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boxster7614 · 08-26-2012, 02:04 AM

Pothole is correct when he mentions the different tires sizes. To clarify this please pick up any high school physics book (or Google) and read the chapter on friction.

So lets talk about a little myth that is based on partly to keep you safe and mostly to sell you tires. lets look at a statement on the tire racks website talking about mismatched tires.
" it's best to have a set of four tires that are the exact size, brand and model. While matching the tire size and performance category is a step in the right direction, without an exact match of rubber compound, speed rating and tread design you can be risking unpredictable handling and braking performance...... In some cases, the safest option may be to replace all four tires instead of mismatching models that would not be close enough."

Whoa what about friction? If this statement were 100% correct it would read.... exact size (width), brand, model, exact match of rubber compound (manufactured on the same day and out of the same batch of rubber), speed rating, tread design, and then apply the same amount of force (weight of your car) to each tire.

So we have 2 things right off the bat that make it impossible for our cars to have "matching tires"

#1 The tires are not the same size- the surface area of the rear tires is greater than the front, this alone will change the friction between front an rear tires. Also just because the tires are of the is the "same" tread design putting it on a skinnier tire will change the characteristic of the design. Even changing the width of the tire can vary the wall height and diameter of the tire, which can drastically have an affect on the performance of the tire.

#2 They do not have the same amount of force (weight) applied to them- even though our cars have a very good 46/54 front to rear weight distribution ratio, There is still a difference. Even if you could put the same size tires on all four corners it is impossible to apply the same amount of force to each one.

So even when you think you are buying matching tires because they have the same name on the side of them.......you are not! Sorry blame science.

08-26-2012, 02:04 AM	#28
boxster7614 Registered User Join Date: Mar 2005 Location: utah Posts: 96	Pothole is correct when he mentions the different tires sizes. To clarify this please pick up any high school physics book (or Google) and read the chapter on friction. So lets talk about a little myth that is based on partly to keep you safe and mostly to sell you tires. lets look at a statement on the tire racks website talking about mismatched tires. " it's best to have a set of four tires that are the exact size, brand and model. While matching the tire size and performance category is a step in the right direction, without an exact match of rubber compound, speed rating and tread design you can be risking unpredictable handling and braking performance...... In some cases, the safest option may be to replace all four tires instead of mismatching models that would not be close enough." Whoa what about friction? If this statement were 100% correct it would read.... exact size (width), brand, model, exact match of rubber compound (manufactured on the same day and out of the same batch of rubber), speed rating, tread design, and then apply the same amount of force (weight of your car) to each tire. So we have 2 things right off the bat that make it impossible for our cars to have "matching tires" #1 The tires are not the same size- the surface area of the rear tires is greater than the front, this alone will change the friction between front an rear tires. Also just because the tires are of the is the "same" tread design putting it on a skinnier tire will change the characteristic of the design. Even changing the width of the tire can vary the wall height and diameter of the tire, which can drastically have an affect on the performance of the tire. #2 They do not have the same amount of force (weight) applied to them- even though our cars have a very good 46/54 front to rear weight distribution ratio, There is still a difference. Even if you could put the same size tires on all four corners it is impossible to apply the same amount of force to each one. So even when you think you are buying matching tires because they have the same name on the side of them.......you are not! Sorry blame science.