Wheels and speedo

360 Views 6 Replies 7 Participants Last post by a747ba, Nov 29, 2001

Scorrado

Discussion Starter · Nov 28, 2001

Alot of you have bigger wheels. I know the bigger the wheel is, the lower profile tire you would need to have, but I sure alot of your wheels are taller than the stock 205/50/15. Does this affect the speedo much?

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Pinepig

· #2 · Nov 28, 2001

Re: Wheels and speedo (Scorrado)

Depends on what size tire you run on the new wheels.
I run 215/40/16's and I remember somebody posting a chart showing that I am just about perfect as far as old vs new diameter.
The first # is the new width of the tire (215mm in this case)
The second # is the pecentage of height from the width of the tire
The third # is the diameter of the wheel.
I believe this is called a plus one on the corrado, you can also do a 205/45/16's and be still at about the same overall diameter and it may ride a bit better, I'm 35 and the 215/40/16s don't ride to bad for me.
I'm sure somebody will post it up again, or possible a search in the wheel and tire fourum will bring it up. ( yes the search sucks )
To answer the original question, yes if you change the overall diameter of the tire your speedo will not be acurate, how much would just take a little math.
Good luck
Charlie

[Modified by Pinepig, 1:36 PM 11-28-2001]

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Iceman666

· #3 · Nov 28, 2001

Re: Wheels and speedo (Pinepig)

im running 215/45/16's and my speedo is about 10 mph off

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Zyrod

· #4 · Nov 29, 2001

Re: Wheels and speedo (Iceman666)

Hahaha,
I haven't had time to replace the rubber on the stock vr6 jetta rims I have and I'm running 205/55r16. I think my speedo is off, but I don't how by how much.

Can you 215/40r16 or is better to run 205/45/r16?
Thanks

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snowbird

· #5 · Nov 29, 2001

Re: Wheels and speedo (Zyrod)

You should be able to calculate it from the circumference of the stock tire size vs. the circumference of the new tire (you can get this info from http://www.tirerack.com etc). If your new tire is a little bit taller, then that means the rolling circumference is a little bit longer, so your speedo will be reporting a lower speed than what you're actually travelling.
If you divide: (new circumference)/(stock circumference) you might come up with a number around, say, 1.04 - meaning that the new tire travels 4% more than the stock one for each full rotation of the tire. That means that you're probably going about 4% faster than your speedo is saying.

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B(C)orrado

· #6 · Nov 29, 2001

Re: Wheels and speedo (snowbird)

215/35/18s for me

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a747ba

· #7 · Nov 29, 2001

Re: Wheels and speedo (B(C)orrado)

205/40/17 my speed seems to be the same, at least that what was showign on the big police radar trailer at the port

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