Front end pushes question
 

After having my alignment done last week I was hoping that it would somehow cure the squeeling sound my front tires make when adding power while turning in a 180 degree freeway on ramp.

Unfortunately, it still sounded the same even after the front end was lowered 1 1/2 inches and the camber was increased to -1 on both sides and toe was set to zero.

So my question is, why the additional negative camber did not seem to address this problem?

On a hunch, I deceided to try reducing the amount of negative camber to see if that would help. So what I ended up doing was raising it back up 1 1/2 inches and 1/2 degree positive on both sides with an 1/8 inch toe out which made a dramatic difference in road feel and cornering. Oh, I almost forgot to mention, she no longer squeels like a pig in tight corners!

I know this dose not make any sense at all and goes against everthing I have ever read, but can somebody please explain to me why it works?

Puzzled,

Joe Garcia
86 Carrera

Just a thought. Assumming there are no obstructions that the leaning tires rub against in a turn. It may be the tire itself or actually the rubber/tread/road combination. I had tires on my family car that squealed on turns. The squeals stopped when I changed tires. That may be too simple an explanation though.

I too think it could be tire compound. I run Cooper Cobras and they don't squeal even when pushed on the offramps. probably not a great wearing tire though, they seem to be a very soft compound. they really stick well.

I think is all a matter of what your lowering operation did to the steering linkage geometry. A drop of 1.5" is far too much to try without steering rack spacers! At that much uncompensated drop, your tie-rod ends are no longer flat or level ... not having the operating 'length of the pivoted part of the tie-rod at hand, I can only estimate an upward angle of 12-15 degrees. When you adjusted the toe-in after dropping, you had to lengthen the tie rods, right? What that means is that at any other position otherthan straight ahead, the tires will assume a much greater toe-out attitude than the front-end geometry was designed for!

Since 911's are so lightly loaded at the front end low-speed turns assure that the inside tire in any significant turn with be mostly unloaded, and the resulting toe-out condition causes the tires to squeal badly in PROTEST ... hence when you restored the ride height and straight ahead toe-in to 'normal,' the squealing went away!

Any questions?

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Warren Hall
1973 911S Targa

Thanks for your advice guys but I may have left out some minor details like the front height before it was lowered was at 27 1/2", down to 26" and then back up to 27 3/4". I don't think rack spacers are necessary, do you?

I even tried Pirelli, Goodyear and Yokohamas in the past and they squeeled too, so it couldn't be the compound.

I can tell they aren't rubbing inside the wells either.

I wonder what would happen if I removed some of the caster. I'm guessing it might make it stick even better, but if it doesn't, I know it will only take me 5 mins. to put it back to where it was.

Cheers,

Joe

I thought caster was basically fixed. But I know when to listen and I'm listening.

My car pushes when I drive it hard. I can get tires to squeal too, but my complaint is the pushing effect. It looks as if my front end setup is pretty stock, though I have not verified this. My rear has very visible negative camber. I think this rear negative camber lessens oversteer and contributes to the pushing.

I bought the car a year ago and a friend (SCCA instructor, with grey hair a LOTS of trophies) told me to wait one year before making any suspension decisions. Well, it's a year and I'm tempted to get rid of some of this negative camber in the rear. The car is a little 'darty' to drive but I like the excitement. it's the pushing on hard cornering I want to get rid of.

there's your question, Warren.

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'83 SC

Joe, Do you have any 'factory-spec.' measurements (axle center to torsion bar center) to go with any of your fender-lip height measurements, so some relative relationship to the original factory specs for the front end can be considered? And, what size tire are you using in front? At this point I have no idea where your ride height has been for the experiment -- with respect to factory specs!

Jim, I agree that large negative camber angles in the rear needs to be minimized with our wider tires, and Bruce Anderson recommends -1 degree. In your quest for more rubber on the road, have you considered 951.362.117.00 8 x 16 Fuchs and using your 225/50-16 tires up front? 245/45-16's in the rear would complement the fronts nicely on 9 x 16 Fuchs. How's that for thinning your wallet ... need any more help in that area?

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Warren Hall
1973 911S Targa

Such a card, Warren. Actually, thinning my wallet is not something to worry about, as it is already abotu as thin as it can be. You make a good point though. I would need only two tires and wheels, not four.

I'm pretty tempted to get rid on most of the rear negative camber. I think I'll solicit the opinion of Greg Fordall, our (Seattle) resident P-brain. I'm told he's 'the man' when it comes to suspension.

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'83 SC

Maybe that's why I like these cars so much. Something is finally thinning faster than my hair!

Joe,

Sounds similiar to me in my '85. I had 6 & 7 x 16s with 205 and 225s. I had my front end done by Custom Alignment in Mountain View CA. I asked for the front to be lowered at the recommended 1 degree downslope. For me, this was about a 1/2" drop. They set the front up with 1/16" toe -in and zero camber.
I almost drove off the road the first exit I took from the front-end push. I have since changed it to negative one degree camber in the front and have found out I am running 1 1/2 degree negative in the rear.
I have also changed to 7 and 9 fuchs with 205 fronts and 245/45 rears. The 7 sevens in front even though they are still 205s seem to help quite a bit. Next I am looking to get some 225s in the front as soon as these 205s warrant.

I think the torsion bars in the rear might have something to do with it as well. I think it was Bruce Anderson's book that points out in the mid 80's, Porsche made the cars understeer due to some accidents and flak from the press. It is not said how this was accomplished though.
I believe Porsche went with a little heavier rear torsion bars in '87. This could also be because of the increase in horse-power, not sure.

If anyone has better info PLEASE let me know.

Nick
'85 Carrera

Nick,

The 1 degee negative in front did not seem to work for me but what I ended up with is 1/2 degee positive with 3/16 toe out which seem to make it corner even flatter, very little body roll and gives me a very linear stearing wheel feel.

In the rear, I settled on what I call a NASCAR setup of 0 camber and 0 toe, which seems to help my 9x16 (993) with 235/60 16's stick to the pavement as I power out of corners without breaking traction.

In front, I'm running 215/60 16's on 7" 993 wheels.

Setting the front caster to the minimum as I mentioned earlier that I would try also had a positive effect as far as increased cornering. I accomplished this by moving the top of the left strut to the far NW corner of its adjustment window and the right strut to the far NE corner of its opening.

And according to my spec book, my ride height pretty close to what the factory calls for based on tosion bar centers. Might also explain why it handles so well.

Cheers,

Joe

27 3/4" in front? Mine is set at 25 1/2" and doesn't even look lowered. What are you planning to do, the Paris-Dakar Rally? Set your car to the Euro-spec. height (about 25.5" to the fender lip in front and 25 in rear.), set the alignment specs to 0 camber in front, -.5 in rear, .25 deg. toe in in the rear (total), +6.5 deg. caster, and do the the understeer/oversteer tuning with the swaybars. You need more roll stiffness in the rear to reduce understeer. Is your swaybar still there in the rear? Are its mounts broken? Did you put new struts in front but left the old rear shocks? Tire pressures? Try running 28 front and 30 rear. I bet your car has a limited slip. That really makes them push in slow speed turns. Stiffer torsion bars, shocks, and sway bars in the rear will help. I also think highly of a strut tower brace up front, the kind with the extra diagonal brace. These really help to plant the front end.

The alignment guy did set it down to 25 1/2 but it didn't handle, so I put it back up to 27 3/4 and now it does.

I also eliminated that rear sway bar years ago because it tended to be noisey and caused my inside rear tire to break traction while punching it out of a driveway to get into fast moving traffic.

When I needed the power, it wasn't there because my inside tire would unload, loose traction and squeal. So now my inside tire stays planted and I can punch it without that annoying loss of power and tire noise.

And yes, it is a lot more fun to power out of turns now than it was before I removed the rear bar. And no, there are no poisonous handling side effects as you might expect without the bar.

I'm running my tires at 36/45psi.

I also notice that with my front ride height at 27 3/4" it now has taken on the level appearance of a C2/4, 993 or 996 rather than a Paris-Dakar rally car. My rear height is 25 1/2".

Cheers,

Joe

"Experience is what you get when you don't get what you want."

[This message has been edited by stlrj (edited 10-30-2000).]

[This message has been edited by stlrj (edited 10-30-2000).]

Joe,

As we are getting more background data, a 'picture' of your handling problem is beginning to form ... so, you can take this assessment with a grain of salt:

1. Your tire pressures are too high ... 29/34 psi is recommended, and 45 psi in the rear is WAY TOO HIGH!

2. Removal of the rear anti-roll bar contributes to understeer rather stongly, and is not the way to get to 'neutral' handling ... which is what I assume you would like!

3. Positive front camber contributes to understeer by limiting front-end traction.

4. Your car's 'nose-up' attitude seems rather odd/bizarre to say the least ... 2.25" higher in front than rear? That seems to me to be as much of a 'bump steer' situation as lowering ... just change my original discription to 'down angle' rather than up angle for the tie-rods, and you get the idea!

The only possible suggestion I could make is to set EVERYTHING back to normal ... rear bar, ride height, camber, tire pressures, and see what it handles like there! I suspect it would be a 'different' car, but that may not be what you want ... or wanted to hear, either!

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Warren Hall
1973 911S Targa

[This message has been edited by Early_S_Man (edited 10-30-2000).]

Sounds like my golf swing. I'm no expert, so you should be able to dismiss my advice easily.

Joe, believe me I am respectful as I say this, but your setup sounds like a series of radical departures from original spec taht have necessitated each other. If you remove a rear sway bar, you might wind up increasing tire pressure way above normal to compensate, for example.

I see golf swings that are constructed using this same method. Again, Joe, I say all this respectfully. Perhaps your setup works better than stock, I just noticed that it is certainly different.

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'83 SC

I understand these settings are rather unconventional to say the least, however I haven't heared of anyone who has actually gotten their hands dirty and experimented with their alignment first hand as I have.

Until then, I doubt I will change anything since I finally have delightfully neutral and predictable 911 that even feels good in the rain.

Armchair philosophizing is fun but it seems to fall short of what happens in the real world.

Cheers,

Joe



[This message has been edited by stlrj (edited 10-30-2000).]

Looking back in some of my old manuals I just realized that most of my alignment settings are factory settings.

Clymers Rear Axle Specifications

Toe-in (1965-1972) 0 +/- 10'
Toe-in (1973-1976) 0 +/- 20'
Camber (1975-1983) 0 degrees +/- 10'


Front Specifications 1975-83

Toe-in 0 degrees
Caster 6*5' +/- 15'
Camber +30' +/- 10'

This probably explains why it handles so good.

I think the factory must know more than we do or at least if all else fails then why not rely on factory settings.

Works for me...

Cheers,

Joe


[This message has been edited by stlrj (edited 10-30-2000).]

I had similar problems with push, and took the car in for an alignment and four wheel balancing. What seemed to solve the problem, though was adding wider rear wheels (245s on 8 inch wheels). I would think that this would make things worse -- since the 225s I wanted to put in front wouldn't fit. But the car handles great now. Had it all over the big track at Willow Springs today with great handling; no spins, no plow, just fun.

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Jack Olsen
1973 911 T sunroof coupe

The prosecution rests. http://www.pelicanparts.com/ultimate/cool.gif

I was looking through my Haynes Techbook on Suspension, Steering & Driveline Manual and found some interesting similarities between the factory settings of a 930 Turbo and a Corvette.

911 and Turbo
1983
Front
Caster............. 6.00-degrees
Camber............. 0.50-degrees
Toe-in............. 1/8-inch
Rear
Camber............. 0-degrees
Toe-in............. 3/32-inch

Corvette
1990 thru 1996
Front
Caster............. 6.00-degrees
Camber............. 0.50-degrees
Toe-in............. 0-inch
Rear
Camber............. 0-degrees
Toe-in............. 0-inch

I think that the similarities are probably due to the fact that both cars are shod with such wide tires that leave a good contact patch without the need of negative camber.

Cheers,

Joe



[This message has been edited by stlrj (edited 11-01-2000).]