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Discussion Starter · #1 ·
I was wondering what other size options are there, I want to have a higher sidewall.

I have mugen GP's on that are 7.5 wide i believe, just cant seem to find the right combo with the tire calculator.

215/45 would fit but 225 is a good tread width all around but just want a little higher sidewall.

In any case i am on aspec suspension and having a higher side wall would fill in the gaps a little more.


Any suggestions?
 

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That's Doctor
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If you're worried about sidewall height, go with 225/45-18. That'll keep you within the +/-2% rule-of-thumb needed to keep VSA working correctly while maximizing sidewall. 235/40 is closest to the stock size but it's actually smaller than stock.

As a comparison, for Hankook Ventus V12, our stock (215/50-17) takes 814 revolutions per mile and 225/45-18 takes 801 revolutions per mile. That's about 1.6% larger. At 60MPH, your speedo will only be off by about 1MPH (taking into account your speedo is perfectly calibrated for 215/50-17).
 

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Discussion Starter · #4 ·
If you're worried about sidewall height, go with 225/45-18. That'll keep you within the +/-2% rule-of-thumb needed to keep VSA working correctly while maximizing sidewall. 235/40 is closest to the stock size but it's actually smaller than stock.

As a comparison, for Hankook Ventus V12, our stock (215/50-17) takes 814 revolutions per mile and 225/45-18 takes 801 revolutions per mile. That's about 1.6% larger. At 60MPH, your speedo will only be off by about 1MPH (taking into account your speedo is perfectly calibrated for 215/50-17).
I ran 225/45 on the tire calculator and its 3.43% different
 

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That's Doctor
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I ran 225/45 on the tire calculator and its 3.43% different
Not sure what calculator you're using but I provided you actual numbers that you can verify:

(814-801)/814=1.6%.

Or, if you assume that a tire is a rigid circle, you can use geometry:

c=2*pi*r

where r=(radius of wheel) + (sidewall height)

The radius of a 17" wheel is 8.5". The 215/50 tire has a sidewall height of (215mm)(0.5)/(25.4mm/inch)=4.2323". So our stock tire circumference is:

c=2*pi*(8.5+4.23)=79.9994"

An 18" wheel has a radius of 9" and a 225/45 tire has a sidewall height of (225mm)(0.45)/(25.4mm/inch)=3.9862". So the circumference is:

c=2*pi*(9+3.9862)=81.5947"

Ok, so the % difference is given by:
diff = (81.5947-79.994)/(79.9994) = 1.99%

So, since radial tires are not rigid circles, you can expect that the geometry changes as the tire is under load contacting the pavement. Therefore, manufacturers tell you how many revolutions per mile you will get from that model and size of tire, making this calculation more accurate. In summary, a 225/45-18 is only 1.6% larger than our stock size.
 

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That's Doctor
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Well, 225/40-18 is 1.5% smaller than stock and 225/45-18 is 1.6% larger than stock. So, of course the difference between the two 18" sizes is about 3% but it's like this:

225/40-18 < 215/50-17 < 225/45-18
(1.5%) (1.6%)
 
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