.Tire Pressures
08-10-2014, 06:12 PM
#16
Race Director
Mike. On the track we never run anywhere near the manufacturers pressures especially for the rear. For example on the 993 on 18" the factory say 36/40 at 20C. On the track most 964 and 993 owners are aiming for a hot pressure around 30/32 or often 30/30! Too much pressure in those rears and they will act like balloons.
AutoX is different from the track tho as you need to set the pressures closer to target at the beginning I suspect.
I dont believe the 991 GT3 is as sensitive to pressures on the track as my old 993. I have only had one session at the track in the GT3 but felt it handled ok in the 30-34/34-36 range. I will however be targeting something around 30/34 next time out and bring those gradually down during the day to closer to what Sam is suggesting.
Mike how was your autoX experience? How did you find the car?
AutoX is different from the track tho as you need to set the pressures closer to target at the beginning I suspect.
I dont believe the 991 GT3 is as sensitive to pressures on the track as my old 993. I have only had one session at the track in the GT3 but felt it handled ok in the 30-34/34-36 range. I will however be targeting something around 30/34 next time out and bring those gradually down during the day to closer to what Sam is suggesting.
Mike how was your autoX experience? How did you find the car?
I had a great autox experience yesterday. Thanks for asking. Yes, the GT3 is bigger and wider but you just don't feel that from inside the car. It's humbling in a way because clearly the car is much more capable than I am. Ok, I haven't been on track since I sold my Carrera early last year, it was the first time out in the 991 GT3, and it was a particularly tight and technical course which didn't favor the GT3. None of that is an excuse for my taking some bad lines and overdriving the car. Corners where my Carrera would have just given up the front end because of a bad entry, the GT3 just sort of says, all right, this isn't optimal but I'll work with you. Front grip and turn in are just exceptional and the car rotates and gets power down so well.
We had 40 cars at the event and despite my shortcomings, I got things partially worked out and finished 2nd at 33/100 off TTOD. There's no question that the car was TTOD capable. My quickest run was in manual mode as there were a couple of sections where a downshift to first was possible and advantageous but PDK sport seemed reluctant to shift out of second. I'll continue to experiment with sport auto and manual mode as the advantage may shift from one to the other depending on the course.
I want to have the alignment checked before the next event as I know factory settings are frequently off, and I'd like to have a little more camber dialed in. I know some people think using a GT3 for autox is a waste, but this GT3 actually makes for a really good, competitive autox car and I had a blast in it.
08-10-2014, 06:23 PM
#17
Yup, it's pointless to call them. I found a PDF of a brochure for the Sport Cups on line and it had a lot of great information on pressures and temperature ranges. I'm hoping they publish something similar for the SC2.
I had a great autox experience yesterday...None of that is an excuse for my taking some bad lines and overdriving the car. Corners where my Carrera would have just given up the front end because of a bad entry, the GT3 just sort of says, all right, this isn't optimal but I'll work with you. Front grip and turn in are just exceptional and the car rotates and gets power down so well.
We had 40 cars at the event and despite my shortcomings, I got things partially worked out and finished 2nd at 33/100 off TTOD.
I know some people think using a GT3 for autox is a waste, but this GT3 actually makes for a really good, competitive autox car and I had a blast in it.
I had a great autox experience yesterday...None of that is an excuse for my taking some bad lines and overdriving the car. Corners where my Carrera would have just given up the front end because of a bad entry, the GT3 just sort of says, all right, this isn't optimal but I'll work with you. Front grip and turn in are just exceptional and the car rotates and gets power down so well.
We had 40 cars at the event and despite my shortcomings, I got things partially worked out and finished 2nd at 33/100 off TTOD.
I know some people think using a GT3 for autox is a waste, but this GT3 actually makes for a really good, competitive autox car and I had a blast in it.
). The reason? I didn't have my lucky socks on.
08-10-2014, 10:06 PM
#19
Rennlist Member
Here are pictures of the rear tires outside shoulders and tread of right rear. Tread is fine and the shredding is not extreme but certainly there. Does it make sense that this is from leaning on an under inflated tire early on in the session or is there another reason? I have plenty of rear negative camber (around -2 degrees and forty some minutes). Again, driving with higher pressures decreased grip. I welcome opinions.
1). Initial tyre pressures. This wear could be caused by under inflation in early sessions. You are definately using every bit of teh width of teh tire looking at teh wear line on teh shoulder - infact you are using more than I would have imagined so you are either running too hard with too low pressure or...
2). Too much negative camber at the rear. Typically Porsche Cup/RS and race cars seem to have historically run 1/2-1 degree less negative camber at the rear than the front. This is certainly the case with the 964/993 generation with which I have experience and the 996 GT3 too. Having said this we are pioneering it on this GT3 as it has a far gripper front end and it has RWS both or which may enable equal front and rear negative camber to be run without any compromises. Generally negative front camber is to offset understeer and provide a more even spread of heat across the face of the tyre under cornering loads, turn in etc where the front wheels work much harder than the rear. Im not a geo expert so I will not want to say too much here (you should also take advise form your geo guy) but I dont think we need tonnes of negative rear camber on the rear of these cars - the tyre is doing less work.
My only advise here would be to pull back rear to -2.30" and leave fronts at -3.00" (well you are close enough now anyway) and run a bit more pressure at the beginning of the day, bleeding off after 1st and 2nd sessions and see if the situation continues to deteriorate on these used tyres or gets worse. Probably in reality you will need to wait till you have some cycles on a fresh set to know for sure if its worked. Right now I think low pressure and heat have caused this to happen mostly.
Overall those tyres have worn pretty good - how many sessions/days on those?
08-10-2014, 11:20 PM
#20
Sam. Its not that bad. Having said that in my humble experience I would say you should look at two things that I think may be contributing to this:
1). Initial tyre pressures. This wear could be caused by under inflation in early sessions. You are definately using every bit of teh width of teh tire looking at teh wear line on teh shoulder - infact you are using more than I would have imagined so you are either running too hard with too low pressure or...
2). Too much negative camber at the rear. Typically Porsche Cup/RS and race cars seem to have historically run 1/2-1 degree less negative camber at the rear than the front. This is certainly the case with the 964/993 generation with which I have experience and the 996 GT3 too. Having said this we are pioneering it on this GT3 as it has a far gripper front end and it has RWS both or which may enable equal front and rear negative camber to be run without any compromises. Generally negative front camber is to offset understeer and provide a more even spread of heat across the face of the tyre under cornering loads, turn in etc where the front wheels work much harder than the rear. Im not a geo expert so I will not want to say too much here (you should also take advise form your geo guy) but I dont think we need tonnes of negative rear camber on the rear of these cars - the tyre is doing less work.
My only advise here would be to pull back rear to -2.30" and leave fronts at -3.00" (well you are close enough now anyway) and run a bit more pressure at the beginning of the day, bleeding off after 1st and 2nd sessions and see if the situation continues to deteriorate on these used tyres or gets worse. Probably in reality you will need to wait till you have some cycles on a fresh set to know for sure if its worked. Right now I think low pressure and heat have caused this to happen mostly.
Overall those tyres have worn pretty good - how many sessions/days on those?
1). Initial tyre pressures. This wear could be caused by under inflation in early sessions. You are definately using every bit of teh width of teh tire looking at teh wear line on teh shoulder - infact you are using more than I would have imagined so you are either running too hard with too low pressure or...
2). Too much negative camber at the rear. Typically Porsche Cup/RS and race cars seem to have historically run 1/2-1 degree less negative camber at the rear than the front. This is certainly the case with the 964/993 generation with which I have experience and the 996 GT3 too. Having said this we are pioneering it on this GT3 as it has a far gripper front end and it has RWS both or which may enable equal front and rear negative camber to be run without any compromises. Generally negative front camber is to offset understeer and provide a more even spread of heat across the face of the tyre under cornering loads, turn in etc where the front wheels work much harder than the rear. Im not a geo expert so I will not want to say too much here (you should also take advise form your geo guy) but I dont think we need tonnes of negative rear camber on the rear of these cars - the tyre is doing less work.
My only advise here would be to pull back rear to -2.30" and leave fronts at -3.00" (well you are close enough now anyway) and run a bit more pressure at the beginning of the day, bleeding off after 1st and 2nd sessions and see if the situation continues to deteriorate on these used tyres or gets worse. Probably in reality you will need to wait till you have some cycles on a fresh set to know for sure if its worked. Right now I think low pressure and heat have caused this to happen mostly.
Overall those tyres have worn pretty good - how many sessions/days on those?
Thank you very much for your input and advice, I will certainly be more cautious with at least the first session starting temps. Quick question, though: if the outside shoulder is wearing out more, wouldn't you expect that the tire actually needs more negative camber? Not that I want to add any, as it may increase inside tire wear from street driviving and also increase understeer if the rears grip more. I too find it interesting the stock F/R negative camber are identical.
Those tires have a total of 4 1/2 track days, where each full day is 4 X 30 minute sessions. I also drove those on the road, with a total (road and track) mileage of about 2,500.
08-10-2014, 11:30 PM
#21
Rennlist Member
Sam. Those MPSC2s sure go the distance!!! Looks like you will get 6 track days and 3000 miles out of them which is impressive!
Agree with you on what you say but the low first session pressures have created the outside wear I feel whilst the tyre is rolling on the rim so impossible to determine what camber changes if any are required till that input is eliminated. I should say for the rest of this set do nothing other than increase initial pressures. Once new set on you will be able to establish true wear characteristics again. Remember the RWS may also be contributing here and also the the of track. Our local track has it's tightest corners and fastest sweeper as right handlers and we only rub clockwise so for example on that track we get far more ear on the tyres on the left of the car etc...
Agree with you on what you say but the low first session pressures have created the outside wear I feel whilst the tyre is rolling on the rim so impossible to determine what camber changes if any are required till that input is eliminated. I should say for the rest of this set do nothing other than increase initial pressures. Once new set on you will be able to establish true wear characteristics again. Remember the RWS may also be contributing here and also the the of track. Our local track has it's tightest corners and fastest sweeper as right handlers and we only rub clockwise so for example on that track we get far more ear on the tyres on the left of the car etc...
08-10-2014, 11:39 PM
#22
Sam. Those MPSC2s sure go the distance!!! Looks like you will get 6 track days and 3000 miles out of them which is impressive!
Agree with you on what you say but the low first session pressures have created the outside wear I feel whilst the tyre is rolling on the rim so impossible to determine what camber changes if any are required till that input is eliminated. I should say for the rest of this set do nothing other than increase initial pressures. Once new set on you will be able to establish true wear characteristics again. Remember the RWS may also be contributing here and also the the of track. Our local track has it's tightest corners and fastest sweeper as right handlers and we only rub clockwise so for example on that track we get far more ear on the tyres on the left of the car etc...
Agree with you on what you say but the low first session pressures have created the outside wear I feel whilst the tyre is rolling on the rim so impossible to determine what camber changes if any are required till that input is eliminated. I should say for the rest of this set do nothing other than increase initial pressures. Once new set on you will be able to establish true wear characteristics again. Remember the RWS may also be contributing here and also the the of track. Our local track has it's tightest corners and fastest sweeper as right handlers and we only rub clockwise so for example on that track we get far more ear on the tyres on the left of the car etc...
08-11-2014, 01:26 AM
#23
Rennlist Member
Only have one track day so far on mine and found they worked well pretty close to the MSCP1 pressure of 32f/35r hot. Cold depends too much on driving style and setup to target.
08-11-2014, 01:41 AM
#24
Rennlist Member
Hey Chris. Thanks for that. It ran good for me in that range too. Looks like you are/were a 997.2 GT3 owner? Care to share how the 991 GT3 compared on track to your 7.2 GT3?
08-11-2014, 04:21 AM
#25
Rennlist Member
Macca: Purely a lurker and still 997.2 GT3 owner. Follow this forum because I am curious about the 991 and could find myself owning one one day. Happy to offer a comparison if someone wants to volunteer a car for some seat time 
I have no doubt it is an immensely capable car just based on a run I did with Mike from CA. Took quite a bit of diving just to keep up.
I tried the MSCP2's because of the NT01 drought. They are great tires with fabulous grip. If they end up lasting significantly longer than the MSCP's, they will be a nice addition for us .2 folks too.
I have no doubt it is an immensely capable car just based on a run I did with Mike from CA. Took quite a bit of diving just to keep up.I tried the MSCP2's because of the NT01 drought. They are great tires with fabulous grip. If they end up lasting significantly longer than the MSCP's, they will be a nice addition for us .2 folks too.
08-11-2014, 04:31 AM
#26
Rennlist Member
Hi Chris. All good. Realised shortly after posting that you were on an earlier thread saying you would be trying the MPSC2 on your 7.2 GT3. Glad they are working out well for you. From what Ive experienced so far short of a Hoosier R6 or a Hankook Z221/214 (none of which are available in our sizes anyway!) they appear to be a great road/track R comp with very few downsides and surprising durability. The only other tyre right now Id like to try them against on track when they wear out is the Trofeo R. Although it may be in part due to the 991 Chassis, it would appear that most are getting at least 4-5 track days and 2-3000 road miles out of a set in Europe. Some have made 6 track days (dependant on track and pace). I have 3000 road miles on mine and one track session with two full track days (70 laps a day) and a further 1500 road miles coming up in September. I figure if they survive all of that and have enough left in them for a full track day then they are definitely good for 5-6 track days and a wee bit of road miles - and I cant really ask for more than that (Hankook Z221 on 993 track car good for around 7-8 track days and 1500 miles touring)...
08-11-2014, 02:36 PM
#27
Mike and I had a great battle going, me in my BMW 1M, also on Pilot Sport Cup 2s- he got me on the very last run. Good times.
I found the turn-in for the MPSC2 poor on my 1M- the steering felt heavy and dead, and I needed to turn in very early to attack apexes. On the other hand grip, progressiveness and high speed stability were great, and it's fast once it warms up. No turn-in issues on the 991 GT3, obviously- that car works with the tires beautifully.
08-11-2014, 04:01 PM
#28
Race Director
^^It was great to meet Pete in person this weekend. As fate would have it we also ended up working the same corner. I had the opportunity to ride in his very quick and extremely well driven M1. That car has some torque! His tip on how I was missing the entry to the first corner eventually helped me to pip his time but it was very close all day and great fun.
08-11-2014, 06:14 PM
#29
^^It was great to meet Pete in person this weekend. As fate would have it we also ended up working the same corner. I had the opportunity to ride in his very quick and extremely well driven M1. That car has some torque! His tip on how I was missing the entry to the first corner eventually helped me to pip his time but it was very close all day and great fun.
Seriously, the 991 GT3 is going to be bloody impressive against the clock. I know a few guys running some of the fastest AX Porsches in the country- 997.2 GT3 RS, 3.8L 2600 lb Cayman, 650+ hp GT2 weighing 2800 lbs, shelled out, big winged 914s. I co-drove the TTOD winner at Parade last month...
Mark my words: the moment someone releases 20" race/ DOT R rubber or someone fits 19"s with the same, every one of those cars will be obsolete. The 991 GT3, otherwise stock, will go a second clear of basically any of them around the average course. I think it's literally that fast... Which means the RS is probably nearly another second clear... I can't quite get my head around it, but what happens then?
10-12-2014, 05:10 PM
#30
Have any of you ever measured tire temperatures?
When I was racing, I would do a few hot laps at tire dealer recommended pressures. I'd do a quick pit stop & have my 4 tires measured for temperature across the tread. The goal was an even spread from one side to the other. The front tires were always hotter on the inside from slight negative camber. (You have to take that into account.) Setting pressure by tire temp resulted in my best lap times.
When I was racing, I would do a few hot laps at tire dealer recommended pressures. I'd do a quick pit stop & have my 4 tires measured for temperature across the tread. The goal was an even spread from one side to the other. The front tires were always hotter on the inside from slight negative camber. (You have to take that into account.) Setting pressure by tire temp resulted in my best lap times.