mark kibort

They would have no effect on the sway bar forces on the sub frame brackets.
I have no outside tire wear with only 1.7 degrees of camber so I suspect the flex everyone talks about is not as bad as thought. But I dont know for sure, as i havent tried it. The fender cam showing 1.4 G turn video shows no flexing that could cause camber changes. sure, all chassis stiffinng could be a good thing, but it also is part of the compliance of the system. anyway, its too low on the frame and would bottom out on my car running down the corkscrew at laguna, so it wont work anyway. I barely scuff the alternator as it is.

mk

928SS

nice writeup! kinda what I was planning to do on a skid pad area at willow after I get the mounts reinforced. HP driving in public areas is kinda frowned upon out here...

imo, the challenge is that during the AX series, we'll run everything from a road race track w/banked turns to what feels like a go cart track on a tennis court, so the "average" will have a pretty healthy std deviation most of the time.

how sensitive is it normally? ie if tuned on a turn w/a 50' radius, about how much will it be off on a 100' or 200' radius turn? best to err on the large side or smaller side for the average?

thx for the insights!

928SS

yiikes! thats some wicked g forces! do you hit the pan ever? I noticed I bottomed out on a dip recently and did a nice polish job on a few fins... scared the poo out of me at the thought of trashing my motor so easily.

belgiumbarry

don't we have to mention that sway bar settings ( soft-stiff) are different as the mounting holes to choose from are on the bar or on the wheel hubs ?

Lizard928

Mark the other thing to note for stiffer springs vs stiffer sway bar is that stiffer springs in the front also help prevent nose dive under heavy braking, and on the rear help prevent squating and in turn lifting the front tires up.

I am running 1000/500lbs front/rear on my car, and the front is good, could go stiffer without any real downside, but the rear REALLY needs to be stiffer, I have a set of 600lbs to go in there, and that will help. But I am thinking for my driving 1100-1200 front with around 750 rear would be prime.

As well Belgiumbarry, All the discussion here as stated in the OP is based on the adjustments on the bar ONLY.

RKD in OKC

The 928 is not nearly as sensitive to the radius as other cars, but it is better to err on the side of larger radius turns. The general tendencies when driving at the limits are that in tighter turns cars tend to understeer, when the curves get larger and speeds get much higher it tends towards oversteer. A typical skid pad is 100' radius which is generally considered an average turn for tracks.

The good thing is that a 928 responds very calmly to steering input to bring the rear under control under braking if you over cook corner entry on a high speed or banked corner.

Preloading.
On cars that make both left and right turns preloading is only necessary to help remove torque steer when under heavy acceleration. Torque steer is most noticeable in straight line acceleration with less than optimal traction. The front of the car dolphins or waggles back and forth. Espeically as PSD or LSD tries to transfer power to the non-slipping wheel. Adding a little downforce to the right rear with swaybar preload (adjustable link length not stiffness) will help.

WallyP

If you are thinking about gymkhana...


http://video.kenblockracing.com/flas...FFF&autoplay=0

You could do that, right?

RKD in OKC

Those drifting cars are set up with more steering, ie., the front wheels turn farther. That is the secret to how far you can hang the rear out and maintain control without just spinning.

928SS

holy smokes!! now that was friggin amazing! so will my 928 do that if I use the 928 SP bushings?

mark kibort

You are going to open an entire can of worms if you start talking "dive" under braking. . Things like rebound shock settings on the rear,, bump settings in the front, front grip, alignment, bump steer changes, rear brake bias, weight balance, technique, etc all are factors here. But looking at steady state braking, the 750lb springs i have now up front give near the right amount of dive. I think anderson has proved that the 800s are the best best, as he was as stiff as the 1000s, and his car was not handling well at all. He changed somethings during our races with Speedvision /SpeedGT and he has not really changed much since then. 1000 lb springs may feel good because you car will be more gocart like, but actually you will introduce a lot of oversteer and push, even with the front bar disconnected. He is even running slicks, and big ones at that, which would require more spring and bar in theory. probaby one of the reasons he is way faster on slicks than he is on DOTs for the same track, where the 'tuned" pro teams dont see quite as much difference in times as mark saw betweek the two tire types.

At glowing rotor points at Laguna, dive currently is not that bad. That laguna shot above, is diving down 10 storys, 60-80 mph, and a very tight turn.

At the Thunderhill track event this next week, we will be able to see two cars with different suspension setting on the same track at near the same speeds. (ie Dennis and me) he is sprung much tighter than I am. You will be able to watch the video and see what you think.

mk

928SS

ah! very good! sounds like the skid pad will be perfect for testing, although the airport in wally's video looks like a total hoot

I did notice it tended to understeer a bit on tighter stuff, so I just made sure I had all my braking done a bit earlier and tried not to unsettle the car w/abrupt power changes to give the fronts all the help I could.

gotta admit - when it was in stock trim, it was a very balanced, forgiving and easy to manipulate car at it's "natural" limits. w/all the extra power, better brakes, tighter steering, etc it is MUCH more sensitive to inputs and requires a lot more effort to make transitions super smooth. and due to the higher cornering speeds there is less margin for error/corrections. makes for a faster, more exciting ride for sure. but one must really stay ahead of it or it'll make you look like a 'tard in a hurry.

but after playing instructor in a 996 the other day at willow for a few laps, I think it's still a llitle easier to drive than it's rear engined counterpart. however, the 996 is decidedly one incredible HP machine for something that simply rolled off the showroom floor.

mark kibort

The only time ive hit the pan , I was straddling a birm at thunderhll. actually one more time. there was a dip in the road when i was going 100mph plus on 280hywy. I saw it at the last second, and it was the sickest sound you have ever heard. i was amazed it was only pan gouging for how hard we bottomed out. otherwise, i just scrape the big bolts on the lower control arm brackets occasionally and barely scrap the alternator cooling hoses. a Carl Bar would not work. it would be too low and hit often. remember, my ride hight is near 110mm.

mk

mark kibort

Here is what a push looks like on the track. this was induced by only wing settings and look how barely driveable the car is.
http://www.youtube.com/watch?v=GRG6Y791iBE

mk

928SS

kinda why I didn't bother w/adjustable koni's. didn't want to get into the suspension tuning game. I suspect another slippery slope is only a phone call/credit card charge to one of the big 3 away, lol.

IIRC, Mark A. hasn't left much of a stock 928 under there, so using him as a reference point for springs might not work out too well for a stockish 928. I suspect you and dennis are prolly better examples in that regard, although U guys are still pretty out there compared to a street/AX junkie like me.

mark kibort

To a certain extent, yes. however when he made the changes to go much softer, his chassis wasnt much different than ours at all. now he has bars everywhere. Joes is still like mine. not much difference in the chassis.

My car is still pretty stock. I have less mods than you will find in your local high school parking lot. i have one of the most simple 6 point cages you will ever see, yet it does the job in the chassis and its almost there in the saftey area.

one of the things that you might see , is softer is sometimes better. I often see over sprung cars that handle like crap, yet the owners are in denial of why they handle so bad. Guys like dennis, like the slidey feeling of a tight sprung car. But, its not going to be as fast as one that is just near the edge with a little oversteer for most turn exits. IMHO.

Ive got over 110 race days with this chassis. after all this time, i think 50lb heavier springs front and rear would provide an advantage at some tracks. (that would be 800/500). You also have to look at my weight and tires. If i was going to run street tires, im fine where i am.

mk