quick help

[ShAkE N BaKe!!]

My brakes are almost done which means i will be going to get my tires this weekend. I notices some people run...
for ex. (front-225 45 17 and rear-245 40 17)
-Now my question is, why would you guys get a thicker sidewall up front than the rear? would you want the rear to be thicker?

 

[iskwezm]

sometimes you cant get the right size front and rear, for exaple a 40 series on my front would match the rear, but be too short, so a 45 series is better

 

[ShAkE N BaKe!!]

wait i don't understand... if i have 255/40/17(rear) and 235/45/17 front would the front tires(45's) sidewall be thicker that the rear(40's)??

isn't it, the bigger the number, the wider it is??

 

[66ccode]

wait i don't understand... if i have 255/40/17(rear) and 235/45/17 front would the front tires(45's) sidewall be thicker that the rear(40's)??

isn't it, the bigger the number, the wider it is??

No, the 75, 70, 40, 45 or whatever is actually a percentage of the width of the tire, not a measure in mm.
Its all about keeping the rolling diameter the same.
For your example the 225/45 17 will have the same rolling diameter as the 255/40 17. The sidewall is actually exactly the same size on both examples (give or take)

 

[JDS68Stang]

OK Shake n bake, are you as confused as I am now on this after reading the replies to your post?

It was my understanding, say a 235x70x15"
was smaller in diameted than a 235x75x15" which I understood was larger in diameter (height). 70 series tires are lower than 75 series correct?
So why would it change in the 17" series tires?

 

[66ccode]

OK Shake n bake, are you as confused as I am now on this after reading the replies to your post?

It was my understanding, say a 235x70x15"
was smaller in diameted than a 235x75x15" which I understood was larger in diameter (height). 70 series tires are lower than 75 series correct?
So why would it change in the 17" series tires?

Its not this complicated.
The profile of the tire is a percentage of the width, measured in millimeters.
a 225/45 means the tire profile is 45 percent of the width - 101.25mm
a 255/40 means the tire profile is 40 percenct of the width - 102mm
See how close they are?
If you go wider on a tire, you need to reduce the profile to keep the same outside diameter. Im sorry, its just so simple I don't know how to dumb it down any further.

 

[Grabber70Mach]

Hope this helps







Width x Aspect Ratio = Section Height
Section Height x 2 = Combined Section Height
Combined Section Height + Wheel Diameter = Tire Diameter

Example: 185/60R14 85H or 185/60HR14

185mm x .60=111mm
111mm x 2=222mm
222mm + 355.6mm(14")= 577.6mm or 22.74"

The first number is the width of the tire in millimeters, measured from sidewall to sidewall. To convert to inches, divide by 25.4 In the example above, the width is 185mm or 7.28".

The second number is the aspect ratio. This is a ratio of sidewall height to width. In the example above, the tire is 7.28" wide, multiply that by the aspect ratio to find the height of one sidewall. In this case, 185x0.60=111mm or 7.28"x0.60=4.36".

The last number is the diameter of the wheel in inches.

To figure the outside diameter of a tire, take the sidewall height and multiply by 2,(remember that the diameter is made up of 2 sidewalls, the one above the wheel, and the one below the wheel) and add the diameter of the wheel to get your answer.