Quick - I need some alignment help please
 

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

bumpidy bump bump.

thanks

db

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.

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.

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

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.

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

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

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.

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

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.

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.

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

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!

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

Great - so we agree!!! SmileWavy 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. :rolleyes:

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

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.

[ 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

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

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.

interesting thread!

interesting cause i've got a similar problem.

my car handles great in left handers (slow and tight or sweepers, it turns lovely) but in right handers it "pushes or understeers".

at the track (which had two left handers!) the problem slowed the car - VERY FRUSTRATING.

i've been chasing this thing for months.

i thought the left side front may have positive camber but it seems to be the same as the right (negative).

i've no track experience, but i've read a book or two to try and find a solution. from that i totally agree with what randy and tyson are saying. try "how to make your car handle" or ba's book.

the problem is that understeer or push is caused by any one of a number of things. mine has had new front torsion bars, but i believe the rears are original. the rear bushes are also shot to hell. softness in the rear will contribute to understeer, which is where (i hope!) i think my problems are.

i just gotta locate the f*cker.....................

Thanks Randy - I still hope to hear from Joe as well.

I was also reacting to his mudslinging as well - whenever anyone starts resorting to their experience to back up a claim I start to wonder where their facts are. Also reminds me of Napoleon and his horse!

Nevertheless Joe did get me thinking and he may have a point that his settings are more suited for everyday driving. I know that I enjoy pusing quite hard through tight stuff because its challenging to do well and I'm going slow enough to compensate for anything that may happen (like all those erratic moving chicanes on the roads). I'm too nervous to tackel fast stuff off the track though which, IMHO, is where the more aggressive camber and castor settings seem to come into their own.

Also, the extra braking of less camber is attractive

This is all an attempt at opening up the debate and learning not to give a definative answer (or even opinion)

Guys:

Allow me a "centrist" view on all of this...

Yep...let's stop the mudslinging and view the facts...

There is no denying that some negative camber will result in superior cornering abilities. Let's also recognize that the USA 78-83 cars were set up higher to simply comply with US bumper height and headlight height laws...and had VERY little to do with what was "right"...form a vehicle dynamics perspective. therefore, on this point alone...we can't assume that what Porsche engineers specified is without criticism.

Yes...increased castor promotes straight line stability...in excess this can lead to the wheel simply "flopping" over when turned and would create understeer or push. Think of a Harley chopper with an extemely extended front fork...and this can be easily visualized.

That said..it IS interesting that the C2 and later cars use a much lower positive castor setting than the earlier torsion bar cars...something like 2.5 degrees vs 6 degrees as I recall.

So....we al had something to contribute and think about...OK?


---Wil FerchSmileWavy

Sorry to keep everyone in suspense, but work and family obligations always seem to get in the way whenever things get interesting.

As it happens, my primary test track for testing my suspension tweeks before I head for the hills are the high speed overpasses and freeway onramps on nearby highway 101 and 37. Only when I'm satified with the high speed performance do I move on to our famous Lucas Valley road and on to Mt Tamalpias. So to answer your question, high speed stability is a major concern, in fact, it feels more composed and stable at all speeds. I may be mistaken, but I do believe that Porsche has done some high speed testing of their US ride height 911s in Zuffenhausen before turning them loose on our shores, not to mention all those Road and Track/ Car and Driver reviews on US ride height 911s, raving on how well they handle.

Something that may have been overlooked is when the factory sets the camber positive is the fact it is not static, it does not stay positive for very long but goes negative the moment you turn the steering wheel 90 degrees off center, so a positive initial setting means little due to high amount of caster designed into the 911 suspension that automatically goes into negative territory without you realizing what just happened. At full 20 degree steering wheel lock, you could end up with as much as 2 degrees or more negative when you initially started with 1/2 degree positive with the wheel pointed straight.

What may be causing all that push that everyone complains about is too much negative camber(great for the autobahn)instead of the wheels going positive which is virtually impossible with 6 degrees of caster but it is very possible to have too much negative.

Basically, my ultimate goal was to optimize the tire contact patch for all speeds and all conditions which I have finally done to my satifaction and just as important, I have been able to prove my theory on my track.

Looking forward to the rain for some real excitement.



Joe

Dickster;
It sounds to me like your car is not "square". Since winter's coming, if it were me, I'd put it in the garage and do a complete set-up on it. This should include a complete corner weight, ride height and alignment. For the sake of academic curiosity, It would be interesting to look at your initial settings to see if something jumps out that could be causing the problem. The problem that you describe could be caused by bad corner weights, alignment, shocks, springs or tire pressures to name a few.

As far as Stlrj's suggestions, if it were me I'd try to get my hands on tire pyrometer and take some tire temps after a run up his favorite hill. (I've got one, but I'm on the wrong side of the country.) I've always found that set-ups which provide even temperatures front to back, and across the tread of each tire with a slight (~20-30 degree) increase in temperature on the inside of the tread provide the best handling. Without that data on his set-up, I'll hesitate to comment on it directly. I can only comment on the settings and changes which I've seen or done myself. I also agree that Stlrj's driving style (once again sight unseen) could certainly have an impact on his car's handling and the settings that make car and driver happy.

Will - some nice points made and Joe is your car at the US or European ride heights?

on the point Will made about the setup of the newer cars, it makes me wonder whether the difference in wheel offset has anything to do with it. I know from my limited experience with fwd cars that it was beneficial to have the kingpin axis as close to the centre of the tyre contact patch as possible (which is why most wheels today have the dish on the inside). Now this looks as if the new porsches (C2 onwards?) also seem to have these type of wheels so I'm guessing that the may have changed the front wheel geometry in this direction and this may effect the camber etc.

Excuse the rambling and poor explanations:rolleyes:

Good thread though

still chasing the problem
 

so i took my car in to the shop and had them bring the ride height up by about 3/4 of an inch in the front via the adjustment screws. then i went off to the alignment shop and had them set the toe properly (steering wheel was off center previously) and check the front alignment. the car is allegedly at 1 degree of negative camber at the front. the car does feel better but i still hear the "clunking" sound on a hard right hard turn. i'm running 7.5 inch wide rims in the front of my narrow body car, do i need camber plates to clear them properly? i still don't quite understand why this would happen post installation of new shocks when i had no such problems on my blown out boges.

dickster, you having similar issues?

db

Wow, i'm so glad I did a search on "caster" before I started a new thread!
I didn't even know this thread was going on!


Ok, so here's the scoop. Some of you might remember my "Got beat by a Honda" thread... and some of my "alignment woes" threads.
The situation is as follows: My car was "pushing" horribly at last weekends race (where I was slower than my roomates civic). I had originally thought that the problem stemmed from the difference in the front and rear camber (the rear was mistakenly set to -3.5 deg and the fronts were a mystery) It was visibly obvious that there was allot more neg. camber in the rear than in the front. At the time i thought this was causing the understeer I was getting on the track. Well now i have it set to:

1.6 in the rears
And L 1.5, R 1.6 in the front.

But this hasn't stopped my understeer problem.
While the car was on the alignment rig, I found that the "caster" was sitting at 5.2 degrees of positive caster on both sides.
I wanted to ask you fellas about this... now I've seen some pretty good explainations and suggested settings, but, I have to ask.... how the hell do you move the shock tower back and forth????? Are you just supposed to smack it with a hammer? I couldn't get it to move at all, front to rear...

Dr Pate,

You may not be able to remedy the problem you have with push unless you could duplicate the alignment settings of the 99 Civic SI: caster 1.66 degrees, camber 0 degrees. I managed to get my caster down to 2.5 degrees after modifying my camber plate and relocating my strut outside the bushing. The stock plate has very limited adjustment.

Just Joe

Optimal settings will depend entirely on how the rest of the car is set up. With tire spec being the most important.

If you have very sticky tires, you will want very aggressive settings. ie: lots of negative camber, positive caster.

More grip from the tires equals more load placed on the sidewalls. More load on the sidewalls makes them roll under more, necessitating more negative camber.

Stickier tires will also cause more body roll, and with it, camber loss. Most cars have at the most a 3/4 ratio of camber compensation built into the suspension. This means that if the car rolls 4 degrees, the camber is only compensated 3 degrees, resulting in 1 degree of camber loss. That is why 1 degree of negative camber is a good setting for a mildly set-up car. Play with the big dogs, and you'll need all the negative camber you can get. But your driving skill has to improve along with the set-up, or the car will feel odd-handling to you until you learn car control, and can push the car hard enough to exploit it's level of grip.

Reducing the caster will quicken the steering because more of the angle will be dedicated to the steering direction and less to the camber change. But in a set-up car, you want the extra negative camber that the extra positive caster gives you much more than the quicker steering response, since stiffer rebound on the shocks and swaybar tuning can get you so much more turn-in that it isn't necessary.

Another note: Lowering the car a great deal will cause poorer initial turn-in due to bump-steer. That is why many people feel better percieved turn-in when they raise the front suspension. Ideally, you would lower the car, and install the dropped outer tie-rod ends and the steering rack spacers to compensate.

All that said, a 911 will always understeer in the slow speed stuff. It's the nature of a rear engined car. It's one of those epiphany moments when you realize you have to slow down to go fast. Some day you will get it Leland, and the Civic will be far behind. Carry too much speed into the tight turns, and you will have to do so much undoing that you will lose seconds in each hairpin. Watch the fast guys in the turnarounds. They are smooooth. They stay in tight, and keep a steady smooth arc, modulating the arc with the throttle and almost no steering. The whole time they are looking way ahead to the corner's exit point.

I get this vague feeling that there are just too many OTHER variables going on....

Tyre pressure, sway bar settings, standard or otherwise torsion bars... blah blah blah.

No a Porsche, but it will do - the BMW - I turned the Koni adjustable front shocks 1 full turn tighter (on rebound) and it understeered like a PIG into tight corners. It is also extremely sensitive to tyre pressures.

Its a package - I'm not sure who said it in the posts above - but you need it all to be set up together.

Cam

The change in your beemer's handling is because the shock's compression setting has a big effect on the transitional cornering of your car - it basically controlls the rate at which the car rolls and takes up the steady state cornering "stance". This will be felt especially in tight turns because everything happens much faster.

My guess is that the stiffer setting overloaded your outside front tyre and the inside tyre was too light to help - result understeer!

If you dont want to back it off (the obvious solution) because it helps on other parts of the track you can try to reduce the roll bar stiffness at the front

Also - and this is just a guess - getting on the power earlier may lighten the front a little and bring out the back a bit and compensate for the front shock setting

Enjoy the playing!

Tyson, you did a great job of explaining the inter-relationship of all that is potentially adjustable in the 911 suspension. I also agree that the very best drivers will want the car set up so that it is way too twitchy for most people. By cranking up shock compression, dialing in lots of negative camber, and running race tires you are not only asking more of the car, you are also asking more of yourself. A novice will get in the car, complain about it pushing in the slow turns and snap oversteering in the slaloms, when someone like Greg Fordahl will get in the car, run ten seconds faster, and jump out of the car remarking "It works for me." From my own experience having autocrossed seriously for six years, and graduated up the ranks (winning a National Tour and two regional series championships), the way you set up your car will continue to change as you gain more experience in what the 911 will do and what it won't do when driven at the limit. Becoming truly confident in yourself and the car, so that when you are going faster everything you do slows down in the car, has alot to do with it.

Here's a couple of other facits of the rubics cube that you need to keep in mind:

1) The roll center of a McPherson strut suspensions will move quite a bit in compression and droop. If the roll center goes below ground level (where all of the forces are coming into play) you will have a lot of handling headaches. If you lower the front end of your car so that the front A-arms are lower at the inside mounting point then the outside, or even enough that this happens when the suspension is compressed, you will have problems. If you really want to burn some brain cells on what this means, check out this thread. Keep in mind this is why the factory raised the spindles of the RSR. This allowed them to lower the front end of the car without putting the front suspension into this severly compromised situation.

2) Cam; I think that you may have done the exact opposite change to what you ineeded to cure the understeer. As a rule if you are going to change shock stiffness in rebound, you want to do it at the opposite end of the car. You might want to try resetting your front shocks to their original settings and then increasing the stiffness of the rear shocks in rebound. This will slow down the transition of the car's weight to the front-outside wheel when turning and increase the transition of the car's weight to the outside rear wheel. This change should decrease push/increase oversteer when transitioning into the corner. As Dave points out, you did the opposite. Give it a shot and let us know what happens.

3) I'm not convinced that "fixing" the castor is going to make a big difference in a car's handling as long as it is even on both sides. If everyone's problem is similar to Lelands, it sounds like the understeer is happening long before enough lock is put into to make caster a factor. I think it's a question of ride height (see above), shocks, T-bars and sway-bars. And most importantly driving style.

4) While in general I agree with what Tyson said, I'm not of the belief that a 911 can't be made to handle well in slow tight corners. I just think its a question of figuring out the suspension settings and driving inputs which are required to make the car operate up to its full potential. That's the fun of working on a race car.

For comparison, my car has 6 inch wheels all around, stock T-bars, 19mm front and rear sway bars, and stock shocks. I've got a hair-pin at the corner of my property which I drive around fairly often. My car has nothing resembling understeer in dry situations. In fact it rolls around the corner fast enough that I can feel it in my neck and the steering is heavily loaded. Here's my technique:

1) Complete most of the braking in a straight line.

2) Initiate the turn-in as I roll off the brake and move my foot to the gas. Think of it as going from 100% brake to 100% turning in equal amounts. So I've added 10% steering when the brakes are at 90%, 20% steering while braking 80%, etc.

3) Since it's a hairpin, I'm taking a late apex. Prior to reaching the apex I'm already on part throttle. I'm giving it just enough throttle to hold my line. More throttle if I need to open my line, less if I need to tighten it up.

4) Once the car is mostly straight and approaching the apex, I start to feed in the thottle. I can usually feel the rear end squat and the rear suspension geometry steering the rear end around. As I take out steering lock, the car straightens out and rockets down the straight. OK, it doesn't rocket since I need to immediately get off the gas again in order to turn into my driveway, but you get the idea.

How does that compare with the way that others are driving hairpins??? SmileWavy

Sounds good, John. Left foot braking makes the 100% total that is split between brake and throttle easier to modulate, but it can be done if you are really good with doing both with your right foot. Also the presence and type of limited slip will influence this ratio somewhat, with a Quaife allowing less entry understeer and easier hook up on exit.

So..... it's not "killing" the car to be running 5.2 degrees of caster???

Leland;
According to my Tech Spec book, my car is supposed to have between 6 degrees 45' and 6 degrees 5' of caster. The smaller number was a change that Porsche made starting in '70 to reduce the caster. In order to reach that setting , they had to modify the upper strut mounts slightly on the body. This was done to reduce kick-back in the steering as well as lesson the effort when at full lock.

You have less caster then that and your suspension is essentially the same as mine, with the exception of wider tires and a heavier car. So no -- your not "killing" the car. In reality, unless your running on a oval, caster really doesn't make a huge difference to a car's handling unless you are running at the limits of the cars ability. The most important thing is that it be consistant side to side, otherwise the car will pull.

Randy;
I agree with the left-foot braking making the process simplier. Given that I'm driving on a public road, I generally don't left-foot brake since I many need to stop due to pedestrians or traffic and I don't want to get my feet crossed up while trying to find the clutch etc. On the track, my objective would be to do a clutchless downshift while left foot braking. But even that would depend on my total commitment to the corner, so any sort of traffic would put me back to right foot braking.

I don't really want to muddy the waters with BMW handling traits! My point was that camber and castor aren't the only things affecting understeer.

Thanks for the tips guys. I had tightened the rebound up in an effort to get more rear traction (no LSD :( ... yet). It worked perfectly at achieving this goal at the expense of understeer. Unfortunately my swaybars aren't adjustable (and neither are my back shocks). I think I am already at max camber too. More money...

I've put the front shocks back to where they were - when stiffer, other than being able to put the power down properly out of the hairpin at the track I was at, there was no benefit. Well, I suppose it felt incredibly reassuring in fast sweepers.

In fact, since it was hard to get the car to turn into the hairpin well, the extra traction probably made my times worse. It is almost impossible to tell because I am learning and it was my first time there, so of course I got faster...

Thanks for the help. I really need to buy and try an LSD. I have to ship one over from the US though, because they are unobtanium here. And I've spent all my money!

Cam

John, if you can (and want to), try practicing switching between right foot braking (when using the left foot for clutchwork - recommended) and left foot braking (when in a single gear for a corner or a series of corners). Once you get comfortable with this, you can left foot brake when you need to settle the car under throttle and still use the clutch for shifting - no problem, even on public roads. It takes some time to master, but it is faster on the track. This is the way all the rally guys used to drive before sequential shifting was introduced.

Dickster

I had another look at your post today. Another factor is that your weight in the car will keep it more level in left hand turns (assuming it is a LHD car). See if it handles the same with a passenger in the car and it will give you more info.

What to do about it? That will take a bit more thought or suggestions from some of the gurus lurking on the board. Maybe have the alignment checked with you in the car. But I think that the unequal L/F weights is one of the unsolveables in saloon car racing. I know that some guys imported LHD cars to race over here at Kyalami because most corners on a counter-clockwise track favour LHD cars

Regards

DC