Tire Sizing for '94+ GS-R

About Tread Wear Ratings

Quoted from the Tire Rack web page:
"Treadwear is a measurement of tread durability. Tested against an industry standard, the assigned numerical grade indicates how will the tread lasts compared with a reference standard of 100. A treadwear rating of 200 means the tread wears twice as well as the standard. Actual wear depends on conditions under which the tire is used. Driving habits, service practices, differences in road surface and varying climates all affect treadwear. The treadwear number is only accurate for comparison within the same brand and should not be used for brand to brand comparisons."

Manufacturers do their own testing and don't necessarily follow the same exact procedures and testing conditions as another manufacturer would. For example, if Goodyear takes a Pirelli tire and does the UTQG tests, they may not get the same numbers as Pirelli because their testing environment may be different than Pirelli's. So the Uniform in "Uniform Tire Quality Grading" only applies within a manufacturer, assuming they keep their own testing procedure and environment consistent.

Tire Pressures

What I've found with the stock Michelins is that side wall flex plays a bigger role than contact patch in autoxing.

The Michelins has a very hard compound so they grip really bad to begin with. On an autocross course, there are a lot of quick transitions, left and right, in combination with hard braking and accelerating. Now, let's imagine what the tire is going through during all this, especially the sidewall.

Let's keep this in mind: A tire with a flexible and/or tall sidewall will respond later than a tire with a stiff and/or short sidewall.

Now let's execute a turn: First the tire and the wheel is pointed straight-forward. The steering mechanism turns and then turns the hubs which are attached to the wheels. The wheels are now turned at this moment with the tires still pointing forward. The tires will then respond to the forces exerted by the wheels and then start to turn with it.

Visualize the sidewall of the tire having a delay in reacting to the wheel's turn. A flexible sidewall almost acts like a soft rubber band when it finally responds and matches the angle of the wheel. This is what is happening with the tall flexible Michelins. By DECREASING the pressure, it makes the Michelin's sidewalls more FLEXIBLE. When the rear tire's sidewalls are more flexible, the rear end with "squirm" or feel much more loose. I set it this way to make the rear end come out better in tight autocross turns.

Now remember this only applies to the stock Michelins that I have. On the Michelins, even though reducing the tire pressure will increase the contact patch, the Michelin's hard compound does not stick to the ground very well anyway. This is an example of tire sidewall stiffness being more important than the size of the contact patch. In autocrossing this phenomenon is generally true because of the dynamic nature (as opposed to a constant force) of the quick left and right turns.

In drag racing where a static or linear contact patch is more important than sidewall stiffness, my comments do not apply.

Remember that this also does not apply to soft compound, stiff sidewalled autocross tires.