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Best tire size? 18x8.5” wheels.

I’m wondering what alternative (from oem) size tire is the best fit for essentially the oem aero wheels. Performance and aesthetics are my main concern, and I doubt a slightly wider or narrower tire is going to have a huge effect on range.
I just bought some nice Martian wheels for my ‘21 M3, size 18x8.5”. I’m putting on Michelin pilot sport 4S tires but the size I want (235/45r18) is out of stock EVERYWHERE; so I’m looking for an alternative size. As of now I’m leaning toward a 245/45r18, but I’d love to know what people have run on their cars, what the differences are like compared to the 235/45, and just people’s opinions on the matter.
thanks!
 

MODEL+

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I’m wondering what alternative (from oem) size tire is the best fit for essentially the oem aero wheels. Performance and aesthetics are my main concern, and I doubt a slightly wider or narrower tire is going to have a huge effect on range.
I just bought some nice Martian wheels for my ‘21 M3, size 18x8.5”. I’m putting on Michelin pilot sport 4S tires but the size I want (235/45r18) is out of stock EVERYWHERE; so I’m looking for an alternative size. As of now I’m leaning toward a 245/45r18, but I’d love to know what people have run on their cars, what the differences are like compared to the 235/45, and just people’s opinions on the matter.
thanks!
If you don't mind the range lost, you can use 265/40/18.
This will keep the same exact overall diameter as 235/45/18.
Your tire is going to sit blocky on a 8.5 though.

DSC_9318.jpg
 
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If you don't mind the range lost, you can use 265/40/18.
This will keep the same exact overall diameter as 235/45/18.
Your tire is going to sit blocky on a 8.5 though.

View attachment 647633
If you don't mind the range lost, you can use 265/40/18.
This will keep the same exact overall diameter as 235/45/18.
Your tire is going to sit blocky on a 8.5 though.

View attachment 647633
I don’t think I’d want to go that big in width on an 8.5” wheel. I’m not super concerned with a minute discrepancy in speedo reading, but I think the range hit from a 265 might be a concern.
 
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MODEL+

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Oct 21, 2020
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I don’t think I’d want to go that big in width on an 8.5” wheel. I’m not super concerned with a minute discrepancy in speedo reading, but I think the range hit from a 265 might be a concern.
Well... you did say "Performance and aesthetics are my main concern", so that's the prescription I gave for your case.

You can also 255/40/18 if you don't mind -1.1% smaller diameter. You're right though, it will barely make a difference on the speedometer. More of a visual difference as it increases wheel gap.
 
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Well... you did say "Performance and aesthetics are my main concern", so that's the prescription I gave for your case.

You can also 255/40/18 if you don't mind -1.1% smaller diameter. You're right though, it will barely make a difference on the speedometer. More of a visual difference as it increases wheel gap.
No, thank you for the reply! I appreciate all feedback.
You think acceleration is negatively affected much from a 0.4” OD difference?
 
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Nah, I don't think you'll feel anything different on the "butt dyno" with that little amount of difference in diameter. Your speedo will read 1 mph slower @ 90mph haha
I do value my good ole butt dyno, strangely accurate lol.
Yeah, I was concerned as well with just the idea of adding 2lbs per corner of unsprung weight and the slightly larger OD. Luckily the new wheels I bought are lighter than the oem aeros; at this point instead of trying to gain range (performance aside), I think I’m just trying to negate negative range hits. Stickier rubber, slightly wider tire, not great for that but whatever I guess, I avoided the temptation of wider wheels which I wanted at first. That would’ve meant much wider/heavier/more$ tires and a noticeable range hit, for a trade off of benefits I’d only really see on the track.
I think 245/45 will end up being a good size 👌🏻
 
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Sam1

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No, thank you for the reply! I appreciate all feedback.
You think acceleration is negatively affected much from a 0.4” OD difference?

You will see zero acceleration differences because the motors' torque is electronically limited, and it's not even close to being maxed out. I removed over 40 pounds of mass on the brakes and wheels, moved to a stickier rubber with the light weight, and it wasn't even 0.01 faster on 0-60mph logged with dragy, literally the same exact times. When you accelerate while at highway speeds, it does 'feel' like the initial hit is harder (probably from the reduced weight, but my 60-130mph times are also the same exact times as they were with the OEM setup.

If you're looking for contact patch, the PS4S in 18/245/45 non-T0 has a tread width of 8.1". If you compare that to the 18/245/45 PZ4, that tire has a tread width of 7.6" (same as its 18/235/18 model) Or the 18/245/45 Ecsta PS91 has a tread width down to 7.4" ... that's 3/4 of an inch thinner than the PS4S. I used to think tire width measurements were how wide the tread was until someone on here corrected me, tread width has nothing to do with the profile width spec, so make sure you look at that.
 
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