Dmurph

Hey guys, In an effort to prevent a divorce and keep me from being admitted to a mental care facility, I've got to do something to prevent my wife from ruining tires and wheels on her C350 4matic Coupe. The car has the OE AMG 18" wheels- 18x8 50mm in front and 18x8.5 54mm in rear. The stock tire sizes are: front-225/40R18 rear-255/35R18.......and that's just not enough sidewall cushion for someone that can't grasp concept of looking at the road surface that you are going to be driving over in the next few seconds....
I've spent the last few hours reading through archives on here and not found a clear concise answer to this question: Can I go up 5% in aspect ratio (sidewall height) on the front and rear tires of this car without causing problems in the 4matic system?

The guys at the Nat Tire and Batt I used to go to said no. Dealership just passed me back and forth between parts and service like they did when I asked about differential capacities(won't ever call them again period....not even if they were giving away cars (longer story)).

The fronts would go from 25.1" > 26", rears from 25" > 26". Revs per mile will go down 804 > 776 front, 804 > 777 rear which will cause speedo to read slightly lower than actual. It's basically a 15/32" top and bottom front and a 1/2" top/bottom rear height increase which comes out to 3.6% increase front and a 4% increase rear. And possibly a 100% increase in my sanity!

Odd Piggy

As long as the 4 tires are the same diameter, the 4matic won’t care.

Fender and suspension parts clearance is another matter that I can’t comment on.

Dmurph

Do you mean same diameter as OE?
or
Same diameter relationship between front and rear axles as OE?

Dmurph

​​​​​​I got it, was on way out door when read your answer and sent that reply. Figured out what you meant by bottom of driveway

​​​​4matic system prefers that all four tires be the same diameter whether 25", 26", or 40" Thank you.

​​​​​​ A set of Interco Super Swampers will solve this problem once and for all!

mercs4life

I got 18 inch rims that are squared and am running 245/40r18 all around. E class size. I got lots of sidewall to not mess up the tires. But it would be best to downsize to 17 inch rims as that will give you even more tire sidewall.

Dmurph

By squared do you mean 0 offset?
Our 4matic came staggered w/ 225/40 front 255/35 rear and 18" AMG Sport package wheels. Going down to 17's would def help, but is a last resort.

My wife has what may be the world record of 17 road hazard claims with this car lol. In fairness 6 weren't her fault, 4 reverse rotation at NTB and 2 from an accident in front of her where she ran over the scattering debris. All but one happened while under the wheel/tire warranty. That one resulted in a cracked front wheel which I TIG welded about 2yrs ago. The weld finally gave out last week so I sanded, cross hatched and repaired with 3 thin layers of JB Weld; and started looking for a new wheel. The 18" AMG 7 spoke 8" 50 offset front wheels are 4x the cost of a rear and as much as 4 low end aftermarket wheels! So I started entertaining an aftermarket set or possibly buying two more 8.5" rears and running them on the front?

She drove about 4400mi after NTB rotated the 255's to the front and put the 225's in rear. During that stretch the 255's rubbed the paint off the front struts. So I know the 8.5" 54mm rear wheel with 255/35R18 is just a little too big for the front end...

Granted she's a much better driver now but I still want to give her some taller sidewalls to work with...

Best case scenario would be to get away from the staggered setup so tires can be rotated to all 4 corners, increase sidewall height to mitigate potential future issues, and do both W/O sacrificing ANY lateral grip!?!?

Just put car up to replace front and rear diff oils, trans oil, and rebuild sticking pass rear caliper. When done with those I'm going to pull all 4 wheels and measure meticulously to see what I can get away with on tire size. I'll let you know how it goes lol

mercs4life

Squared is when all the rims are the same width, so not staggered. Look for a set of rims from a cla250 17 inch or a w205 c class. The are a squared set. 17 would be your best option

Dmurph

Ahhh..... had never heard it referred to as squared. Makes perfect sense though, thanks

17's will be last resort honestly. I realize that would make this puzzle a lot less difficult to put together, but aesthetically Im afraid 17's might rekindle her fire for an S5 lol. I just talked her into keeping this by giving her interior a reverse colors makeover, changed all black buttons to satin silver and changed steering wheel trim piece and emblem from silver to gloss black. Wrapped all burgundy wood in textured black Ash vinyl and clear coated. Turned out gorgeous but I love no payments and having a vehicle that I know the history of

mercs4life

One of my friends got a c300 with 18x8.5 rims all around with the 255 tires. He bought 2 additional rear rims and it’s not rubbing anywhere on the suspension but I know the fronts are close to the strut. A 10mm spacer would fix that tho

Moto_Guzzi

I would guess with larger tyres you might miss out on 7th gear more driving 1500rpm speeds leasurely along at previous preferred speed.

Dmurph

So we ended up nowhere remotely close to what my goal was in the beginning lol.

In the week of expanding my offset knowledge, available space measurement skills and trying to decide on new wheel/tire size; I kept checking my local market for a set of usable 5x112 wheels.....and kept seeing these 3 sets of 19" Audi factory wheels. Two had decent list price and no tires. One set had some very meaty Michelin Pilot Sport AS4's and low list price $700. So after some research into reaming out the center bore from Audi's 57.1mm to our 66.56mm, I made an offer of $125 a piece on a set of 19" wheels off of a 2019 Audi RS3, and he accepted. I went picked them up, spent about 2min per wheel using a router w/carbide bit removing less material than half my wife's bracelets, along with about an hour turning the center caps from black w/four rings to something that looks like it could've been there all along(?)

And the result: Def not a purist route, but I've seen much worse.

For $500 bones I got: RS3 Fronts 19x8 42mm offset and 235/35ZR19 Mich Pilot Sp AS4 & RS3 Rears 19x8.5 46mm and 255/30ZR19 Mich Pilot Sp AS4. New the wheels are $3300 + install. Ebay used wheels $1449. Tires new $278 front, $320 rears; came with 10/32nd new and I gauged at 9/32 11 of 12 places, 8/32nd in the 12th.

No rub at all and the extra 8mm in poke fills out the space nicely. The over/under on her destroying one or more was set at 55 days. I took the over out of a show of support for my wife's promise to be more attentive DOWN the road! I got about even money from my boys, 42 days to go lol

B4 center caps

w/remodeled center caps

front stance

rear stance