mercster4life

I would be interested in hearing your thoughts:
Why is the rear tire diameter 0.3 inches smaller than the front on the c43? The rear is a 245/40Z-R18 which is 25.7 inches in diameter. The front tire is a 225/45Z-R18, which is 26" in diameter. Why would they not install a 255/40Z-R18 in the rear which is also 26" in diameter?

mercster4life

Update 9/20/17. Dealer said the diameter difference was for improved traction during aggressive driving.

Lazz83

I have to agree with you I don't like the stance on my C43, I have the 19" AMG rims with 225/40Y/R19 up front and 255/35Y/R19 in back, the front tires look noticeably taller to me, maybe because of the fender flairs, but enough to make me want to put 35's all around or 40's all around to balance it.

I need to buy all season tires for the winter, as mine came with summer tires and am curious about making this swap? I did some research and AMG seems to do the staggered sidewall dia with all of the C class models?


I wonder if it would affect anything? unknowingly, I once put a shorter sidewall ratio on a '79 Trans am going from 70 to 60 and it changed the gear ratio a tiny bit- allowing the automatic trans to chirp second gear. Just my thoughts

Not sure about the improved traction answer, as I never have any spinning issue with my AWD even in the rain.

I'm glad someone else noticed this as well.

alexasa

iTrader: (1)

That's just the ratio, it means nothing without the width specified in conjunction.

Lazz83

I am saying put 225/35Y/R19 in front and 255/35Y/R19 in the rear- My car came stock with 225/40Y/R19 front & 255/35Y/R19 in back

Would switching to all 35's effect the car at all? I know the smaller tire makes the gear ratio taller.

alexasa

iTrader: (1)

There's absolutely no reason to do this IMO.

Lazz83

I said earlier that the back tire is smaller and so did the original thread starter. It makes the car look unbalanced in my opinion, as there is a clear difference in height between front and back tires.

alexasa

iTrader: (1)

and you'd be making it much worse, in the other direction. It's actually outside of spec it's such a drastic change.

diameter should be kept within 3% of OEM size. I really doubt you are seeing a tire height difference, visually, of half a centimeter. I think you're making more of it than what it really is.

ErikM

I don't understand the reason for a staggered rear anyway.. I'd rather have 18" x 8.5" all around maybe a 245/40/18 Non Run Flat like a Michelin AS/3+

alexasa

iTrader: (1)

Car is prone to understeer so if you could easily fit an 8.5 and 245 on the front, I'd have no problem with that either. But, that fitment is unlikely to work within the tolerances available on this car (IIRC someone is doing that, however - nevermind it was 18x8 on around).

Audi is shipping their TTRS with wider front tires than rear to reduce understeer. Less rear traction also allows the car to rotate more freely with throttle application.