C4, Correcting understeer. More Camber or softer front sway bar?
10-15-2008, 03:54 PM
#1
Le Mans Master
Thread Starter
Member Since: Feb 1999
Location: Hawaii
Posts: 8,522
Likes: 0
Received 3 Likes
on
3 Posts
St. Jude Donor '03 & '05
UPDATE: C4, Correcting understeer. More Camber or softer front sway bar?
Out of the two options in Title, what will correct the understeer push more (autocross, not road racing), Camber or a softer front sway bar?
Mine is a 30S front, 26S rear, and ZO7 springs with -2.2 front camber, -1.7 rear camber.
I cant find a 30mm bar for cheap, and I am not going to spend a ton of money to overcome push/understeer. I have a "trick" suggested to me to soften up the front bar, or I can take a couple shims out for more negative camber as I have OFFSET lower bushings.
This is a 93 Vette, lowered 2 inches, poly bushings, DRM brackets etc etc.
Mine is a 30S front, 26S rear, and ZO7 springs with -2.2 front camber, -1.7 rear camber.
I cant find a 30mm bar for cheap, and I am not going to spend a ton of money to overcome push/understeer. I have a "trick" suggested to me to soften up the front bar, or I can take a couple shims out for more negative camber as I have OFFSET lower bushings.
This is a 93 Vette, lowered 2 inches, poly bushings, DRM brackets etc etc.
Last edited by steve40th; 11-10-2008 at 04:04 PM.
10-15-2008, 04:17 PM
#4
Melting Slicks
You have a good bit of static front negative camber. More will likely help some, but for all intents and purposes you are there in that regard.
Note too that with a later 17 inch wheel car the kingpin angle is high and that results in a big loss of negative camber in slow corners where you have large steering angles. If your push is lower speed corners that is more likely the cause of your push. You area losing camber when you crank the wheel a lot. You need to add caster to address that. You need at least 7 degrees of caster and more if you can get it. I am assuming that if you have -2.2 degrees of negative camber you have offset bushings in the lower arms or something like that to get that much camber. You also might try giving up a little bit of negative camber for some caster. If you could get 8 or 9 degrees of caster and have around -2 of camber you might find that works better.
If you haven't already, take out the poly front bar bushings for sure. The front bars is really stiff, and it responds more to stiffer bushings than the rear bar. If the push is in higher speed corners that will take care of it..
Note too that with a later 17 inch wheel car the kingpin angle is high and that results in a big loss of negative camber in slow corners where you have large steering angles. If your push is lower speed corners that is more likely the cause of your push. You area losing camber when you crank the wheel a lot. You need to add caster to address that. You need at least 7 degrees of caster and more if you can get it. I am assuming that if you have -2.2 degrees of negative camber you have offset bushings in the lower arms or something like that to get that much camber. You also might try giving up a little bit of negative camber for some caster. If you could get 8 or 9 degrees of caster and have around -2 of camber you might find that works better.
If you haven't already, take out the poly front bar bushings for sure. The front bars is really stiff, and it responds more to stiffer bushings than the rear bar. If the push is in higher speed corners that will take care of it..
Last edited by Solofast; 10-15-2008 at 04:20 PM.
10-15-2008, 04:22 PM
#5
Melting Slicks
you need to post your tire sizes before anyone can seriously help you.
generally, bigger tires up front.
smaller tires in the rear.
or since your autocrossing, your probably going too heavy into the corners, and your car may be OK.
generally, bigger tires up front.
smaller tires in the rear.
or since your autocrossing, your probably going too heavy into the corners, and your car may be OK.
10-15-2008, 04:24 PM
#6
Melting Slicks
Note too that larger caster angles actually act like a softer bar at higher steering angles. That is, the caster effect pushes the inside tire down and lifts the outside tire when the wheel is cranked a lot. That does the same thing as softening the front bar (it reduces push) but you still get the stability effect of the higher front roll stiffness in faster corners and offsets, so the car doesn't get as tail happy as it would if you just reduced the front roll stiffness...
10-15-2008, 05:28 PM
#7
Team Owner
Member Since: Mar 2001
Location: Boston, Dallas, Detroit, SoCal, back to Boston MA
Posts: 30,596
Received 238 Likes
on
166 Posts
32 front bar at an autox???
I think that's your problem, well one of them, C4's understeer to begin with.
Put as much camber on the front as you can.
I think that's your problem, well one of them, C4's understeer to begin with.
Put as much camber on the front as you can.
10-15-2008, 06:03 PM
#9
Melting Slicks
I wasn't thinking about that, the Z07 front bar was a 30mm and with that they used the 24mm rear bar....
He has the 26mm rear bar and if he uses that with a 30mm front bar the car will have serious oversteer, and, it could jack in the back end too, so if he goes to a smaller front bar he will have to downsize the rear bar at the same time.
First, get some more caster in the car and then fine tune it with the front bar bushing stiffness....
If it isn't pushing like a pig right now, you have plenty of adjustment with the front bar bushing stiffness...
He has the 26mm rear bar and if he uses that with a 30mm front bar the car will have serious oversteer, and, it could jack in the back end too, so if he goes to a smaller front bar he will have to downsize the rear bar at the same time.
First, get some more caster in the car and then fine tune it with the front bar bushing stiffness....
If it isn't pushing like a pig right now, you have plenty of adjustment with the front bar bushing stiffness...
10-15-2008, 06:11 PM
#11
Le Mans Master
Thread Starter
Member Since: Feb 1999
Location: Hawaii
Posts: 8,522
Likes: 0
Received 3 Likes
on
3 Posts
St. Jude Donor '03 & '05
You have a good bit of static front negative camber. More will likely help some, but for all intents and purposes you are there in that regard.
Note too that with a later 17 inch wheel car the kingpin angle is high and that results in a big loss of negative camber in slow corners where you have large steering angles. If your push is lower speed corners that is more likely the cause of your push. You area losing camber when you crank the wheel a lot. You need to add caster to address that. You need at least 7 degrees of caster and more if you can get it. I am assuming that if you have -2.2 degrees of negative camber you have offset bushings in the lower arms or something like that to get that much camber. You also might try giving up a little bit of negative camber for some caster. If you could get 8 or 9 degrees of caster and have around -2 of camber you might find that works better.
If you haven't already, take out the poly front bar bushings for sure. The front bars is really stiff, and it responds more to stiffer bushings than the rear bar. If the push is in higher speed corners that will take care of it..
Note too that with a later 17 inch wheel car the kingpin angle is high and that results in a big loss of negative camber in slow corners where you have large steering angles. If your push is lower speed corners that is more likely the cause of your push. You area losing camber when you crank the wheel a lot. You need to add caster to address that. You need at least 7 degrees of caster and more if you can get it. I am assuming that if you have -2.2 degrees of negative camber you have offset bushings in the lower arms or something like that to get that much camber. You also might try giving up a little bit of negative camber for some caster. If you could get 8 or 9 degrees of caster and have around -2 of camber you might find that works better.
If you haven't already, take out the poly front bar bushings for sure. The front bars is really stiff, and it responds more to stiffer bushings than the rear bar. If the push is in higher speed corners that will take care of it..
10-15-2008, 06:14 PM
#13
Le Mans Master
Thread Starter
Member Since: Feb 1999
Location: Hawaii
Posts: 8,522
Likes: 0
Received 3 Likes
on
3 Posts
St. Jude Donor '03 & '05
I can remove one thick shim right now total. That may help. But, what about the difference between front and rear. I am under the impression not to go more than .5 difference, or is that more road racing? I have QA1 shocks too.
10-15-2008, 06:16 PM
#14
Le Mans Master
Thread Starter
Member Since: Feb 1999
Location: Hawaii
Posts: 8,522
Likes: 0
Received 3 Likes
on
3 Posts
St. Jude Donor '03 & '05
I wasn't thinking about that, the Z07 front bar was a 30mm and with that they used the 24mm rear bar....
He has the 26mm rear bar and if he uses that with a 30mm front bar the car will have serious oversteer, and, it could jack in the back end too, so if he goes to a smaller front bar he will have to downsize the rear bar at the same time.
First, get some more caster in the car and then fine tune it with the front bar bushing stiffness....
If it isn't pushing like a pig right now, you have plenty of adjustment with the front bar bushing stiffness...
He has the 26mm rear bar and if he uses that with a 30mm front bar the car will have serious oversteer, and, it could jack in the back end too, so if he goes to a smaller front bar he will have to downsize the rear bar at the same time.
First, get some more caster in the car and then fine tune it with the front bar bushing stiffness....
If it isn't pushing like a pig right now, you have plenty of adjustment with the front bar bushing stiffness...
10-15-2008, 06:17 PM
#15
Melting Slicks
for autox you dont need toe in at the rear, i'd 0 that out (or maybe even a tad out. I'd also jack up the front toe out until the car feels better. 1/16 out is nothing. I run about 1/10 out in front on my road race car.
If i recall correctly some autoxers run nearly .25 out infront.
If i recall correctly some autoxers run nearly .25 out infront.
10-15-2008, 06:21 PM
#16
Le Mans Master
Thread Starter
Member Since: Feb 1999
Location: Hawaii
Posts: 8,522
Likes: 0
Received 3 Likes
on
3 Posts
St. Jude Donor '03 & '05
for autox you dont need toe in at the rear, i'd 0 that out (or maybe even a tad out. I'd also jack up the front toe out until the car feels better. 1/16 out is nothing. I run about 1/10 out in front on my road race car.
If i recall correctly some autoxers run nearly .25 out infront.
If i recall correctly some autoxers run nearly .25 out infront.
10-15-2008, 08:01 PM
#18
Le Mans Master
The OP specifically said "Of the two options in title"
Still, I'll offer a third - increase the rear spring rate.
If the suggestion about using toe-OUT at the rear of an otherwise
stock C4 is tried, my vote is to test where there is some room for
run-off and work up the speeds to see how this feels for you.
.
Still, I'll offer a third - increase the rear spring rate.
If the suggestion about using toe-OUT at the rear of an otherwise
stock C4 is tried, my vote is to test where there is some room for
run-off and work up the speeds to see how this feels for you.
.
10-15-2008, 08:07 PM
#19
Racer
Member Since: Jul 2006
Location: Wisconsin
Posts: 492
Likes: 0
Received 0 Likes
on
0 Posts
There are 2 things you can do to remove the push: add traction in the front or remove traction in the rear. There are many different things you can try to help that out.
The large difference in tire sizes doesn't help any, our car pushed with 335 in the rear and 315 in the front, 275's are too small. What kind of tires and what kind of pressure?
a 32 bar especially doesn't help when the tires are that small, a smaller bar would be a good route to take.
I'm not sure how much more bite you'll get out of the front, you may have better luck with a larger rear bar.
The large difference in tire sizes doesn't help any, our car pushed with 335 in the rear and 315 in the front, 275's are too small. What kind of tires and what kind of pressure?
a 32 bar especially doesn't help when the tires are that small, a smaller bar would be a good route to take.
I'm not sure how much more bite you'll get out of the front, you may have better luck with a larger rear bar.
10-15-2008, 08:12 PM
#20
Le Mans Master
Thread Starter
Member Since: Feb 1999
Location: Hawaii
Posts: 8,522
Likes: 0
Received 3 Likes
on
3 Posts
St. Jude Donor '03 & '05
There are 2 things you can do to remove the push: add traction in the front or remove traction in the rear. There are many different things you can try to help that out.
The large difference in tire sizes doesn't help any, our car pushed with 335 in the rear and 315 in the front, 275's are too small. What kind of tires and what kind of pressure?
a 32 bar especially doesn't help when the tires are that small, a smaller bar would be a good route to take.
I'm not sure how much more bite you'll get out of the front, you may have better luck with a larger rear bar.
The large difference in tire sizes doesn't help any, our car pushed with 335 in the rear and 315 in the front, 275's are too small. What kind of tires and what kind of pressure?
a 32 bar especially doesn't help when the tires are that small, a smaller bar would be a good route to take.
I'm not sure how much more bite you'll get out of the front, you may have better luck with a larger rear bar.