911 Understeer Issues at Auto-Cross (long)

[911st]

Thanks Tom.

[rfloz]

Follow up report - The 2/21/ OCR A/X started off a little damp but soon dried (mostly).

Changes - front toe from zero to 1/8" out (total), tried 24/27 psi f/r, about 25# removed from rear (ugly bumperettes and new exhaust).

All practice runs were with a student and so not all out. In timed runs several corners might have brought out the dread understeer.

First - a hard right after a medium speed slalom. This was in fact the only place I had any understeer. After the tight part in opened a bit and I was able to give it full throttle there.

Second - a hard right approached at a good speed and hard braking. This was fine and I could pull the car in more to the right after the exit for the next left. I think I took this one about as hard as possible and the car was good. Real improvement noted.

Third - a pretty fast sweeper the got tighter about 2/3s of the way around. I had trouble figuring where to slow/brake and never got it really right, so not fast enough for any issues to arise. I worked this corner after I ran and saw some really good drivers blaze through there, just tapping the brake before the kink. Humbling, to say the least.

Fourth - another sweeper after pretty hard braking. I could hold it tight and about 1/2 way around and start to feed in some gas. About 2/3s around it was full throttle - no issues. Definite improvement.

I had no brake locking issues and hit them pretty hard in at least three places.

So, a lot of improvement and the car is more fun to drive. I did well in my class, but most of us that ran yesterday are mid-level drivers and so not real consistant making it hard to make valid comparisons. Still, the car felt good everywhere except the first turn mentioned above and slowing a bit there made it doable.

As mentioned above, I probably need to go a bit too far with the changes and then dial it back. So, I'll try adjusting the rear anti-sway bar a bit stiffer for the next event.

Thanks again for all the input.


Addendum - I drove a friend's "new" car at the car control clinic we had the day before the A/X. It's a stripped early car with a stock 2.4 and weighs almost 500# less than my car. What a hoot! Thanks Eric. Even with less power and less tire, it was faster than my car and just too fun to drive. If my car loses any more weight, I have to jump up a class, but it's very tempting.

[450knotOffice]

Bob, you did well yesterday, as always. I'm always hard pressed to keep up with my much skinnier Nitto NT01's and stock sway bars. I was talking to James Buck yesterday and I think I'll be going for an adjustable sway bar setup, revalved shocks/struts, and V710's - not all at once though. See you at the next event!

Btw, the results page is completely messed up.

[rfloz]

Thanks. I am finally getting used to this beast. Unfortunately, Lorrie is getting the hang of her car, too! I think she was only one tenth back.

Now that Chris has moved up the class is closer that ever. Good fun.

Don't be in a rush to get those 710s. They are not so great. Really.

Results messed up? Well, it is the first time I have been as high as 7th in the BRI index. So what if it is just alphabetical.

BTW, are you the Scott R. who gave me advice on who to have repair my front pan a couple of years ago? If so, thanks, I went to Dave at TRE and have been happy with his work.

[450knotOffice]

Bob, until Steve Wong casually noted that the driver of car 84 is a fellow Pelican, I never knew who was driving that white widebody with the HUGE rear tires. All I ever knew was that the I had to keep an eye for that car because it's always been fast and in my class (we have a big class, eh?). I've always thought, damn, that's a nice car, but how can I possibly compete with those huge tires back there! It always gives me motivation to push just that much harder. Luckily for me, my car is pretty easy to drive near the limit and has good balance. I will need the v710's though to keep up with all of you guys in my class who already run them (or the A6's). My Nitto NT01's are not quite in the same league.

I'll stop by and say Hi and chit chat next time.

[Randy W]

Originally Posted by rfloz

First - a hard right after a medium speed slalom. This was in fact the only place I had any understeer. After the tight part in opened a bit and I was able to give it full throttle there.

Did you trail brake here?

Originally Posted by rfloz

Third - a pretty fast sweeper the got tighter about 2/3s of the way around. I had trouble figuring where to slow/brake and never got it really right, so not fast enough for any issues to arise. I worked this corner after I ran and saw some really good drivers blaze through there, just tapping the brake before the kink. Humbling, to say the least.

Did you throttle steer here?

Glad to hear the car is better. If the car was neutral in the big sweeper, you do not need to change the sway bar. I would just focus on the driver for now. You could spend years, just on that. I still do.

[rfloz]

Originally Posted by Randy W

Did you trail brake here?

Did you throttle steer here?

Glad to hear the car is better. If the car was neutral in the big sweeper, you do not need to change the sway bar. I would just focus on the driver for now. You could spend years, just on that. I still do.

Good point. I was so focused on getting the slalom right (and I think I did) and then the hard braking right after the last slalom cone, I didn't even think to trail brake a little. Doh.

On the other, yes. A little. Probably could have done more throttle steering there (as one of the other instructors is always me nagging about).

There is no doubt the car is much, much better than the driver. The brake lockup seems to be gone and the understeer seems much better which makes me more comfortable. Amazing what a couple of small changes will do. But, yes, I will work on the driver. I may try the bar one setting stiffer just to see what happens. Probably at practice rather than timed runs.

Thanks for pointing out what was probably obvious to everyone but me. As I am sure you know, putting all the elements together is one of the toughest things to get right. To cite Cool Hand Luke - "Workin' on it boss."

[rfloz]

Scott-

Yeah, I know your car (450 Black Cab, right?), but wasn't sure of the driver. Car guy syndrome, I guess.

Do say hello - fat old guy w/ short grey hair and scruffy beard. I'll look for you.

FWIW, those huge rear tires may be part of my understeer issue - the rear grip is so much better than the front. Not to mention I have to be about 4 inches farther from the cones. So, they are a mixed blessing.

Aaarrrgh - You just reminded me I was going to talk to Steve Wong about a chip to go with the new ("can you hear me now?") exhaust.

See you at the March event.

[racer]

Forgive me for not wanting to re-read 4 pages.. but what size tires again (I recall them being large, but can't recall specifics)? I still think its tires that are too big and then add in your driving style. Just because a 911 is rear engine doesn't make it a "drift" car ready for snap oversteer at every corner.

[Jeremy Cottrell]

Bob, there was a red wide body 911 that was running for time during the orange run group. You were working at station 5 and I was at 6. The driver sent that car into a drift going into the right hander before the left hand sweep I was working and man, did it look good the way he slid that car into the right hander and flicked it back to the left. The transition was great and that car had no sign on understeer. We may want to have a talk with that guy and take a good look at his tire sizes.

[Evan Fullerton]

Jeremy, the well set up and driven red wide body car is Jerry Griffin, it is a modified SC. If Bob F. wants his email I can give it to him in a PM.

[rfloz]

Thanks guys. I know Jerry, he's the head instructor for OCR A/X. He was running 255/315 last time I checked.

Mine is 245/315. Unfortunately, V710s don't come in 255/17. I tried 255/295 in A6s and the car was more neutral, but I didn't really like the Hoosiers (nor did my VISA card.)

On his third run, Jerry got about 20 degrees of opposite lock in the faster part of that righthand sweeper. Great driving or great save?

Oh yeah, he's the one telling me to throttle steer more.

Gary Thomason was really fast through there, too, in the newish MIata. Looked like he was left foot braking just before the the two green cones. I wish I had worked before running as I was pretty timid through there. Lesson learned, I hope.

[450knotOffice]

He WAS left foot braking. I was working turn 8 and was having a great time watching his brake lights come on while he was still hard on the gas. That was one quick Miata!

[Randy W]

Gary Thomason is one of the best - could learn a lot from him!

[Evan Fullerton]

All the fast guys left foot brake . It isn't something that I could manage in the old 914 with its close ratio box but in the 993 it is really really easy, especially with ABS that comes in and saves your bacon when you overdo it. I think your car has boosted brakes which should help you learn it as I find 911s without boosted brakes require too much effort to be able to modulate them well with my clutch foot. Left foot braking is a very valuable tool for autocross, especially in slaloms and the like.

[450knotOffice]

I'll need to get comfortable with that. I'll work on it.

[rfloz]

2nd OCR A/X event - Thinking about things some more (always dangerous), I decided to leave the car as is and not stiffen the rear sway bar. After all, my biggest concerns, locking the front brakes and too much understeer, had gone away but for one turn I coulda/shoulda/woulda trailbraked into.

So, this event was at California Speedway (parking lot 12). On arrival the wind was up and it was pretty chilly.

First practice session and, guess what? Massive understeer and brake lock! After calming down, and consulting others, I hoped this was a result of cold tires that never got up to temp due to weather conditions.

Second practice session - it warmed up and the wind died down and the car worked fine. I didn't see a lot other people's times, but I felt I should be competitive.

Timed runs - the first run was after a long layoff and the cold tires worked poorly. The next three runs the car worked well and, although I didn't go quite as quickly as in the last practice run, I did well in class. Not all the usual suspects were there due to the distance and a POC event conflict, but my time stood up well compared to some others from out of my class.

So, lesson learned - cold weather sucks! I'm not sure how to compensate for that. I didn't think I should lower my tire pressures any more - 24/27 f/r. Overdriving didn't warm the tires. Maybe get a tire warmer?

'Nother lesson - car is good enough (for now), work on driver (yes, Mr. Wells, I am listening). On that note, I have been instructing lately and find it helps me as much as it helps the students. Anyone who has taught some will recognize this syndrome. You want to do a good job for your student so you really work at showing them what to do. That requires both thought and action. And, you spend more time on sourse. So, you get better (and, one hopes, so do the students). The down side is you spend so much time practicing, instructing, working and running, you can't find time catch a ride with other instructors. Still, a net gain as far as I can tell.

Finally, after viewing the videos of this event from two much better drivers, I find I am pretty much doing what they are. Maybe not as well, but before, I could see glaring mistakes on my part. Now, it's just a little more gas here, a little less brake there. I'd sort of plateaued for a while and I'm seeing progress again. I like it.

[Evan Fullerton]

I am not sure what your Carrera weighs but in the white '75 911 (2400lb no driver) I was sharing with my Dad on sunday, we were running lower cold pressures than that on 205s. We ran A6s for timed runs and the side wall on them is tremendously stiffer than the 710 sidewall so this may be some of the difference. It is my understanding from the suspension books I have read that the majority of the grip gained from wider tires is due to the ability to run lower pressures and thus the ability of the tire to follow surface imperfections. The limited experience I have with my 993 (2400lb no driver) supports this though. When I ran it last month at ElToro, I was down to 16psi front and 20psi rear on 245/295 tires to get any grip at all and there was a big difference between 22/26 which was like ice and 16/20 which actually wasn't bad considering they are 10 year old tires trying to put down 300+hp. I use tire rollover to gauge how low I can go.

On a cold day there is not a whole lot you can do to build heat and tall wide tires are going to be more difficult to get warm than even the same width tires in a 15" or 16" size. I rode with Christian in the morning and he was having some slight tire heat issues as well. Cold whether just isn't fun for the driver or the tires.

[rfloz]

I had been running 28/32 f/r and a couple of people suggested 24/27-28 which is where I am now. The car feels good there (at least when it is warm out), but I am intrigued by even lower pressure, especially in the cold. Certainly worth a try.

My car was night and day different from cold to warm weather. Usually by the second practice run the car is working pretty well. Sunday it was awful all four runs in the first session.

Is your car #101/110? I think you were parked just north of me. I didn't see it run as 110, but 101 was very quick.

[Evan Fullerton]

Yep, my Dad is #101 and I am #110. My best clean run was a 58.9 and my Dad put in a 60.4 I believe.

23/27 is what we were running but we were on a square 205/50/15 A6 combination for timed runs. The Rat Rod 911 as I call it has a rather peculiar suspension setup though so I wouldn't advise those pressures necessarily even if you were on a square setup with a similar weight car.

I recommend you mark you tires for rollover (we use White-Out) and if you don't have one pick up or borrow a tire temp gauge. If you can't find a better one, we have a $20 infrared one you are welcome to borrow to get a rough estimate of what is going on but the more expensive probe type are supposed to be more accurate.

I won't be at the 4/11 event as I will be in San Diego for a SCCA AX but I imagine if you go, it will be another low attended event with time for some testing as the PCA Speed Fest is that same weekend.