what's the deal with larger diameter tires...
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what's the deal with larger diameter tires...
on the rear and smaller diameter on the front? better heat capacity/dispersion? less rotations per mile giving you better longevity?
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IIRC, the larger rear is for durability/strength. Think that is what my buddy that works all the ALMS races for Michelin told me
I will see him tomorrow and double check
I will see him tomorrow and double check
Last edited by Mike Buck; 10-13-2006 at 12:29 AM.
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Originally Posted by smlporsche
Another possible explanationis that with a larger diameter tire the contact patch will also be larger, all other things being equal.
#5
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Larger diameter tires will have a large contact patch than a smaller diameter tire. This is because the OD of the tire has less of an arc and more of it is contacting the ground. Additionally, a larger diameter tire on the same size rim has more air in it and a larger sidewall which aids in the loading of a tire. For instance, for the guys running Daytona, you would want to run a 680 rear tire over a 650 on the banking, particularly on the right rear tire where there will be substantial loading. I would not be surprised if the 650 diameter tires on a stock class car come apart during the club races.
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Originally Posted by Geoffrey
Larger diameter tires will have a large contact patch than a smaller diameter tire. This is because the OD of the tire has less of an arc and more of it is contacting the ground.
Originally Posted by Geoffrey
Additionally, a larger diameter tire on the same size rim has more air in it and a larger sidewall which aids in the loading of a tire. For instance, for the guys running Daytona, you would want to run a 680 rear tire over a 650 on the banking, particularly on the right rear tire where there will be substantial loading. I would not be surprised if the 650 diameter tires on a stock class car come apart during the club races.
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On most cars including the GT3 cup.RS.RSR it's about loading, which Geoffrey mentioned. A larger/taller tire will support heavier loads and more side loads. Remember all the people blowing out super low profile 18" rear tires on the heavier stock cars (Hoosiers and Michelins)? they were using a tire that could not support the heavy loads on the rear of a 911. I think Hoosier even claimed the tires were designed for the front axle. Using taller tires solved the problems.
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Originally Posted by analogmike
On most cars including the GT3 cup.RS.RSR it's about loading, which Geoffrey mentioned. A larger/taller tire will support heavier loads and more side loads. Remember all the people blowing out super low profile 18" rear tires on the heavier stock cars (Hoosiers and Michelins)? they were using a tire that could not support the heavy loads on the rear of a 911. I think Hoosier even claimed the tires were designed for the front axle. Using taller tires solved the problems.
#9
The notion that the tire contact patch area won't change is incorrect. If the tire was a
perfectly flexible balloon, then that would be true, like the elementary physics lesson
would teach. However, modern tires with their stiff sidewalls are significantly rigid,
and consider the run-flat tires too. The other elementary physics lesson concerns a
rigid cube. The surface area contacting the ground does not change with increasing
weight, only the pressure per square inch.
A modern tire is somewhere between the perfectly flexible balloon and the solid
block, so all other things being equal, a wider/taller tire will increase tire contact patch,
and the contact patch shape will change, and the average contact pressure will go down.
The one sure calculation is that the contact patch area times the contact pressure will
be the same for either tire. NB: the contact pressure is not constant over the whole patch
either, for the same tire-as-significantly-rigid reason.
Tire tests also show that maximum lateral friction increases with weight (as you'd expect),
but the increase is less than one-to-one. Therefore, within reason a given load placed on
a wider tire is like a lesser load on an identical tire, and should stick better. The head of
Michelin's F1 tire team said that in the absence of tire regulations, tire widths would be
significantly wider.
Joe Weinstein
perfectly flexible balloon, then that would be true, like the elementary physics lesson
would teach. However, modern tires with their stiff sidewalls are significantly rigid,
and consider the run-flat tires too. The other elementary physics lesson concerns a
rigid cube. The surface area contacting the ground does not change with increasing
weight, only the pressure per square inch.
A modern tire is somewhere between the perfectly flexible balloon and the solid
block, so all other things being equal, a wider/taller tire will increase tire contact patch,
and the contact patch shape will change, and the average contact pressure will go down.
The one sure calculation is that the contact patch area times the contact pressure will
be the same for either tire. NB: the contact pressure is not constant over the whole patch
either, for the same tire-as-significantly-rigid reason.
Tire tests also show that maximum lateral friction increases with weight (as you'd expect),
but the increase is less than one-to-one. Therefore, within reason a given load placed on
a wider tire is like a lesser load on an identical tire, and should stick better. The head of
Michelin's F1 tire team said that in the absence of tire regulations, tire widths would be
significantly wider.
Joe Weinstein
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great answers guys. since i have a street car and the ABS can't handle too much diameter stagger, would using a 17" wheel/tire be better for loading? the rear tire diameter is still stock-ish so the contact patch is the same as with an 18" wheel/tire but the 17" tire has more volume.
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Originally Posted by Joe Weinstein
............................................ The head of
Michelin's F1 tire team said that in the absence of tire regulations, tire widths would be significantly wider.
Joe Weinstein
Michelin's F1 tire team said that in the absence of tire regulations, tire widths would be significantly wider.
Joe Weinstein
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Originally Posted by Geoffrey
You can run different diameter tires if you change the number of teeth on your front ABS rings.
hmmm.... i'll have to look into it some more.
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Originally Posted by Geoffrey
You can run different diameter tires if you change the number of teeth on your front ABS rings.