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.