CClement

Hey guys, I know the OEM 19s have about a 0.23% size difference between front (225/40/19) and rear (255/35/19)
which is obviously acceptable by MB specs but I'm wondering what % difference starts to be a problem with our AWDs?
I'm looking at front/rear combo that has about 1.07% difference so 0.85% more difference than OEM. Any thoughts?
That's still quite a small difference however thought I'd see what people thought. Thanks.

mjs1190

The dealer mistakenly but C63 tires on my car 245/35/19 and 265/35/19 which works out to a 1.92% difference which is obviously more than yours. However, it was enough for it to throw off the wheel speed sensors that impacts the traction control and cause the engine to cut power when on flat roads and driving normally. The car would be undrivable for a few miles and then would be fine. When they swapped back to the OE tire size, that issue never resurfaced.

CClement

Ya, almost double what I would be but surprised to hear how bad that was. Thanks!!

alexasa

iTrader: (1)

visually/aesthetically that wouldn't be ideal IMO. But nobody would probably notice. It would bug me though.

CClement

The reason I'm asking is that I run 8.5" rims all around for my summers. I need new tires this summer (Pilot Sport S4)
and my current OEM Pirellis run a bit of a stretch in the front, they work but definitely a bit stretched.
If I went 245/35/19 front and 255/35/19 rear, the look would be much improved!

alexasa

iTrader: (1)

You don't think you can pull off a square set-up with the offset? That'd be my move.

CClement

Ya, that is another option, go 255/35/19 all around. Might work well actually. Thanks!

mo11

That’s the same size I run up front currently, 255/35 19 Michelin Ps4s on 19x8.5 +30, it’s fine for as long as you’re ok with how close the clearance is from the control arm.
My first setup had a 2.75% f/r ratio, never gave me any problems even at over 100mph speeds. From what I’ve read, for as long as f/r ratio is within 3% you shouldn’t have any issues.

CClement

Ok thanks, I might try the square setup.

hlieberg

I recently read about this on some Norwegian website. For Mercedes I'm pretty sure the 4wd-system allows up to 5% difference in wheel ratio between f/r axle. I was surprised, because I know 4wd-systems on some other brands don't allow any difference at all.

CClement

Ya I was told anything under 3% should be ok but then the post above had me concerned. 5% seems like alot but who knows, the dealership doesn't seem to.

hlieberg

Yes, I also thought 5% seems like a lot. I think it was someone from the official MB importer who said it. I have tried to find the article again without luck. Not that it would help you as it is in Norwegian, but to see if I remember correctly.

CClement

My dealership says anything around the 1% is no worry but that's one heck of a difference from the 5%!!
Seems to be alot of different info out there.