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TTS Tire Size on Rear

 
Old 10-16-2018, 09:55 PM
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tonosity
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Default TTS Tire Size on Rear

What tire size fits best on a 12x20 wheels, on the rear of a 991.1 TTS? HRE recommends 305/30/20. However, I’m concerned with the fit (width-wise). Is it going to be too much of a stretch? Thanks!
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Old 10-16-2018, 10:16 PM
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From https://www.tyresizecalculator.com/c...rim-size-chart

295 minimum
305-315 preferred
325 maximum
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Old 10-16-2018, 11:14 PM
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Thank you! Yes, I have been playing with tire/wheel calculators. I’m just concerned, in practice, that 305s will be a stretch to install, and the sidewall be pulled, un-esthetically, away from the rim edge. In other words, I’m also trying to avoid messing up the car’s suspension and geometry.

I would jump to 315, but that really limits my tire choices to P-Zeros. I was hoping for Michelin Pilot Sport 4Ss.

Anyone done through this before? I wish I could see 305s mounted to a 12” wide wheel, and how, or if, the rim edge sticks out beyond the sidewall of the tire. It’d be great if they were flush. But you can’t really be sure with the calculators...

Thanks!
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Old 10-16-2018, 11:40 PM
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Yeah, I understand your concern. I used 11.5" HREs on my prior 991 and thought that the 305 MP4S's were already starting to looked stretched there. It so happens that I took a comparison photo of that vs the 11.0" original wheels with P-Zeros. Here that is, along with a shot of the HRE 11.5"/305 on the car just in case that helps you visualize where things stand at 11.5". Of course you'll get an extra ¼" on each side with the 12" wheels. I could definitely see going to 315s with 305s still being tolerable.



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Old 10-17-2018, 12:03 AM
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The .2 GTS also has 12" rears and again 305 is the stock fitment. I'm sure a few here have Michelin pics to share but I wouldn't say my pzeros look stretched, pretty much like StormRunes left pic even on a wider wheel. Also the N-rated tire has the nerf ring around as also in his left pic and adds to the stretch look, and I'd think the right pic is a non N-rated pzero with a more comfort look on the smaller wheel.
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Old 10-17-2018, 12:07 AM
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Originally Posted by _RS_ View Post
The .2 GTS also has 12" rears and again 305 is the stock fitment. I'm sure a few here have Michelin pics to share but I wouldn't say my pzeros look stretched, pretty much like StormRunes left pic even on a wider wheel. Also the N-rated tire has the nerf ring around as also in his left pic and adds to the stretch look, and I'd think the right pic is a non N-rated pzero with a more comfort look on the smaller wheel.
I thought you were probably right about the P-Zero's N rating, but I zoomed in on the full resolution original out of curiosity and see that the Pirelli was actually an N0 tire (lower left of center in photo). Good point about the rim-guard ridge making the left one look more stretched though!



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Old 10-17-2018, 12:17 AM
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Aha, mine are N1. That may be one of the differences.
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Old 10-17-2018, 12:28 AM
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Beautiful choices on the build of your Carrera S, Stormrune! Thanks so much for the photos!

Yes, _RS_, I hope you’re right. I have the wheels on order, 9x20 and 12x20. As recommended by HRE, for the TTS. Before I order the tires, I’d just like to see before I choose. So, thank you for your take on this. And I hope others do have photos.

The tech I’ve befriended at the dealership (one of the beauties of center lock wheels, unless you can break those wheels nuts yourself, is you get to go to service department for any wheel-related work) opinion is that Michelins Pilots are more supple than the P-Zeros. And span wider rims easier than P-Zeros. Opinions on that are also welcome.

Also, I’m interested in what somebody who’s fitted a turbo 991.1 with new wheels has to say, having dealt with the room within the those particular wheel wells, and have learned how the spacing, within, effect the choice of tire size.

Thanks again!

Last edited by tonosity; 10-17-2018 at 12:47 AM.
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Old 10-17-2018, 01:37 AM
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Old 10-17-2018, 01:50 AM
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Thanks very much! Just to be clear, with 305s, you believe they fit so comfortably on your 12” wide rim/wheel, it could also run well on a wheel that’s even wider?
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Old 10-17-2018, 03:35 PM
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Okay, after reading all the responses and doing additional research—on the information I could find—here’s where I am.

I am trying to find tire sizes for the Forgeline wheels I have coming, in the wider-than-stock (9” & 12”) sizes, as recommended by HRE and Forgeline, using a worksheet (attached). What I’m trying to achieve is two things: 1. Not throw the suspension, chassis control, drive train, etc., out of whack. 2. Choose tires that fit these wheels well, without being stretched out (with their performance compromised), and/or rubbing in any turning position or compressed suspension conditions.

The chart I’ve attached is something I put together to help me sort things out. The yellow highlighted sections indicate the sizes that I’m hoping will work the best—given the goals above. Though, I don’t have enough data on clearances to be confident regarding the rubbing issue. (Because I can’t get in there to measure, due to the center-locks, I’m hoping to get a sense of that here.) The green highlights the speedometer error percentage. The thing there is I’m trying to keep the roll ratio between the front and rear wheels as close as possible. While both selections will create an over 1% deviation for all wheels, the difference between them is small. I understand that the all-wheel drive and transfer case can handle up to a 3% variance. Also, that variances can throw error codes from the ECU.

The conclusion, so far, is 255/35/20 front, and 315/30/20 for the rear. Not great sizes for tire choices, but otherwise, I’m hoping it’s the best solution overall.

Any comments, assessments, or opinions would be greatly appreciated.

Thanks!





Attached Images
File Type: pdf
wheel and tire size.pdf (20.1 KB, 20 views)

Last edited by tonosity; 10-17-2018 at 05:19 PM.
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Old 10-18-2018, 09:45 AM
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Forgeline on my car 20 x 9 front and 20 x 12 rear running pilot super sports in stock size



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Old 10-18-2018, 01:36 PM
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Wow! Those are carbon-barrel fitted, Forgelines, right? Looks beautiful! Thank you!

When you say “stock size,” do you really mean the OEM stock sizes for the 11 - 11.5 stock wheels (295/30/20)? (The fronts not being an issue, by the way.). Or 305/30/20s?

Thanks again!
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Old 10-19-2018, 08:24 AM
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Originally Posted by tonosity View Post
Wow! Those are carbon-barrel fitted, Forgelines, right? Looks beautiful! Thank you!

When you say “stock size,” do you really mean the OEM stock sizes for the 11 - 11.5 stock wheels (295/30/20)? (The fronts not being an issue, by the way.). Or 305/30/20s?

Thanks again!
Yes they are CF201 Forgeline carbon fiber and forged. Stock size tires front and rear, car came with Pirelli's and they would spin on cool days, thanks to Sam at By Design, so I wanted Michelin's PSS. After talking with Michelin and Forgeline, and Michelin seeing and checking the mounted of the wheels and tires, they said there were no tire stretching issues on rear tires, fronts are 245/35/20 rears are 305/30/20, and thank you I have them on my 2019 ZR1 too, different tint color
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Old 10-19-2018, 12:43 PM
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Thanks for the info. It’s reassuring in making that same choice. I’m really trying to be careful not to mess up the geometry and control systems of the car! Your offsets on the front and rear are 52 and 47 respectively, correct? Do you feel a change in the driving characteristics, compared to stock? Better grip, I’d imagine, with the Michelins?...

Also, have you gone through a set of tires yet? If so, do you feel they lasted a reasonable number of miles?

BTW, what are we talking for the set of wheels (without tires), $17k?

Thanks very much!
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