Need helps on wheel size
08-02-01, 04:40 AM
#1
Need helps on wheel size
I am planning to change my rims and tires in a few days, but I don't know what's the right size for my 88 TII. I want to use 215/45/17 for the front and 235/45/17 for the rear. I don't if it's the right size. I heard from people that for the rear tires I better to run 235/40/17. I don't know which one is correct. I really need some experts' advice.
08-02-01, 11:15 AM
#2
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I'm gonna go with the "give a man a fish... " quote here and just tell you how to do it yourself, so in the future you can calculate the right sizes.
In brief, you want to keep the outside diameter of the tire the same so that the speedometer is correct and so it doesn't rub the car. The outside diamater is made of three parts, Lower Siderwall, Rim, and Upper Sidewall. You need to convert all of these to the same units (mm's work cause they're pretty accurate), and then calculate the new size from that.
1st... Rim is staying as 16" = 16x25.4 mm = some number that means jack **** to you if you keep the same size, cause you'll add it in just to subract it again.
2nd... Sidewall height is Width x aspect ratio. Stock case is 205/55/16, so take 205x55 = 112.75 mm.
3rd... use the same formula but solve for aspect ratio. Use 112.75 as sidewall height and divide by thickness (in your case 235).
Basically what you (or I) just did was say that you want to keep the same sidewall height to maintain the same overall height. You calculate the initial sidewall height, assume the final height is the same, then find the necessary AR. It probably won't come out to an even number, so you have your choice to what you want to give up and what you want to gain.
In your case, you get an AR of 48. This means a 50 series would be very close, but slightly taller, and a 45 series would definately fit hieght-wise, but may make the speedo a little inaccurate.
Hope this helps. also the 2nd gen FAQ has a list of all the tire sizes, OD, and variance and all. Might want to check that out if you REALLY don't want to do the calculations.
In brief, you want to keep the outside diameter of the tire the same so that the speedometer is correct and so it doesn't rub the car. The outside diamater is made of three parts, Lower Siderwall, Rim, and Upper Sidewall. You need to convert all of these to the same units (mm's work cause they're pretty accurate), and then calculate the new size from that.
1st... Rim is staying as 16" = 16x25.4 mm = some number that means jack **** to you if you keep the same size, cause you'll add it in just to subract it again.
2nd... Sidewall height is Width x aspect ratio. Stock case is 205/55/16, so take 205x55 = 112.75 mm.
3rd... use the same formula but solve for aspect ratio. Use 112.75 as sidewall height and divide by thickness (in your case 235).
Basically what you (or I) just did was say that you want to keep the same sidewall height to maintain the same overall height. You calculate the initial sidewall height, assume the final height is the same, then find the necessary AR. It probably won't come out to an even number, so you have your choice to what you want to give up and what you want to gain.
In your case, you get an AR of 48. This means a 50 series would be very close, but slightly taller, and a 45 series would definately fit hieght-wise, but may make the speedo a little inaccurate.
Hope this helps. also the 2nd gen FAQ has a list of all the tire sizes, OD, and variance and all. Might want to check that out if you REALLY don't want to do the calculations.
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