Implications of wrong tire size

[Tolahouse]

I am running stock wheels on my '06 - ordered new tires online and ordered 255/35/18 instead of 255/40/18. What effect if any will this have on the car since the rolling diameter of the front wheels will be wrong.

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[komp55]

Stock tire sizes on an E55 are 245/40/18 front and 265/35/18 rear. Incorrect tire diameters will result in your speedometer displaying an inaccurate speed.

[myntk12]

As your overall diameter is smaller you will be turning higher revs for the same speed which will also result in increased fuel usage even if negligible. You can use the following to compare.

http://www.onlineconversion.com/tire...conversion.htm

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

[Forrest Gump 9]

They are for the front right? If so, you'll be alright. The difference will be so small that it'll not affect anything. The wider front tires will help your car corner better.

[amdeutsch]

Originally Posted by Forrest Gump 9

They are for the front right? If so, you'll be alright. The difference will be so small that it'll not affect anything. The wider front tires will help your car corner better.

Redo your math on those vs OEM

Yep, you are F.G.

[Jon2007E63P30]

It is not a big deal. Calculate your speedo error and move on. I don't even know if the fronts are where the speedo is connected. I would have thought the rears with a sensor on the tranny.

Gotta be the rears.

[amdeutsch]

Originally Posted by Jon2007E63P30

It is not a big deal. Calculate your speedo error and move on. I don't even know if the fronts are where the speedo is connected. I would have thought the rears with a sensor on the tranny.

Gotta be the rears.

Nope. Its the fronts. And yes, IMHO it is a big deal if you constantly have to remember your error on the speedo and the odo. Its just plain human nature to ignore after a while.

[RacerX0911]

Originally Posted by Jon2007E63P30

It is not a big deal. Calculate your speedo error and move on. I don't even know if the fronts are where the speedo is connected. I would have thought the rears with a sensor on the tranny.

Gotta be the rears.

if it where rears your speedo would go nuts when you burn out... instead of staying at zero!

[Forrest Gump 9]

Originally Posted by amdeutsch

Redo your math on those vs OEM

Yep, you are F.G.

I still don't see the big deal here. The stock E55 front tires are 245/40/18 and he bought 255/35/18. Just by my rough estimate, those two tire sizes above have almost the same diameter. And no, I did not use any kind of calculator, just on top of my head. Please enlight me with your math. I'm here to learn.

[r-magic]

stock 245x.40x2=196/25.4=7.716+18=25.71

not stock 255x.35x2=178.5/25.4=7.027+18=25.02

So the difference is .69

The new tire will be .69 inches shorter. You will not notice that much of a difference in speed. If it was over an inch than yes. This is just my opinion. I use to work at NTB selling tires.

[jangy]

Changing tire sizes has much more impact than just speedo reading.

In this case, I agree with Forest Gump that going from a 245/40 to a 255/35 is within the rule of thumb. Back in the day, we called it a 1 plus. You go one step wider and drop one step in sidewall.

Aside form the speedo and gearing implications, there are a few things to consider when changing rolling diameter on a benz.

Varying the rolling diameters from the OEM leads to more and more ESP intervention, especially when applying power in a transition. Wider tires don't always add handling but this was a lucky move by the OP. He would have had some issues had he actually gotten his 255/40s. Tall fronts will hit the fender CONSTANTLY when the wheel is turned and the car hits the smallest of dips.