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991 Turbo Turbo and Turbo S

TTS Tire Size on Rear

 
Old 10-19-2018, 11:46 AM
  #16  
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Originally Posted by tonosity View Post
BTW, what are we talking for the set of wheels (without tires), $17k?
About $15.5k but Forgeline is no longer accepting orders on these wheels as of August 20th due to the Carbon Barrel supplier no longer manufacturing the parts.
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Old 10-19-2018, 11:56 AM
  #17  
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Well, nice snag! And thanks again!
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Old 10-20-2018, 08:36 AM
  #18  
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Originally Posted by tonosity View Post
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!
Yes on the offsets, the biggest thing to get used to was how the carbon fiber absorbs bumps, it's a complete different feel, in a good way, very solid. The grip difference with the tires is huge, for where I live and drive. First set of tires they only have been on the car for 3 months. I am the poster child for Forgeline, or so I am told, not really sure about the price because there were so many sets of wheels for so many cars. I ordered all mine when I was told of a future manufacturing issue, which they are working on
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Old 10-20-2018, 10:41 AM
  #19  
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Originally Posted by tonosity View Post
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!
Choose a N-rated tire (a Porsche approved tire) in 305 size. The 911 is heavier in the back than most cars, and a Turbo puts additional load due to its power.

Pictures are misleading when comparing different brands and models of tires. Two 305 tires from different brands, and even two 305 tires from the same brand and with the same model can have different widths.

Examples: My stock 991 GT3 RS tires measure 349mm but they are labelled 325. My old 991 Turbo S 305 Pzero were wider than the 305 Trofeo R (a track ready tire) on the same 305/30R20.

The 991 GT3 uses 9x20 and 12x20 wheels, tires: 245/305, but they are N-spec tires (wider than generic 245/305 tires).
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Old 10-20-2018, 02:52 PM
  #20  
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Default Michelin Sport Pilot 4S

Thanks very much for your contribution! Really helpful.
So, okay... The tires that I’m picking are 305/245s, Michelin Sport Pilot 4S, “N0.” I’ve been told that they are more supple than say, P-Zeros, and the 305s fit on a 12” wheel width much easier and better. Or, as you say, they may manufacture them wider than others. Have you had any experience with them?

There’s one tire size comparison calculator (https://www.wheel-size.com/calc/?whe...cl=50mm&sr=0mm) that gives a result warning that I find worrisome. When trying to determine fitment—using a stock rear wheel as a baseline—it warns of a 8mm positive scrub radius, which, they state, may effect handing (assuming the scrub radius is zero, with the stock wheel). Is that something to worry about, in terms of handling, wear, or any of the control systems of the car?

Just FYI, here’s the sectional view produced by this calculator:


Thanks again!

Last edited by tonosity; 10-21-2018 at 07:35 PM.
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Old 10-22-2018, 02:39 AM
  #21  
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Default Using the 21” GT3 RS wheel on a 991.1 Turbo S

The 325/30R21 RS tire is about 1.6” taller than the 305/30R20 tire the Turbo normally uses. Using the 21” RS wheel with a 325/25R21 tire is only 0.2” taller. Is there any reason that won’t work. The height seems close enough to stock unless the AWD sensors are too sensitive to that small a difference.
Help please.
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Old 10-22-2018, 08:57 AM
  #22  
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I know of at least 6 owners running the same size wheels and tires as I am, and they have had this setup on their cars a lot longer than me without any issues. I didn't go with 21" wheels, why I liked the 325 tire width, it was the extra weight I didn't want. I wanted a wheel and tire combo that was lighter and stronger than stock, that is why I went the way I did.
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Old 10-22-2018, 11:13 AM
  #23  
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So I like your set up but Im looking to run the GT3 RS 21” wheel. The stock sidewall ratio is 30 amd 1.6” taller. Michelin makes a 25 side wall that is only 0.2” taller.

what im really wanting to know is whether the 0.2” sidewall difference will cause any traction control issues.
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Old 10-22-2018, 12:40 PM
  #24  
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Originally Posted by hcvone View Post
I know of at least 6 owners running the same size wheels and tires as I am, and they have had this setup on their cars a lot longer than me without any issues. I didn't go with 21" wheels, why I liked the 325 tire width, it was the extra weight I didn't want. I wanted a wheel and tire combo that was lighter and stronger than stock, that is why I went the way I did.
With these 21” wheels you and your friends are running, what width wheel and offsets are people pairing with these 325/(?)/21 rear tires?

You fitted your Turbo, above, with 305/30/20s, right? So, you have two?

Thanks!
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Old 10-22-2018, 01:02 PM
  #25  
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Originally Posted by Centerlocknut View Post
So I like your set up but Im looking to run the GT3 RS 21” wheel. The stock sidewall ratio is 30 amd 1.6” taller. Michelin makes a 25 side wall that is only 0.2” taller.

what im really wanting to know is whether the 0.2” sidewall difference will cause any traction control issues.
I’ve read somewhere that the Turbos’ systems geometry can tolerate a 3% difference in tire sizes. What wasn’t clear was exactly where that 3% was measured. My assumption was that it’s the rolling ratio between the front and rears. So, if it is the rolling ratio—and not other ratios or dimensions—then the 0.2” could be factored in to determine the acceptable variance. (I’ll try to find that statement, and verify it.)

Last edited by tonosity; 10-22-2018 at 02:10 PM.
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Old 10-22-2018, 01:33 PM
  #26  
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Originally Posted by tonosity View Post


With these 21” wheels you and your friends are running, what width wheel and offsets are people pairing with these 325/(?)/21 rear tires?

You fitted your Turbo, above, with 305/30/20s, right? So, you have two?

Thanks!
255/30/21 fronts 325/25/21 and two cars 345/25/21, they are hanging out the wheel wells but don't rub, have to get offsets, don't know them off the top of my head, and yes gt2rs
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Old 10-22-2018, 01:47 PM
  #27  
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Default Widths & Offsets

Originally Posted by hcvone View Post
255/30/21 fronts 325/25/21 and two cars 345/25/21, they are hanging out the wheel wells but don't rub, have to get offsets, don't know them off the top of my head, and yes gt2rs
Wow, a GT2RS. Great for you! Okay, just so I understand, you also have another 991 Turbo that you’ve fit with 21”s?

Thanks again!
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Old 10-22-2018, 04:27 PM
  #28  
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HRE R101LW from David at Wheel's Boutique. 20x13 running 335/30/20 MPSS in the rear and lowered on TA springs. No issues with rubbing at all.





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Old 10-22-2018, 04:47 PM
  #29  
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Thanks for this! How’s handling and grip compared to stock? Notice any differences? Lastly, did you increase the tire size up front, to come close to the the original rolling ratio?
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Old 10-22-2018, 04:51 PM
  #30  
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20x9 fronts on 255/35/20 MPSS. Can't really compare the ride to PZeros since I switched out the wheels right when I picked up my car. The TA springs definitely firmed up the ride. I also have the DSC Sport V3 module and that improved the ride and handling a bit too. ride is still firmer than stock but not too bad. Handling is much better.
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