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PNW Wider is better, even 265/35/19 f and 285/35/19 r if they are available. Not totally sure that setup will fit. I do know that 265/35/18 f and 285/30/18 work. You may need to use a 255/35/19f and a 285/35/19r. On slick tracks like concrete, more rubber is better, just more grip. If you are road racing, then other factors come into play, but you are just using 1st and 2nd gear. I don't have a reference point for your front using the larger tire in 19 inch. At the outside you can use a 5 mm spacer to get the tire away from the shock or spring on a coilover.
 

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2006, Cayman S, Manual, Quaife TBD, Billstein Damptronic
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Discussion Starter · #22 ·
I went ahead and ordered a set of Bridgestone RE71RS. 255/35/19 front, 285/35/19 rear. I got a text after ordering saying that there is a 30+ day wait on the back order. Hopefully get them with a few events left this year.

Going to get the wheel stud conversion ordered soon. Leaning towards motorsport hardware. Anybody have any experience with those?
 

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PNW, I checked out Tirerack research on the RE71RS tester review. They were using a BMW 430I 2020 Grand Coupe and square 245/40/18's. They had some interesting comments about the tire,

"Interestingly, in the wet the Potenza RE-71RS held an even larger advantage in lap times, but our drivers universally preferred the old Potenza RE-71R for subjective characteristics. The new tire's most obvious strength was its amazing ability to put the power down at corner exit. It continually challenged our drivers to apply more and more throttle, yet the rear end seemed to always remain firmly planted. The counterpoint to that was its rear axle behavior through the slalom. When dealing with the more-abrupt lateral transitions through that element, there was very perceptible movement at the back of the vehicle. Adding to the equation, the front end grip couldn't match the dominance of the rear, which created a strong tendency to understeer at corner exit and required that the driver ensure the nose of the vehicle was pointed in the desired direction before committing to the throttle. Lastly, even though the Potenza RE-71RS led the 50-0 mph braking objective results by a considerable margin, it still didn't seem to scrub speed as effortlessly as it built speed, which created an imbalance and made it difficult to accurately judge braking zones. Even so, when dealing with Extreme Performance Summer tires, what really matters are lap times and objective results, and in that regard, the Potenza RE-71RS was the clear winner once again."

I was thinking about 265/35/18 f and 29535/18 r, but after reading the above statement about causing a strong tendency to understeer at corner exit, I'm going down 1 size to 255/35/18 f and 275/35/18 r which is what I have been using for years. My class allows Hoosier A7's so that is my race tire. But, I need to replace these old RE71R's so that's the size I'm going to use for the street and rainy days at the track. You might be getting yours before mine. Let us know your thoughts.

 

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2006, Cayman S, Manual, Quaife TBD, Billstein Damptronic
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Discussion Starter · #24 ·
I'm hoping that I get them before too long. The A052s that I was planning on using are not available until who knows when. I was planning on 255 front, 275 rear in a 19". I will try getting them once they are available, as I already have a single new 275/35/19 that I got deal on.

I have an event next weekend, my second with the car. The last one was a single, 4 run session that was pretty wet. It looks like the weather should be good for this next event. I am currently on Michelin Pilot Super Sports 245/40/18 front, 275/40/18 rear. I have seen some conflicting information, but what tire pressures would you suggest?

It's good to see that the new Bridgestones are getting good reviews. Visually, they look like a big departure from the previous model.
 

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We will see in Lincoln, Nebraska this fall at the Solo Autocross SCCA Nationals, which tire comes out on top. I believe the new RE71RS will again be the favorite for the top line drivers. My thinking is that Bridgestone has waited until they got the tire rubber matrix correct for the American market. i would be surprised if the American tire does not have a different rubber compound than the current RE71RS tire in other markets.
 

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2007 Cayman Base, MCS 2-way remote dampers, Tarett top damper mounts and sway bars, OS Giken LSD
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Agreed, as it has been for the 20+years I have been AXing, tires are the BIGGEST factor in determining standings at the end of the race day.

This is the greatest 987 AX discussion on Planet-9 I have seen in some time. Can we push it a little further? Is anyone using coil overs with stiffer springs? Is the standard toe-out front and toe-in rear working for everyone?

My current suspension on the 987.1 Cayman Base:
MCA 2-way remote damper with 11Kgf/mm front and 13Kgf/mm rear springs
Tarett top mounting hardware for Dampers
Tarett 26.8mm front and 19.1mm rear sway bars
Front GT3 lower control arms
OS Giken Super lock LSD

The setup:
20mm lowered from stock ride height
Camber front 3.3 rear 2.7
Toe 1mm out each side front, 2mm in each side rear
Sway bar front 3 of 5, rear full soft,
Damper compression (bump) and rebound setting do not have a sweet spot yet, but generally compression is stiff with rebound mid-scale.
I know that the spring rates are aggressive, but my home AX site is Crows Landing, super flat and high grip surface. I am also limited by STR class to 255 tires, so running the same front and rear. Using 18X8.5 wheels front and rear, with a 10mm spacer in the rear to get offset correct for tires tracking square front to rear.

This build was to compete with NC Miata’s & S2000’s and did an ok job with that. Then ND Miata’s showed up and sure destroyed that idea. The SCCA is looking to move the Cayman Base to STU with the S. (Bottom of page 24 Item # 31259 of this Fastrack news April meeting)

I agree that SCCA Solo classing cars is an impossible task. I know a couple of the SFR guys on the committee and they are trying hard. But SCCA is generally not kind to Porsche’s in classification because top tier drivers like to drive them. Also a track change, plenum, is going make a Porsche even less competitive in AX or Solo. Sorry PNW, changing a plenum is not that difficult for an owner to do, the ECU maybe the bigger challenge.
 

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I believe the new RE71RS will again be the favorite for the top line drivers.
https://m.tirerack.com/tires/tests/testDisplay.jsp?ttid=285

.3 seconds faster on a 30 second autocross

The new tire focuses more on track use than autocross competition,
with specific emphasis placed on dry traction, consistency over multiple laps, and wear.

less precise and didn't offer the feedback of its predecessor.
The lack of feedback meant it was harder to
read and didn't communicate its limits quite as well

our drivers universally preferred the old
Potenza RE-71R for subjective characteristics

...rear axle behavior through the slalom. When dealing with
the more-abrupt lateral transitions through that element,
there was very perceptible movement at the back of the vehicle.
Adding to the equation, the front end grip couldn't match the dominance
of the rear, which created a strong tendency to understeer at corner exit

if someone isn't happy with the way the new tire feels, they're almost
certain to forgive that shortcoming when they see their improved lap times
 

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This is the greatest 987 AX discussion on Planet-9 I have seen in some time. Can we push it a little further? Is anyone using coil overs with stiffer springs? Is the standard toe-out front and toe-in rear working for everyone?
I don't have anything to add as I'm running in Street class, but have you already seen the content in these two sites? Steguis Motorsports Kay the Cayman
 

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AX 987.1- I have gone down that pathway you describe but ended up in the GT3 class with Keith Brown, a former SCCA national champion, using a sponsored modified GT4. Well its not fair, so second place was the goal in his class over the 12 races for the past few years.

I am using Ohlin R&T and their standard spring set up of 400 lbs/in f and 458 lbs/in r along with Tarett Cup LCA's f and r as well as their down links. I use -2.9 degree camber f and -2.5 degrees r with about 5 minutes of toe out in front and 12 minutes of toe in in the rear. I've had the car corner balanced with 200 lbs weight in the drivers seat and lowered to about 30 mm lower than OEM. I am running Hoosier A7's 255/35/18 f and 275/35/18's on Signature SV104's that are 9 in wide in f and 10 in r, The other tire/wheel set is Titan 7 TS 5's, 9 in wide f and 10 in in r with RE71R's which I will be replacing with Bridgeston's new RE71RS as soon as they are available.

The interesting part of this discussion is I am using my car as my bike carrier, so it gets a lot of use during the week, but even with the suspension camber, I would expect that the inner shoulders of my old RE71R's to wear rapidly, but the rain groves are still in the shoulders and the face tread is not to the wear bars. I have rotated the tires once so that camber is working well for street use after 15k miles. I also use a Wavetrac LSD which does have the ability to almost lock up both rear wheels when the inside tire is lifted. Its not as radical as the clutch LSD's, but I don't need to rebuild it. Not sure how it compares to your OS Giken Super Lock LSD. I also upgraded my motor mounts, using a new OEM front mount with a FF orange insert and the FF Orange transmission mounts. I also use the Numeric shifter and cable system.

This car works extremely well in canyon driving as the balance is very good with great turn in and good traction out of the corners. I'm using OEM R brake pads and GT2 brake ducts f and r. I'm also using the Soul long tube catless headers and a Milltek muffler for a little more power and great sound effects.
 

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Discussion Starter · #31 ·
Loving the discussion going on here. I am several years of development behind you guys. I am trying to keep my car comfortable enough for street use, but I'm hoping to pick up some good info from you guys.

Sadly my car didn't have the Bilstein damptronic coilovers listed in my signature (tried editing my signature, but I can't figure out how to remove that). I made my profile while I was waiting to take delivery of the car. Apparently one of the shocks failed, and it was put back to stock PASM suspension. I am very pleased with the comfort/performance of that setup for now though.

I guess I just can't catch a break weather wise this autocross season. It looks like it is going to be raining again this weekend. I think last time I was running 35psi all around for tire pressures. It was wet without much grip, but it felt pretty good. This was with 245/40/18 front, 275/40/18 rear Pilot Super Sports.

What would you guys suggest? Would it be different in the dry vs wet?
 

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Hoosier's A7 22f and 24r wet, 26f and 27r dry, RE71R's 25f and 26r wet and 27f and 28r day. Some use lower pressure dry. Also wider wheels allow for a little lower pressure. I have yet to hear about anyone loosing pressure seal around the bead of the tire during autocross. With that knowledge, your marks (diamonds) or chalk on the top of the sidewall before the tread cap are key to figure out how far the shoulders are rolling. Then if you have a quick temp gun, you can quickly check the actual both shoulders and middle of the tire for final determination of the PSI. If the temp is equal across the tire thumbs up, but you will need to be fast to get accurate measurements. Focus on the fronts as they tend to roll a little more than the rears. The other part is are you experiencing understeer or oversteer. Use your TPI to help the balance as wrenching the swaybars takes too long in the staging area.
Those Michelin Super sports need a higher TPI as their sidewalls are thin and lack a good amount of spring rate than the two tires types I'm using.
 

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Thanks for your numbers. I've been running somewhat higher - 32F/34R - on my RE-71R on 18x8.5/18x10 but now you've got me thinking to try lower. Ryan did suggest that I start with 32F/30R. I'll be running on Saturday and it's likely to be both dry and wet running. Will be sharing the car with the creator of SoloStorm so looking forward to that.
 

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Ryan was using 265/35/18 f and 285/30/18 r so that maybe the difference while I'm using 9 in f and10 in rear wheels, a little wider base to help stabilize the sidewalls and 255/35/18 f and 275/35/18 r so slightly smaller tires as well. Most importantly, i'm just much slower than Ryan.
 

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My wheels are O.Z. Alleggerita HLT 18X8.5 with 255/40ZR18 Falken RT660 currently mounted. I have found with sidewall chalk and cross tread temperatures the RT’s like lower pressures, 28psi all around right now. Not sure this will be much help with my odd rear wheel and tire size.

My 255 fronts are the biggest I can fit between springs and the lip rolled fender. Even then at full steering lock the tire edge rubs on the front wheel well. If Ryan is running 265 in the front he must be doing something to get them to fit, or is there that much more room in later Caymans?

Some thought running around SFR AX group is that the Kumho‘s run consistently wider in tread than a similar sized Falken or Yokohama. So going down a size in tire width will not impact rubber on the road but increase sidewall stiffness. The Kumho’s are also the lowest cost tires in the group and tires are always better when newer. Less crying when tossing a tire with a bit of tread left on them. 😕 The on going balance between tread compound and sidewall response.

Odd question, the dash Tire Pressure on my Cayman constantly runs 2psi lower across all wheels than actual. Does anyone know a way to calibrate it? (yes I can do the math, just annoying)

Thanks Arthur, I had not seen Kay site
I don't have anything to add as I'm running in Street class, but have you already seen the content in these two sites? Steguis Motorsports Kay the Cayman
 

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If Ryan is running 265 in the front he must be doing something to get them to fit, or is there that much more room in later Caymans?
I last year literally owned the rims/tires on which Ryan won Nationals and I never had any rubbing issues while autocrossing or driving around pits. Perhaps it's the extra ride height of a stock (PASM) suspension. His car was a 2006, same as mine.
 

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Not only the -2 lbs difference from the dash reading to my hand held big headed gauge , but if you try to run less than 25 lbs, you get a red flat tire warning all over the speed gauge. Its really annoying. I just am used to that TPI gauge letting me know what was programmed into the Porsche tire management system in 2007. I did find it useful when I had an outside Michelin PS2 sidewall start leaking. I backed up along side a curb and scuffed enough side wall to create a rubber flap, that started to leak. That was the end of that set of tires, ordered a new set of Bridgestone RE71R's that I still have and run for everyday usage. I am replacing those old ones with the new model RE71RS as soon as they are available from the Tire Rack.
I have no idea how Ryan got those 265/35/18 tires to fit inside his front wheel well, but he had to remove the tire at the Nationals to prove they fit without rubbing.
 

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arthurc604 do you have a dash TPI gauge? Just wondering as I read that feature/option was added in 07.
 

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I have no idea how Ryan got those 265/35/18 tires to fit inside his front wheel well, but he had to remove the tire at the Nationals to prove they fit without rubbing.
Unfortunately I no longer have them so couldn't give you an idea of tight they are. I'm now on 255/35R18 which is 0.5" more narrow and 0.3" less diameter according to specs. This is the best photo I could find from last year. Also our surface is pretty low grip so the suspension won't be seeing as much compression as at other sites.
Wheel Tire Car Vehicle Automotive lighting
 
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