danny_fkn_a

hey guys... New to the forum and looking for help. There has to be somone else who has had this happen to them... I just recently put 20" wheels on my 09 c300 and noticed my odometer is reading faster than it should. Navi said the trip is 38miles car clocked in 48 miles!!! Somone help, is there a way to calibrate the car for the larger wheel???

jctevere

Generally, the odometer is changed by how many turns the powertrain makes. This is related to the rim size. If you get larger rims, the rim or powertrain will turn less to get the same distance traveled... What you are reporting is the exact opposite. Theoretically your speedometer should be reporting slower speed and lower miles from the odometer after you changed out for bigger rims. But if your car is doing the opposite, then you have me confused... The only answer for sure is to contact your mercedes dealer. You can change the way the odometer calculates the distances, but only through star diagnostics (capable only at a authorized MB dealer).

Bottom line, contact your dealer immediately to avoid excessive mileage.

JimPap

Distance traveled is based in part to the tire's outside diameter.

When you upsized the rims, you were suppose to use tires that maintain the same outside diameter than the original tires. Sounds like you went with tires that had a smaller outside diameter. Takes more revolutions to travel the same distance....which has got to be killing your fuel economy and ride hard on rough roads.

RLE

What you meant to say was circumference. It's revolutions per mile that count and that number is available from the tire manufacturer. I would like to hear what his rear tire size is. It's easy to calculate revs per mile with the tire and wheel dimensions. Generally, a 2% difference is considered to be the limit by the experts.

danny_fkn_a

i have the c300 which is all wheel drive as you all know. I was told I couldnt do a staggard wheel with the all wheel drive so all 4 wheels are 20x8 with 225x35x20 tires.

amdeutsch

You are kidding, right?
Std tire on yours is 225/45-17. 225/35-20 is larger so your post about the odometer doesn't make sense.

RLE

Since the 17" and 18" stock sizes have the same diameter or near enough, I calculate for 225/45-17, the revs per mile would be 807. Your twenties with 225/35-20 revs per mile are 770.

Which means your tire/wheel combination is 4.5% smaller overall than the stock tires were. So, you register 4.5% more miles than you actually travel. Which also means your warranty will expire that much sooner at 47750 miles actual if the larger wheels were installed at mile zero.

Your fuel consumption is also higher.

FrankW

225/45/17 Rev per mile is 832.9 with overall diameter of 24.97

225/35/20 rev per mile is 793.8 with overall diameter of 26.20 inches

(number courtesy of tiresize calculator)


his tire is larger, not smaller. (according to what he posted anyway)

JimPap

His odometer reads fewer miles than the navigation system.

Wonder what happened.

danny_fkn_a

Its got me confused also! im not too worried about the warranty as of right now because the rims are only on for a few months as I live in New England.
I'm def not an expert on tires, but I know for a fact that is the size of the tires.

Can mercedes reconfigure this to corret the issue? or should I just ignroe it and live with the 4.5% increase in mileage. the gas isnt an issuse either as this car is more or a weekend/night car I rearly drive it.

If i bring this to the dealer like this will it void my warranty??
oh and just so you know the car is a lease figured it was the best option for me as like I said I dont drive it much.

flagman

Not true that you couldn't do a staggered set-up because you have all-wheel drive - my C350 4Matic came standard with staggered set-up - 225/40 ZR18 on the front, 255/35 ZR18 on the rear

It's right in the Owner's manual

RLE

You were OK until you quoted revs per mile and then it all went to hell. Go here and recalculate:

http://www.miata.net/garage/tirecalc.html

My revs per mile were correct but I got the effect backwards:

"Which means your tire/wheel combination is 4.5% smaller overall than the stock tires were. So, you register 4.5% more miles than you actually travel. Which also means your warranty will expire that much sooner at 47750 miles actual if the larger wheels were installed at mile zero."

Forget that because it's wrong.

What is correct is that the larger wheel/tire combination will make the car slower to accelerate PLUS throw off the odo and speedo readings.

FrankW

got the number off

http://www.1010tires.com/TireSizeCal...?action=submit

RLE

So I see. They are wrong.

Why don't you do the final calculation yourself. 5280X12 (inches in a mile) and divide by the circumference. There it is.

Maybe all the car owners here with 20" wheels should see how far off their speedos may be.

FrankW

did it myself using 63360/(2*pi*(half of the diameter) same thing you did and got 807. don't know why the 1010 calculator showed a difference.

however 1010 tire size calculator as well as tirerack showed 225/45/17 tire rev per mile at 830-831.

I think the lower number calculate for the squish factor and one does not.

danny_fkn_a

Thats all great guys but is there a way to fix this?

FrankW

change your tire to proper size. 225/30/20

Reaperman

Its all to do with what they call "Rolling Circumference"...heres a site I have used in the past. In summary if you increase your rim size then the tyre profile will need to come down to compensate.

http://www.ukzero.co.uk/calculator1.htm