OK... My Koni's are nice, but how do I get rid of this roll?

[adamnitti]

Enjoyed autocrossing this past weekend for the first time at Turner Field. I could definitely tell that the Koni gas adjustables I just installed made the car handle much better, but I still have more body roll than I would like.

The checkbook quivers as I ask each of you what the next step would be for me in order to keep my car stuck to the ground even more. Do I need bigger torsion bars?

Also, what is the net effect of changing sway bars versus changing torsion bars on an '85 911? Thanks in advance-

[jluetjen]

Before I venture an answer; why do you think that you have too much roll? While you were running, did you do the "chalk test" on the tire sidewalls? Was the car understeering or oversteering? Was it doing it on the entry or exit of the corners? Did it happen on left or right hand turns? Was it consistant throughout the day or did it change during the course of the event? In general, what kind of alignment do you have on the car compared to stock? Additional camber front or rear? What are your toe settings? Has the car ever been cornerweighted? What were the tire pressures?

Answering those questions will help to determine where you need to go next. And BTW; many of the set-up changes you might make are free! Also, what is your competition driving background?

[89911]

New shocks will improve but not greatly change your cars body roll. Your next improvement should be stiffer torsion bars, perhaps 22/28 or 23/30 depending upon track/street use. The last step would be adjustable sway bars, changing the front bar to a through the body setup. Yes it will cost a few more bucks but it is some of the best money spent.

[adamnitti]

john-

first of all, i am pretty new to this autocross thing, but i drive my car pretty hard in general whenever the roads and conditions allow it within reason. no, i didn't chalk test or try different tire pressures, and i realize i should probably do that first before even posting a question like this. but, i'd like to learn more about fine tuning suspension settings and what to expect from the changes.

i was running 1 day old kumho ecstas, and the shop set the tire pressures to 32/36 front/rear. i've got 205/55 front on 7.5's, and 245/45 rear on 9's. the car did behave pretty consistently the whole day, but to me it was as if i was dealing with understeer a little more than i would have expected. i have the car set up with some extra negative camber. don't know what my toe-in settings are. in the morning autocross school on sunday i ran both a skidpad run in both directions and a slalom. the car felt good to me in general but the front end felt a little 'slippery'. (i know that the understeer thing is normal.) after installing the koni's all of the 'sponginess' that was bugging me is gone, but some 'slipperyness' is still there. right and left turns felt pretty even; i've never had the car corner balanced, either.

probably just my inexperience shining through.

[Clark Griswald]

Adam

What is your ride height set to?

Assuming you can stand to lower it some without ground scraping, that would be the most cost-effective way to reduce roll! It will also reduce dive and squat. All without compromising ride quality.

Tbars then sway bars are the next steps and in that order. But start with lowering the car, if you do it yourself it is FREE.

A great way to get the car extra low for the track without compromising street ride height is to use lower profile tires / smaller diameter wheels at the track/autocross event.

My track tire ride height is a full inch lower than my street tire ride height! With a cooresponding lower center of gravity.

[jluetjen]

Adam;
It sounds like you are thinking about the problem the right way. Personally I like to get the most out of a car and driver prior to pouring money into it. Lots of people will tell you to put this bit or that bit on the car to make it faster -- I personally believe that early on most of the improvement will come from the driver and optimising the settings that you have available to you. There are also others on this board with a lot more experience then I with Autocrossing.

Here are some thoughts:
1) Since you are "New to this autocross thing" keeping the car soft will make it more "forgivable" while your driving skills come down the learning curve. You have most likely discovered the designed in understeer which helps to keep the car stable for the world's drivers. Unfortunately, stability often gets in the way of turn-in "sharpness" that racing drivers prefer. It sounds like you have specifically identified this "slipperyness" as being an issue to you getting more comfortable. I'd suggest that you come up with a plan prior to your next event of things to try which might resolve this issue. Such as:

a) Do your first run with the car as it is and chaulk the sides of all 4 tires. Are any tires "rolling over" onto the sidewalls? Take note of the results.

b) Try increasing the front tire pressures by 2 lbs? Did you feel a change? Do you want more or less of the change? Adjust accordingly.

c) Check your toe, both front and back. (You can do this with a string set-up that is described elsewhere on this BBS under alignment.) Since the front toe is easy to adjust, try adjusting it out by 1/16 on both sides of the car. What does it feel like now? Do you want more or less of this change. Adjust accordingly.

d) Keep an eye on the results of the chalk test as you make the changes and note what happened there compared to your "seat of the pants" results. Finally, the ultimate measure: What has happened to your times?

By the time that you have finished this, you will have learned alot about yourself as a driver and the car, you will have had a lot of fun and spent very little money.

Once you have maxed out on any improvements using these settings, here are a couple of other ideas in order of rising cost:

-Try using wider front wheels and the same tires
- Try using wider wheels on all 4 corners and the same tires.
- Try using "Track only" tires designed for solo racing.

If you have at this point completely overrun the tires because you are cornering so fast and nothing that you are trying is keeping your tires square under the car, then you need to consider changing roll-bars and T-bars. Ideally, the cars springs and bars should only be stiff enough to keep the car off of its bump stops and in the suspension's "sweet spot". Stiffer then that just makes for a twitchy and hard to control car. There is a lot of information about the recommended T-bar diameters and the importance of T-bars versus sway bars. I think that this is covered in earlier posts to this thread. If you find that all of your issues are on corner entry and corner exit, then adjustable shocks may been in order.

[adamnitti]

chuck:

at the alignment shop a few days ago my ride height was 25 1/4 all the way around, which is probably a little more than a 1 degree nose down attitude. i'm not sure i'd want to mess with the front ride height any more...

maybe i just need some stickier tires!!!!

[orbmedia]

I would go with anti-roll bars first, then torsion bars. Get a good set that's adjustable.

[jeff91C2T]

Regarding the effect of sway bars vs torsion bars: I'm guessing you'll get more change/effet out of the torsion bars.

I did the following:

Changed Sway bars (to Weltmeister 22mm F and R). Slight change to roll stiffness but still soft ride.

Changed to Koni adustables. Slightly stiffer ride when set to firm but still overall a soft ride.

Changed torsion bars to autocross sizes (can't remember #'s). Most dramatic change to handling. Firmer ride with much nicer turn in. Way more fun to drive.

If I had to do it over again, I'd start with the torsion bars first, then shocks, then sway adj sway bars.

[turbo dave]

You know, I wouldn't do too much to the car yet, as a matter of fact I wouldn't even use sticky tires to start with. I've heard from many people that tons of stick & chassis control can mask driving mistakes, so that people go fast early, then very quickly plateau at a mediocre level, with a lot of fundamental driving errors that they need to unlearn.

A car that moves around a little, with crappy tires, forces the driver to drive cleanly and smoothly. When you get quick with a 'difficult' set-up, you can reward yourself with upgrades that you will be fully prepared to use. I'm always amazed at how fast a really good driver can be in a really mediocre machine- this past weekend, a PT Cruiser put up some respectable times in our local event!

[adamnitti]

david-

point well taken. i'm definitely one of those who wants to 'get good the more challenging way'.

before i do anything else, i'm going to firm up the setting on my rear shocks and just experiement with tire pressure. after that, i'm going to continue driving the car and learning before spending any big money.

[katigbr]

Adam,
I just want to echo some of the good advice above and add my two cents.

I think there is a lot you can do to the tire pressures to "tune" the ride. However, upgrading the t-bars and swaybars really does reduce the roll. My experience has been that the t-bar upgrade is a good first step and then the swaybar upgrade. I initially upgraded my swaybars to some pretty stiff (22mm) bars front and back without upgrading my torsion bars first. I ended up putting a lot of strain on the A-arm sway bar mount and broke one off. However, the roll was siginificantly reduced. After upgrading my t-bars to 21mm/27mm the ride was even better. It was a lot stiffer and responded better to steering input.

I'm not sure if I would have broken the mount if had I done the change the other way around. Perhaps the t-bar upgrade would have provided some additional support and might have prevented the breakage. It was probably going to break anyway. I have since welded in additional supports to the front a-arm swaybar mounts and "beefed" up the infamous rear mounts with some added bracing.

Rick

[Randy W]

Adam, there is lots of good advice here. I would also suggest staying with your new Kuhmo street rubber for a season. You will become a better driver sooner than if you were to jump up to race rubber now. Since your goal is to reduce your 911's inherent understeer in the corners, you may want to try this technique first, if you haven't already. Try braking smoothly a little earlier and extending your braking a little farther into the corner - this is essentially a trail braking trailing technique that will slow the car down more so that the front tires are not forced to, which is what they are doing when they scrub off speed while understeering. This technique also allows the weight transfer to the front to be extended longer so that the front tires will respond to your steering input when you most need it. If you are still finding understeer with the steering wheel turned, try unwinding the wheel a little until you feel the front tires bite and then smoothly reapplying your steering input.

As far as suspension upgrades, I will repeat myself here and recommend torsion bars to match your shocks first and then sway bars to fine tune your car's balance. Since you reported setting your front Konis to full firm for better performance at your autox, that's an indication your torsion bars are not firm enough. With stiffer torsion bars your front Konis would only be set to 2/3 firm compression, which is the max I would recommend. You might consider making your suspension changes one at a time so that you can learn what each one does to your car's responses. Have fun learning your "new" car and keep us posted of your progress!

[jluetjen]

katigbr: Philosophically I question the perception that "Roll is Evil ==> Thus eliminate Roll." Doing that on most non-purpose-built-racecars (ie: formula cars) will merely transfer a lot of weight to the outside tires when cornering. The result can overwhelm the outside tires and underuse the inside tires which results in slower cornering speeds. Ideally you want to tune the car so that you are maximizing the total traction and allowing smooth transitions. In order to do that, each tire needs to be "pulling its fair share" and the suspension needs to be able to use its designed-in compliance. Even F1 cars have a degree of roll designed in to the cars.

Adam; BTW -- Randy has great Autocross credentials so I would weight his input accordingly. He did mention something that made me think about the shock settings. If you car is understeering on turn-in, stiffening the front shocks will make it worse since they will transfer more weight to the front during the transition. Try backing off a couple of clicks on the front shocks and see what that does. Stiffening up the rear shocks will have a similar affect.

BTW: Koni (Carroll Smith and Allan Staniforth of Racetech) all recommend starting out with the shocks at their SOFTEST setting and then incrementally stiffening them until the car feels hard and jolty at either end under braking or hard cornering. Then back off that end by 1 or 2 clicks and continue the process at the other end until you reach the same point. Since the shocks are easily adjustable, it might be a fun test to perform at your next event.

[89911]

Added roll really disturbs the "settling" of your car prior to turn in. I have been using my car for the last 3 years at the same tracks and have gradually added all the above recommendations. I added new Bilstein's immediately, then torsion bars and sway bars. Prior to these changes, there was a few nanoseconds when changing directions that, if the car was leaning the wrong way, the whole turn would be effected. Now the timing is greatly reduced and you can just point and turn. As far as waiting to do these, it depends on what condition your car is in and how hard you drive it. Using a car the has lousy shocks, soft torsion bars and no antiroll will just afirm that, yes, your cars handling sucks! It doesn't take long to figure this out. The first event at Mid-Ohio I thought my car was the best handling thing out there. Then I got a chance to see some photos on some hard turns. Holy cabin cruiser!

[89911]

The after photo.

[R22tech]

Adam- give Jack Lewis of Jack Lewis Enterprises a call. He is an awesome Porsche tech and Porsche racer and is a suspension guru. He'll chew your ear off if you visit his shop off Buford Hwy. and ask him these kinds of questions. His number and ad. is in excellence and panorama and peachstate press.

[jluetjen]

89911: It sounds like you and your car have progressed to the point where you want the car to transition faster at which point stiffening the car (to a point) works. It also looks like your car has been lowered so you'll need a stiffer suspension to keep it off of the bump stops. Hitting the bumpstops in a corner is serious evil. Shorter suspension travel and stiffer settings = faster transitions. We're in agreement that the suspension will need to be stiffened to make it work. Throwing that set-up at a new driver may not be so successful.

BTW: It looks to me like your car is understeering a little bit. Is that the entry to the keyhole at Mid-Ohio? That set of turns curtainly rewards a car that transitions quickly from side to side as we're discussing here.

[Early_S_Man]

Adam,

I also think it is a bit early to be talking major upgrades, and that tire pressures can be adjusted a bit for gains and better 'feel.' One change that can be made at very low cost, and is even reversible for street driving is the installation of poly-graphite rear anti-roll bar bushings ... they will reduce understeer a bit for autocrossing, and may quicken turn-in response a bit. If you like them, you should probably get the rear bar mounts reinforced, as that is a weak point with 3.2 Carreras, and they frequently crack after autocrossing or track use has started.

[89911]

John, good eye. Yes that is the keyhole and it sounds like you know the entry to this is a quick series of esses of the front straight. Before, my car would load up the on the outside and would plow as the turn progressed. Now the plow is gone with throttle applied oversteer as its replacement. If done correctly, the right foot is all that is needed to get the back end around until the back straight.