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tire width or sidewall aspect ratio?

Looking at 235/45/17 for a 2002 Passat.
Any good? will I have rubbing issues? I am lowered with Eibach Prokit
 

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This size should work ok. The speedometer is based on the height diameter of the tire size which is determined by the aspect ratio. The height of a 235/45/17 is only .3 inches taller than the stock tire size, so shouldn't affect the speedometer. I believe others have said they've used this size with no rubbing problems.
 

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Gord said:
The pedal on the right! (sorry could not help but state the obvious)
:lol:

*ahem* Well, as Clay said, you should be okay with that size.

Now, back to the question in a more general sense...actually, both treadwidth and aspect ratio play a part in speedometer accuracy, since both have the potential to change the overall rolling circumference of a tire.

Let's say you start out with a tire that's a 215/45-17 and you go up to that 235/45-17 you mentioned. Now, the aspect ratio has stayed the same. But because aspect ratio is a function of tread width, the sidewall gets taller even though you didn't change the aspect ratio. It's still 45% of the tread width, but you're now 45% of 235 (or 106mm) instead of 45% of 215 (or 97mm). Taller sidewall = larger overall diameter = bigger rolling circumference = change in speedometer accuracy.

BUT...let's say you started with a 215/50-17 tire and THEN went to a 235/45-17 tire. If you do the math, the sidewalls are pretty much the same (50% of 215 = 107.5 mm, 45% of 235 = 106 mm), so the overall diameter is the same, so the rolling circumference is the same.

SO...if you want to keep the same rolling circumference so that you don't mess with the speedometer, you have to change the aspect ratio if you change the tread width. You can't just change one and not the other.

Hope that helps...

Andy
 
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