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Same tire size wall height for front & rear tire question
Hi Gang,
So I've read lots of posts explaining why Mercedes decided to recommended a shorter tire, wall size for the rear, and all the explanations about how "supposedly" you could screw your speedometer and ABS braking system up by having the same wall height for front & rear, but honestly I'm super skeptical of this and I'd appreciated it if somebody (who is also running the same wall height thickness front & rear) could give me some real world feedback.
I'll be running 275/40R18's in the rear and 245/40R18's in the front that I have yet to put on, and I'm seriously doubting that they will prevent the cruise control from working properly, or cause the brakes not to work, or throw the speedometer off enough to notice.........but I'd love to hear from any of you that may have experienced these things.
I had a ‘14 e350 coupe rwd, so idk how similar the electronics are to your model SL but, I ran 275/30 20(r), 245/30 20(f) and didn’t have problems with ABS nor the speedometer. As a matter of fact, I tested it against one of those radar speed signs and it registered the same speed on my dash at 60mph. However, using a tire size calculator, the tire diameter difference from my OEM 255/35 18(r) wheels was -1.31mph (slower). Using the same calculator, the difference in diameter on 20’s was, 3.84 mph faster (front).
From what I’ve read and my tire guy’s experience, for as long as the f/r diameter ratio is within 3% it’s ok. My 275/30 20 and 245/30 20, was 2.67%. I guess I was pushing it but it never had any issues and I had them on for a couple of years. I also used the same exact sizes on my current c43 4matic for for a few months before switching to different wheel tire setup with no issues.
In your case, the tire sizes you intend to use have a 3.54% difference. That’d make me nervous.
Any reason why you wanna use those sizes? If you do 275/35 18, and 245/40 18, you’ll be golden!
I had a ‘14 e350 coupe rwd, so idk how similar the electronics are to your model SL but, I ran 275/30 20(r), 245/30 20(f) and didn’t have problems with ABS nor the speedometer. As a matter of fact, I tested it against one of those radar speed signs and it registered the same speed on my dash at 60mph. However, using a tire size calculator, the tire diameter difference from my OEM 255/35 18(r) wheels was -1.31mph (slower). Using the same calculator, the difference in diameter on 20’s was, 3.84 mph faster (front).
From what I’ve read and my tire guy’s experience, for as long as the f/r diameter ratio is within 3% it’s ok. My 275/30 20 and 245/30 20, was 2.67%. I guess I was pushing it but it never had any issues and I had them on for a couple of years. I also used the same exact sizes on my current c43 4matic for for a few months before switching to different wheel tire setup with no issues.
In your case, the tire sizes you intend to use have a 3.54% difference. That’d make me nervous.
Any reason why you wanna use those sizes? If you do 275/35 18, and 245/40 18, you’ll be golden!
Thank you so much for the reply, all of that makes sense.
To answer your question, honestly, it comes down to astechics for me, I've never liked the "look" of different sidewall heights on cars.
I have an 89 BMW E24 that had shorter sidewall tires on the rear, and I absolutely hated the way they looked
So when I restored the car, I purposely put matching sidewall height tires on the rims all the way around.
Its a staggered set, but I didn't notice any appreciable difference in the ride and it didn't affect any of my gauges, or speedo, or anything.
I don't know if it's sacrilege to post pics of different car brands in here, but here's a pic of my Beemer and you can see what I mean. (all 4 tires have the same sidewall height)
The tires I have for the SL are mounted on the wheels (but not on the car yet)
Once they're on, I can write back and report any issues I may have with them, and If I do, I'll be forced to go with a setup that I won't like..........we'll see.
All 4 tires on the SL right now have a sidewall height of 35, take a look:
Thank you so much for the reply, all of that makes sense.
To answer your question, honestly, it comes down to astechics for me, I've never liked the "look" of different sidewall heights on cars.
I have an 89 BMW E24 that had shorter sidewall tires on the rear, and I absolutely hated the way they looked
So when I restored the car, I purposely put matching sidewall height tires on the rims all the way around.
Its a staggered set, but I didn't notice any appreciable difference in the ride and it didn't affect any of my gauges, or speedo, or anything.
I don't know if it's sacrilege to post pics of different car brands in here, but here's a pic of my Beemer and you can see what I mean. (all 4 tires have the same sidewall height)
The tires I have for the SL are mounted on the wheels (but not on the car yet)
Once they're on, I can write back and report any issues I may have with them, and If I do, I'll be forced to go with a setup that I won't like..........we'll see.
All 4 tires on the SL right now have a sidewall height of 35, take a look:
Thanks for your input, much appreciated....
If you absolutely have to have matching aspects ratio f/r, then I would suggest you go wider on the tire up front or narrower in the rear. Your 275/40-18 (r) will be within 3% if you go 255/40-18 up front. Or, if you keep your fronts at 245/40-18, then going 265/40-18 rear will also be within 3% f/r ratio. Personally, I always choose to go wider, so if you can squeeze the 255/40-18 without rubbing issues I’d go for that instead.
01-18-2021, 09:29 AM
