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914World.com _ 914World Garage _ Help Fine tuning suspension
Posted by: harlenl Sep 26 2008, 11:28 AM
I searched the topic in this forum and I apologize if I missed it, but I need guidance on suspension tuning. The car is a '73 914 2.0 driven on the street only, narrow body, with a recent conversion to 5-lug. My problem is the car tends to understeer then oversteer through corners (tight to loose for you NASCAR guys). It's a real white knuckle ride. Shocks up front are Koni yellows set at full soft, rears are Bilsteins. Torsion and sway bars (frt & rr) are stock. Springs are 100lbs and I'm running new Dunlop Direzza Sports all around.
I'm thinking that I need more bite in the front, but I'm already at full soft so my only choice is to firm up the rear which means I have two options: Koni yellows and/or 140lb springs in the rear? I like the softer ride of the Bilsteins, but confidence in a corner is more important.
Other consideration would be sway bars or torsion bars, but have no idea which would be best. So the questions are:
1) Is my handling analysis correct?
2) Solutions to the problem correct?
3) Consider using 165lb progressive springs?
Thanks for your help.
Harlen
Posted by: jhadler Sep 26 2008, 12:07 PM
One word: Alignment.
First thing is to check the existing alignment. You've got a moderately good package on the car, spring rates and bars, that is.
Get the alignment checked...
-Josh2
Posted by: jmill Sep 26 2008, 12:15 PM
Whats happening in the transition between over to underseer? Are you on the throttle, brake, coasting, etc..? Do you set the car before you enter a turn? I would need those answers to help you out.
From the limited info you gave I'd guess that your car actually has a understeer problem. Your actions when that happens induces the oversteer. Stiffening the rear and softening the front will help cure understeer. Vice versa for oversteer. With some more info I could be sure.
Posted by: blitZ Sep 26 2008, 12:23 PM
Try disconnecting the rear sway bar and go for a test ride. It's a typical source for oversteer issues.
Posted by: Bruce Hinds Sep 26 2008, 12:30 PM
I agree with checking the alignment, but more specifically, rear alignment. Make sure someone that knows what they are doing does it.
Bruce
Posted by: Dr. Roger Sep 26 2008, 12:49 PM
alignment, alignment, alignment, alignment, alignment.
Posted by: SirAndy Sep 26 2008, 12:56 PM
I agree with checking the alignment, but more specifically, rear alignment. Make sure someone that knows what they are doing does it.
Get the car aligned and corner balanced, then fine-tune the suspension.
Having an adjustable front sway bar and adjustable rear spring perches is a must, otherwise you're taking the word "fine" out of "fine-tuning" ...
AndyPosted by: jmill Sep 26 2008, 01:18 PM
I assumed you had your car aligned after the conversion. If you went with re-drilled rotors and hubs you might not have. Without out a good alignment fine tuning wont help.
If your car is aligned and it goes from under to oversteer it's usually driver induced. The front starts plowing and a driver responds by hitting the brakes because a wall is coming up. Weight is then transfered to the front. The front grabs and the rear gets light inducing oversteer.
A car that understeers or failing to set the car before the turn can lead to the above scenario.
Posted by: SGB Sep 26 2008, 03:55 PM
Tire pressure? I keep front pressure pretty high to reduce understeer altogether. As I transistion through the corner, I feel neutral going to oversteer.
What tire pressure are you running? Bump the front a little and see how that feels.
Posted by: sgetsiv Sep 28 2008, 10:32 PM
I finally have my car running well enough to start pushing it through corners. I had some issues today when the front end started to slide out (oversteer) hitting a corner at about 45mph going uphill. It was not a comforable feeling, that's for sure.
Compared to my Audi S4 which I have had on the track and autocrossed, the 914 feels way too soft in the front when it is pushed hard. It feels like it is floating once it breaks loose. I did not get on the brake either, I just turned out a touch.
Front: Koni Sport Shock Damper - Front: koni-8641-1077 Sport; these are adjustable but I don't know where they are set. I'll try some stiffer settings first to get a feel for handling.
It has the adjustable perch Koni's in the rear; Koni Sport Shock Damper - Rear: koni-8241-1050 Sport, not sure which springs.
Tire pressure is set in the high 30's. Stock suspension otherwise. 195/60-15 tires.
Not sure if this is helpful, but I can post results of adjustments. Any suggestions?
Posted by: SirAndy Sep 28 2008, 11:01 PM
the front end started to slide out (oversteer) hitting a corner at about 45mph going uphill.
That's understeer ... Oversteer is when the rear end is lose ...
Ride height set? Swaybars? Aligned? Corner balanced? Rear springs sagging?
Btw. if you make the front shocks stiffer, your problem will get worse ...
Andy
Posted by: sgetsiv Sep 29 2008, 12:19 AM
Yes, understeer. Sorry. But it was the dive into the corner that surprised me, which is why I was thinking stiffer in front would help. Maybe a front sway bar?
Ride height is set about 1/2" lower in front than in rear, and it is dropped pretty low overall.
I did the alignment myself. Front has approx 1/16" toe in, max caster, and very slight negative camber.
No corner balance done.
Posted by: harlenl Oct 1 2008, 02:51 PM
Thanks for the reply everyone and I apologize for the delayed reply. I replaced the front from a '72 911 with Koni yellows, new bushings, etc. Then it was aligned both front and rear. Not much you can do in the rear. The rears have new hubs from Eric Shea and new bushings, etc were also installed. Four fuchs were installed with brand new Dunlop Direzza Sports (205/50-16).
During a turn, the front pushes a little and then the back wants to step out. I have the fronts on full soft, but the Bilsteins on the rear obviously are not adjustable. The only adjustment is the ride height as the Bilstein has grooves on the body in which the spring perches can be adjusted by about 1/2 an inch. The springs are 100lbs from Weltmeister, but are about 20 years old. Shocks about the same. I only drive the car during the summer so it's not like they've taken a beating.
Since the front sway bar is stock, they're not adjustable. I will try putting on 140lb springs, then remove the rear sway bar. Of course I'll test each case separately. If this is all I need then I'm getting off cheap.
Thanks
Harlen
Posted by: messix Oct 1 2008, 03:27 PM
Yes, understeer. Sorry. But it was the dive into the corner that surprised me, which is why I was thinking stiffer in front would help. Maybe a front sway bar?
Ride height is set about 1/2" lower in front than in rear, and it is dropped pretty low overall.
I did the alignment myself. Front has approx 1/16" toe in, max caster, and very slight negative camber.
No corner balance done.
max caster is gonna be a problem.
Posted by: jhadler Oct 1 2008, 04:08 PM
max caster is gonna be a problem.
I disagree...
Caster is your friend. You should get as much as you can, as often as you can (well, within reason of course). Caster is dynamic camber, the more you turn the wheel, the more negative camber you get.
Typically, a 914 can get around 6-7 degrees of caster, and that is good. Better to give up a little static camber in exchange for caster.
-Josh2
Posted by: messix Oct 1 2008, 04:38 PM
max caster is gonna be a problem.
I disagree...
Caster is your friend. You should get as much as you can, as often as you can (well, within reason of course). Caster is dynamic camber, the more you turn the wheel, the more negative camber you get.
Typically, a 914 can get around 6-7 degrees of caster, and that is good. Better to give up a little static camber in exchange for caster.
-Josh2
ok
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