MickM

I can not find my answer no matter where I look. What is the largest tire size I can put under my 99 CLK 320 on my 8"X17" rims? I really need a straight answer from someone who knows what they are talking about. Car is stock height and will not be lowered. Also it is a convertible.

A1EK

Theres actually quite a few resources on the internet to give you this answer, however Why are you wanting to put the largest size tire on your 17” wheels is the real question?? You are not really supposed to just put larger diameter tires then recommended on your car as it can upset the balance, performance and speed and the guide is that you are suppose to keep within 2.5% of the outer diameter. This is due to a new tire that has 7mm tread will have greater circumference then a worn tire with 2mm tread, also for weather changes the air inside the tire will expand and contract in summer and winter and also effect the size, (This is why people are using nitrogen in the tires as it remains the same density I think).

Therefore if you put larger diameter tires on the car at then your speedo will be out and will show that you are travelling at a slower speed then you actually are! However if you are just trying to fill the gap around the wheel then its up to you! I’ve tried myself with larger profile tires and it looks terrible, the wheel appears smaller due to the extra rubber! If you go to 18" or 19" then the tires circumference still remains around the 2.5% but the wheels look bigger due to more metal and when the car is lowered a little it adds to the effect. My car is lowered, the tires are 255x 35x 18 on 9.5J and I also have 25mm spacers but the overall circumference is still the same as 215 x 45 x 17 or 255 x 55 x16.
IF your only wanting to put wider tires on then you can do this but drop the profile to match the width,
e.g
http://www.alloywheels.com/Tyre_Calculator

HWYSTAR

What A1EK said was true,don't increase the overall diameter. a situation to explain would be and I will use a mustang 17 X 9 as and example. Stock tires on a 2004 Mustang GT are 245/45/R17ZR, to get the wider profile and not increase the overall diameter the largest size for the vehicle would be 275/40/R17. In this you get a much wider footprint,but do not increase overall diameter. What size tires do you have now?

MickM

I appreciate your responses. The car has AMG look a likes that all four are 17" X 8" with Goodyear Eagle Ones 235/45-17 and I'm very disappointed with the ride, not Mercedes like at all. These are the tires that came on the car when I bought it last year. I thought going to a larger profile might get me more sidewall and a smother ride.

A1EK

hmm I would perhaps look into why your ride is so firm first as with 17" and 235 x 45 tires should definately give you a more cushioned ride, its really only when you get to 19" that it can get a little firm.? I have both your size in 17" wheels for winter and 255 x 35 x 18" in the summer and to be honest there is not much of a difference in firmness, but it may be because its winter and the rubber is harder so the benefits of smaller 17" is not noticed.

Has your car been lowered with poorer quality springs? I hear H&R are firmer then Eibachs.
What air-pressure are you inflating your tires to, shold be around 32 PSI for your 17".?

dlbehrns

did you check your tire pressure? I never run more the 34psi. Are you running stock springs and shocks?