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Old 05-29-2019, 10:27 PM   #31
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Mine are dented but still balanced, but post when you sell.
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Old 08-08-2019, 12:14 AM   #32
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I figure I should update here. I got the 18" tires with Michelin 4s.

TL;DR: Overall the tires are great. Love them. And I don't stress over hitting potholes now. But they are louder and require lower pressures.

Details:

There is no issue with sidewall squirm relative to the 20's. My 18" snows have a lot more turn in squish which makes them less fun. I assumed that was mostly tread squirm or softer sidewall material, and this confirms it. The 18" 4S still feel great.

However, they are louder. There is more road noise than Tesla's 20" variant, which had some kind of foam strip embedded in them. The model 3 lets in a decent amount of road noise and it's noticeable. The current noise level is a little disappointing, but I can live with it. It's still like a Mercedes compared to the Cayman R.

Inflated to the same tire pressure (40psi) the 18" tires are actually more harsh than the 20" variant. I was always amazed at how complaint they were. However they needed even higher pressure to avoid denting the rims. The 18's allow me to safely lower them a few PSI at which point they become as comfortable as the 20's.

WTF you ask, how can an 18" be more harsh? I'm not entirely sure I understand, but I believe it's the little understood phenomenon of tire casing pressure and barlow's law. Think about bicycle tires. The larger the tire, the lower pressure you run to achieve the same ride quality and sag pct. A 1" road bike tire may be pumped to 100psi, a 2.5" mountain bike to 25psi, and a 5" fatbike tire to 8 PSI. The 18" wheel's tire has a larger rubber surface area.

This article gets into the math http://flocycling.blogspot.com/2014/...less-tire.html

Last edited by rumatt; 08-08-2019 at 12:26 AM.
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Old 08-08-2019, 09:21 AM   #33
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Quote:
Originally Posted by rumatt View Post
WTF you ask, how can an 18" be more harsh? I'm not entirely sure I understand, but I believe it's the little understood phenomenon of tire casing pressure and barlow's law. Think about bicycle tires. The larger the tire, the lower pressure you run to achieve the same ride quality and sag pct. A 1" road bike tire may be pumped to 100psi, a 2.5" mountain bike to 25psi, and a 5" fatbike tire to 8 PSI. The 18" wheel's tire has a larger rubber surface area.

This article gets into the math http://flocycling.blogspot.com/2014/...less-tire.html
I ran into this when considering going from 23mm to 25mm width tires on my road bike.
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Old 08-08-2019, 09:24 AM   #34
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At the same tread width and total diameter, they should have very similar contact patch area; but the higher sidewall simply has more air; so it could support more weight. If you are looking for a certain drop on the sidewall (bicycle style), you might need less air in the larger profile. I'll read about the casing tension, that probably has some to do with drop; but think about the supported weight as well.

Last edited by equ; 08-08-2019 at 09:45 AM.
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Old 08-08-2019, 09:56 AM   #35
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Are you surprised that the tire that Michelin is giving super stiff sidewalls is stiff?
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Old 08-08-2019, 11:52 AM   #36
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Originally Posted by Nick M3 View Post
Are you surprised that the tire that Michelin is giving super stiff sidewalls is stiff?
No. The original 20's were the same tire
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Old 08-23-2019, 10:45 PM   #37
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Seems I'm not the only one.

https://youtu.be/H6sPc9dFsGw
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