Ben'z

Actually, when I upgraded 215/55/16 to 225/55/16, I didn't do anything to NAVI.
I noticed that the NAV recalculate by itself during driving.

Ben'z

I know what you meant.
The problem is Goodyear F1 supercar is too expensive.
I checked tirerack.com, the tread of Goodyear's eagle F1 GS-D3 looks different.
The one look similar is eagle HP ultra plus.

Then, you mentioned the safety issue.... :p

Also, tirerack.com doesn't carry supercar 255/40/17, only 245...

awtrott

Hey guys,
What is your thoughts on 18" wheels with 235/50/18 tires all around? The diameter difference is 0.92 (Pretty good), but I am hoping that the side wall being 50 will help to soften the ride for less rod vibrations.

Whitey

I'm not sure how you got the 0.92 difference (probably comparaing the tiresize of a 17" with and 18" wheel?) but according to my calculations, 235/50 is way off and your speedo would be reading much slower - at 60mph, you're actually travelling 64.4mph, not to mention less responsive steering in the front. If you want a softer ride, you're gonna have to keep a smaller wheel....but handling is compromized. If by "vibrations" you mean the wobbles at high speeds (typical of stock E's), then shorter and harder springs is what you need.

awtrott

You’re correct; I messed up on my calculations. The recommended size is 235/40/18 all around, unless I want to stagger the sizes. I would really prefer 45 sidewalls and therefore is considering sacrificing width and go with 225/45/18 with a 2.55% difference. Maybe even break the rules to go with 235/45/18 with a 3.84% difference. Do you think a 3.84% speedo difference will affect my ABS or traction control system? If not I will simply pay attention to speedo difference to judge my speed.

Your input is greatly appreciated.

lexrex

Awtrott, there's more to smooth ride than just the sidewall height ratio. The two major factors are the absolute sidewall height and the relative width of the tire to the rim. All things being equal, a taller sidewall and a wide tire/narrow rim will give better ride quality at the expense of handling.

Regarding absolute sidewall height: The 45 sidewalls simply mean that the sidewall is 45% as high as tread is wide. This means that a 225/45/18 sidewall is 94mm tall, whereas as 235/40/18 sidewall is 101mm tall. I doubt that a 6mm taller sidewall will make much of a difference in ride quality.

What will make more of a difference, I think, is that the 225/45 tire must be stretched more than the 235/40 tire to fit on the same rim. Since the 225/45 tire is narrower, its maximum rim width is smaller too. As a mounted tire approaches its maximum rim width, the ride quality suffers. A wider tire mounted on the same rim bulges more at the sides, which allows greater sidewall flex that cushions bumps in the road.

I'm no expert, but I'd bet the ride quality might be worse with 225/45/18s than 235/40/18s.

Regarding ABS & traction control, the diameter shouldn't make a difference as long as all the tires are the same. The only difference you might encounter is the threshold speeds where ABS/traction control kick in. ABS shuts off below ~5 MPH indicated and traction control shuts off over ~80 MPH indicated (on the 4Matic at least). But the basic function won't be affected.

Fast55

I'm practically positive that the speed/odometer is from the front. My owners manual says the nav calibration is for the front tire size. Anyway, had the 255 40 F1's on the rear of my 430 with the factory sport wheels, no problems. Didn't quite look like a 55 without the staggered wheel sizes, but it was noticeable and definitely an improvement.

E-Klasse

How is it that the speedo runs when the car is on a dyno? The front wheels are standing still and only the back wheels are turning?

Fast55

Is it possible that the nav is calibrated for the front tire revs, but speedo/odo is the usual (rear) driven?

awtrott

Thank you very much for the information you provided. It was extremely helpful and subsequently I decided to go with the 235/40/18 Toyo Proxes 4. To my greatest surprise they are not as harsh as I thought they would be. I will be taking it to Butler Tires to have them do the high speed balancing and inflate the tires with nitrogen.

Tell me if you know. I currently have #5 spring pads in the front and #4 in the back, and am planning to change them to #1 all round for roughly a 1/2 drop, which is enough for me. Do you feel it will have a profound affect on my alignment?

mysticblu999

i don't think it would be worth the money...