mark kibort

Just wanted to have a friendly discussion. im not on the bumpstops, but could touching them. dont know if thats the issue. open to checking it out. just pinging the guys here to get some ideas and some experiences.
nothing more nothing less. instead, the discussion becomes a pissing contest.
Like i said, im open to checking it all out with whatever tools i have available.

danielyonker

Mark - I think I hear your phone ringing. It's probably Penske himself calling to offer you a job. Hurry......quick!

ProCoach

mark kibort

[QUOTE=danielyonker;12911201]Mark - I think I hear your phone ringing. It's probably Penske himself calling to offer you a job. Hurry......quick![/QUOTE
.....DxxK

mark kibort

What are you, 7???

Alexandrius

Mark wins, #1 troll on rennlist. I have been quietly following this with much amusement.

Veloce Raptor

mark kibort

Grow up!

multi21

I truly believe Mark has long periods of time where he doesn't work, have a job or project and is looking to be entertained. This is one of those instances.

The very nature of having 17 year old bump stops that you "may be touching" would be the first thing I would change out -- others have suggested shocks, etc. If you don't have a baseline with new "variables" how can you start trying to correct what is perceived to be wrong much less your driving style?

mark kibort

Look, for those of us that have been around this sport and have raced for 10s of years, this is a normal discussion. many of us here can wheel a car around a lap as fast as anyone. as far as style, there is not too many variations to get around a track fast. in fact, most of us can run near or best times using several lines. however, i do believe the main differences between drivers really is in the decision making. (risk /reward decisions during a race and how well respond to the unexpected ..... hitting dirt or grass on exits of tuns, how we correct from instability, etc)

As far as a push, or being loose, its the drivers decision to overwork the rears or the fronts on every turn during a lap. Too loose, and you need to slow down slightly to reduce it, too much push and you might be faster than someone that slows down to remove the push in the same car. (at the cost of wearing the fronts even more, you can still be faster in some cases). lots of factors, too many to go through here, but the point is, if you take the ego out of the discussion, its really about providing information of a quality that anyone with experience has seen. a push. and how to tune it out is as varied as the types of push you might see in a race car.

I was going after a few ideas, and clarifying as to what i think might be causing it, as well as to look at ideas from the list as to anyone else has address it.
https://rennlist.com/forums/images/editor/separator.gif
as i mentioned, i had a push. it was on bad front tires, after the change, things dramactically improved and went back to the " normal" state. still erring on the push side. i want more oversteer and some said it might be a function of the front engine weight balance.

I know i can put on a new set or even better set of tires and make the car handle as I would like it. its been there before and has run surprising fast laps at laguna. over the past 6 years, its been constantly in the same time range without exception within 1 second of the best times. I dont see a push in areas where suspension loading is at its greatest (down the corkscrew) i dont know for sure if the bump stops are being engaged , or to what level they are being engaged and i will investigate. my comment earlier on the smooth surface was to ask the question of what happens if you were riding on the bumpstops around a turn with little vertical accelerations. there is never an infinte level of spring rate, due to the bump stops, and coil over mounts as well as flex in the suspension component couplings. Heck, i had a blown out rear shock for probably over 5 years and it really didnt hurt the handling that much. in a BMW, when a shock was blown, it was obvious. there is a lot of stuff going on in a 928 that doesnt fit the mold of other cars. makes it hard to find problems (good and bad)

the main point of asking the question was to find out ways that i might not have thought of, to remove a push.. maybe some things that were counter intuitive or unique. so far im left with (if im not running on the bump stops at all) , better tires, rear toe change, and primarily , stiffening the rear sway bar.

the tires solution brings me back to tuning, as i want the car more loose for as the tires wear out, for the majority of their life. Rear toe change.. too much, and that could provide some bad stability, or make it better if its causing things to be too tight. stiffening the rear swaybar is easy to do. shock changes, would help with setting the car before a turn, but i dont think they would help in constant radius constant g loading turns. and if i am on the bump stops or near them , certainly i can raise the car up a 1" and see how that effects things. loose the CG advantage, but gain in roll centering, and lowering the negative effects of the increase spring rate of the bump stop or worse.

as far as shocks. I did have them rebuilt and still trying to find settings that work. havnt played with spring rates, but im near Andersons car (the 600hp verson of the 928 that won much of the time overall, POC races out west) that did well in speedvision, which ended up with the spring rates i have now, but he ran the motons vs my Koni set up. (i drove that car and it didnt have the understeer, but 4 " wider front track, 13" slicks, and bumpsteer addressed, etc)

multi21

A lot of people here who are real professions oN RL have offered their opinions, but you seem reluctant to take advise of some and that's fine, but you did ask.

It took me a long time to dial in my race car after purchase because I was reluctant to change out parts that I thought were perfectly good. in the end it was futile and having new shocks, bump stops, tires etc.gave a baseline and as those tires wore I understood what handling characteristics it would have and learned to live with it (deal with it).

Have you figured in fuel loads as well?

Age? Unfortunately we all like to think we're as fast as we once were, but father time is brutal.

mark kibort

Yes, There is always several psychological factors in athletecs that are resistive to change, but im generally open to it. age? the car's or mine?
my performance in the car has not change. physically, reaction time, conditioning is still unchanged. times are relatively unchanged. (A little more adverse to risk, as far as on track decisions... its not life or death mode any more,but still drive the car hard)
the nice thing about my car is that its relatively unchange for over 15 years, so any changes that are made , if they are minor, i can sense pretty quickly. (shock setting, sway bar, tire pressure, tire quality or brand , etc)
yes, ive tracked the balance and changes to weight over the years, and fuel is part of that balance both with starting fuel loads and ending. i have the car dialed in for the best performance mid to the end of the race, however, the tires dont always cooperate, and end up running the fastest laps about lap 4-5.
with good tires and conditions, i can run the fastest laps near the end if needed.
Ive maximized balance of the car by moving things around and setting ride height best i can to get 50/50 cross weights.
but, going back to the your first point, i have settled into this car like an old glove. good and bad. when i put new shocks in the rear , dynoed and set to give me more range (i was maxed out bump and compress prior), i set it at the middle and then adjusted from there. i didnt notice any differences, which is kind of weird, due to one shock being completely blown out. its a problem tuning a car with a lot of rubber and resistance. if I was to change out all stock rubber bushings (and there are more on a 928 than any car you would ever see), i think all changes wold be more noticable and predictable. however, i cant afford to heim -joint everything , anytime soon.

i am taking the advice and figuring out what to test first . it seems i need to see if im near the bumpstops and get that rear swaybar tighter and see if that helps. (plus change the rear toe or at least check to see if it has too much toe in ...... pinning the weisach loosens things up a bit too and i havent done that)

again, I'm just asking here what folks have seen with tight cars and what are the easiest things to try first.

333pg333

How about mounting a Go-Pro or similar around the suspension and take a look at what is actually happening? Short of fitting suspension pots (which aren't that expensive) and doing qualitative testing this might be the quickest way to answer some of your questions.

gbuff

Boy, Mark, you really do bring out the best in people --please, I'm kidding. Really.

I'm the farthest thing from a suspension guru that there is, and as such can't really offer any advice, but casually reading through some of this thread (no time/patience for the entire thing) there seems to be some really good info being offered....I'll stop there.

Best of luck--really.
Gary

mark kibort

Im not a guru either, but have a lot of grass roots experience in trying new things. I've had things break at the track, in races and have seen their effects.
yes, there is some great advice here. some of the responses were only to clarify things that might not be clear at first.... going all the way back to the suspension design, since it is such a departure to what is normally seen on street or track cars. (as well as back to back comparisons that fixed the problem in a dramatic fashion. , or had caused the issue) anyway, ill be taking a lot of the suggestions and do what i can with them. Some, not all of the "experts" want to bag on driving technique here, and im here to say, its pretty easy to know when the set up is not working right. no technique in that first video could allow the the car to behave in any normal way as far as the push. it was something solved with less wing, splitter, hood vent and better tires. proof is in the snap shot of the same turns, at a later time , with lap times, and approach speeds being the same (actually slightly faster). Much of this is hard to discuss on these threads because all the information is not available to all that review it.

did you see the go pro footage of the rear suspension from t-hill.. thats exactly what i did? Ill try that on the front if i can find a place to get a decent angle. heck, i might even cut a peak hole and look through that for the camera.