Front-end push
 

After an at-home lowering (24 3/4" front, 24 1/2" rear) and corner balance, then off to an alignment shop (twice). I am still having problems with a front-end push.

My corner balance was within 15 lbs of (L&R to front and rear) each other. Without driver weight.

IIRC - the front end is
1/16" toe-in
negative 0.9 and negative 1.1 (Left and Right)
Caster at ~ 6. (I forget both sides right now).

This was done on a laser (somename) 4000 alignment machine.

The rear camber is negative 1.3 and 1.5 (L & R)
Toe is 1/16" (or less, I forget this one too).

I have 205/55 Bridgestone RE730s up front (on Fuch 7") with
245/45 RE750s (Fuch 9") in the rear.

I seem to get the squeaky tires in a complete U-turn going slowly, as well as the front-end is pushing WELL before the rear-end gets at all loose. I get the front-end tire howlling in long fast sweepers as well.

I replaced the Tie-rods, lubed the rack (that was fun) and adjusted front-bearings with no noticeable difference.


The car seems VERY succeptible to bump steer. Is it TOO low?
I am thinking of having someone else do a corner balance and bring it back to factory heights (25 1/2 front, with a 25" rear).

The tires are wearing evenly albeit they are low on tread in the front.

Before I just thought this was a tire size difference (205 vs 245), but it seems too weird now in slow turns, let alone fast sweepers.

It's as if, the turning amount between left and right tires are incorrect whenever the wheel is turned in either direction.
Could it be a steering rack (alignment) problem?
In other words, could the steering rack be off of it's left and right steering center?

I am at a loss as the laser alignment is mostly appropriate.

I get this same nasty front-end push with my Kuhmos VictorRacers running 225/50s front and rear on 7 & 8 15" Fuchs.

So it must be a problem with the alignment or something is not right with the front end. :(

I have checked the rear swaybar brakets and mounts, all appears to be in tact.

TIA

Nick

What torsions and sways are you running?

Stock Torsion and sway bars. I have replaced the rear bushings.

I was going to do the fronts, but I don't have a lathe. :(

Coupla things:
1.) all 911'a will have some low speed push , especially if you get on the gas too soon/ too hard. Is this 911 different in this respect to other 911's ?
2.) 7 front and 9 rear is recipe for understeer, especially with 205 fr / 245 rear. 7" front can go 225 to help...or rear can be 8" to help. Personally , I run 7 front / 7 rear on my 85 with stock 19 fr/ 24.1 rear TB's. I find better "balance" to be more important ( to me) than optimizing grip at one end of the car.
3.) Rack may no longer be on-center. How many turns lock-to-lock?...how many turns left-to-stop....how many turns right-to-stop? Are left/right equal amount of turns?
4.) sloppy, worn front bushings don't help.

Wil

Thanks for the reply.

1) This seems to be more than a low-end push. I would not expect this to exist in long fast sweepers (at constant speed). As I recall, it is different than other 911s. I have been hesitant to drive anothers 911 as agressively I drive mine.

2) I understand the 7 & 9 recipe, so why do I get this with my 225/ 50 F&R on 7 & 8s?

3) Lock to lock = just over 3 turns.
Left from center just over 1 1/2 steering wheel turns
Right from center the same - 1 1/2

4) How can I check the front bushings.

It seems like it is something more than front bushings. :(

Basically, I wonder if it's too low. This has been a problem since I lowered the car. But I thought an alignment (or two) would cure it.

Could it really be front bushings?

Our cars do push very much, in low-speed, open-throttle maneuvers. Very frustrating at times. Autocross is a GREAT place to understand and learn to overcome this understeer, or at least get used to it. There are some things you can do, but some of those things can cause high-speed handling to suffer.

Shouldn't front toe be 0 deg?

generally you want a little toe in on the front unless the car is an autoX car. some front toe in gives the car more high speed stability.

I've done a bit of autocrossing, even the instructors were wondering about my front squealing tires. :(

Front Tire pressure is 29
Rear is at 41 - 42. (they wore in the center faster at 36).

I have tried lowering the front psi by 2 and going up as much as 34 in the front. No noticeable affect on squealing or handling in the front.

If I go up more pressure in the rear (44 - 45), the front seems to be better. :confused:

The front-end push is worse with a full tank of gas.

First of all, you don't necessarily need a lathe to install front a-arm bushings. It helps if you are super particular. You could just buy Elephant's polybronze in that case. Or, you can play around until you get the best fit mixing parts. Install the grease zerks.

Do you have a bump steer kit? Although I don't think they are good for more than an inch of lowering, if that, they do help somewhat. I get that from my 914 which had a 911 front end in it. That doesn't matter much either; for all practical purposes, they are the same.

Last, what tire pressures do you run? After you dial in the alignment and experiment with the tire pressures, you might try messing with sway bars. You can change one or the other for not that much money.

I'm not a 911 handling guru. I know you can get some of that understeer out w/o breaking the bank and by driving a little differently.

Wait on this thread to develop. It will all come out. What do the rest of you guys think about a heavier sway bar on the rear?

EDIT: Sorry, I didn't see your tire pressures. I probably was taking my time typing this. :D They sure look out of whack. You must be trying too hard to compensate with the pressues. Cancel that thought.

Nick--
Have you tried a different set of tires? Reason I ask is tha IIRC, one of the knocks on the 730's I heard from the Tire Rack guys was that the 730's begin to 'howl' when they were worn. I ended up passing on the 730's and buying Kumho Ecsta 712s, though admittedly I don't drive mine that agressively.

Also, I run 32/36, which seems to help eliminate the push I used to feel in my front end on higher speed sweepers.

just my less than .02

You're running 205's and 245's with toe IN on the front, of course you have understeer.

I actually run about 1/32-1/16th toe OUT on my racecar. Turn in is great with the compromise being dodgier steering at high speeds and under braking.

Not only that, but the rule of tumb is that you increase pressure to the tire that's getting the least traction. You've got the opposite.

This has me wondering about the tire setup I've been contemplating: 225/40-18 on 8.5" wheels in front and 295/30-18 on 11" wheels in back. I've got 22mm adjustable sway bars front and rear and I figure I'd have to change to a 19mm bar in front. I don't know what torsion bars I have since the PO didn't have it in his records.

Thanks for everyone's reply.

Zeke -
the bushings would not go. I had a hard enough time with the rear-end. With it on jackstands in my garage, I was not willing to push and pull on the car with me under it. :D

I have the bump-steer kit (thick washers).

I have tried the Weltmeister 22MM adjustable in the rear. Set on full anti-sway (closest to the perpindicular), with the thought that closer to the bar (as opposed to being fruther on the outside of the lever) it would be harder for the sway bar to be leveraged.

Barely noticable against my stock rear sway bar.


Steve -
I thought it may be the RE730s in the front. As my RE730s in the rear MOANED when they were low. They MOANED SO LOUDLY I thought I lost a rear-bearing or two.

I have a set of Kuhmo VictorRacers 225/50 front and rear on anothe set of 7 & 8" fuchs. I still get this squirrely feel/noise in the front tires when I am turning. These are really noticeable when making a U-turn, it's like a 4-wheel drive vehicle in the front (if you own a 4WD you know), when these tires are hot.

I tried going up in front pressures up to 4 more than recommendations with nothing really noticeable.


CSTREIT -
I will bring out the toe and try it. It's seems more mechanical problem than tires, because of the slow and higher-speed driving turning issues.
I just didn't think a laser alignment could be that far off.. twice.

I will get the toe more out tomorrow, by turning one of the tie-rods (1/2 turn? 1 turn?) and see? How much should I go for in ONE tie-rod revoution? anyone?

Thanks for the help, any other suggestions?

I wonder if it's not Camber. The car is VERY darty with little bumps and road abnormalities.

Stock torsions are set so that the car has lots of understeer. They're dumbed-down for the masses.

If you want to keep it streetable, I like 26mm in the rear with stock in front. And shock valving has a huge effect on transitional handling.

Is the understeer on initial turn-in, or steady-state? Shock valving will help immensely with initial turn-in and corner entry understeer, and torsions/sways can be tuned for steady state, and transitions.

Understeer is on both initial turn-in (not so pronounced though) and steady-state. It is steady-state like on long fast (70 - 80 MPH) sweepers. On these sweepers, I am not accelerating or decellerating, I just hear the annoying front-end howl (eeeerrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr).

If I decel, it's better, accelerate a little worse. I can "wiggle" the steering wheel on the tires will also yell more if I turn MORE into the long sweeper. They yell less, as I turn out of the sweeper. So definately, the front tires.

It's like the TOE is incorrect for the turn, IIRC - this is called the anker-man angle (sp?).

And as such, the toe is incorrect for speed and slow turns.

I don't understand your reply to Zeke. The front bushings come off with the A arms, and then off of those with a knife and a little heat. ABSOLUTElY no machining required on the Elephant polybronze bushings, they are really easy to install. I did it, that's proof enough!

Ed, I understand his reply. The polyurethane bushings can be a beotch. I have assembled the whole shebang on a bench and then bolted it on as a unit. Only way to go.

And, the ratio of the inside wheel turning in vs. the outside is called the ackerman and is pronouned as it reads. You can't really do anything to change that w/o reworking the steering arms, etc. So, that is not the problem as your car is the same as the next in that respect.

Your tire pressure of 29 front and 41 rear is plenty reason alone to cause understeer, especially with 205/245 tires. You should be running more like 2-3 lbs higher in the rear than in the front (maybe even the same pressure with those tires, you need to experiment). eg. 30 front 32 rear.

32 REAR?!?!?!? WOW, then the inside of my 245s would wear VER VERY fast... :(
I usually run 80 + MPH on the hiway. At these speeds, as I understand Bruce Anderson, the inner side of the carcass will flex and cause more wear because of the centrifugal Gs on the tire. IIRC - the centrifugal force at 75 MPH is something around 21 Gs. Therefore higher pressures are needed on a radial tire to keep the center of a wider radial tire from flexing outward causing center tire wear. Hence, I found 41 PSI on the rear tire to be the best tire wear and handling characteristics (for the rear).


I have found my car handles like absolute dogmeat at 36 psi or lower pressures in the rear. I will try it tomorrow just to confirm my experiments from previous years.

Thanks for the replies, again.