Hi,

I recently ran a set of Pirelli slicks 245/65/19 and 295/68/19 on my car. They ran fairly well with PASM disconnected, but the ABS was not working properly due to the diameter difference, and ceter diff probably wasn´t liking it either.

Trying to move to more ABS and AWD friendly sizes, anyone has practical experience with full slicks on this car? Stevo?

Thanks!

 

Do you have PSM physically disconnected or just turned off with the dash switch? I recently switched to a 1" taller rear tire and run 25.55" fronts (245/40/18) with 26.42" rears (305/35/18). There is no issue with ABS whatsoever but PSM has been removed on my car. I mainly run my car at the track constantly braking at the threshold of ABS and if anything, ABS feels like it is not as intrusive now due to the fact that the front tires are rotating a touch faster than the rears thus allowing more "lock up" on the fronts prior to ABS intervention. Incidentally the 1" taller 305/35/18 provides a huge improvement in grip and handling compared to the popular 315/30/18 on the 996 platform. I'm beginning to understand now why Porsche runs the taller rears on the CUP cars and also switched to that on the 997 platform.

Unless you drive your car in the snow, another solution is the remove the marginal AWD system and add a good LSD. You will have a lighter car, better steering feel, greater choice in tire sizes, and more traction compared to the factory AWD open diff setup.

 

Pzero Slicks.

245/645-18
305/645-18
http://www.pirelli.com/tyre/ww/en/mo...eet/slick.html




work perfect, and are magical. I have done it, i had someone else try it... works like a charm. 0 PSM issues. 0 ABS issues. Me and the other car AWD.

 

PSM is disconnected (front connector unplugged).
What I felt with the ABS was an overly-sensitive engagement. Braking distances and braking G loads were similar to previous tires (R888) which reafirms something was not working optimally.

The LSD is going in, definetly. Car suffered the dreaded coolant hose failure so engine is going out, Carbonetic LSD in. I´m still unsure on the decision to remove the AWD system, is the car any faster without it?


F1crazydriver thanks for sharing that, seems like a nice option if I decide to stay with the AWD system. Where have you bought them from? I´ll request a quote.

 

That's interesting regarding the ABS. I don't know but I have not had any issues. Like I said if anything, ABS has become less intrusive running the larger rear tire than before. The only thing that I can think of is that I am running 380/350 997GT3 brakes which do shift brake bias to the rear by about 30% and that changes the ballgame. The stock TT brakes or the popular 350/350 997TT brakes are heavily biased towards the front and I can see how that can further aggravate the ABS with sticky tires.

On a dry road course the car will definitely be faster in RWD w/LSD form compared to AWD w/LSD or open diff. I have data logged my car on the same track under the same conditions in AWD (open), AWD (LSD), and RWD (LSD) form. The car was faster in that same order with RWD (LSD) being about 2 seconds quicker than AWD (open) on a 2.5 mile 15 turn course. Removing 75lbs of weight allows you to brake a little deeper, corner a touch harder, and accelerate out of corners a bit quicker as the LSD allows you to really put the power down out of corners. You will also free up a little parasitic drag and will put down a bit more power as a result. Your straightaway speeds will improve by a couple of mph as a result. My top speed rose 6 mph at the end of our straight from 137 to 143 as a result of dumping the AWD. It's really no rocket science. Make sure you get someone who has the proper tooling to install and correctly shim the LSD as it's easy to trash the R&P if done incorrectly. Some specialized tools are required..

 

John, WOW that is a massive gain in time with a LSD. I was already making GT3's GT2's and other Turbo look silly at my track days. I can't imagine going 2 secs faster with RWD on LSD

 

It really is a huge improvement Enrique. Our track is rather technical and 2.5 miles with 15 turns. Very few cars lap it at 2:00 or less. If you can shave a tenth of a second between each corner through increased straightaway and cornering speeds, later brake points and better grip out of corners, it's easy to see how that will add up to 1.5 to 2 seconds per lap. If you ever wanna come down and do a track weekend with us you've got a free place to stay. We've got a good group of trackhounds down here...

How's the hunt for the GT3 coming?

 

That is quite a remarkable improvement, thanks for sharing the data.
I have the LSD on my desk, and haven´t installed it precisely because of what you mention: fear of incorrect installation since there are no specialized Porsche shops in this country. There are quite a few DIY guides but I´m still not confident in the procedure. I will have to find a way to do it, you have convinced me it´s necessary

 

I run the 265/645/18 and the 325/650/18, they are much wider than the 305's. Really great grip for the first few sessions. Gnarly after about 8 sessions.

My experience has been different from powderhound, I have found no appreciable difference between RWD and AWD. Nearly identical lap times. RWD has higher top end for sure. But AWD is much easier to go flat on corner exit without worrying about putting the power down to rear wheels only. Even an LSD is still only using 2 wheels for traction while AWD uses 4. All of my tracks have lots of elevation changes or long sweepers where it's simply impossible to put all of the torque down if your car is tuned.... AWD.

Your mood may vary, but I'm certain I could put AWD back in my car and run similar times. I think landjet had a similar experience switching to RWD, no real gain. But I think I recall Tom Kerr gain some significant time when he went RWD. Car setups, track layout, surface grip, tires and driver style will certainly play a role though.

But I can't say there are any givens in that regard.

 

Everyone's results will vary. I'm just reporting my experiences which mirror those of Tom Kerr and Carl (Mr.White) on this forum who I believe has a pretty long professional Porsche racing resume unlike the rest of us weekend track warriors. I used to be in the AWD camp until I was convinced last year to go RWD by Chris Cervelli who is a retired cup driver and by far the fastest Porsche driver in the Rocky Mountain region. The man has an impressive racing resume and is simply amazing at setting up these cars and making them go fast. Over the last two months I've been able to shed 2.5 seconds off my previous best lap times through his driver coaching and set up changes to my car's alignment, sways, uprights, spring rates and tire sizes. My $0.02, and no, I did not stay at a Holiday Inn last night..

 

I fixed your post for you Enrique...

 

To quickly chime in, I have done exactly as pwd... at seca, and noticed a significant improvement. In my case I went from AWD to RWD with LSD (suspension setup remained the same), later added rear GT3 A-arms and rear bushing that helped further.

Hope that helps.

 

I'm not doubting your experience, only pointing out that all experiences may not be the same.

 

If I were you, I would check into Chris Cervelli's background VERY, VERY, VERY thoroughly.. I wouldn't trust that guy as far as I can throw him. Seriously; be careful with that guy.

 

Really? I've never heard anything but near worship for Cervelli. What's the down and dirty?