Quick - I need some alignment help please

[bento]

okay guys, a bit of help would be appreciated.

here's the story: I have an 88 carrera which i recently had the shocks ball joints and tie rods replaced on. previously the car had been riding on clapped out oem boges. when i got the car back from the shop, the car's steering wheel was about 1/2 inch off center to the right. then, when i drive the car and turn hard into a right hand turn, the front left tire appears to be bumping into the inside fender well. the car wears 17x7.5 w/ 205s in the front and 255 on 17x9 in the rear. the PO had rolled the fender lip to accomodate the previous 7 and 9 fuchs that came with the car when i bought it. i haven't had this problem before and i am surprised that it started to happen because i figured that the new shocks would give me a bit of a lift to the front end. i made an appointment to take the car to the shop where the suspension work was done so that they can crank the ride height up a bit in the front. then i plan to take it to the alignment shop so that they can redo it on all four wheels. so my questions are:

1) what is the proper ride height in the front?
2) do you think i'm on the right track for getting this solved? is there another factor i could be overlooking?
3) I was using the torsion bar settings as outlined in Bruce Anderson's book w/ 1 degree of camber in the front and a degree and a half in the rear. is this all good? the car is used for auto-x and DE as well as street.
4) is it possible to get a bit more camber out of the front end with all stock componentry (aside from turbo tie rods and bilsteins)?

thanks for the prompt replies, car goes in tomorow morning.

david

[bento]

bumpidy bump bump.

thanks

db

[Randy W]

Raising the front end will probably help the rub you are experiencing, depending on where it is rubbing. Whenever you go with 17 inch wheels up front you are likely to have issues with rubbing somewhere (and will need a solution): if on the fender outside lip (try different wheel offset or tire aspect change), if on the inside body with lock to lock turns (wheel spacer), or if at the top of the fender where the metal ridge surrounds the upper shock tower (raise ride heigth or less negative camber).

BA's recommendations are a good start, depending on how competitive you want to be. Getting more negative camber out of the front is best done with front strut monoball camber plates, but not all club rules allow them. Sometimes a front strut bar like the Weltmeister when tightened laterally will allow you to get a bit more negative camber up front.

[Tyson Schmidt]

With new tie-rods on your car and no realignment, you're problems are from the toe being way off. You said the tire rubs on the inside fender well when turning right. I suspect your car is toed-in excessively, making the left tire turn sharper than the right one on a right-hand turn. (And vice-versa for the other direction)

As for camber, the most you can get from the front is usually -1.8 to -2.0 and then you make the rear a half a degree more negative than what the front results are.

I like my cars lower than Bruce Andersons Euro-height recommendations. I like 24 3/4" at the front fender lip, and 24 1/4" at the rear. Especially for Autocross and DE. Have them put in as much positive Caster up front as the adjustment will allow.

[stlrj]

It seems that all that additional negative camber and positive caster in front will increase understeer or push in tight corners.

How can that be an advantage?

Joe

[jluetjen]

It seems that all that additional negative camber ... in front will increase understeer or push in tight corners.

Not unless you go "over the top" with the negative camber. In general a little negative camber is good since it generate's "camber thrust" which creates a force pushing in the same direction that the tire is leaning. So negative camber on the RF will introduce some force pushing the RF towards the left. In addition, 911's have MacPhearson Strut front suspensions which are great for front end packaging since they leave a lot of room between the strut towers. They are also OK in compression since they only gain a little camber, and thus keep the tires fairly upright. The place were McPhearson struts are "challenged" is when the car leans. Because of the long long swing-arm of the strut's geometry, the suspension can generate enough camber to offset the car's lean. The result is that the tire goes positive and traction is lost. The way to avoid this is to start with more negative camber then you really need. This is why you always see the SCCA IT guys running lots of negative camber on cars which have strut front suspension. They will often keep going until they run out of adjustment or loose so much braking ability that it negatively affects lap times. BTW - this much camber will also wear out the insides of the tires a lot quicker unless you spend a lot of time in the turns. On the other hand, stock camber settings will often wear out the outsides of the tires if used on the track a lot.

In regards to caster, some positive caster will increase the negative camber on the outside tire when turning, especially when a lot of lock has been added to the steering wheel. So this is another "crutch" to make up for the strut's shortcoming. The problem is that if you go too far, the steering will become heavy and have significant kick-back. This is why Porsche actually reduced the front caster 1970.

So in general terms, with a McPhearson Strut equiped car, more negative camber and positive caster (compared to street settings) will increase front end grip and reduce "push" -- as long as you don't go too far.

[bento]

thanks for the help. car is in the shop right now having the ride height cranked up a bit and then it's off to the alignment shop. Just to clarify, i did have an alignment done after replacing the tie rods, it's just that i thought that it was improperly done (steering wheel off center). Further, the car has had the 17 inch rims in the front for about a year and a half without any rubbing problems (previous owner rolled the inner fender lip), that's why i was so surprised that this suddenly happened post shocks and tie rods.

hopefully it will be sorted by late afternoon and i can get back to driving without having to be hyperconscious about every movement of the suspension.

db

[stlrj]

more negative camber and positive caster (compared

That being said, why does my car push even more at 20 degree lock with more negative camber and positive caster?

I have yet to hear where this has solved or reduced front end push. If anything, it seems to increase push and reduce traction in tight turns to the point where driving in wet conditions would not be prudent or recommended.

Joe

[jluetjen]

When your talking about suspension tuning, there are no absolutes, everything is a compromise based on the specific situation. Based on your brief email, its tough to suggest anything. Some questions:

1) Obviously it does it in tight corners. Does it push on entry? In the middle portion of the corner? At the exit?

2) Are you braking in the corner? How far into the corner?

3) Is it pushing while the car transitions into the corner? How does the car feel once it "settles" into the corner?

4) The situations when it pushes, are you driving "normally" on the street or are you on an autocross course? Are you on a track? Which track and which corners?

Some things to keep in mind:

1) Does your car have a limited slip or torque sensing diff? Either of these can increase tight corner understeer.

2) What size wheels and tires are you running both front and back? Are you using spacers behind the wheels? If so what size?

3) What size springs/T-bars are you running front and rear?

4) What size sway bars are you running front and rear?

5) Has your car been lowered? How low in the front and rear?

6) What are your existing alignment settings?

7) What are your tire pressures?

If you can answer as many of these questions as possible, maybe we can come up with some ideas.

[stlrj]

John,

None of my other cars push like the 911.

My autocross consists of driving the back county roads like on Mt. Tam here in Marin Co. When I drive the wifes 86 Olds 98 (fwd) on Mt. Tam, I feel very confident throwing it around those tight hairpins even in the rain. But try that on the 911 and I would end up off the cliff or against the side of a hill.

I have tried the same roads on a Honda Civic and a Grand Caravan without any of the uneasiness of the familiar 911 push which takes all the fun out of the experience.

I tried tire pressures, bigger front tires, larger sway bars, lowering etc. without any success. I even tried more negative camber and maximum positive caster with disaterous results. What else could I do?

Sooooo, I started looking into and comparing alignment specs of all these cars that cornered without push. I noticed that none of these cars ran with more than 3 degrees of caster, some with as little as 1 degree and camber was minimal varying from 1/2 degree positive to no more than 1/2 degree negative.

To make a long story short, I tried reducing the camber and caster on my 911 and the results were nothing short of phenomenal! At the moment I have my alignment set slightly positive (if I could get it to 1/2 degree positive, I would, but it's virtually impossible to get that on a 911) and I reduced my caster to about 2 1/2 degrees. With these settings, push has gone down dramatically and turning tight corners at 20 degrees steerig wheel lock in a parking lot has eliminated all that annoying tire squeal.

Bottom line...it's gotten to be a lot more fun to drive in the real world where I spend most of my time.

Cheers,

Joe

[jluetjen]

Ok -- if that solution works for you great!

I find it curious because the cars that you mentioned are so very different.

Olds/Honda/other FWD: 60% forward weight distribution. Front wheel drive which pull the front end.

Porsche 911: 60 rear weight distribution. Rear wheels push the car (but don't necessarily cause "push")

I'm confused why the alignment solution for one type would have the same affect on the other.

BTW: To me negative camber is when the top of the wheel leans towards the center of the car. Does it mean the same thing to you?

I'm happy you found a solution.

[pete98m3]

how much camber really depends on both the weight distribution of the car (as far as dialing in its actual handling)...

buut, a street tire typically hits max grip around 1.5-2 degrees, and a slick likes up near 3.5-4 degrees...


.5 positive your definantly sacrificing some grip... hate to say it but if you put the porsche into a corner much to fast it'll just push all over the place, then hook up and go sideways all over... that works for FWD's because u can drift them by kicking all the weight up front under breaking then cranking the wheel, this drift'll scrub off so much speed that it'll straighten out and come out of the corner... well pretty slow...

try slowing down a lot more before the corner, setting it up properly then rolling hard onto the gas... don't just punch the gas tho... you'll probably find that the porsche is, if anything, tail happy, thanks to its extremely tail heavy nature.

[stlrj]

As for someone who has been aligning all autos for over 30 yrs, I may have a slight advantage over some self proclaimed armchair suspension experts who must rely on opinions of those who know even less than themselves but are willing to venture opinions based on pseudo science and wishful thinking.

As a matter of fact, 0.5 degrees positive is the factory spec for the 911S, 911SC, Turbo USA,Canada, Japan form 1976 until 1983.

It's quite possible the engineers at Zuffenhausen had more knowledge on optimum alignment settings than we could ever duplicate since they built the car and have the test track to prove it.

Cheers,

Joe

[Tyson Schmidt]

So I guess all the racers in the world have it wrong, including the Porsche Factory, and you have it right? HA!

You set your car up like your mini-van and front wheel drive cars, and you think that's the way it should be? Unbelievable.

BMW's run way more caster than Porsches. Like 7-10 degrees and more on some models. They handle quite well.

Positive camber for better handling??!! Now I've heard it all!

[stlrj]

No, the racers have it set correct for the extreme conditions they encounter. But for the street and occasional autocross, the factory settings seem to be the best compromise.

As far as my alignment settings are concerned, the only deviation I made from factory spec is a slight decrease in caster which is far less radical than all that negative camber that is more appropriate on a rice burner than in an autobahn classic.

Believe it or not, the factory even saw fit to reduce the caster on the 92 C2 Cabriolet compared to the earlier 911s without any input from me. Imagine that!

Assuming your 92 C2 suspension has not been modified from stock, my settings are actually very similar to yours. HA!

Cheers,

Joe

[jluetjen]

...self proclaimed armchair suspension experts who must rely on opinions of those who know even less than themselves but are willing to venture opinions based on pseudo science and wishful thinking.

Great - so we agree!!! People like that can be a drag. I'm sure that they'll recognize themselves after they read your description and not bother continuing with this thread.

[Randy W]

Yeah, guess I'll have to re-educate Greg Fordahl and send all those trophys back

If your 911 is pushing on initial entry with race settings, you are probably coming in too hot and/or not trail braking deep enough. Note I said "probably", it could also be your front shock settings or a host of other reasons, but I would not look at reducing negative camber or castor first.

[stlrj]

[ Front Caster Effects
Effects of Positive Caster
Vehicles usually have some positive caster specified since this promotes directional stability, however, excessive positive caster can cause two problems. The first is that excessive caster will cause a high level of road shock to be transmitted to the driver when the vehicle hits a bump, etc. The second problem is that a tire/wheel assembly with positive caster has a tendency to toe inward when the vehicle is being driven. If one side has more positive caster than the other, this causes it to toe inward with more force than the other side. This will cause a lead or pull to the side with least amount of positive caster.

Effects of Caster on Tire Wear
When set with a substantial amount of caster, the spindle travels in a vertical arc, causing it to move up and down and raise and lower the wheels as the steering wheel is turned. Because of this, camber changes occur. With a high amount of positive caster, the camber changes that occur, especially at low speeds in tight turns, cause the tires to show wear on their shoulders. In high speed cornering, the vehicle tends to continue straight ahead when the steering is initially turned. Due to this, and the amount of camber change that takes place when a spindle travels through its arc of travel, the shoulders of the tires on a vehicle may scrub and wear. When a left turn is made at a fairly high rate of speed with a vehicle which has positive caster, the caster of the left front wheel changes toward positive but the momentum of the vehicle is in a straight ahead direction. This causes the inside of the left front tire to scrub as it is turned. Just the opposite effect takes place on the right wheel as the vehicle is turned left at high speed. The right front wheel's camber will go negative but the outside edge of the tire is scrubbed because of the vehicle's momentum to go straight. On some vehicles setting caster more than +2.5° will cause scrub problems. ]

http://aligncraft.com/terms/terms.html#Front%20camber

[David Ceruti]

Calm down guys! This is a very interesting thread and all the name calling and getting onto high horses doesn't help. I find I learn most when someone (Joe in this case) comes up with a different point of view. OK now to get off my soapbox and start to contribute

After thinking it through Joe'settings make sense for the conditions he does a lot of his driving in - slow speed corners. There wouldn't be much weight transfer or body roll and there would probably be more lock on the wheels.

In these conditions, less camber would a work better because there would be more tyre in contact with the road at those speeds. The way I understand it it is the lateral force acting on the tyre in fairly high speed corners that "pushes" the contact patch sideways. If there is little or no camber then the inside of the tyre would lift up and reduce the contact patch. With more negative camber, the inside of the tyre is forced down onto the tar and the contact patch and grip increases.

Reducing castor would also help because in the relatively extreme lock positions you get in slow speed corners there would be quite a lot of extra camber generated. From his discription of the reduced squeal (from scrub) in parking garages, it seems that the steering is closer to Ackerman, though I haven't quite worked out how the camber change causes this.

NOW - what I would like to know is how Joe's car handles in high speed corners, both long sweeps and sharper corners when you are on the brakes quite hard as you are turning in.

Also any comments or clarification on my attempts to get my head around all this will be welcome

And lastly thanks for getting the grey matter back in action

DC

[Randy W]

David, since Joe has not responded to your question, may I venture a guess? ..... not very good.

We all need to feel like we have the answer to the questions proposed on this board. Heck, that's part of the reason we visit so often isn't it? I think that Joe may have struck a nerve in Tyson and myself with his proclamation about how to align a 911:

"As for someone who has been aligning all autos for over 30 yrs, I may have a slight advantage over some self proclaimed armchair suspension experts who must rely on opinions of those who know even less than themselves but are willing to venture opinions based on pseudo science and wishful thinking."

You see, people like Tyson and I have spent years trying to come up with a 1/10th of a second improvement on a 50 second autocross run. The course usually consists of slow speed tight hairpins, slaloms and fast sweepers. This is very much like what you would experience on a Santa Monica Mountain/Topanga Canyon run (I wouldn't know about Mt. Tam). We don't care if the changes we make to go faster comply with what somebody wrote in an alignment manual. All we care about is the time displayed on the scoreboard at the end of our run.

What we have come to realize over time (with the help of 30 year 911 veterens like Greg Fordahl) is that a certain amount of negative camber and positive castor over the stock settings allow us to post times better than anyone else. Of course, over all this time we have learned how to adjust shock settings, sway bar settings, and tire pressures to affect this result which we aspire to. And yes, we know how to drive a 911 and we know it's not easy to drive the car in this configuration, but we know it is ultimately the most rewarding, and we have the trophys to prove it. Speaking for myself, I don't wish to propose that everyone make the same changes we have made from the stock suspension settings, but the reality is it works - IF you have taken the time to learn how to drive a 911 and you want to go faster.

I don't want to beat a dead horse here. I just know there's no easy answer, and although it might be nice if you could make several runs up and down a mountain, consult all the books written on the subject and come up with a new solution on how to make your 911 handle "better" - it just isn't likely to happen, at least not in the way that Joe has proposed. We've already tried that - it doesn't work, at least not for anything other than slow speed hairpin turns.