Front-end push

[Chuck Moreland]

"Dogmeat" is somewhat vague and hard to diagnose. If your tires like more pressure, fine. D ifferent tires like different pressure. But start with a delta in the 2-3 lb range, then adjust to taste.


32 is not a low tire pressure and is likely to provide significantly more grip than 41 lbs. Don't confuse grip with under/oversteer characteristics.

If your tires say 41 psi max pressure, it is exactly that. MAX pressure, it is not recommended pressure.

[nhromyak]

"Dogmeat" is the opposite of good.

I will try lower pressures in the rear tomorrow morning.

But would higher pressures (or lower pressures) in the rear affect the the front tires grip (or smoothness) during a U-turn as well?

Something just doesn't seem right. It's like my old Chevy Blazer ('73) in 4WD when I make a U-turn on the street.

[HarryD]

To get your tire pressures dialed in, you might want to try the Autocrossers trick of putting some chalk marks on the shoulders fo the tires and adjust the pressures until the shoulders are clean right to the edge. I know for my car with 205/60-15 M&S street tires all around, normal driving has my pressures set at 29F/32R. For AutoX I increase to 34F/37R to get full coverage of my tread without getting onto the sidewalls. FWIW, on long decreasing radius turns, I do develop a push (20-30 mph) but I hold my nose and drive through it.

Hope this helps

[nhromyak]

The one long sweeper that I have been "having fun" with is not (or does not appear to be) a decreasing radius turn.

Interesting psi numbers for street and auto-x.

Will any ol' chalk do? Or is there something special I should use?

Last time I tried chalk, the tread wiped away within the first block...

Or am I supposed to chalk the edges of the tire, and then lower pressures until the side of the chalk wipe away in turns?

Thanks for the reply.

[nhromyak]

I just measured my front toe with string, pins, and measuring tape.
It looks like it is 1/8" toe-in.

I have 55 1/8" on the front string with 55 1/4" on the back string. Of course, I would never say this is more accurate than the laser alignment. Could this 1/8" toe-in by my problem? It seems too insignificant to be a like the problems I am having.

[HarryD]

Originally posted by nhromyak
The one long sweeper that I have been "having fun" with is not (or does not appear to be) a decreasing radius turn.

Interesting psi numbers for street and auto-x.

Will any ol' chalk do? Or is there something special I should use?

Last time I tried chalk, the tread wiped away within the first block...

Or am I supposed to chalk the edges of the tire, and then lower pressures until the side of the chalk wipe away in turns?

Thanks for the reply.

I have used both my kids sidewalk chalk and white shoe polish. The polish lasts longer. I start low and bump up 2 psi (plus re-chalk) until the sidewalls keep their chalk marks but the square to the road thread is clean.

[RaceProEngineer]

Nick,

Like most of these mystery problems, you undoubtedly have more than one malady acting together. I have a couple suggestions:

(1) Stating the obvious, some tires howl at very slight slip angles. Others "speak" more readily as the tread wears down. The important thing is not to equate tire squeal with understeer.

(2) Have you eliminated the possibility that your car has front end damage from a former life? The alignment figures and corner weights seem to indicate that the pieces fit together correctly, but it is something to check.

(3) Barring damage, your solution will be found in the suggestions of Chuck and Tyson - a combination of problems. To elaborate:

- Let's leave the tire squeal out of the equation for now.

- Make certain you have no "binding" in the up and down movement of the front or rear suspension. Push down hard on each fender to ensure the travel is smooth.

- You claim your handling balance improves when you inflate your 245 rears beyond 42 PSI. Naturally! You are crowning those tires so that only a fraction of the contact patch is touching the pavement. It now "balances" the poor traction at the front, and the car handles more neutral.

- As Chuck suggests, take your pressures down in the 27F / 30R range, for starters.

- Somewhere buried in the thread, and glossed over, was Tyson's keen questions about shocks, and specifically shock valving. Where to begin?
(a) If you have adjustable shock absorbers, make certain the fronts are not set to "full hard" while the rears are set softer.
(b) If they are not adjustable, are they "matched" (the same brand and model on front and rear)?
(c) If matched, do the fronts "bottom" when you press down hard on the fender? Do they resist downward movement entirely?

Concentrate on looking for front end damage, on getting tire pressures into a sane range, and explore what those shock absorbers are doing.

Ed LoPresti
RacePro Engineering

[KobaltBlau]

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

what combo did you have on Scruffy, Tyson?

Also, what compromise street/track bar combo do you favor for an SC (full interior) weight car?

TIA!

[stlrj]

Nick,

I had a similar experience when I had my SC lowered and aligned by the a very experienced fellow who used to work in San Rafael who aligned Redwood PCA member cars on a regular basis, so I was more than confident that he knew his way around 911's.

When he was finished my alignment numbers were very similar to yours and the handling was just what you experienced: lots of tire squeal front and rear, more front end push, rear would break loose at a lower speed than before with lots of noise. This was not what I expected or wanted but longed for an improvement that would have given me a competative edge. This was clearly not the path I wanted.

So off to my garage I went, not wanting to pay again to undo everthing, I deceided to meticulously take it back up to stock height and align it to the book on my own. After a test drive with everthing to stock, I was rewarded with superb handling, less tire noise, much less push than before and the rear end stayed planted so much better that I could hardly get it to break loose at all. What a surprise!

Later, I wanted to see if I could eliminate the front push once and for all with further tweeking. What I finally settled on was a reduction of caster to 2.6 degrees instead of the stock 6 and camber of 0.5 degrees positive, just what it calls for in the Spec Book.

Not only does my front end not push at all but it sticks so well that I now get that classic 911 inside wheel lift with more control than ever.

If you ever get down to Novato, I invite you take it for a spin and see for yourself.

Just send me a PM.

Cheers,

Joe Garcia
Redwood PCA since 1976

[dickster]

nick

is the problem the same in right and left handers?

the reason i ask is that i have been chasing the same problem - but mine only does it in right handers! in lefties it handles like its on rails! (plenty of posts on it)

i have done loads too. i am now running 22/31 t/bars and still have the same!

i am hoping an alignment shortly will sort it once and for all.

good luck.

[Wil Ferch]

chuck's tire pressure comments are v. good...

Try something like 32 fr / 34 rear ( Cold!)....and don't be surprised that they go up 6 psi hot. Yikes ! ....40+ cold ????

The counter point you make on how the car handles at lower pressures is indicative also of the wide split in front and rear section widths ( 205/245 as someone mentioned). Therefore, also try 30 fr / 36 rear ( cold).

Wil

[nhromyak]

Thanks for everones replies.

I had a '73 911 before this one. I fully expected the rear to come out, I absolutely NEVER had the front end loose its grip before the rear on this car. I give it more gas, and the rear-end would plant down. This is what I expect out of this '85 911. This is how it was before I lowered it.

Should I simply start looking for some 225/50 front tires?

HarryD -
I am off to buy some shoe polish. Just to be clear, I am to put the polish over the edge from the tread over to the sidewall, correct?


RaceProEngineer-

(1) Perhaps these lower treaded RE730s are simply "speaking" more easily and are losing grip much faster than they have in the past.
(2) I have not eliminated front end damage.
But I did not have this problem before lowering the car. I certainly can not see anything, I will have to have it checked. Scary

(3) I can't make the car go up and down in any corner more than 1/2". I don't think I can make any corner go much beyond 1/4" movement really.

Hmmm, when I am in the long sweeper if I turn the wheel more into the long sweeper the car doesn't respond as I would expect, therefore, along with the sqeal in the turn, this is understeer, yes?
Especially, as this happens when I am going slow as well.

- You claim your handling balance improves when you inflate your 245 rears beyond 42 PSI. Naturally! You are crowning those tires so that only a fraction of the contact patch is touching the pavement. It now "balances" the poor traction at the front, and the car handles more neutral.

Then why would the Turbos run 45 psi cold with this tire, and rim size? Do they crown too?
I know they are a little heavier in the rear and have stronger Torsion bars. Additionally, when I inflate the rear to the higher pressures, the rear still does not come out. I gain more speed in the long sweepers judging by the speedo in the same sweeper, and how the front end handles in low and higher speed curves seems to get better.
Additionally, when I run 225/50s all the way around, I still have this horrible front-end push....

STLRJ -
What car, tire sizes, torsion bars, sway bar combination(s) do you have?
I fully expect the front-end to stay planted, and the rear to come out. After the lowering, and alignment, I have only been able to make my rear-end wiggle, not really come out. I hit the gas when it does, and the front-end gets worse.

Dickster -
Same issue left and right handed turns. Same issue with 225/50s tires front and rear.


I know my problems are something simple, I will go for a drive, get some shoe polish, lower the pressures, and see that sweeper.
If not much comes of that, I will make some changes to my toe.

[Chuck Moreland]

You might have multiple issues at play. But you definitely have a tire pressure problem, and that is easy to fix.

So why not do that, then see where you are.

[HarryD]

Yep, put the polish on the thread and a bit down the side wall. you are looking for the polish to stay on the sidewall but wear off of the thread.

[jluetjen]

I concur here that your tire pressures are pretty far out of the norm. I've noticed (on other cars) that radial front tires can be noisy and pushy if they are down by a few pounds. BTW, my two cents is that adjusting the rear tire pressures up to 40 lbs + to reduce inside shoulder wear is like using a chisel as a screw driver. Sure it might work in a pinch, but it is definitely the wrong tool for the job. I'd put the rear pressures back to the normal zone (low 30's) and back off on the camber if you really want to reduce the tire wear. Basically, put the suspension settings back to stock and your wear problem will be pretty close to minimized. Inside shoulder wear is just a fact of life on a lowered 911, especially with increased negative camber. If your car is over-lowered, that could be sending your front end suspension geometry off the scale (specifically the roll center could now be way too low) which would also show up as chronic understeer. If you look at the front A-arm, is the inside noticably lower then the outside? If the answer is "yes", then your car is too low. If you want it that low, you need to use RSR style front spindles to keep the geometry in the zone where it can be happy.

If you're tuning a car, it not unheard of to adjust yourself down a dead end. When that happens your best bet is to go back to your baseline settings (ie: Factory alignment settings and pressures) and start again. BTW, when you have your car cornerweighted, it's best to have it done with the car ballested in as-driven condition. This means half a tank of fuel and drivers weight in place. If you usually have a passenger, have that ballested too.

As far as adjusting the tire pressure by wear, I wouldn't do it. If you're going to do it right, use a Pyrometer. For street use I'd strongly recommend that you consider staying pretty close to the factory settings -- they really did know their stuff. Keep in mind that guys like Vic Firth (and more recently Walter Rohl) have done the test driving for Porsche.

[69911e]

If the understeer changed significantly due to the lowering of the car, I would suspect the front end may now be on the bumpstops. I have heard there was a time when Porsche put spacers above the struts due to the higher US req., if this is the case these need to be removed when the car is lowered to reasonable a height.

[nhromyak]

Thanks again for everyones replies.

I did not get the shoe polish, as myself and another Pelicanite went on a "fun-run" today. That's what my incentive was for fixing this front-end push (that I have had for two years).

Apparently, I did not listen to reason, nor the collective opinions and experience of this board before.

Just for fun, I decided to go with 29 and 32 pressures, F & R respectively COLD before I drove the car today.

OH MY GOSH! MY GOSH !! OH MY GOSH!


That was fun!

The front end would not howl like it did before (still howlled a little though). The whole car handled SO much better. Although it feels like a boat swaying on turn-in.

Turn-in seems reduced a little, I suspect it is because the rear-end loads up (or down) on initial turn-in. Now I see why everyone LOVES stiffer-torsion bars.

Tomorrow, if it doesn't rain here in CA, I will play around more with some shoe-polish and tire pressures.


jluetjen-
I guess I wasn't clear, my rears seemed to wear on the centers, not the inside. I do have a pyrometer, and with these pressures (freeway commutinng) My rear tire temperatures were within 10 degree from inside to center, to outside. Again, this made me think I was correct with my psi on the rear tires.

69911E -
I too thought, it maybe on the bumpstops. So, I took the shocks off the inner fender tower, and confirmed the shocks will go about another 2 inches further than my "at-rest" tire heights on the A-arm.

But again, it looks like it was (is) a tire pressure problem.

WOW! What a difference a day makes!

Thanks again to all the Pelicanites here!

BTW: My friend and I swapped cars, he has Kuhmo Ectsas with 205/55 and 245/45 on 16" BBS rims. The kuhmos are definately a harder riding tire, he was at 24 all the way around, after we were driving up at 8,000ft level with snow, and wet spots on the ground, so I am not sure how "hot" the tires were.

"Hot" pressures for me (again it was cold about 50 degrees outside) were 29 and 32 F & R. Since this is about the same as my cold tire pressure, I suspect the tire kept cooling down when we hit the water or little bits of snow.

I have new pics, if anyone is interested in some Freshly laid snow in the Sierras!.

Thanks again to EVERYONE for responding!

[stlrj]

Nick,

My ride is a 74 w/SC flares and an 86 3.2, 6" Design 90's front and rear with 215 60 16's on all corners, 30 psi f/r, stock bars, rear sway bar removed.

A little off subject, but my turquoise 63 VW beetle "Herbie" came stock with over 1 degree positive camber in front and rear, skinny 165 SR 15 tires, tiny front sway bar, no rear sway, was very nimble, fun to drive, could run circles around any 911 in a lot just like that mini Cooper video, never pushed or squeeled around turns.

Anyone remember the camber compenstors they used to put on the rear swing axles to keep them from tucking in and rolling over? I think they put them on 356's too.

Joe