THT

iTrader: (8)

I went from the stock 15" tires to 225/50/17s; how will this affect my speedometer accuracy and odometer accuracy?

~THT

E55AMG2

iTrader: (4)

what width/aspect are the original 15". Nissan had a few different sizes.

THT

iTrader: (8)

OE Tire size is 205/65/15

~THT

E55AMG2

iTrader: (4)

ok so take the 15" and multiply it by 30.48. Then take the 205 and muliply it by .65. Take the second number you got, and double it. Then add that to the first number. Now you have the height of the tire. Now, do the same thing for the new tire and/or rim you intend to use. You can divide the new by the orig to get the % vs stock. If the tire is taller, the answer will be over 1 and vice versa.

Cliff Clavin

iTrader: (11)

Or, you could just go to the tire calculator in the stickies and find out that the 225/50/17 will make your speedo reading 1.4 percent too slow.

95whitese

how would someone fix the speedometer so it would read correctly, cuz when i bought my car a month ago, it came with the same size tires/wheels as THT.

E55AMG2

iTrader: (4)

Its actually only 1.01% too slow....

Cliff Clavin

iTrader: (11)

According to the tire calculator in the stickies, 205/65/15 replaced with 225/50/17s shows up as being 1.4 percent too slow. I double checked to make sure I didn't punch in something wrong. Maybe the calculator is wrong? I am not so good at math

I don't know if there is any kind of speedo recalibration for our cars. I have never really looked into it because the difference is negligible. At freeway speeds, it's only off by about 1 mph.

E55AMG2

iTrader: (4)

I built a spreadsheet in excel to do the calculations back when I went from 225/50-17 to 235/50-17 to see how much (if any) the speedo would be affected. Sure enough, it was right on the nost at 1.015%. This is, of course, after determining the error in my instruments by testing them against GPS then a radar gun. According to the math that the spreadsheet comes up with, the error is 1.01xxx%

95whitese

ahh that 1mph difference is good to know. dont have to spend money on recalibrating

{-_-}

iTrader: (2)

i don't think you can recalibrate the speedo anwyays, you would have to take it into the stealership to do that.

Norm Peterson

Tire calculators and spreadsheets are only approximate due to compression of the tread within the contact patch, which varies slightly among (and even within) tire makes/models.

You'll get a better answer if you go to the online specs page for your tire and base your calculations directly off the "revs per mile" figure. This is because not all tires with the same nominal size are identical in dimensions and stiffness. Tirerack.com and several other sites provide this information.

For RE92's, the 205/65-15 is listed on tirerack at 817 revs per mile (for one "part number") and also at 814 revs per mile (on three other lines). The 225/50-17 is 804 revs per mile. So something in the neighborhood of 1.2% - 1.6% is about right. That's only a 1 mph difference at 70 mph, which is worth zero further thought (your speedometer could be off by more than that).

Norm

E55AMG2

iTrader: (4)

This is correct, but its not a huge difference. As you will note, even the tire mfgs state that those are estimates. Basically, we are trying to get close.

95whitese

hehe i got re92's they came with the car when i bought it, good tires