noka

C55 stock wheels/tires

Front = 7.5x18 (ET:30mm) and 225/40-18 tire
Rear = 8.5x18 (ET:34mm) and 245/35-18 tire

Can anyone confirm? As a spare, will front fit on rear given:

a. Offset difference (30mm front vs. 34mm rear).

b. Rolling circumference difference = 26.7mm between left and right if front is used as spare on rear (see calc below).

Note:
Diameter calculation:
d1 = (225)(0.40)(2) + (18)(25.4) = 637.2mm
d2 = (245)(0.35)(2) + (18)(25.4) = 628.7mm
Circumference difference = (pi)(d1-d2) = (3.14)(8.5) = 26.7mm

Rgds,
Norm

rbaker

Can't confirm that, but don't see why the fronts wouldn't fit on the rear, as the front's have much larger brakes. The rear's are just 20mm wider on the outside & 5mm on the inside than the front. I imagine you're considering this for a spare, so it'll probably work. I'd just try swapping to check.

FYI, I think you have the offset wrong unless your C55 came with optional wheels, as my C55's stock wheels are:
ET 37 front
ET 30 rear

FrankW

yes they will.

BlackC230Coupe

of course it will.

noka

Miscalculated rolling circumference (just edited in my initial post). Difference between stock front and rear setup appears to be 26.7mm (a little over an inch). Will this make make a difference or hurt anything given that the difference will be on the same (rear) axle between left and right?

Rgds,
Norm

smgC32

I believe your formula is incorrect. Yes you can run the front in the rear as the offset is eaten up by difference in wheel width. Problems can be had by running the rear in the front. Why don't you just take off the front wheel and install it on the rear??? to check fitment yourself?

noka

- What do you think is wrong with the formula?
- I am more concerned with circumference than with offset.

Rgds,
Norm

noka

My wheels are stock Double Spoke AMG wheels for the C55 and are:
ET 30 front
ET 34 rear
These offsets are stamped on my wheels and listed in the Owner's Manual.
Did you buy your C55 used, or any possibility the dealer swapped wheels w/o your knowledge? I suggest you check again.

Rgds,
Norm

FrankW

go check the Mercedes-Benz.com/amg they have the ET listed for each rims.

these are the one's listed for the C55 standard rims


AMG light-alloy wheel (Style IV)
7,5 x 18 ET 37 B6 603 1310 tyre size 225/40 (for FA and RA)
8,5 x 18 ET 34 B6 603 1342 tyre size 245/35 (RA only)
8,5 x 18 ET 30 B6 603 1305 tyre size 245/35 (RA only)
Optional:** tyre size 255/35 (RA only)

noka

Thanks for the web-site and I have already seen it. I (and others whose posts I can find on this site) physically removed the stock C55 staggered wheels and confirmed the offsets match what is in the Owner's Manual and what I posted. I choose to believe my Owner's Manual and what I physically see stamped on the wheels over the web-site you posted. YMMV.

Rgds,
Norm

rbaker

No, my car & wheels are original factory AMG. The wheels are made in Austria and have all the factory p/n's & info on the wheel interior. I personally verified these offsets are listed on the inside of the wheel casting. I wouldn't be surprised if the manual is wrong, as it shows the car coming with 245/35/18 rears and every C55 I've seen has 255's.

If your car has 30mm offset front wheels, want to trade!?!?

noka

Just for kicks, I will verify offset, wheel and tire size tonight and post here. I'm starting to think maybe there was some running production change.

By the way (if you choose to believe it), amgpower.com lists for C55:
Front Rims 7.5J x 18 in
Rear Rims 8.5J x 18 in
Front Tires 225/40 ZR 18
Rear Tires 245/35 ZR 18 (CLK55 has 255/35 ZR 18 rears).

Rgds,
Norm

05C55

Well since the wheels are sitting in my garage I decided to actually measure the rolling circumference, the front wheel is 1/4 inch greater than the rear. The wheels are likewise stamped ET 30 front, ET 34 rear and came with 245's in the rear.

noka

My calc was 4x your actual measurement. Let's say 0.5" and split the difference. So the question is whether that would cause any problems if rear left and right differed by that much. I am inclined to think not. Your measurement did agree with my calc in the sense that the front circumference is greater than the rear. Thanks for checking your wheel offset and tire size. They agree with my stock sizes. Either the other posters were wrong or there was some running production change.

Rgds,
Norm

05C55

I agree that it would probably not affect the car at all. It may wear differently, but my guess is you would have to be using it an awful lot to make any difference at all. As a spare I wouldn't think you wouldn't have any issues.

noka

I just confirmed the following for my C55 (09/04 build date):

Front:
Tire: 225/40 ZR18 92Y P-Zero Rosso
Wheel: 7.5J x 18 H2, ET30
MB p/n A 203 401 4102
Made in Austria

Rear:
Tire: 245/35 ZR18 92Y P-Zero Rosso
Wheel: 8.5J x 18 H2, ET34
MB p/n A 203 401 3902
Made in Austria

Rgds,
Norm

rbaker

OK, so it sounds like AMG did a running change (my build is 05/04), so your offset probably is the new design. That would make sense, as a 30mm offset would widen the track 14mm total & help reduce understeer (a problem I sorely hate in mine). Also the rear tires occasionally rub on a hard bump, so that may be why they changed the rear. When I scan the old AMG catalogs i have, it looks like most all the old 7.5" fronts have 37mm offset, so it seems the 30mm is new.

Mine was only the 2cd C55 that South Bay Mercedes rec'd here in SoCal, and it came with Continental Sport Contact 2's. I don't have a photo of the front rim handy, but the rear shows:
P/N: A 209 401 1502 (normal double spoke you see on C55's)
8.5J x 18 EH2 ET30

Weight wasn't too bad at 26.5 lbs (with a few oz of wheel weights on).

noka

Thanks for confirming that. I suspected something like a running production change. We both can't be crazy!

All the brochures I have (two hard-copy color for "C-Class" and "AMG" and online E-brochure on MBUSA) show "245" rear for C55 (but "255" for CLK55). If there were no rub problem, I would prefer the 255, for aesthetics really. Perhaps if it causes a problem for you, you could convince them to swap your wheels and tires, if you even care about it.

The funny thing is that the 255x35-18 is closer in rolling circumference to the front 225x40-18 than the 245x35-18 is. That's why I was asking the question about using a front as a spare, because if used on the rear there would be a greater difference between left and right rolling circumference with e.g. my setup vs. your setup. So, I am still not quite sure if it will hurt anything.

Rgds,
Norm

smgC32

Have you ever measured the difference in RC on a donut spare?! If it is used for the purpose a spare tire was made for, don't worry about it. If you plan on driving the car hard, ESP will surely be affected as both rear tires are rolling at different rates.

noka

Yes, I did think about it but that would require inflating it (to some specified pressure) and it's too damn cold where I live right now to play with that!

However, I could always use one of my snows because the 'RC' of those is also quite close to the stock setup. There is a different tread pattern of course, but I think that is not really signficant for temporary spare use.

Rgds,
Norm

noka

Just curious if the plackard inside your driver's door jamb says 255 for rear tire size (mine does say 245 to match what I have).

Rgds,
Norm

smgC32

Is it possible that the dearler swapped the wheels with a CLK55? Maybe they needed to chrome a set of C55 wheels and when you bought the car, they gave you CLK55 wheels as they look the same, but have a larger rear tire. Someone should check the stock offset of a set of CLK wheels in the CLK forum.

noka

If you are asking "RBAKER", I doubt it, ... but he could confirm. I asked him to check plackard on door jamb.

Rgds,
Norm

rbaker

The door jamb on mine lists 245's for the rear also, so no help there. On the other hand, all the other C55's I've seen at my dealer here had 255's on the rear just like mine. Maybe it was as simple as tire availability or the need for more traction? This thing still lights up the 255's like nobody's business, so it could use 265 or 275's if they could fit with a little fender rolling. Of course it would probably need 245 or 255's on the front then to be balanced in corners.

I've actually thought about asking the dealer to check or swap the wheels (mostly to get the new offset, not narrower tire), but I'm probably going to wind up just buying another set of wider, lightweight wheels soon with slightly different offset. It's just difficult finding wheels to fit this thing that are light & have correct brake clearance.

Back to your questions about a spare... our cars don't have a limited slip diff, so really no issue about different diameter tires on the rear for temporary use. The slight suspension height change is not an issue. I also got to verify this the hard way after a flat right rear.

smgC32

All in 7.5" front and 8.5" rear, the C32's offset is ET37 front and ET34 rear in a 17" wheel. The AMG double spoke 209's in 17" are ET37 front and ET30 rear. It seams that the generic AMG double spoke new design is made for the aftermarket to fit a variety of Mercedes vehicles in the ET37/30 fitment. The C55's ET30 front and ET34 rear is rather unusual and maybe they make a special wheel just for this application in order to widen the track in front, and narrow the track in the rear compared to the ET37/30 for more neutral handling. Go to the dealer and look up the part in the computer system that should list offsets for all the vehicles in question as stock offerings.