Unsprung weight - 19 vs 18-inch wheels
11-22-2005, 12:33 PM
#1
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Unsprung weight - 19 vs 18-inch wheels
As I spend more time with the 997, on mountain road with lots of twisties, I think the larger 19-inch wheels are a disadvantage because of the increased unsprung weight. PSM is kicking in a LOT as the wheels leave the road. I've got PASM, and it doesn't really matter whether I'm in Sport mode or not - in fact I think Sport mode causes the wheels to leave the road more. I'm actually thinking about stepping down to 18s (but the 19s look AWESOME). Looks be damned, I want maximum handling (I do 12 miles of intense twisty road driving every day!).
2005 997 Arctic Silver, PASM, 19" Sport Design
2005 997 Arctic Silver, PASM, 19" Sport Design
11-22-2005, 01:25 PM
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There is a 2 piece aluminum wheel that BBS has made for Manthey Racing available now for the 997 cars. Weighing only 12 kg, sizes are 8.5X19 fronts and the choice of 10.0X19 or 11X19 rear.
With the combonation of the Michelin Pilot Cups, tesing on the Nordschleife and Nurburgring, was very positive for BBS. Therefore proceeding with production of wheel for Manthey.
Theo
With the combonation of the Michelin Pilot Cups, tesing on the Nordschleife and Nurburgring, was very positive for BBS. Therefore proceeding with production of wheel for Manthey.
Theo
11-22-2005, 01:33 PM
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I do not believe what you feel is traced to wheel sizing and unsprung weight. There is not a big weight difference b/t the two, and 18's on my GT3 'left the ground' more than the 19's on my S.
Having run various wheels and tires on the racetrack on several different cars, ltw wheels are felt in acceleration and the nimbleness of the car (ie, how quickly the car transitions). Tire/road contact is far more a function of suspension setup than wheel choice. PSM if fairly aggressive on these cars, slightly better in Sport mode (if you have it).
The solution to what you feel is (i) smoother inputs and better driving, and/or (ii) more sophisitcated suspension setup. Since you are running PASM, (ii) is probably off the table. Having been in/owned/driven Bilstein, Koni and Moton equipped cars, better dampers permit better tracking and minimized loss of tire contact with the road.
Having run various wheels and tires on the racetrack on several different cars, ltw wheels are felt in acceleration and the nimbleness of the car (ie, how quickly the car transitions). Tire/road contact is far more a function of suspension setup than wheel choice. PSM if fairly aggressive on these cars, slightly better in Sport mode (if you have it).
The solution to what you feel is (i) smoother inputs and better driving, and/or (ii) more sophisitcated suspension setup. Since you are running PASM, (ii) is probably off the table. Having been in/owned/driven Bilstein, Koni and Moton equipped cars, better dampers permit better tracking and minimized loss of tire contact with the road.
11-22-2005, 03:07 PM
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First of all, the PSM envelope on the 997 is much wider than it was on the 996.
The 996 was really noted for intervention, but if your inputs were really smooth you could get the rear end to step out a bit without intervention. A common complaint at track events...PSM is coming on, 99% of the time it is due to overdriving the car.
My best guess as to why it is activating is that you are "OVERDRIVING" the car. Your inputs need to be smooth and only as much as needed. Don't be braking in the corners , get that done in a straight line (light trail braking to get a little weight forward is OK).
The cool part of PASM is that when you really are driving the car in the regular setting the shock dampening will increase almost to the "Sport" mode setting, the computer knows.
The switch from 19's to 18's will not significantly impact the un-sprung weight of the car. Tire weights are the same.
The 997 in it's stock trim can be pushed way farther than you can imagine without PSM intervention.
I've gone for hotlaps with some of the finest drivers in the country, and it is not an issue. Ask anyone who has done PDE and I think they will agree.
Consider signing-up for a two day PDE your eyes will open wide and you'll be really amazed.
The 996 was really noted for intervention, but if your inputs were really smooth you could get the rear end to step out a bit without intervention. A common complaint at track events...PSM is coming on, 99% of the time it is due to overdriving the car.
My best guess as to why it is activating is that you are "OVERDRIVING" the car. Your inputs need to be smooth and only as much as needed. Don't be braking in the corners , get that done in a straight line (light trail braking to get a little weight forward is OK).
The cool part of PASM is that when you really are driving the car in the regular setting the shock dampening will increase almost to the "Sport" mode setting, the computer knows.
The switch from 19's to 18's will not significantly impact the un-sprung weight of the car. Tire weights are the same.
The 997 in it's stock trim can be pushed way farther than you can imagine without PSM intervention.
I've gone for hotlaps with some of the finest drivers in the country, and it is not an issue. Ask anyone who has done PDE and I think they will agree.
Consider signing-up for a two day PDE your eyes will open wide and you'll be really amazed.
11-22-2005, 03:25 PM
#5
Burning Brakes
I'm a rear-engine n00b and I was able to take the 997S on VIR with no PSM intervention. Just be smooth. If PSM does intervene, it's for your own good. Be smooth, be balanced, and the car will fly.
11-22-2005, 05:33 PM
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Some of the posts I read on this site are unusual, to be diplomatic. " If I put helium in my tires instead of oxygen can I go 200 mph" "If I can save 4 ounces of unsprung weight will my car handle better?'
There probably aren't a handful of drivers here that can drive a Porsche even to 80% of its potential, including foremost yours truly. Maybe I'm just in a ****ty mood today, and no disrespect is intended, but sometimes I cringe when I read these unrealistic posts.
There probably aren't a handful of drivers here that can drive a Porsche even to 80% of its potential, including foremost yours truly. Maybe I'm just in a ****ty mood today, and no disrespect is intended, but sometimes I cringe when I read these unrealistic posts.
11-22-2005, 05:39 PM
#7
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Originally Posted by Larry Harris
Some of the posts I read on this site are unusual, to be diplomatic. " If I put helium in my tires instead of oxygen can I go 200 mph" "If I can save 4 ounces of unsprung weight will my car handle better?'
There probably aren't a handful of drivers here that can drive a Porsche even to 80% of its potential, including foremost yours truly. Maybe I'm just in a ****ty mood today, and no disrespect is intended, but sometimes I cringe when I read these unrealistic posts.
There probably aren't a handful of drivers here that can drive a Porsche even to 80% of its potential, including foremost yours truly. Maybe I'm just in a ****ty mood today, and no disrespect is intended, but sometimes I cringe when I read these unrealistic posts.
You have hit the nail on the head. Porsches are generally WAY over the heads of probably 90% of their owners. While I have been a Porsche driver for 31 years, I'm still learning and no way competent at the potential these things can go. Several years ago I was out with a good friend of mine and my mechanic (and president of his automotive company) (all one guy) and I offered to let him show me how to get around Hallett raceway. In his first lap,--totally new to the car, he took 3 seconds off my fastest time. He was an extremely competent race driver,--and a rare person. I can count on one hand the people I know personally who could exploit the potential of the 911. Worrying about a little unsprung weight here and there and commenting on a car's capability in the turns when you're a relative novice driver is just so much talk.
Dan
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11-22-2005, 06:01 PM
#8
Burning Brakes
Originally Posted by Edgy01
Larry,
You have hit the nail on the head. Porsches are generally WAY over the heads of probably 90% of their owners. While I have been a Porsche driver for 31 years, I'm still learning and no way competent at the potential these things can go. Several years ago I was out with a good friend of mine and my mechanic (and president of his automotive company) (all one guy) and I offered to let him show me how to get around Hallett raceway. In his first lap,--totally new to the car, he took 3 seconds off my fastest time. He was an extremely competent race driver,--and a rare person. I can count on one hand the people I know personally who could exploit the potential of the 911. Worrying about a little unsprung weight here and there and commenting on a car's capability in the turns when you're a relative novice driver is just so much talk.
Dan
You have hit the nail on the head. Porsches are generally WAY over the heads of probably 90% of their owners. While I have been a Porsche driver for 31 years, I'm still learning and no way competent at the potential these things can go. Several years ago I was out with a good friend of mine and my mechanic (and president of his automotive company) (all one guy) and I offered to let him show me how to get around Hallett raceway. In his first lap,--totally new to the car, he took 3 seconds off my fastest time. He was an extremely competent race driver,--and a rare person. I can count on one hand the people I know personally who could exploit the potential of the 911. Worrying about a little unsprung weight here and there and commenting on a car's capability in the turns when you're a relative novice driver is just so much talk.
Dan
11-23-2005, 08:48 AM
#9
Three Wheelin'
Originally Posted by GREEK-TURBO-RACER
There is a 2 piece aluminum wheel that BBS has made for Manthey Racing available now for the 997 cars. Weighing only 12 kg, sizes are 8.5X19 fronts and the choice of 10.0X19 or 11X19 rear.
With the combonation of the Michelin Pilot Cups, tesing on the Nordschleife and Nurburgring, was very positive for BBS. Therefore proceeding with production of wheel for Manthey.
Theo
With the combonation of the Michelin Pilot Cups, tesing on the Nordschleife and Nurburgring, was very positive for BBS. Therefore proceeding with production of wheel for Manthey.
Theo
11-23-2005, 10:25 AM
#10
Rennlist Member
Kinesis f110s (or Champion RS98s) are 18 and 20 lbs in 19" sizes, weighing in less than factory 18s.
I do agree, though, that if your getting the suspension that out of shape on a normal (i.e. not unusually rough) road you need to work on driver inputs/smoothness. Also, check your tires pressures, alignment, and make sure you don't have a PASM issue.
This thread has some good info, too, since you're id challenged and don't mention your experience in rear engine cars.
Strange Handling
I do agree, though, that if your getting the suspension that out of shape on a normal (i.e. not unusually rough) road you need to work on driver inputs/smoothness. Also, check your tires pressures, alignment, and make sure you don't have a PASM issue.
This thread has some good info, too, since you're id challenged and don't mention your experience in rear engine cars.
Strange Handling
11-23-2005, 10:54 AM
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Originally Posted by MrBonus
Okay, I've scoured Google for more information with no success. You need to post more details and/or pics.
MrBonus, I will try to reach my guys now before they leave for the day. I will ask for current pics as they have them. Also will verify waiting time.
Theo
11-29-2005, 05:59 AM
#13
Instructor
Thread Starter
Some wheel weights:
8x19 11x19
23.10 28.11 Carrera Classic
24.3 28.3 Sport Design
Note: 12 kg = 26.4 lbs. Is this for the 10" or 11" BBS/Manthey wheel?
FWIW, the twisty mountain road (to home) where I notice the PSM kicking in with PASM is Page Mill Road in the SF Bay Area (Palo Alto / Los Altos) - this is a fairly uneven road that's been patched many times, and PSM usually kicks in on the hair pin turns (there are two very sharp 180-degree turns). But even the less aggressive turns with uneven patched pavement produce some interesting rear-end responses that I didn't see in my 996. But, yes, driving school and some DEs are on the list of to-do's.
8x19 11x19
23.10 28.11 Carrera Classic
24.3 28.3 Sport Design
Note: 12 kg = 26.4 lbs. Is this for the 10" or 11" BBS/Manthey wheel?
FWIW, the twisty mountain road (to home) where I notice the PSM kicking in with PASM is Page Mill Road in the SF Bay Area (Palo Alto / Los Altos) - this is a fairly uneven road that's been patched many times, and PSM usually kicks in on the hair pin turns (there are two very sharp 180-degree turns). But even the less aggressive turns with uneven patched pavement produce some interesting rear-end responses that I didn't see in my 996. But, yes, driving school and some DEs are on the list of to-do's.
11-29-2005, 06:04 AM
#14
Instructor
Thread Starter
Oops, the formatting was lost - trying again...
8x19 wheel
23.1 lb Carrera Classic
24.3 lb Sport Design
11x19 wheel
28.1 lb Carrera Classic
28.3 lb Sport design
I think I can reduce the unsprung weight by switching from the colored crest center caps to the engraved crest center caps. Should save 20-30 grams per wheel. (you know I'm kidding, right?)
8x19 wheel
23.1 lb Carrera Classic
24.3 lb Sport Design
11x19 wheel
28.1 lb Carrera Classic
28.3 lb Sport design
I think I can reduce the unsprung weight by switching from the colored crest center caps to the engraved crest center caps. Should save 20-30 grams per wheel. (you know I'm kidding, right?)