tire size option ?'s for 2008 c350sport
 

i'm going to need new tires on my c350 sport w/ the optional 18" amg wheels soon. i'm considering using wider tires w/ the same profile for both front and rear. the rim width up front are 8.0" and the rears are 8.5". can i put on 245/40-18 fronts, and what's the widest i can go for the rear without changing or modifying anything on the car for the rear so it still clears fenders and suspension? 265/35-18.... 275/35-18?

right now i have 225/40-18 fronts and 255/35-18 rears stock.

Tire size
 

Hello.
One first thing, remember that the first number in a tire size is the with. The middle is use to calculate the height of the tire, but it is a % of the first number. If you use 245/40-18 in the front the tire will be more wide and heigher. As a tire dealer myself, i recommend to use 225/40 in the front and 255/35 in the back, but if you want to try yse 235\40 in the front and 265/35 in the back, but check the clearance

Absolutely true. What you do NOT want to do is increase the overall diameter because it will cost you performance and make your speedometer inaccurate.

I use this site to see the exact differences in tires.

http://www.1010tires.com/TireSizeCalculator.asp

last year for a few months in the summer I ran a pair of 275/35/18's on the back of my C350 but I have a set of C63 wheels so my rears are 1/2" wider than the stock 18"s our cars come with. 275 might be a bit much for a 8.5" rim. 265/35 is probably your sweet spot.

I did notice my car seemed slower with those taller tires on there. Was like I had a full tank of gas and a passenger at all times... Sucked, but it sure looked nice from the back. No rubbing issues in the rear.

In the front you'll have no problem with a 235/40/18 tire. Mine did rub a few times when I was backing out of my driveway with my wheels turned as far as they go. But it was very minor, never saw as much as a blemish on my fender or the tires. And it was only in reverse coming off the curb on my driveway...

And like the other guys said above, be careful if you go anything larger than 235/40 front and 265/35 rear because the taller tire will have more mass rotating farther from the hub and will effect your stopping distance and since larger tires weigh more, it will have some effect on your handling (especially over bumps), and as I said before it will slow you down. Unsprung weight is not your friend. :y

Safety becomes a serious issue if you increase the diameter more than 2%-3% so keep that in mind.

Good luck with whatever you decide! :y

What would be the theoretical benefit of going from the stock 245 on the rear to 255 on the rear?

The stock 245 is on 17" wheels. 18" wheels have 255 stock in the back.

In reality the stock 17" wheels/tires are going to offer the best performance for sporty street driving. Less rotational mass, less unsprung weight, and a smaller diameter, each of which will help you accelerate faster. Additionally the reduced weight and taller sidewall of the 17" setup will give you a smoother ride.

Since our cars can't spin the tires from a stop anyways, the added 10mm of grip does nothing. However if you're on the track then the generalizations I've made go out the window.

thanks a bunch! i guess i'll be going for the 235's fronts and 265's for the rear. now, on to better things... what brand tire should i get? aaaaaah! oh noooo! more questions from newbieeeeee! :naughty:

I just put a set of Goodyear Eagle F1 Asymmetrical tires on and cannot say enough good things about them. And they are reasonably priced too. :y

Yes and on top of it you don't want the car to run in 6th gear 80% of the time rather than 7th when cruising at speed limits.