Handling issues - need adjustment advice Options

[Brian Fuerbach]

When driving large sweepers like freeway on ramps at high speed I experience what I can only describe as front end scrubbing. Not understeer, more like the front is just not planted and tracking. Things get better with a full tank of fuel. Is that just the nature of the 914, full tank factored into weight bias, or can the suspension be tuned to emulate the weight.

Here is what Im working with;
-19mm adjustable sway-bar set about 1” back from full soft.
-Koni yellow adjustable shocks
-Stock front torsions
-Rear springs are aftermarket (reddish orange color) but I do not know the poundage.

Any input would be appreciated.

[brant]

Does the rear come around or just a front push?
Any rear sway?

You did not mention a 4 wheel alignment after the components were installed?

You can usually dial push out. No matter the fuel level

Anything else??? Limited slip?

[Root_Werks]

Somethings not right, a 914 shouldn't push or plow the front end like a Bug or early 911.

Could be the front is over sprung along with very off toe setting?

Drove a 996 months back the rear toe was in hard. Darn thing started hunting for grip at 30mph.

[Van B]

Are your top mounts good? If so, increase front damping and see what changes.

If you’re getting a boat sort of feeling from the front, but no actual under steer, that’s generally a sign of being over sprung or under damped.

Van

[Freezin 914]

Is there ride height difference between front and rear? I notice a lot of these cars ride a bit high in the front compared to the rear. Are the front torsion bars adjusted to high? If you can get the front down a couple mm, should make the car more “darty”. Had this affect with my last driver.

[Superhawk996]

When driving large sweepers like freeway on ramps at high speed I experience what I can only describe as front end scrubbing. Not understeer, more like the front is just not planted and tracking.

(IMG:style_emoticons/default/confused24.gif) What you've described is the very essence of understeer.

19mm is a lot of front bar that can lead to understeer. Especially so without a lot of rear spring or rear bar behind it to balance it.

(IMG:style_emoticons/default/popcorn[1].gif)

[914_teener]

When driving large sweepers like freeway on ramps at high speed I experience what I can only describe as front end scrubbing. Not understeer, more like the front is just not planted and tracking.

(IMG:style_emoticons/default/confused24.gif) What you've described is the very essence of understeer.

19mm is a lot of front bar that can lead to understeer. Especially so without a lot of rear spring or rear bar behind it to balance it.

(IMG:style_emoticons/default/popcorn[1].gif)

(IMG:style_emoticons/default/agree.gif)

Stock bar is more than enough. Think also it is alignment and oversprung on the front end.

[Superhawk996]

Stock bar is more than enough. Think also it is alignment and oversprung on the front end.

I'm with you that there could be some alignment issue embedded in this but he's on stock torsion bars so not oversprung with big 21mm torsion bars or something like that.

These things are always hard to sort out based on words since handling is so subjective. Once man's balanced neutral handling is another's oversteeer or understeer.

The fact that it varies with fuel load is very typical of 914 handling with the inherent understeer improved at full tank or lugage loading. It could also be a symtom of what Freezin referenced, front end sitting too high and the fuel load brings the geometry back toward what it ought to be.

Keep in mind 914 track width is asymetric (narrower in front) with a design intent toward keeping a stock car biased toward understeer which is the "safe" design parameter. Further staggering tire widths toward wider rear & narrow front can further push this bias deeper into understeer. Not saying that is the case here since there was no mention of tire sizes (I'm assuming same widths front & rear at this point).

[Brian Fuerbach]

Does the rear come around or just a front push?
Any rear sway?

You did not mention a 4 wheel alignment after the components were installed?

You can usually dial push out. No matter the fuel level

Anything else??? Limited slip?

Rear is planted and never feels loose. Front just feels like it is not biting the corner. After I installed the swaybar it did make the car much better all around.

Front had been aligned by previous po but I have no paperwork. An alignment at a shop that know what they are doing will be next.

No limited slip

[brant]

Take a picture of the front sway adjustment

ie: how tight is the drop link on the bar end?
Can you loosen the front sway links to lessen the spring rate of the sway

I always disconnect both of my sway bars before alignment

[Brian Fuerbach]

Are your top mounts good? If so, increase front damping and see what changes.

If you’re getting a boat sort of feeling from the front, but no actual under steer, that’s generally a sign of being over sprung or under damped.

Van

Top mounts have been replaced. I will try turning up the damping on the fronts. I have turned up the rear damping and found that it initiated corners much better. I have the fronts set at 1/2 turn and rears at 1.5 turns from full soft.

[Brian Fuerbach]

Is there ride height difference between front and rear? I notice a lot of these cars ride a bit high in the front compared to the rear. Are the front torsion bars adjusted to high? If you can get the front down a couple mm, should make the car more “darty”. Had this affect with my last driver.

The car is pretty much level.

[Brian Fuerbach]

When driving large sweepers like freeway on ramps at high speed I experience what I can only describe as front end scrubbing. Not understeer, more like the front is just not planted and tracking.

(IMG:style_emoticons/default/confused24.gif) What you've described is the very essence of understeer.

19mm is a lot of front bar that can lead to understeer. Especially so without a lot of rear spring or rear bar behind it to balance it.

(IMG:style_emoticons/default/popcorn[1].gif)

I guess it is possible that if I pushed it harder it could turn into noticeable oversteer but it just does not feel like understeer that I have experienced before.
Need find out what springs are in the rear now. Can you tell by diameter?

I used to drive this on the street, talk about oversteer. (IMG:style_emoticons/default/evilgrin.gif) (correction: "Understeer")

[Brian Fuerbach]

When driving large sweepers like freeway on ramps at high speed I experience what I can only describe as front end scrubbing. Not understeer, more like the front is just not planted and tracking.

(IMG:style_emoticons/default/confused24.gif) What you've described is the very essence of understeer.

19mm is a lot of front bar that can lead to understeer. Especially so without a lot of rear spring or rear bar behind it to balance it.

(IMG:style_emoticons/default/popcorn[1].gif)

(IMG:style_emoticons/default/agree.gif)

Stock bar is more than enough. Think also it is alignment and oversprung on the front end.

Can larger rear springs be installed to balance?

[Brian Fuerbach]

Stock bar is more than enough. Think also it is alignment and oversprung on the front end.

I'm with you that there could be some alignment issue embedded in this but he's on stock torsion bars so not oversprung with big 21mm torsion bars or something like that.

These things are always hard to sort out based on words since handling is so subjective. Once man's balanced neutral handling is another's oversteeer or understeer.

The fact that it varies with fuel load is very typical of 914 handling with the inherent understeer improved at full tank or lugage loading. It could also be a symtom of what Freezin referenced, front end sitting too high and the fuel load brings the geometry back toward what it ought to be.

Keep in mind 914 track width is asymetric (narrower in front) with a design intent toward keeping a stock car biased toward understeer which is the "safe" design parameter. Further staggering tire widths toward wider rear & narrow front can further push this bias deeper into understeer. Not saying that is the case here since there was no mention of tire sizes (I'm assuming same widths front & rear at this point).

Stock 2.0 Fuchs with 195/65r15’s

[Superhawk996]

I used to drive this on the street, talk about oversteer. (IMG:style_emoticons/default/evilgrin.gif)

Please don't take this the wrong way. I'm trying to help. Honestly. I've done chassis tuning as my day job for a decent part of my professional career as a chassis engineer.

That buggy by definition will have steady state understeer. Beam front axle without camber gain, wide rear tires, narrow font tires, lack of weight on the front tires.

I don't think we aren't talking the same terms.

I do agree the buggy could have massive lift throttle oversteer at initial turn-in due to the inherent rear weight bias. Likewise, it could develop on-throttle oversteer with enough horsepower. Both of those are transient conditions.

As I understood your original post, we are talking steady state condition, after you've entered the corner, steady state throttle, and the front end isn't tracking. You're putting in more and more steering input to the point that you feel the tires are scrubbing but yet it's not turning or following your steering input.

Do I understand correctly?

[Brian Fuerbach]

I used to drive this on the street, talk about oversteer. (IMG:style_emoticons/default/evilgrin.gif)

Please don't take this the wrong way. I'm trying to help. Honestly. I've done chassis tuning as my day job for a decent part of my professional career as a chassis engineer.

That buggy by definition will have steady state understeer. Beam front axle without camber gain, wide rear tires, narrow font tires, lack of weight on the front tires.

I don't think we aren't talking the same terms.

I do agree the buggy could have massive lift throttle oversteer at initial turn-in due to the inherent rear weight bias. Likewise, it could develop on-throttle oversteer with enough horsepower. Both of those are transient conditions.

As I understood your original post, we are talking steady state condition, after you've entered the corner, steady state throttle, and the front end isn't tracking. You're putting in more and more steering input to the point that you feel the tires are scrubbing but yet it's not turning or following your steering input.

Do I understand correctly?

No worries, your not going to hurt my feelings and I appreciate your tuning knowledge. You are totally correct, I meant to write "understeer" and we are talking the same terms. Your assessment of the power on power off are spot on. The car was almost not drivable in the twisties until a sway bar was added.

Now back to a car I still drive. In my original post I described it like a scrubbing but not over steer as I dont feel the front is going to wash. I drove the car today on my 60 mile commute which has opportunities to create the condition on four onramps and interchanges. I filled the tank completely and the extra weight up front made the front feel more planted like it should. I have to note that the scrubbing seems to come with some roughness that when weighted with extra fuel seems to lessen. More damping needed?

I have been working with the adjustments that I have to improve this. The two things that made the most improvement was adding the swaybar and then tightening the rear shock rebound.

[roblav1]

Soften the end that's not working. FARB is probably too stiff. Probably too much front toe-in too.

[yeahmag]

I'm in Pasadena and do some suspension tuning on the side if you want to drop by and show me what it's doing.

[Superhawk996]

Soften the end that's not working. FARB is probably too stiff. Probably too much front toe-in too.

(IMG:style_emoticons/default/agree.gif)

I think you've got to much stiffness on the front between the dampers and the Anti-roll Bar (ARB).

As Brant suggested. Move the ARB links toward the absolute end of the adjustable bar. I.e. increase the length of the arm - decreasing stiffness of the front ARB.

As Roblav1 suggested. Dial out dampers (softer). Adjustable dampers are only adjusting rebound damping. Lots of front rebound damping ends up fighting the ARB on the inside wheel. In additon, the net effect of too much front damping only further stiffens the front end in addition to the what the ARB has already added.

What we're working on here is to soften the front end relative to the rear.

My impression is that you like the extra body roll control that the front ARB added but that it's been over done with the 19mm front bar. I don't think you have mentioned yet if there is a rear bar. The OEM set up added a bar on both front (15mm) and rear (16mm). The dual bars provides a more balanced split of body roll control. If you don't have a rear bar, you're trying to do all roll control off the front end which stiffens the front end, inducing steady state understeer.

When you added some damping to the rear, you stiffened it - which has the same net effect as softening the front end relative to the rear. Hope this makes sense the way I've written it.

All tuning is done on a relative basis. You can soften the front or stiffen the rear for the same net effect. Sometimes you will have to do both to achive a desired result. But for right now, no need to get into additional rear spring or damper changes. Just work on one end of the car at a time with the overall direction of softening the front relative to the rear. Ideally, you work on the end you want to affect. I.e. if you want to soften the front; do the work in the front. When you run out of front "knobs" to turn then you can start stiffening the rear further.

I'm in Pasadena and do some suspension tuning on the side if you want to drop by and show me what it's doing.

Take Yeahmag up on this. It is always way easier to tune when you can see and feel what is happening vs. trying to do it by words on a forum like this.