Increase tyre profile.

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New Member
Mar 16, 2017
Hello. Currently have 255 40 18 tyres all round (8.5" width wheels) on my 2012 cls 350. I'm looking at all season tyres and the range is massively increased if I look to 245 45 18 or 245 40 18. The 245 40 18 are a much closer overall size match to existing (diameter ) but the 45 profile appealed more for a bit more cushion in ride but it is adding 7mm of sidewall. In principle they appear to fit but I noticed the front suspension spring cup is not that far from the existing tyre which then had me questioning "will they even fit!?" . I don't want to end up fouling on this so wondering if anyone had tried this. I know the 245 45 18 is used on the E class and there is some commonality with the cls but I don't know if that extends to suspension ( not airmatic).
Putting aside the whole non standard tyre thing. I would trial fit one first. A decent tyre place should help you out if you go at a quiet time. If it was me I would stick with the 40.
Were 17 inch wheels an option on your car when new? If they were then you could get a set of 17" wheels from a breakers (they are relatively cheap) and fit all season tyres of the same size as the original summer tyres to those. There is much more choice in 17 inch - and the tyres are cheaper.
I ended up going for 245 40 18 (Hankook kinergy 4S2 all season). So a marginally narrower tyre and slightly less tyre wall. Just had them fitted a couple of days ago actually. Got them road force balanced at Ninemeister at the same time (previous set I had balanced the standard way 3 times and was never happy). RFB cost more than I was expecting at £270 but the ride is so much smoother with no shimmy. I will be absolutely fuming if I get a puncture!
Yes, this is correct but as the Speedo overreads by several mph anyway it doesn't have a big impact. It just edges me closer to accuracy!
Got them road force balanced at Ninemeister at the same time (previous set I had balanced the standard way 3 times and was never happy).
I learnt an interesting lesson about balance on one of my other cars with similar wheel size and setup to the Mercedes. We couldn't get it right, balanced at least 5 times, sometimes better sometimes worse when on the car. In the end it turned out to be the brake disk, there was a chunk missing from the edge on the inside that you couldn't see, didn't affect braking and the MOT tester didn't spot or didn't worry about it. New brake disks and the annoying steering shimmy at 70mph immediately went away.
New disks and pads were to be my next port of call after the RFB. It can be an expensive game the process of elimination!
As a mathematical calculation to differentiate between 2 theoretical sizes, it (or any other calculator) is spot on. The issue, as you allude, is that tyre manufacturers all have their own wildly differing interpretations of any given size, therefore it's the best estimate we can hope for.

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