? About handling....
 

During an autox this past weekend I noticed more understeer than oversteer. I thought these cars were more prone to oversteer? Anyway, I basically had to vary the throttle to get the rear end to come around. Is this normal? I guess I wasn't pushing the car hard enough.

I am running 225's up front and 255's in the rear. Also, I know the allignment is a little off. It appears that the rears have too much positive camber. Not too sure about the fronts.

I kept playing with the tire pressure until it the wear pattern just touched the wear indicator. I had some people in the grid help me on that.

38psi/40psi front/rear

Any ideas?? advice??

Thanks!

How much gas in the tank?

hmmm a little less than 1/2.

Go to a full tank and report back. Before you get ape over suspension changes and the such, play with weight. I'm guessing a gallon of gas weighs...what 10 lbs? So a full 22 gal tank might weigh 220 lbs vs 110 or so? Big diff in weight over the front. If that helps it might give you some clues about what to change.

Disclaimer- never done an auto-x in my 911...I'd just try the easy stuff before tossing money at tires, t-bars, etc.

Thanks.. I am in not hurry to throw money at it yet. I am still learning to drive my new obsession :D I have just read alot about how these cars are tail happy and I have not really experienced that yet. I do plan on getting a good alignment done sometime in the near future. For now, I just want to become a better driver with what I have, then I will do some susp upgrading.

To get neutral steering at high speeds, Porsche engineered in understeer at lower speeds. But if you're not tracking the car the same day, there's a lot you can do (with swaybar adjustments and tire pressures) to counter this. You can also counter it with driving technique, using the throttle to induce a little oversteer.

But before you start changing anything, I'd make sure that your baseline setup is where it should be. Make sure the car's alignment settings are consistent all the way around, and that they're set up for the type of driving you want to do.

911's tend to understeer esp at low speeds. It's only when pushed to the edge or over it, that they oversteer. With every generation they tamed the handling "vices" a little bit more.
-Chris

911Brian, Try lifting at the turn in point and then report back about oversteer. Don't try this on a public road! More seriously though try a little more air pressure in rears than the fronts, 911 are famous for trailing throtle oversteer maybe try and "plant" the fronts just prior to turn in, turn, then back on the go pedal..easy..the trick to auto crossing is not upseting the car to much. All your transitions should be smmoooth. I usually start an AX with about 3/4 full tank and it is a little tail happy until its down to just under half. A slightly more aggressive alignment and CORNER BALANCE can work wonders for a car on an AX course.

Brian,

For starters, get an alignment and corner ballance!

For a low-speed course ... more suitible to 1963 Mini-Coopers (or 1972 Honda S-600) ... try lower rear tire pressures, 28 psi - 32 psi, I can guarantee you will feel the difference in a 600 ft slalom of cones!

Jack, what are you running for a suspension?

This thread often comes up on Rennlist and such.
Jack Olsen and others are correct in what was said so far here.
Another thing....high "g" loads for autocross ( when you crank-in a large amount of steering wheel angle) is an altogether different proposition than the *same* amount of high-g loads at high speed turns, like on a racetrack. There, you'll feed-in lots less steering wheel angle for the same load, and the wheels are more "straight-ahead" than for low speed corners. If you dial-out the understeering characteristics at low speed/high angle corners...the car will be diabolical and tending toward oversteer at high speed/ low steering angle corners. Result: the basic chassis set-up will likely get you low speed understeer. This will get you less understeer ( or even neutral) at high speed corners. Like Jack said, unless you'll go to both types of track on the same day, you *can* dial-out the understeering tendency for low speed...but don't forget to reset before you get back on the highway !!

---Wil Ferch

Wow! Thanks for the wealth of info guys! I know my alignment is a little out of whack. As far as using the throttle, I was doing that and it helped a bunch. I am still learning, I am a total newbie when it comes to performance driving. And I WILL not try this techniques on public roads! I enjoy staying out of jail and trouble:D

First off, I don't autocross.


But, since you asked:

Suspension and Brake mods
- 9.5x11x17 2-piece Lindsey Racing Fuchs-centered wheels with polished spokes
- 930 Brakes
- Lowered to 24.25 inches front, 24 inches rear
- Front JRZ single-adjustable struts, with 400# coil-over springs
- Front end components designed and modified by Tyson Schmidt and TRE Motorsports, including extended control arms and raised and re-cambered spindles (some of the work also done by JRZ and Fabcar)
- Front upper strut mounts modified for additional caster and entire front end repositioned slightly by TRE Motorsports
- Elephant Racing front Monoballs
- Turbo Tie Rods with ERP drop links to correct bump steer
- Elephant Racing lightweight triangulated strut brace
- Aluminum front crossmember
- Smart Racing front antiswaybar
- Aluminum rear trailing arms, repositioned with with Smart Racing Camber Boxes and monoballs
- Smart Racing 23mm rear antisway bar
- ERP 935-style spring plates
- Rear Bilstein struts with 600# coil-over springs

Jack is running 400/600 lb springs frt/rr and amazingly enough the miata spec suspension kit includes 700/325 lb springs frt/rr and miatas, stock weigh in between 2200 and 2300 lbs and apparently have a 50/50 weight dist.

Too bad the Miata gives up 800 - 900 lbs to Emma Peel's white '64 or '66 powder blue Lotus Elans ...

That reminds me, I just read a test in a magazine I can't remember (English mag) in which the original Elan (a Sprint coupe 5spd - not soft top) beat more modern equivalents.

They are VERY fragile though, have diabolical electrics and a few items of really suspect design/engineering, and 60k mile engine rebuilds are REQUIRED.

I believe that's the newest EVO that you saw that article in. I bought it the other day. Interesting article. Also of note in the same issue is an article on the Dauer 962, street legal 0-100 7.3 and 250 mph top speed.

Warren, even more importantly the miata is also WITHOUT Emma Peel.

I thought it was interesting that the spec racer springs for the miata were stiffer than the springs Jack is using.

Smart move - keep your money in your pocket. You just need more seat time.

Do get your alignment sorted. That is worth spending money on. Use a reputable specialty shop with experience doing performance alignments on 911s. Get recommendations here. Dont' go to the local tire / wheel shop.

Try to get onto a skid pad with an instructor. You can experience under/oversteer and the impact of throttle with utmost clarity.

Get instructors to ride along and give advice. I have a dollar that says if you brake and feed in throttle at the right time you won't have these problems.

Thanks Chuck

I plan on attending autox school when it becomes available. Hopefully I can squeeze in an alignment between now and the next autox.

Not that this is the case (I don't know anything about Miata suspension geometry), but the "effective" spring rate is a function of the actual spring rate and the suspension geometry, so just because the lbs/in rating of the spring is higher, doesn't necessarily mean the car is more stiffly sprung.

Mike

high "g" loads for autocross Wil,

How is it possible to generate a high "g" load if your car understeers so much? Seems like it would be impossible to make enough centrifugal force if you could not turn a tight enough circle at speed.


Joe

Joe:
Look at the entire context of my text...and don't pull out one sentence.
I'm simply saying that when you're at some considerable cornering load....a low speed autocross scenario puts you into a relatively large amount of steering angle. Let's say you're generating 0.7g cornering load. We're using this only as a reference point. To generate an equivalent 0.7 g load on a racetrack, you're more likely to be in a wide radius sweeper, and the steering wheel angle will be relatively low, and the actual road wheels will be relatively more "straight-ahead" ( hence better "geometry"). This is much more favorable than when the steering wheel has lots of angle cranked-in and the front wheels are almost turned sideways. In both cases you're generating "X" amount of cornering force, but the wheel placement situation is all different.
OK with this ... ?

--Wil Ferch

Wil,

I understand what you are saying, but my confusion stems from what you said about being able to dial out low speed understeer. How is that done? I thought it was designed into the 911 chassis dynamics and not possible to eliminate regardless of steering angle.

Joe

Joe:
What I'm saying is this:
....you *can* dial out a large measure of understeer by the common methods that work for all cars...wider front tires, wider front track, less front roll resistance, more rear roll resistnace, less rear track... or any combination of the above. etc, etc. For example ( extreme) you might go with stock 19 mm front torsion bars, and 31 mm rear bars ( stock 85 Carrera would come with 19 front / 24.1 rear, for example). The rear now would be VERY stiff and a large measure of understeer would be dialed out. That might be fine for the autocross you're entering today, where speeds might get to 45 mph and the front wheel are cranked over at a large angle for the small radius turns you're at... to generate big number g's.

NOW... drive the same car at a 90 mph around a large radius corner, like on a highway or racetrack, and at the same high-g load....the car would likely exhibit very nasty oversteering characterisitics ( had been neutral or slight understeer before mods. ) Why ? Becuase all cars will likely have different low speed vs high speed characteristics due to the front tires being at wildly different angles for the same cornereing loads. If you don't re-balance the car, the car will have high speed oversteering charactieristics which make for a very high pucker factor ! :)
---Wil Ferch

Brian, has your car been lowered since this pic was taken?
http://forums.pelicanparts.com/uploads/rightside.jpg

If not that I would start w/ a good lowering/corner balance/alignment

Due to the LSD in my 930 I have even more tight turn understeer to deal with than the average 911. It took a lot of empty parking lot experimentation and auto-xes before I felt comfortable pushing my car to its limits.

Depending on the type of auto-x course I have to deal with, for example will it be relatively fast with sweepers or slow and tight, I usually will either run less than a quarter tank of gas up to about 3/4 of a tank depending on how much weight on the front wheels I think I need.

In addition to that easily controlled variable I have also leared to master my decelerations in the tight turns so I can transfer a lot of dynamic load to the front wheels when I really need it. This is a skill you really need to master if you want to get your 911 through a tight turn as quickly as possible.

I concur with the above advice to get your ride height and alignment straightened out and then focus on mastering the nuances of the 911 to your advantage before doing any major hardware changes.

Hi,

I have ben AutoX'ng my almost stock 911 for 2 years and am still very low ont he learning curve.

Last AutoX I decided to get very aggressive with the throttle and discovered that, as noted above, the car will plow thru turns or quickly transition to a full spin if I lift in the middle of a turn. In the next event, i will be attempting to take a bit more speed off prior to turning in to see how that works. Each AutoX, I give myself an assignment to explore handling option in my car. i was playing with my sway bar settings and tire pressure a while back but now realize that I need to work on basic technique.

Go out there... have fun... get an instructor to ride with you.

Wow Bill! Good find. No I haven't lowered it. Still at the 4x4 height :D I believe it is set at US spec height. I plan on lowering it, just not sure on how much I can. I have 255's in the back and they are real close to the oil lines on the right and close to the inside fender wall on the left. Plus, I would like to get more neg camber in the rear. That will probably be very hard with the tire setup I have.

I don't plan any hardware changes now. Just more seat time. Heck, I think it handles great now. Better than anything I have drivin. I would like to think it will handle better once I lower it a bit and get it alligned correctly.

Harry....

I played with the throttle in the turns and found it very easy to "steer" the car with my right foot. I would brake hard right before a turn then turn in and give it some gas. The front would begin to plow then I would let off a bit. I kept doing this until I got around the turn (without the brake of course) . Seemed to work great! I assume this is proper technique. This may sound funny but, I would do this in video games hehe.. before I had a chance to try it out in real life.


Thanks guys!

Brian,

I was doing what you are sayng but was coming in Waaaayyyyyy too fast and didn't have enough room to play. I have ridden with nationally ranked drivers and they were much smoother so I know I have a long way to go.

Like I said, my plan is to brake sooner to come in a bit slower and then hit the accelerator to finish the turn. Thatr way, I am doing less "saving" and should be holding a better line.