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And these bad boys fit perfectly on the standard spec C63s rims without any issues/tinkering? great effort. I'll look to stick these bad boys on my car in a few k miles once i've destroyed my pilot sports.
I would read it this way: when the speedo shows 30 mph with the new rubber, you're actually doing 29.38 mph. Likewise from the other post (80 mph the speedo would read 81.68 mph),
I extrapolate that when your speedo reads 80 mph, you'll actually be doing 78 to 79.something mph. In both cases, your speedo is getting to the figures on the speedo long before the
car is actually doing those speeds.
confused..why does this site show speedo reading less
This is correct. The new larger width tire has a larger diameter, which takes longer to rotate once, hence showing a slower speed on the speedometer than the vehicle is actually traveling. Several of the above posts are incorrect and they have it backwards.
Last edited by ezatnova; May 28, 2018 at 08:59 AM.
This is correct. The new larger width tire has a larger diameter, which takes longer to rotate once, hence showing a slower speed on the speedometer than the vehicle is actually traveling. Several of the above posts are incorrect and they have it backwards.
You are correct but this one is misleading as what you really want to know is how fast you are going when your speedo is reading 60 which is 61.26 and not that you are going 60 when your speedo is reading 58.77.
You want to know if you are speeding and by how much./
Use this one as it is easier to understand. https://tiresize.com/speedometer-calibration/
I would read it this way: when the speedo shows 30 mph with the new rubber, you're actually doing 29.38 mph. Likewise from the other post (80 mph the speedo would read 81.68 mph),
I extrapolate that when your speedo reads 80 mph, you'll actually be doing 78 to 79.something mph. In both cases, your speedo is getting to the figures on the speedo long before the
car is actually doing those speeds.
You guys are calculating based on assumed sizes. Each model of each brand tire has its own spec sheet. On that sheet you’ll find the actual diameter, circumference and rotations per mile. You need this info to find the exact variation when you upsize.
Also note that even the same tire will read different numbers during its age as it’s diameter slowly decreases with wear.
Of course all of this is really overthinking the issue; however, I found this to be important in a car like R35 GTR that has a very sensitive 4 wheel drive differential and would read these minimal discrepancies as slip and overwork to correct.
@c63Dal - so Michelin P4s 245-35/19 front, 285-35/19 rear fit on the SEDAN (or are you coupe) on stock suspension? You're not lowered are you?
Yes a lot of guys have changed to 285s and with stock suspension and rims they don't rub.
I went the same way that Cyberorth did with 255 and 275 PS4s and I they have more traction and are quieter and I think ride better.
The reason is the 285 are listed for the 91/2 inch rims but not the preferred size as I don't think they give enough shoulder support.
I also think by keeping the ratio front and back to one size up for both might be better for the computer ESC and Traction control calibration mostly in the twisties and not drag runs.
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