ok, this may be stupid, but...understeer
03-31-2013, 02:14 PM
#1
Race Director
Thread Starter
ok, this may be stupid, but...understeer
Perhaps this is me not understanding how to properly pilot a 911, but here is my issue:
On fairly low speed turns, on corner exit, I pound on the gas in true 911 fashion. Rear end traction is perfect, but the front gets light and the car understeers. You can drive around it with some throttle feathering and accelerating a bit later out of the turn, but getting on the gas earlier is part of the benefit of the 911.
Car is a 96 Turbo, bilstein hd and row 030 springs. H&R swaybars soft in the front, stiff in the rear Sumitomo 235s in the front 295s in the rear, 34psi front 36psi rear. Good recent alignment performed by a knowledgeable shop.
What am I missing here? Do I need more rear spring rate? Do I need to learn to drive? Do I need to accept that this is a 911 trait?
any advice here would be appreciated.
thanks.
On fairly low speed turns, on corner exit, I pound on the gas in true 911 fashion. Rear end traction is perfect, but the front gets light and the car understeers. You can drive around it with some throttle feathering and accelerating a bit later out of the turn, but getting on the gas earlier is part of the benefit of the 911.
Car is a 96 Turbo, bilstein hd and row 030 springs. H&R swaybars soft in the front, stiff in the rear Sumitomo 235s in the front 295s in the rear, 34psi front 36psi rear. Good recent alignment performed by a knowledgeable shop.
What am I missing here? Do I need more rear spring rate? Do I need to learn to drive? Do I need to accept that this is a 911 trait?
any advice here would be appreciated.
thanks.
03-31-2013, 02:41 PM
#4
Rennlist Member
this is a complex problem which the solution is car setup, balance, and learning to drive to a 993 out of corners properly. The 4wd 993 makes it even more of a challenge to get the setup correct (996 is worse). These cars were designed to have understeer and for track/racing you have to move away from the initial factory settings. One of the biggest corrections I make with a driver/racer when I do race coaching with a 993/996 chassis is getting the car setup for more loose entry which yields much higher entry speed and corner grip. The ability to return to full throttle is a bit later and is corrective to the car wanting to spin when it is at the traction limit. When you compare the data you see big gains in entry, mid-corner Vmin. At exit you are so much faster than the method you describe that your quite a bit ahead already. I would suggest having a driving coach or club racer take your car out and tell you how it handles to them. If you frequent NJMP I can actually help you there.
03-31-2013, 02:43 PM
#5
RL Technical Advisor
LOL,..You are in good company,..
Several factors affect what you feel and some of them include driver technique (choosing wrong apex), camber settings, insufficient rear suspension stiffness (ROW spring rate differentials are too close), and AWD.
Early apexes almost guarantee corner-exit understeer ('specially with AWD) unless immediately followed by a successive corner in the opposite direction.
Insufficient camber exacerbates everything as the tire sidewalls roll under the contact patches.
All factory springs are designed to ensure that the average driver departs the road nose-first and they did that with a small rate split between the front and rear axles. Stiffening the rear, relative to the front, makes the car more neutral, however thats very tough to do with your current suspension system. PSS-10's are FAR better in this (and other) regards.
In short, its all fixable without resorting to a 2WD conversion.
Several factors affect what you feel and some of them include driver technique (choosing wrong apex), camber settings, insufficient rear suspension stiffness (ROW spring rate differentials are too close), and AWD.
Early apexes almost guarantee corner-exit understeer ('specially with AWD) unless immediately followed by a successive corner in the opposite direction.
Insufficient camber exacerbates everything as the tire sidewalls roll under the contact patches.
All factory springs are designed to ensure that the average driver departs the road nose-first and they did that with a small rate split between the front and rear axles. Stiffening the rear, relative to the front, makes the car more neutral, however thats very tough to do with your current suspension system. PSS-10's are FAR better in this (and other) regards.
In short, its all fixable without resorting to a 2WD conversion.
03-31-2013, 02:57 PM
#6
Rennlist Member
It's all about rotating the car properly.
The more you modify it towards neutral behaviour, the easier it will be to rotate it.
A stock turbo is far from neutral and in order to rotate one, it will require a good driver.
Like Bob and Steve said, go attend a DE and have someone who knows how to properly rotate a 911 coach you.
The more you modify it towards neutral behaviour, the easier it will be to rotate it.
A stock turbo is far from neutral and in order to rotate one, it will require a good driver.
Like Bob and Steve said, go attend a DE and have someone who knows how to properly rotate a 911 coach you.
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03-31-2013, 04:23 PM
#9
Nordschleife Master
A simple fix to the suspension setup is an adjustable rear sway bar where you can dial in a bit more stiffness for the rear. It may even be possible to drill a second hole in your existing sway bar.
03-31-2013, 05:01 PM
#10
I drive a 993 C4S on the track and yes, it behaves different to my 993 without AWD. I basically did the same to suspension setthings (PSS9 settings and sway bars) which improved the situation. However, since I went less wide in the rear due to tire sizes, the car has a very nice balance (for MY driving style). I now have NT01s 235 / 275 vs. AB08 225 / 295). Again, really like how the car is now setup for me.
03-31-2013, 05:05 PM
#11
Rennlist Member
Well hasn't THAT been the culprit since Day One on these things...........
So glad we have the: 1. expertise, and 2. technology to bring us forward from the blind-leading-the-blind days. Pretty embarrassing to think back on how stupid set up most of mine have been over the decades.
But back to Quad's dilemma--nearly everyone here wants a sporting, confidence inspiring car for "aggressive" (when warranted) street driving. Sadly, I don't think many of the cars out there are so outfitted. But easy enough to rectify, even if it might cost a few bucks.
So glad we have the: 1. expertise, and 2. technology to bring us forward from the blind-leading-the-blind days. Pretty embarrassing to think back on how stupid set up most of mine have been over the decades.
But back to Quad's dilemma--nearly everyone here wants a sporting, confidence inspiring car for "aggressive" (when warranted) street driving. Sadly, I don't think many of the cars out there are so outfitted. But easy enough to rectify, even if it might cost a few bucks.
03-31-2013, 08:25 PM
#12
04-01-2013, 08:03 PM
#13
Addict
Rennlist Member
Rennlist Member
Perhaps this is me not understanding how to properly pilot a 911, but here is my issue:
On fairly low speed turns, on corner exit, I pound on the gas in true 911 fashion. Rear end traction is perfect, but the front gets light and the car understeers. You can drive around it with some throttle feathering and accelerating a bit later out of the turn, but getting on the gas earlier is part of the benefit of the 911.
Car is a 96 Turbo, bilstein hd and row 030 springs. H&R swaybars soft in the front, stiff in the rear Sumitomo 235s in the front 295s in the rear, 34psi front 36psi rear. Good recent alignment performed by a knowledgeable shop.
What am I missing here? Do I need more rear spring rate? Do I need to learn to drive? Do I need to accept that this is a 911 trait?
any advice here would be appreciated.
thanks.
On fairly low speed turns, on corner exit, I pound on the gas in true 911 fashion. Rear end traction is perfect, but the front gets light and the car understeers. You can drive around it with some throttle feathering and accelerating a bit later out of the turn, but getting on the gas earlier is part of the benefit of the 911.
Car is a 96 Turbo, bilstein hd and row 030 springs. H&R swaybars soft in the front, stiff in the rear Sumitomo 235s in the front 295s in the rear, 34psi front 36psi rear. Good recent alignment performed by a knowledgeable shop.
What am I missing here? Do I need more rear spring rate? Do I need to learn to drive? Do I need to accept that this is a 911 trait?
any advice here would be appreciated.
thanks.
If you want to drive fast, there is no such thing as "pound" anything. Not either of the three pedals, not steering wheel, nothing. Smooth inputs and finding the edge is what is needed.
04-01-2013, 08:09 PM
#14
Rennlist Member
04-01-2013, 08:23 PM
#15
Perhaps this is me not understanding how to properly pilot a 911, but here is my issue:
On fairly low speed turns, on corner exit, I pound on the gas in true 911 fashion. Rear end traction is perfect, but the front gets light and the car understeers. You can drive around it with some throttle feathering and accelerating a bit later out of the turn, but getting on the gas earlier is part of the benefit of the 911.
Car is a 96 Turbo, bilstein hd and row 030 springs. H&R swaybars soft in the front, stiff in the rear Sumitomo 235s in the front 295s in the rear, 34psi front 36psi rear. Good recent alignment performed by a knowledgeable shop.
What am I missing here? Do I need more rear spring rate? Do I need to learn to drive? Do I need to accept that this is a 911 trait?
any advice here would be appreciated.
thanks.
On fairly low speed turns, on corner exit, I pound on the gas in true 911 fashion. Rear end traction is perfect, but the front gets light and the car understeers. You can drive around it with some throttle feathering and accelerating a bit later out of the turn, but getting on the gas earlier is part of the benefit of the 911.
Car is a 96 Turbo, bilstein hd and row 030 springs. H&R swaybars soft in the front, stiff in the rear Sumitomo 235s in the front 295s in the rear, 34psi front 36psi rear. Good recent alignment performed by a knowledgeable shop.
What am I missing here? Do I need more rear spring rate? Do I need to learn to drive? Do I need to accept that this is a 911 trait?
any advice here would be appreciated.
thanks.
AWD is worse than 2wd
lsd is worse than open diff
S is worse than non S
on throttle is worse than off
you can reduce understeer by,
increasing rear spring rate
increasing rear roll bar rate
increasing front wheel width
using more camber in front, less in back
softer front shock and or harder rear shock
remove weight from the front
higher front tire pressure, lower rear
bigger(more efficient) front spoiler, smaller rear
mre rear brake, less front
a 911 is fastest braking in a straight line, trail braking to aid rotation, get on the gas as quick as possible when you are nearly pointing where you want to go.