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      05-23-2023, 04:31 PM   #1
ralphsmithiii
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Let's Discuss Traction - Roll Racing

I started to write a dissertation about decided to keep this one short and to the point, for now

My question is, for 700whp/620ish ft/lb on an F80 M3 Comp with a KW HAS kit, would you go:

18's on a 275/35/18F and 305/35/18R for the most sidewall/flex/tire but having the front tire be 1" shorter than a stock 666 wheel/tire setup, knowing you can't lower the front another inch (driveway issues).

Or

19's on a 265/35/19F (.1 difference from stock tire) and 305/30/19 for identical OD (based on wheel/tire combo) to stock wheel/tire setup?

My initial thoughts are the 18's are going to hook much better from a roll due to sidewall flex, however, how much better than the 19? The challenge I'm facing is that I'm not comparing the same rear tire (NT555RII/MT SS 100 TW on 18 vs Falken RT660 200TW on the 19's).

I think the 19's on the RT660's would suffice if the tires are warmed although they still may spin some at the initial hit, but, I also think the car would be plenty manageable with my setup (Turner rear diff bushings/plate) plus they would be slightly better as a daily and in the rain.

For twisties, I'd throw my stock wheels back on with a good tires as I only really hit up the mountains once a year for fun with friends.

Thoughts?
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      05-23-2023, 10:11 PM   #2
TRman
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Yea it’s no fun to have that much power in a rear drive car and can’t put it down.

I think the difference between 18” and 19” wheels/tires would be minimal for forward grip, especially at the torque figure you mention. Best to pick the right tire for the task at hand. The Nitto or the MT should be way better for forward traction. That’s what they’re made for. The Falkins are in a different class with a different focus. Also both the Nittos and MTs come in 19” size.

Based on what you said, I’d go with the Nittos as a first try and see how they work for your situation.
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      05-24-2023, 09:10 AM   #3
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I was in a similar position with similar power. I ended up going with an 18" rear setup and am running 315 Toyo 888R's and traction is no longer an issue for me. I have a set of 555RII for my similarly powered Cobra (although the torque is a different story lol) and they're pretty badass as well when they're warm.

Doesn't really answer your question, but that's the route I went and have been really happy with it.
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      05-24-2023, 11:22 AM   #4
ralphsmithiii
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Quote:
Originally Posted by TRman View Post
Yea it’s no fun to have that much power in a rear drive car and can’t put it down.

I think the difference between 18” and 19” wheels/tires would be minimal for forward grip, especially at the torque figure you mention. Best to pick the right tire for the task at hand. The Nitto or the MT should be way better for forward traction. That’s what they’re made for. The Falkins are in a different class with a different focus. Also both the Nittos and MTs come in 19” size.

Based on what you said, I’d go with the Nittos as a first try and see how they work for your situation.
I tend to agree and it looks like the Nitto's are the way I'm going to go. I've had several sets of NT05R's on previous vehicles and I have no complaints about the brand. I did have a set of MT SS's on my previous vehicle, a manual 2017 ATS-V Sedan that was also FBO Flex 93/E85 putting out slightly over 600whp and 670ftlb on stock turbos. But, at higher speeds, the MT's would "float" a little. It was OK if you knew what to expect but still wasn't a huge fan. That was on a an 17x10 Weld rear, and to be fair, I had a pair of 18" 5"wide front runners to pair with it but the tires where BO for MONTHS so never got to run the full drag pack to see if it was more stable.
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      05-24-2023, 12:19 PM   #5
ralphsmithiii
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Quote:
Originally Posted by heitzke View Post
I was in a similar position with similar power. I ended up going with an 18" rear setup and am running 315 Toyo 888R's and traction is no longer an issue for me. I have a set of 555RII for my similarly powered Cobra (although the torque is a different story lol) and they're pretty badass as well when they're warm.

Doesn't really answer your question, but that's the route I went and have been really happy with it.
It looks like you have an M4 which I believe has more room to squeeze the 315's under.

Looking at the tire specs on the Nitto G2's for the front and Nitto 555RII's in the rear, the front sizes I'd consider in 18's would be:

275/35/18 (This is Apex's recommedation for their 18x9.5/18x10 front wheel with ET 22 (on the 9.5) to clear the KW HAS. However, if I look at the specs on the same tire in 265/40/18 its in inch taller but same width.

That interests me slightly more as it would allow me to essentially not have t touch my suspension, as it's setup the lowest I can take it due to my driveway and still fill in the front fender gap. It would be .2ish taller than the rear but nobody would notice it. I don't believe that should give the DSC system any fits unless BMW calculates the thresholds different than other manufacturers.

I've been used to having to keep the front to rear OD's %'s within 1-2% in order to not throw off any of the traction control systems on other cars. However, I believe with 666 wheels on stock tire sizes the front to rear OD is about 3%. I'm now wondering if the opposite is true for this car, that being TOO close OD front to rear would cause issues as they car would see similar wheel speeds and not different...

I'll need to double-check the stock 666 wheel/tire specs one more time.
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