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Discussion Starter #1
Anyone experienced this or is something wrong here?

I had Michelin Sport cup 2s all around with a year on them and some track days. You could say they’re at the later half of their lives.

Swapped the rear for Toyo R888R (315/30R20) and the car is now swaying left and right violently at high speeds and even more so unfer high braking. Handling is also shit now and the rear feels like it takes 5 seconds to catch up whenever I turn. Is this all normal or am I doing something wrong here?

I’ve read that tires with less tread respond faster but I didn’t expect all this. Grip is noticeably better though so there’s that at least.
 

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I've no experience with these tyres, but I would check the basics, e.g. that they're correctly mounted (they appear asymmetric, so need the outside facing out), have the correct pressures, and are flush with the hubs (no dirt) and the wheel bolts are correctly torqued.

With your description, I'd want it looked at before driving it any further.
 

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Running two different types of tire is likely the problem. I have seen that in Corvettes when people put drag radials in the rear.
 

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I have had this issue a few times, different front and rears on this sensitive of a car (or any super car) is going to make it feel very squirrelly.. I have never had success even putting different tires on back vs front.
 

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Discussion Starter #13
I have had this issue a few times, different front and rears on this sensitive of a car (or any super car) is going to make it feel very squirrelly.. I have never had success even putting different tires on back vs front.
It’s just that I saw many people running this setup on the 720S and was surprised no one even mentioned this issue because it pretty obvious (and dangerous).
 

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Discussion Starter #14
Always run same f and r. That's your issue.

Sent from my SM-N975F using Tapatalk
Seems like the most plausible explanation. Ordered the front tires and will see how it works out. Thanks everyone.
 

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Discussion Starter #16
stupid question, are the rear tires brand new? give it some time to wear in.
Stupid answer. Already broke them in and heat cycled them and tried a couple of air pressures to make sure it’s not any of that before asking.
 

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If you haven't switched front ones, that is part of your issue.
Another theory, but much more far fetched, is that your inner cords are bad and you got one or two defective tires. I have seen this happen with R888R's and with PS4's.
 

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What you're experiencing is the difference in sidewall stiffness. This is compounded as you are running a stiffer sidewall in proper size fronts with a different brand and weaker sidewall AND oversized rears. This is totally foreseeable. You doubled the rear slop by both less stiff sidewall and oversized for rim size in rear changing the balance by being greedy.
 

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Discussion Starter #19
If you haven't switched front ones, that is part of your issue.
Another theory, but much more far fetched, is that your inner cords are bad and you got one or two defective tires. I have seen this happen with R888R's and with PS4's.
Might also be true. I know a couple of people running my set-up and none of them experienced results as drastic as I did.
 

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Man I'm probably way off topic, but I once put Toyo Proxes on my Lotus Esprit and nearly killed myself with violent swaying. Turned out to be a bad composite for a supercar and Toyo replaced with another type. I assume hundreds of you can vouch for the compound of the R888 as being safe for a high-speed car ... but just saying.
 
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