Lower front psi = less understeer.
Thread Starter
Instructor
Joined: May 2000
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From: NYC NY
Lower front psi = less understeer.
Would that help? Also on very fast sweeping turns the steering gets a little lite. Does that mean front is loosing or about to lose traction?
Thanks Simon K.
Thanks Simon K.
Team Owner
Joined: Mar 2001
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From: Boston, Dallas, Detroit, SoCal, back to Boston MA
Re: Lower front psi = less understeer. (lemans396)
In general yes, that's what I did at the autocross with my 255f/285r combo
But it also made it squirely, something you need to be ready for at a track.
What tires/wheels size are you running?
How much track time do you have.
I used to cut my apexes too early, which could also be the problem.
But it also made it squirely, something you need to be ready for at a track.
What tires/wheels size are you running?
How much track time do you have.
I used to cut my apexes too early, which could also be the problem.
Thread Starter
Instructor
Joined: May 2000
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From: NYC NY
Re: Lower front psi = less understeer. (BrianCunningham)
275/40-17's all around.
No track time yet, planning on going to Lime Rock. I'm in the process of becoming a PDA member. I just recently did the whole suspension., upgrade/overhaul. I'm new at this level of driving (track time). It all started when I almost missed a exit on the highway and dove in too late. the front sort of plowed out on me. The steering feel is because I take turns faster now, I noticed it and was wondering if it's normal.
No track time yet, planning on going to Lime Rock. I'm in the process of becoming a PDA member. I just recently did the whole suspension., upgrade/overhaul. I'm new at this level of driving (track time). It all started when I almost missed a exit on the highway and dove in too late. the front sort of plowed out on me. The steering feel is because I take turns faster now, I noticed it and was wondering if it's normal.
Instructor
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From: Nampa, ID, USA
Re: Lower front psi = less understeer. (no cure)
I agree with NoCure. To reduce understeer either increase the front tire pressure (experiment with 2 lb increments), or lower the rear tire pressure by a couple of pounds. Other thing to look at is alignment. A little more negative camber on the front than the rear helps with understeer also. You can toe the front out but that tends to chew up tires and makes the steering squirly. Best
to keep 0 toe up front. Search the archives. there have been a lot of posts on this subject.
good luck,
Scott
to keep 0 toe up front. Search the archives. there have been a lot of posts on this subject.
good luck,
Scott
Safety Car
Joined: Apr 1999
Posts: 4,623
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From: Ohio
Re: Lower front psi = less understeer. (lemans396)
First of all, what have you done to the suspension? What kind of tires, and what pressures are you running now? We need some basic info. Given that your butt-o-meter has yet to be trained, you need to get some baseline settings so that the car is fairly neutral to understeering (which you have now) so that you can get some track time and learn high performance driving comfortably. The *worst* possible thing for anyone new to the sport to do, is to start changing the car setup, with the intention of chasing faster times. Get into as many DE's as you can so that you can get the feel of the car, and your laptimes get very consistant. That's not likely to happen for the first couple of schools. If you fiddle around with the alignment settings, tire pressures, shocks swaybars etc. you will never know who (you) or what changed. Give us more info. :yesnod:
Thread Starter
Instructor
Joined: May 2000
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From: NYC NY
Re: Lower front psi = less understeer. (h rocks)
H rocks, changed all ball joints, tie rods, toe rods, GM components. Bushings: Polyurethane
Upper/lower control arms, diff carrier, camber rods, sway bars+ end links,e.t.c.
Sway bars: 3mm/26mm
Bilstein shocks loered 1 2/2,
Rear wheel bearings.
BFG G-Force KD tires currently at 34 psi front, 31 psi rear.
FE1 springs. The suspension I did because of wear and tear/mileage. Sway bars because I wanted les body roll.
Upper/lower control arms, diff carrier, camber rods, sway bars+ end links,e.t.c.
Sway bars: 3mm/26mm
Bilstein shocks loered 1 2/2,
Rear wheel bearings.
BFG G-Force KD tires currently at 34 psi front, 31 psi rear.
FE1 springs. The suspension I did because of wear and tear/mileage. Sway bars because I wanted les body roll.
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Thread Starter
Instructor
Joined: May 2000
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From: NYC NY
Re: Lower front psi = less understeer. (lemans396)
Almost forgot alignment specs:
front rear
camber: .40deg. neg. .70deg. neg
caster: 6.5 deg pos --------------
toe: 0 1/16" toe in per side.
front rear
camber: .40deg. neg. .70deg. neg
caster: 6.5 deg pos --------------
toe: 0 1/16" toe in per side.
Melting Slicks
Joined: Nov 2000
Posts: 2,333
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From: USA
Re: Lower front psi = less understeer. (lemans396)
First off, nobody could answer that question until they knew what kind of tire you were running and what tire pressure. You have answered that.
If you were running 40 psi then I would say to lower the pressure.
If you were running 30psi, I would say raise it.
But at 34 front, 31 rear, I would lower the front by 3 psi and get front and rear the same. If that does not work then try raising the front to 36 psi but I do not think that will work.
On track with similar (not same) tires, I have run as low as 26 psi.
With the changes you made to the car, you may have other issues there affecting the handling.
Now having said all that crap, the easiest and most accurate way to find the answer is to call BFG and ask for a tech person. They will be glad to give you advice on tire pressure. I have done it many times.
I think the number is 800-race-bfg. Anybody else help with the number.
Dave
If you were running 40 psi then I would say to lower the pressure.
If you were running 30psi, I would say raise it.
But at 34 front, 31 rear, I would lower the front by 3 psi and get front and rear the same. If that does not work then try raising the front to 36 psi but I do not think that will work.
On track with similar (not same) tires, I have run as low as 26 psi.
With the changes you made to the car, you may have other issues there affecting the handling.
Now having said all that crap, the easiest and most accurate way to find the answer is to call BFG and ask for a tech person. They will be glad to give you advice on tire pressure. I have done it many times.
I think the number is 800-race-bfg. Anybody else help with the number.
Dave
Tech Contributor
Joined: Oct 1999
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From: Charlotte, NC (formerly Endicott, NY)
Re: Lower front psi = less understeer. (corvette dave)
That is the correct phone number. I don't run into very many people racing C2s or C3s anymore. The ones that I know who autocross do run some pretty low pressures. I have seen them run as low as 25 lbs pressure with aftermarket wheels and Hoosier Autocrosser tires.
Bill
[Modified by Bill Dearborn, 12:37 AM 1/9/2002]
Bill
[Modified by Bill Dearborn, 12:37 AM 1/9/2002]
Instructor
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From: Mt Juliet TN
Re: Lower front psi = less understeer. (lemans396)
Lower pressure gives you more traction in a straight line, but it gives you less traction in a corner. Consider this:
Drag racers, Artic explorers, Rock Crawlers run the lowest possible tire pressure. Why? They want the sidewall of the tire to deform and allow the maximum tire patch in contact with the ground. This gives you great traction for accelerating and braking. The key is the sidewall deformation.
Lower the tire pressure = more sidewall deformation. When there are no lateral loads on the tire both the inside and outside sidewalls deform equally, leaving the maximum contact patch. When you have lateral loads as in cornering the inside and outside sidewalls deform differently which dramatically reduce the contact patch with the ground. Higher pressure = less sidewall deformation and more contact patch under lateral load.
This is why Drag racing slicks with flimsy sidewalls make lousy autocross tires (lots of straight line traction but no ability to turn). In drag racing there is no compromise between straight-line traction and cornering traction, but in road racing (and autocross) there is. Most road race tires have very rigid sidewalls to allow you to run lower pressures than you would with a street tire.
That’s why No Cure and Corvette Dave gave you their advice.
Drag racers, Artic explorers, Rock Crawlers run the lowest possible tire pressure. Why? They want the sidewall of the tire to deform and allow the maximum tire patch in contact with the ground. This gives you great traction for accelerating and braking. The key is the sidewall deformation.
Lower the tire pressure = more sidewall deformation. When there are no lateral loads on the tire both the inside and outside sidewalls deform equally, leaving the maximum contact patch. When you have lateral loads as in cornering the inside and outside sidewalls deform differently which dramatically reduce the contact patch with the ground. Higher pressure = less sidewall deformation and more contact patch under lateral load.
This is why Drag racing slicks with flimsy sidewalls make lousy autocross tires (lots of straight line traction but no ability to turn). In drag racing there is no compromise between straight-line traction and cornering traction, but in road racing (and autocross) there is. Most road race tires have very rigid sidewalls to allow you to run lower pressures than you would with a street tire.
That’s why No Cure and Corvette Dave gave you their advice.
Safety Car
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From: Ohio
Re: Lower front psi = less understeer. (lemans396)
You did a nice job on your choice of lowering, bushing replacement, and shocks. Air pressures look good. You will pick up ~4 psi after a few laps. Here are a couple of things you may want to consider. Most of your push is due to the alignment. (I don't recall the tire sizes you're running, I'll assume 275's square.) You need to get the front - rear camber in sync. By that I would dial in more front negative camber. One degree neg in front, leave the rear alone at -3/4*. If I read you correctly, you have a 1/16" toe in, square. That's good for the rear, but in front, will hurt your turn in. Set the front at zero toe.
These settings should make the car handle much more neutral, and the car will inspire confidence
These settings should make the car handle much more neutral, and the car will inspire confidence
Thread Starter
Instructor
Joined: May 2000
Posts: 246
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From: NYC NY
Re: Lower front psi = less understeer. (h rocks)
H rocks, you are correct, 275's all around. toe is set at 0 front, 1/16" toe in rear per side. I guess that leaves the front camber settings. Increase it from.40 neg . to one full degree neg.
Thanks Simon K.
Thanks Simon K.
Race Director
Joined: Aug 1999
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From: WI
Re: Lower front psi = less understeer. (lemans396)
lemans,
The following reduces a "understeer/push" condition.
INCREASE front tire pressure
increase neg camber/pos caster
heavier front springs
larger rear sway bar
decrease front sway bar
I also find it hard to believe that you (or me for that matter) is a good enough driver to really feel a difference in a pound or two. Tire pressure is used to "fine tune" your set-up. .....redvetracr
The following reduces a "understeer/push" condition.
INCREASE front tire pressure
increase neg camber/pos caster
heavier front springs
larger rear sway bar
decrease front sway bar
I also find it hard to believe that you (or me for that matter) is a good enough driver to really feel a difference in a pound or two. Tire pressure is used to "fine tune" your set-up. .....redvetracr
Le Mans Master
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From: delmont pa
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Re: Lower front psi = less understeer. (lemans396)
a lighter front sway bar will cut down on understeer. for autocrossing i disconnect the front bar when it was a very tight course. test this before you race because you will not believe how fast the car will turn into the corner. :chevy
Safety Car
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From: Ohio
Re: Lower front psi = less understeer. (clem zahrobsky)
Clem, when I used to A-X my B4C '91 Camaro, I used to back off the nuts on the end links ~ 1/4" (just enough to "unsquish" the bushings) of the front swaybar. The net result was that turn in was "now". Especially considering that about all the negative camber we could get out of a stock F-body front end was .9*. (if you were lucky after playing all the legal tricks that you could) It was pretty abrupt, but once you got used to it, it was a major component to a fast setup.
[Modified by h rocks, 8:34 PM 1/13/2002]
[Modified by h rocks, 8:34 PM 1/13/2002]
Le Mans Master
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From: delmont pa
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Re: Lower front psi = less understeer. (h rocks)
you are right, the first time i tried that back in the mid 60s with my stingrays i almost ended up in the passengers seat on the first left hand turn even with a seat belt on.!!!!! this really worked on my front heavy 65 396 and 66 427 vettes. if you are running a very fast course like a road course i would not try this mod. :chevy