Understeering RS and GT3
05-14-2007, 09:21 AM
#46
Instructor
Join Date: May 2002
Location: Canada
Posts: 199
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by DrJupeman
I don't understand the bitching about "out of the box" understeer. What street 911 from the factory has not understeered for the past 30+ years?
Nice vids earlier.
Nice vids earlier.
05-14-2007, 09:25 AM
#47
Instructor
Join Date: May 2002
Location: Canada
Posts: 199
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by frayed
Bob, the 18" MPSCs are smaller diameter than stock I think. You can run Toyos in near factory diameter. I think Noble had some issues when he went to the 18" MPSC setup on his 997S. Food for thought.
Stock
235/35-19 25.5"...............................305/30-19 26.3"
RA1
245/40-18 25.6"...............................305/35-18 26.3
275/35-18 25.5"................................335/30-18 25.9
PSC
265/35-18" 25.2"...........................345/35-18 26.2
235/40-18" 25.4"...........................295/35-18 25.2"
....................................................315/35-18" 25.5"
Hooters
P245/35-18 24.7"...........................315/30-18 25.6"
Nitto
245/40-18 25.55..............................315/30-18 25.35"
Stock
235/35-19 25.5"...............................305/30-19 26.3"
RA1
245/40-18 25.6"...............................305/35-18 26.3
275/35-18 25.5"................................335/30-18 25.9
PSC
265/35-18" 25.2"...........................345/35-18 26.2
235/40-18" 25.4"...........................295/35-18 25.2"
....................................................315/35-18" 25.5"
Hooters
P245/35-18 24.7"...........................315/30-18 25.6"
Nitto
245/40-18 25.55..............................315/30-18 25.35"
I'm not a huge fan of the RA1 as compared to the PSC. Wouldn't the 235/345 PSC be a near perfect combo for the 997?
05-14-2007, 09:43 AM
#48
Still plays with cars.
Lifetime Rennlist
Member
Update - more laps at LCMT yesterday and I was able to pace with Mike K (996GT3). I had a 200 lb passenger aboard and full fuel.
My car still has some residual push - Mike was able to gain exiting Carousel and Bridge. My sways are still as they were, i.e., one from soft F and one from stiff R. I hope that adjusting them will cure the remaining push.
Doc - it appears that opinions vary on the effect of rear toe in. Is there any definitive source I should be looking at? Several sources on alignment claim that toe in back reduces understeer. Perhaps that info was not targeted to a 911? I admit to being puzzled since toe out in the back makes the car dangerous to drive - spins easily!
So I admit that your comment makes some sense.
I can see more tweaking coming but the progress to date has been rewarding The car is now fun to drive if not yet at its full potential.
Apex the thing we need to be careful of is what Frayed was pointing out. The 235/315 PSC 18 inchers will have the effect of lowering the car about 1/2 inch (1 inch less diameter) in the rear. That can be corrected mind you but then the car will be raked more on the 19 inchers.
Best,
My car still has some residual push - Mike was able to gain exiting Carousel and Bridge. My sways are still as they were, i.e., one from soft F and one from stiff R. I hope that adjusting them will cure the remaining push.
Doc - it appears that opinions vary on the effect of rear toe in. Is there any definitive source I should be looking at? Several sources on alignment claim that toe in back reduces understeer. Perhaps that info was not targeted to a 911? I admit to being puzzled since toe out in the back makes the car dangerous to drive - spins easily!
So I admit that your comment makes some sense.
I can see more tweaking coming but the progress to date has been rewarding The car is now fun to drive if not yet at its full potential.
Apex the thing we need to be careful of is what Frayed was pointing out. The 235/315 PSC 18 inchers will have the effect of lowering the car about 1/2 inch (1 inch less diameter) in the rear. That can be corrected mind you but then the car will be raked more on the 19 inchers.
Best,
05-14-2007, 09:59 AM
#49
Instructor
Join Date: May 2002
Location: Canada
Posts: 199
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by Bob Rouleau
Update - more laps at LCMT yesterday and I was able to pace with Mike K (996GT3). I had a 200 lb passenger aboard and full fuel.
My car still has some residual push - Mike was able to gain exiting Carousel and Bridge. My sways are still as they were, i.e., one from soft F and one from stiff R. I hope that adjusting them will cure the remaining push.
Doc - it appears that opinions vary on the effect of rear toe in. Is there any definitive source I should be looking at? Several sources on alignment claim that toe in back reduces understeer. Perhaps that info was not targeted to a 911? I admit to being puzzled since toe out in the back makes the car dangerous to drive - spins easily!
So I admit that your comment makes some sense.
I can see more tweaking coming but the progress to date has been rewarding The car is now fun to drive if not yet at its full potential.
Apex the thing we need to be careful of is what Frayed was pointing out. The 235/315 PSC 18 inchers will have the effect of lowering the car about 1/2 inch (1 inch less diameter) in the rear. That can be corrected mind you but then the car will be raked more on the 19 inchers.
Best,
My car still has some residual push - Mike was able to gain exiting Carousel and Bridge. My sways are still as they were, i.e., one from soft F and one from stiff R. I hope that adjusting them will cure the remaining push.
Doc - it appears that opinions vary on the effect of rear toe in. Is there any definitive source I should be looking at? Several sources on alignment claim that toe in back reduces understeer. Perhaps that info was not targeted to a 911? I admit to being puzzled since toe out in the back makes the car dangerous to drive - spins easily!
So I admit that your comment makes some sense.
I can see more tweaking coming but the progress to date has been rewarding The car is now fun to drive if not yet at its full potential.
Apex the thing we need to be careful of is what Frayed was pointing out. The 235/315 PSC 18 inchers will have the effect of lowering the car about 1/2 inch (1 inch less diameter) in the rear. That can be corrected mind you but then the car will be raked more on the 19 inchers.
Best,
As discussed I'm looking at the GMG Cup wheels in 18X9 and 18X12. I will talk to them today about the tire combos that they have run for the track and discuss the effects on handling. I will report back later today on my findings.
05-14-2007, 10:35 AM
#50
Race Car
Join Date: Mar 2004
Posts: 3,972
Likes: 0
Received 0 Likes
on
0 Posts
Bob, Apex,
It's Noble who originally brought up the issue of running MPSC 18" tires on a 997S. You may want to shoot him a PM. It might be a ride height issue, but Noble was guessing the smaller rolling diameter out back did something to the suspension geometry or that PASM wasn't happy with the smaller tire.
OTOH, that was on a 997S, which of course has PSM. On a 997 GT3 which only has TC and not stability management, we should have more flexibility.
Apex,
Did you try Toyos shaved? They feel squishy to me unshaved. They aren't as precise as MPSCs but they are fast and like to be driven a bit looser than MPSCs. But tires are personal.
Cheers,
It's Noble who originally brought up the issue of running MPSC 18" tires on a 997S. You may want to shoot him a PM. It might be a ride height issue, but Noble was guessing the smaller rolling diameter out back did something to the suspension geometry or that PASM wasn't happy with the smaller tire.
OTOH, that was on a 997S, which of course has PSM. On a 997 GT3 which only has TC and not stability management, we should have more flexibility.
Apex,
Did you try Toyos shaved? They feel squishy to me unshaved. They aren't as precise as MPSCs but they are fast and like to be driven a bit looser than MPSCs. But tires are personal.
Cheers,
05-14-2007, 10:48 AM
#51
Instructor
Join Date: May 2002
Location: Canada
Posts: 199
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by frayed
Bob, Apex,
Apex,
Did you try Toyos shaved? They feel squishy to me unshaved. They aren't as precise as MPSCs but they are fast and like to be driven a bit looser than MPSCs. But tires are personal.
Cheers,
Apex,
Did you try Toyos shaved? They feel squishy to me unshaved. They aren't as precise as MPSCs but they are fast and like to be driven a bit looser than MPSCs. But tires are personal.
Cheers,
Yes I tried them both ways and I didn't love them. I will admit that I haven't tried them on a Porsche yet but I have never driven a tire that I personally liked more than an PSC. You are correct that it is a preference kind of thing.
