RW507

Does anyone know why the rear overall diameter is about 0.5" less than the front (based on the 19" wheels with 235/35/19 fronts and 255/30/19 rears)?

looney100

Why does this matter? What makes me you think it's odd?

zcct04

Because the matching rear for a 235/35/19 front would be a 255/32.25/19 . . . and those are pretty hard to find.

QWKSNKE

Seriously?

Because a rear tire should NEVER be shorter than a front tire. They should always be equal or possibly a bit taller. These cars with stock tires look pathetic from the side IMO.

medamullet

I have wondered that too. BUT those German engineers must know something you don't when it comes to creating performance cars.

Phil Chow

A lot of manufacturers do this actually.

BMW M135i, runs 225/40/18 Front and 245/35/18 Rear. Never understood it.

But, in Asia actually, the C63s come with 225/35/19 and 255/30/19, so they match. Not sure why, who knows.

QWKSNKE

Probably manufacturing cost savings. That tire may go on many other Benz vehicles so the get a good discount from the supplier and thought, that's close enough to go on a C63

Phil Chow

This is what I believe too. They take whatever they can get in a mass quantity at the best deal.

RW507

You're probably right. To be honest, I didn't even know about the mismatch until one of the tire shops pulled out one of their guide books for tire sizing and the guy had to do double take before mentioning it and showing me the 1/2" mismatch in diameter. A call to a MB dealership didn't help as they didn't really know and just said there must be some legitimate engineering reason behind it.

QWKSNKE

this is why I now a 275 with the stock profile out back. Tire fits much better on the wheel plus evens up the diamter between front and back

Adam Lynagh

you realize with 235/35/19 fronts and 255/30/19 rears, the rear tyre will have a slightly larger sidewall than the front. Dont you?

sventastic82

Really you guys are concerned about the 0.5 difference in diameter?

I'm sure they are not using that tire size because the majority of their cars use them. I don't think a C250 uses the same set up.

They spec the tires based on weight distribution and handling. for example the car's alignment and tire size combo is slightly setup towards under steering since it is easier to correct.
If you change the tire size to achieve an even diameter between front and back then that would be just wrong. Besides that it looks like *** because your gap between fender and tire would be smaller in the back (unless adjusted with coil overs or spring pads)

QWKSNKE

Wow, thread resurrection...

No it doesn't. The front does. Couple that with the ugly sidewall lean in due to a 255 not fitting a 9 in wheel properly the overhaul height is almost 1" shorter on the rear than the front.

Adam Lynagh

Sidewall height on fronts would be 82.25 mm and the rears side wall would be 89.25mm.. last time I checked 89 is more than 82)

QWKSNKE

if you were installing a 255/35, you would be correct but we are talking 255/30 which is 76.5mm