Handling balance/setup question

[Trackrash]

911ST, I probably should have mentioned that my car has raised spindles (1") in the front and a strut brace. I am also running custom adjustable tie rod ends to minimize bump steer. I am able to get about 2 1/2 degrees negative camber in the front due to a couple of factors. The car is lowered below "euro" height, (both front and rear fenders measure about 24" above the ground) ,I have enlarged the adjustment holes for the upper shock mounts AND I have used the strut brace to JACK the shock towers together. My car is used mostly for autocrossing and so is most of my experience with my car's setup.
My car, like most older 911s tends to oversteer with the power off and understeer with the power on under most low and medium speed cornering. Yes, driving style makes a difference. I have, however, been working on reducing the amout of pitching I have to do to make the car corner.
I am running Koni classics which when adjusted primarily affect rebound. What has helped me is to soften the rear shocks, tighten the front shocks, while loosening the front sway bar. Keep in mind that shock settings mainly affect transitions, like entering and exiting corners. With the rear shocks set harder I found the rear too loose on corner entry. This was OK for REALLY tight corners, but wasn't very good for most others, especially faster ones. A softer rear also helps on corner exit. The reason for harder settings in the front is to control the weight transfer. It seemed to me like my car was picking up the front end on corner exit, which worsened the under steer. Stiffining the front shocks helped this and loosening the front sway helped maintain grip.
As I mentioned before I also tried lowering the front, which helped both turn in and exit noticably.
As for why lowering helped, well I imagine it is a combination of factors.
Which last week were again confirmed on a big track when I participated in a DE.
I had raised the front up about half an inch for more clearance on the street. I figured on the big track I wouldn't notice or need the extra grip in front.
Well after the second run sesson I was noticing that my front end seemed to be "wallowing" around. It felt as though the front end would roll over too much. So I got out my allen wrench and dropped the front end back down like I had it for the last couple of autocrosses. (I marked the adjustmenet screws the last time I corner ballanced the car, so I have some reference point to go on.) Wow, on my next two run sessions the front felt much more "planted" and secure.
Sorry for being so long.
I am by no means an expert on suspensions and handling, I am only trying to share my experiences with you guys.

[911st]

Thanks for sharing. I love learning about this stuff.

I am a big fan of raising the spindle to try to restore some of the camber curve. Especially on a car that has not been set up extremely stiff.

Sorry but I do not recall most of the above discussion.

What seems to be the best for consistent handling as to the dynamics between throttle lift and acceleration is a good limited slip. Especially the one's that are stiffer on lift than on accel (60/40 or such). A great idea if in fender to fender where you do not want the car to get upset if you have to lift in a corner in traffic.

When one rases the front it effects toe. If you had your toe set at zero when lowered, when you raise the car it will induce tow-out. The will make the car faster to initiate the turn and make the car darty at speed. This might be part of what you are experiencing. Also, raising the front will reduce neg camber and at a faster rate if the spindle has been raised.

Stiffening the front will transfer more weight to the inner rear wheel for more traction up to a point when the other front wheel comes off the ground.

Most the fast track guys are running much stiffer rear suspension with a good LSD's and often a little more stager with something like 225 front and 255 rear.

Every time I see an inside front wheel off the ground I think how much it reduces the neg camber of the inside wheel. Thus, I think at some point stiffening up the rear will make the front stick better.

In my mind a 911 rides fastest on 2.5 wheels. This is because a 911 has 50% more weight on the rear to be contained and most do not have much stagger (225/245's). Thus, one outside front wheel, one outside rear wheel, and 50% of the inside rear wheel for two and a half wheels.

A stiff front is safer I suspect and alows for more room to come into a corner faster under lift or when trail braking. However, a stiffer rear is probably faster comming out of a corner with a good driver that can get on the gas earlyer and exit faster. Especially if that increasses one's exit speed on to the fastest straights. Going fast into a corner dose not seem to be as fast as exiting a corner at the most speed.

Not sure any of this rambling makes much sense. Just how I think.

[BReyes]

Any one seen a spreadsheet (how about have and willing to share a good one or links leading to them) that helps with analysis of these variables; helps keep track of set up and set up changes and the corresponding effect. Something us mere mortals can use to tie together different set up charts. I expect such matrixes and variance analysis spreadsheets have been put together and are being used every week effectively by wining teams.

By using such tools the information may be better digested and understood faster, and therefore applied faster to improving the car, and decreasing lap times.

I know some guys can do this for a 911 in their head (as well as turn the wrenches properly and get the desired effect but these are guys that have ran their successful Porsche racing/service businesses for decades with out computers). Just a mere mortal here seeking knowledge of how to get faster, in order to help keep all four wheels of a race car planted and on the tarmac(s).

Regards,

[BReyes]

Surely many of you have seen one NASCAR guys use, some others. I'm talking something that helps with Porsche 911, both, as something that helps with set up, and greatly improves teaching how to set up a 911 using a what if, then running at at least two tracks.

Regards,

[RaceProEngineer]

Well, at the risk of taking Craig's original thread even further afield . . .


Bernard - It is somewhat unclear what you are asking. If the question is, "What changes will make a 911 faster, and which of those will be the most effective," then we can offer a few guidelines.

We can discuss the use of technology, data, spreadsheets, and many other tools, but there are some basics we need to get out of the way first.

[1] Most good teams treat the Driver+Car+Track+Conditions combination as a single entity, and we are tuning that "entity".

[2] Before much meaningful info can even be gathered, we need good consistancy - the driver must be turning laps within ½ - 1½ second variance, lap after lap. Here the use of some simple diagnostic tools, like a pyrometer, can be helpful.

[3] Assuming the driver and car are running near "their" maximun potential, someone needs to ask, "What is holding this car back? What will allow it to go faster still?"

[4] It is our long-held belief that the car "tells" the driver exactly what it "wants" in order to go faster. It is the driver's job to "listen", and interpret. Craig has obviously gone through this process to arrive at his original set of questions.

[5] Based upon what the Driver+Car "want" (at that Track, under those Conditions) in order to go faster, we make changes - less weight, more power, different gearing, better brakes, suspension modifications, different rubber compound, aero settings - the list is virtually endless.

[6] Naturally, as you suggest, each modification is noted, along with its resultant lap times. And after each "want" is basically satisfied, we pose the question again: "NOW, what is holding this car (and driver) back?"

[7] In this way, a team (or individual) can start to collect "data" in the form of two-way-trends: (A) To remedy mid-corner understeer (in the dry), we increased resistance on the front anti-roll bar. (B) When we increased rate on the front bar, we had less corner-entry oversteer.

[8] These trends can then become predictive. "The last time we switched to the 430 compound, we lost a second per lap. Can we gain that back by NOT having to stop for tires?" Maybe a good use for your spreadsheet, but each Driver-Car-Track-Conditions results will be different

Naturally, there are certain changes or adjustments that will be universally beneficial (like losing weight or gaining power), and many that will be a total waste of time and money. But generally speaking, this is a long, involved, trial-and-error process. And once the driver can no longer identify what the car "needs" (or it has reached its potential within the Rules), it might be time for data acquisition.

This may be too simple an explanation for what you are asking, but it is a process that most of us follow for as long as we race.

Ed LoPresti

[Goth]

What about chassis stiffness? I was surprised at how much the handling improved on my 84 Carrera when I installed Wevo motor and polyurethane trans mounts. I'm just a canyon carver, but the improvement was noticeable for me. It reduced my under steer (especially coming out of the turn).