20Tuning/Tire%... -
"Contact patch pressure is constant and equal to air pressure? No, not even close. Wide tires have a greater contact area? From this data it appears very likely. Which would mean the "wide tires are softer and therefore give more grip" argument is bunk. The contact patch is bigger, and the contact patch pressure is lower"
Also:
http://www.tyrereviews.co.uk/Article/Do-wider-tyre...
Olivera said:
No. No it's not. Because the rigid structure of the tyre doesn't deform like a balloon.
http://www.enginebasics.com/Chassis%20Tuning/Tire%... -
"Contact patch pressure is constant and equal to air pressure? No, not even close. Wide tires have a greater contact area? From this data it appears very likely. Which would mean the "wide tires are softer and therefore give more grip" argument is bunk. The contact patch is bigger, and the contact patch pressure is lower"
Also:
http://www.tyrereviews.co.uk/Article/Do-wider-tyre...
A denial of physics on similarly constructed tyres. If you compare differently constructed tyres like run flats there will be a different relationship. On like for like tyres the relationship holds.http://www.enginebasics.com/Chassis%20Tuning/Tire%... -
"Contact patch pressure is constant and equal to air pressure? No, not even close. Wide tires have a greater contact area? From this data it appears very likely. Which would mean the "wide tires are softer and therefore give more grip" argument is bunk. The contact patch is bigger, and the contact patch pressure is lower"
Also:
http://www.tyrereviews.co.uk/Article/Do-wider-tyre...
The first bloke gives a ton of figures that are actually based on conjectures that he seems to have invented in his own mind. He actually says that in the Avon tests they did not measure the size of the contact patch.
The second bloke compared the differences in tyres that were at different tyre pressures!!! Of course there was a variance. The relationship in pneumatic tyres is weight and tyre pressure = contact patch
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naturalaspiration said:
daniel1920 said:
Pressure = Force (mass x G in this case ) / Area
The pressure hasn't changed
The Force hasn't changed
The Area...
Let's not confuse tyre air pressure with the pressure exerted by gravity force over the tyre contact surface.The pressure hasn't changed
The Force hasn't changed
The Area...
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