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I believe that we must do the right thing for our tires. If the outside shoulders get corded, then you need another set. -2.8 should do the job in front and -2.5 in the rear. You will need a certain amount of toe in in the rear just to prevent some bump steer into a toe out mode. As your rear suspension goes through the arc from bump to droop, you do not want a bump steer happening at the apex, with throttle on.
 

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Discussion Starter #22
I believe that we must do the right thing for our tires. If the outside shoulders get corded, then you need another set. -2.8 should do the job in front and -2.5 in the rear. You will need a certain amount of toe in just to prevent some bump steer into a toe out mode. As your rear suspension goes through the arc from compression/bump to slack, you do not want a bump steer happening at the apex, with throttle on.
Sounds good. I got the GT3 arms on and added 2mm of shims. I'll drop it off for an alignment tonight. I have another event/TT next weekend and i'll report back. Thanks for the info.
 

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Let us know what happened to the rear toe without the adjustable toe links.
 

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Discussion Starter #24
Got it back from the shop. -2.75 up front, zero toe. -2.2 in the rear, 0.20deg total toe in. That's a stock 981 on x73 with GT3 front control arms. Half a tank of gas and 210lbs in the driver seat.
 

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You are set to make those tires work well for you depending on the footprint size f and r. I like 255/35/18 f and 275/35/18 r or 255/35/19 f and 285/35/19 r, these sizes seem to remove some of the inherent understeer built into our cars. If you have a LSD in your hotrod that makes the bigger front size even more advantages as it helps balance the push from the LSD out of the apex so you have more speed coming onto the straight. This is useful in many situations, even through the slalom course where the PVT (torque vectoring) acts like a LSD. I use a Wavetrac to accomplish what the PVT does.
 

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Discussion Starter #26
Unfortunately i'm on stock size RE71Rs. 235/45/18 and 265/45/18. Again for classing points reasons i can't go bigger. I don't have PVT unfortunately.

Basically i'm trying to squeeze this car into a lower class by being super lean on points. The good news is i filed for a waiver on the Elephant eccentric rubber rear toe link bushings and it was approved at no points cost. So i'm now free to add those. Unfortunately the news came just hours after i got the alignment! hah. So i'll run the car as is and see how it goes and have that in my back pocket if needed.

I might have one or two points to play with in the end, especially if i can add a little weight by running a full gas tank. If so i'll have to think about how best to use the them. That'll be a fun thread. :)
 

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txbdan-Do you run with a full tank of gas? That would put more wt on the front axles and the potential for gas movement to the outside of the tank in high G corners. Also, Have you used Hot Lap 7000 on your RE71R's? Seems to improve the hysteresis of the older rubber on top to more of a sticky consistency for both new tires and especially older ones.
 

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Great thread. I'm trying to get a track suspension plan for my 2015 Cayman S; any feedback would be appreciated.

Current Setup:
  • 2015 CS, PDK, sport chrono
  • standard suspension (not x71)
  • no PASM or PTV
  • 987 18" wheels with 235/265 200 treadwear tires (currently Nexen N-Fera SUR4 G, probably RE-71 in the future)
  • Front alignment: 1.1 degrees negative camber (max), 8.5 degrees caster, 0.02in toe
  • Rear alignment: 1.4 degrees negative camber, 0.08in toe
  • Track handling is pretty good. A bit of understeer on turn-in, pretty neutral mid turn and on exit. Steering feels good, not too heavy or light. Too much shoulder wear on the tires, particularly in front.
Goals:
  • car is 80% street, 20% HPDE track. I also have a Spec Miata race car, so this is for "gentleman" track days when I want to run with the fast cars and don't want to deal with the trailer, etc. Just put on wheels, grab a helmet and go to the track.
  • I want good grip while maintaining road manners and minimizing modifications to the car.
  • home tracks are Road Atlanta, AMP and Barber.
Proposed Setup (this is where I need help):
  • Rear: max camber is what, 2 degrees on a stock suspension? Will I be able to keep caster neutral with this much camber?
  • Front: Will I imbalance the car with 2.5 degrees camber if the rear maxes at 2? What size shims for the GT3 control arms? Rubber bushings on the inner end? Rubber, fixed or adjustable thrust arm bushings?
 

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Schroedinger-
I would copy txbdan setup. If you are restricted by rules, then carefully choose your items. I run in an open class except for motor displacement of not over 4.0 L. The Tarett Cup LCA's are really great, but they are costly and do have some noise being generated over bumpy backcountry roads. Regular GT3 LCA's with rubber coated thrust puck and rubber inner bearing would be best as a gentleman's setup.

If you are getting new tires, I would highly suggest 255/35/18 f and 275/35/18 r Bridgestone does not make a 285/35/18 only a 285/30/18 r which would work but it does lower your car slightly in the rear. RE71R's are a great tire, if you are only going to use them for a few HPDE a year. They are noisy for a daily commute, so if you are looking to switch out the wheels/tires after the event, they are a great choice.

New wheels? 9 inch wide in f and 10 1/2 inch in the rear would work very well for this setup if you have that choice. Apex or Titan 7 TS-5 would work very well and look good on the track. Camber of -2.5 would require a 14mm shim in the LCA's in front to get to -2.5. Its a simple math of 1mm shim equals -.1 degree of camber, so you would need 14 mm to get an additional -1.4 on top of the OEM generated -1.1 you already have. Try to have the alignment shop get as close to 8.0 caster as they can. By using adjustable castor center thrust pucks in the LCA's, you may achieve this number.

Finally, yes, the camber of -2.5 f and -2.1 does work well together to protect the outside shoulders of your RE71R's from excessive tire wear. For your daily commute, your inside tire wear should be minimal due to the camber, if you use 0 toe in front and 12 minutes of toe in in the rear.
 

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Discussion Starter #30
Yep, X73 and GT3 front control arms is pretty damn good with no increased noise. X73 shocks/springs are stiffer and the ride is stiffer, but not crazily so. It's also quite low, i scrape the front probably once a trip, but its only rubbing on a sacrificial strip under the bumper. It's quite capable on track as well. Even without the GT3 arms (took them off for SCCA classing reasons) i got 12th overall at the SCCA TT National Tour event with 88 cars a couple weeks ago. So that's bone stock with -1.7deg front and rear against all sorts of modified cars.

This weekend i have the GT3 arms back on and will be doing a time trial with my usual club at the same track. -2.75f, -2.2rear. I'm excited to see how the camber changes the handling and tire wear.

The car is really pretty fantastic stock. People seem a little mod happy around here, but that's what forums are for i guess. And i'm coming from a gutted dedicated E36 track car with MCS coilovers, sphericals everywhere, roll bar/seats/harneses, etc. The Cayman is faster and just as fun. :)
 

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Yep, what Apex said. I just wanted to point out the Apex SM-10s and Titan7 TS-5s are only available in 10" for the rears on our Caymans (we do run 11" rears on the GT4, though)..

Schroedinger-
I would copy txbdan setup. If you are restricted by rules, then carefully choose your items. I run in an open class except for motor displacement of not over 4.0 L. The Tarett Cup LCA's are really great, but they are costly and do have some noise being generated over bumpy backcountry roads. Regular GT3 LCA's with rubber coated thrust puck and rubber inner bearing would be best as a gentleman's setup.

If you are getting new tires, I would highly suggest 255/35/18 f and 275/35/18 r Bridgestone does not make a 285/35/18 only a 285/30/18 r which would work but it does lower your car slightly in the rear. RE71R's are a great tire, if you are only going to use them for a few HPDE a year. They are noisy for a daily commute, so if you are looking to switch out the wheels/tires after the event, they are a great choice.

New wheels? 9 inch wide in f and 10 1/2 inch in the rear would work very well for this setup if you have that choice. Apex or Titan 7 TS-5 would work very well and look good on the track. Camber of -2.5 would require a 14mm shim in the LCA's in front to get to -2.5. Its a simple math of 1mm shim equals -.1 degree of camber, so you would need 14 mm to get an additional -1.4 on top of the OEM generated -1.1 you already have. Try to have the alignment shop get as close to 8.0 caster as they can. By using adjustable castor center thrust pucks in the LCA's, you may achieve this number.

Finally, yes, the camber of -2.5 f and -2.1 does work well together to protect the outside shoulders of your RE71R's from excessive tire wear. For your daily commute, your inside tire wear should be minimal due to the camber, if you use 0 toe in front and 12 minutes of toe in in the rear.
 

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Discussion Starter #32
9"s and 10"s seem like plenty of wheel. I'm running stock 18" tire sizes on Titan7s (9"/10"s) and they're pretty stretched. Which is fine, but i have plenty of wheel for wider rubber.
 

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9"s and 10"s seem like plenty of wheel. I'm running stock 18" tire sizes on Titan7s (9"/10"s) and they're pretty stretched. Which is fine, but i have plenty of wheel for wider rubber.
I run 255f / 285r
 

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Thanks for the feedback guys. I agree that these cars are incredibly capable right from the factory. My lap times are 3-5 seconds faster than my SM times on Hoosiers depending on the track, and I really haven't pushed the car very hard. I'm going to stick with the stock suspension instead of x73 right now because a) it feels really good with the amount of grip I have right now, and b) I have a steep driveway and I'm about a millimeter from scraping the front with the stock suspension. I'm also going to stick with the 987 wheels. After I kill these Nexens, I'm going to go to RE-71 in 235/265-50r18. Same rolling diameter as stock.
 

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Discussion Starter #36
Yep, X73 and GT3 front control arms is pretty damn good with no increased noise. X73 shocks/springs are stiffer and the ride is stiffer, but not crazily so. It's also quite low, i scrape the front probably once a trip, but its only rubbing on a sacrificial strip under the bumper. It's quite capable on track as well. Even without the GT3 arms (took them off for SCCA classing reasons) i got 12th overall at the SCCA TT National Tour event with 88 cars a couple weeks ago. So that's bone stock with -1.7deg front and rear against all sorts of modified cars.

This weekend i have the GT3 arms back on and will be doing a time trial with my usual club at the same track. -2.75f, -2.2rear. I'm excited to see how the camber changes the handling and tire wear.

The car is really pretty fantastic stock. People seem a little mod happy around here, but that's what forums are for i guess. And i'm coming from a gutted dedicated E36 track car with MCS coilovers, sphericals everywhere, roll bar/seats/harneses, etc. The Cayman is faster and just as fun. :)
The alignment seems fine and the car ran well. I won my TT yesterday. Here's me zooming around:
 
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