View Full Version : Wheel Q..

01-01-2006, 03:47 PM
i was just thinking when i topped my car out, i was going faster then what my tach said. I had my 17s on at the time. 17s with bigger tires would read about 5mph slower then what i was actaully doing, right?

01-01-2006, 03:52 PM
I was just about to post a topic on a similiar question. [eek]

If you increase your wheel size does your odometer have to be recalibrated?

01-01-2006, 03:55 PM
Its going to be off, but i wouldnt recalibrate it. Im just not sure how much.

01-01-2006, 04:10 PM
there is a tire calculator somewhere online, its not as big a difference as u'd think, and its not like 5mph, its apercent. my 235/40/18 where off by 1.6mph at 60mph, so at 120 it would be off by 3.2mph.

Also I'm not sure if audi does it, but bmw shows the speedo going faster that you really are. No idea why

01-01-2006, 04:12 PM
At 155mph i think the difference is slightly more. I would think its more then 1.6 at 60mph, since your 2in bigger? wouldnt it?

01-01-2006, 04:44 PM
you do realize that tires come in different sizes, right?

lower aspect ratio (profile) for larger diameter wheels. keeps the same diameter (circumference is actually more important) as stock.

just about every car in the country came with a speedo that is fast at 60 and above. this lets people think they are speeding while keeping the roads a bit safer. or at least it is supposed to.

01-01-2006, 04:51 PM
No, i was not aware tires came in different sizes. I thought it was a 1size fits all type deal.

Stock is what? 205/55/16s? I went to 225/45/17s, which would make a dif.

01-01-2006, 05:15 PM
My 17s are 24 13/16in across. Now im not sure, but i doubt a stock 16 with stock tires is quite that tall. Does anyone have the stock tires on 16s they could measure?

01-01-2006, 05:21 PM
stick to the manufacturers specs and you won't have this problem. Why are you running 235's?

01-01-2006, 05:25 PM
Try this http://www.1010tires.com/TireSizeCalculator.asp


01-01-2006, 05:26 PM
Im not running 235s, im running 225s.

01-01-2006, 05:56 PM
I meant that to Tom Ritt. But how do you know you were going faster than what your tach was reading?

01-01-2006, 05:58 PM
Originally posted by B5Ghost
I meant that to Tom Ritt. But how do you know you were going faster than what your tach was reading?


01-01-2006, 06:08 PM
I don't think so.

01-01-2006, 06:53 PM
The second number in tire sizes is the height of the sidewall as a percentage of the width of the tire. A 225/45 tire would be 202.5mm tall, not counting the space in the middle for the actual wheel. That's 7.97 inches+17=24.97 inches total wheel height. A 16" wheel with a 205/55 tire is 24.87 inches in total height. That difference is where the speedo difference comes in.

At 60, the difference is .2mph faster than the speedo reads. At 120, it's .4, so at 150, you are going less than .5mph faster than your speedo says.