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18x8.5 and 18x9.5 tires

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Old Feb 17, 2020 | 12:57 PM
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2017 AMG C63
18x8.5 and 18x9.5 tires

Hey guys I've seen numerous threads on the 19 inch wheels regarding the widest tire you can go with, but hardly any love for the base c63.
I have the stock 18s x 8.5 and 9.5 that come with 245/40 and 265x40, what tires can I fit on there. My front tires are new on the outside and worn to **** on the inside.

Thanks in advance.
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Old Feb 17, 2020 | 03:01 PM
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There are various "calculator" web pages that can help with this, e.g.:
https://www.tyresizecalculator.com/t...ize-calculator

Some others I've found to be handy when looking at "tire stuff" ...
https://tiresize.com/comparison/
https://www.1010tires.com/Tools/Wheel-Offset-Calculator
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Old Feb 17, 2020 | 03:31 PM
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8.5 can accommodate 255 and 9.5 can accommodate 275.

rolling diameter will be off, therefor speedo with this change. don't know anything about inner clearance being an issue.
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Old Feb 17, 2020 | 03:52 PM
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Originally Posted by alexasa
8.5 can accommodate 255 and 9.5 can accommodate 275.

rolling diameter will be off, therefor speedo with this change. don't know anything about inner clearance being an issue.
Those are the sizes I wanted to run just didn't know if it they should be /40 or /35.
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Old Feb 17, 2020 | 08:59 PM
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Originally Posted by esworld05
Those are the sizes I wanted to run just didn't know if it they should be /40 or /35.
... and that's why I sent the other links that cover items in addition to what you'd asked about (i.e., because when you're diddling with tires 'n rims, you'll need to use all 3 of those resources).
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Old Feb 18, 2020 | 07:52 AM
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Originally Posted by esworld05
Those are the sizes I wanted to run just didn't know if it they should be /40 or /35.
I typically prefer to upsize rather than downsize sidewall height, so go with the same as stock (which still increases rolling diameter because the second number is the percentage of height of the section width).
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Old Feb 18, 2020 | 10:09 AM
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Originally Posted by alexasa
I typically prefer to upsize rather than downsize sidewall height, so go with the same as stock (which still increases rolling diameter because the second number is the percentage of height of the section width).
Okay so I'm guessing I should go with 255/40/18 and 275/40/18. I daily my car and travel 300 miles 2x per week so I'm not going to be getting MPSS or anything else fancy. I'm going to settle for something I can get under 1k for all 4 as I'm sure within the year I'm going to have to replace them again.
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Old Feb 18, 2020 | 04:58 PM
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Originally Posted by esworld05
I'm going to settle for something I can get under 1k for all 4 ...
Seriously?! Tires are likely the single-most important item w.r.t. safety and handling ... and you're going to "cheap out" on tires on a 400+ HP rear-wheel drive car? I'd suggest that you re-examine your choices.

The OEM tires on my C63 S were "Dumb-slop" Sport Maxx RT (supposedly high performance) tires and they were _terrible_ ... poor handling, poor ride and poor grip -- quickly matting the throttle on a wet highway at 130 kph/80 mph would break the tires loose. In contrast, the same activity in the same section of wet highway with Michelin Pilot Sport 4S tires won't break traction above 90 kph/56 mph. As you can imagine, the difference in safety is huge.

Tires and brakes are places to get the absolute best you can, not a place to save a few dollars.
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Old Feb 18, 2020 | 05:39 PM
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Originally Posted by esworld05
Okay so I'm guessing I should go with 255/40/18 and 275/40/18. I daily my car and travel 300 miles 2x per week so I'm not going to be getting MPSS or anything else fancy. I'm going to settle for something I can get under 1k for all 4 as I'm sure within the year I'm going to have to replace them again.
Just make sure you read some reviews before you buy. Tirerack is a good source - they test and user reviews.

Personally, if you want to save some look into Indy Firehawk 500 - they are Ultra High Performance Summer tires. Top within its category and a small step down from MPSS. I had both and for daily driving I found the Firehawk 500 to be a very serviceable tire. Pretty good grip, stiff sidewall for decent cornering, and never had an issue in rain under normal highway conditions (I don't race, track or drift). They also look like a sport car tire. They are 99W rated (same loading as MPSS but one step down for top speed rating of 168MPH (W) vs > 168MPH (Y) Never got in an extreme conditions with them...bot not sure if that's because of me or because the tire prevented it though. 275/40/18 are $169 on Tirerack. I see them often on SRT's or Mustang GT's and they also are well above 400hp cars.
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Old Feb 18, 2020 | 08:19 PM
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Originally Posted by tobeit
Just make sure you read some reviews before you buy. Tirerack is a good source - they test and user reviews.

Personally, if you want to save some look into Indy Firehawk 500 - they are Ultra High Performance Summer tires. Top within its category and a small step down from MPSS. I had both and for daily driving I found the Firehawk 500 to be a very serviceable tire. Pretty good grip, stiff sidewall for decent cornering, and never had an issue in rain under normal highway conditions (I don't race, track or drift). They also look like a sport car tire. They are 99W rated (same loading as MPSS but one step down for top speed rating of 168MPH (W) vs > 168MPH (Y) Never got in an extreme conditions with them...bot not sure if that's because of me or because the tire prevented it though. 275/40/18 are $169 on Tirerack. I see them often on SRT's or Mustang GT's and they also are well above 400hp cars.
I was actually leaning towards those. I bought some nitro 555g2 for my 5.0 procharged 650whp and I had no issues with those. I had some sumitomos on my Hellcat and had no issues. You dont have to go crazy buying 500 dollar a piece tires to be "safe" lol.
Thanks for the tips fellas
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Old Feb 18, 2020 | 08:32 PM
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Originally Posted by esworld05
I was actually leaning towards those. I bought some nitro 555g2 for my 5.0 procharged 650whp and I had no issues with those. I had some sumitomos on my Hellcat and had no issues. You dont have to go crazy buying 500 dollar a piece tires to be "safe" lol.
Thanks for the tips fellas
i guess the Nitto 555g2 are better than the original 555? Those had me slip and slide in rain.
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Old Feb 18, 2020 | 08:47 PM
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Originally Posted by tobeit
i guess the Nitto 555g2 are better than the original 555? Those had me slip and slide in rain.
Yes they're way better. The old 555 performed like slicks in the rain horrible.
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Old Mar 23, 2020 | 03:51 PM
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Mich PS 4S tires for 18" C63 wheels were right around $1000 for 4.
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Old Mar 23, 2020 | 04:27 PM
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Originally Posted by LessIsMore
Mich PS 4S tires for 18" C63 wheels were right around $1000 for 4.
Nice, but I would run through those like crazy. All in all I paid 1100 for four tires, balance, rotation and alignment for life, I know we can't rotate, install and disposal. I think I got a fair deal.
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Old Jan 1, 2021 | 10:29 PM
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Originally Posted by alexasa
8.5 can accommodate 255 and 9.5 can accommodate 275.

rolling diameter will be off, therefor speedo with this change. don't know anything about inner clearance being an issue.
How do you know how wide a tire a rim width can take? I.e. - my stock sizes are 245/35-19 on 8.5" width and 265/35-19 on 9.5" width rim. I want to run 265/35-19 and 285/35-19.
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Old Jan 2, 2021 | 02:34 PM
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Originally Posted by theclutch
How do you know how wide a tire a rim width can take?g
Use one of the web resources, such as:
https://www.tyresizecalculator.com/t...ize-calculator
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Old Jan 2, 2021 | 09:18 PM
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Originally Posted by user33
Use one of the web resources, such as:
https://www.tyresizecalculator.com/t...ize-calculator
Well that sucks... If so, then the biggest width tire we can use will be 255/35-19 for the front with an 8.5 inch width and 275/35-19 for the rear with an 9.5 inch rim. And the rears would be 285/35-19.

Stock Wheels
FRONT 245/35-19 on 8.5" rims = 25.8" diameter
REAR 265/35-19 on 9.5" rims = 26.3" diameter
Difference = 0.5" smaller at the fronts

Largest recommended via that website:
FRONT 255/35-19 on 8.5" rims = 26.0" diameter
REAR 275/35-19 on 9.5" rims = 26.6" diameter
Difference = 0.6" smaller at the fronts
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