Handling issue discussion.
#16
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Thread Starter
im trying to understand the effects if you are riding on the bump stops or shock body, in a smooth turn (no undulations in the road).
im thinking its something analogous to applying the brakes and hitting the bump stops as well, even before max braking has been reached. would that be comparable, and maybe easier to see the comparison to effects on lateral accelerations (albiet there are a couple of more factors involved there)
scott, if you ready my responses, you will see i was answering the assumptions of those responding. one talked about mcpherson struts (i dont have them), you talked about making bump stops, (ive done that), someone asked about tire temps (done that too), and one also mentioned the bump stop rubber, works like a progressive spring, and i agreed , in some cases it can be used effectively... .proof, ive seen no ill effects when hitting the bump stops in teh corkscrew, and im wondering if i am in some other pushy turns. I dont think i am based on markings ive made on the shocks
I really want to know what i can do about the push, assuming that im not on the bump stops and it goes back to your original post i copied here, about roll coupling distribution. maybe tightening up the rear swaybar or higher spring rate in the rear?
what i do know, is with a good set of front tires, the problem goes away for a while. problem is, i want to be able to balance the car with not so good tires up front. either after a few sessions or toward the end of the race.
.,
#17
Rennlist Member
we are not talking about surface quality here, we are talking about surface attributes. (rises and falls where suspension mitigates the effects on instantaneous vertical forces). tire temps across the tire are optimal . hottest on the inside 3rd, gradually going lower to the outside by 10 degree increments.
#18
Rennlist Member
Thread Starter
winders got it, based on his response saying "even on a smooth turn, the effects......" it would make no sense to be talking about surface quality here.
so, what "physics " doesnt change. If the car is going over bumps vs it being flat or smooth (no bumps..... nothing to do with surface quality), the physics dont change... physics doesnt ever change! (the factors can though. ) so, what are the effects on the handling?
Last edited by mark kibort; 01-05-2016 at 07:51 PM.
#19
Rennlist Member
Mark
I noticed all the steering angle you had in that recent thread. Seemed too much just on a visual sense.
What you're describing sounds like something I went through a few years ago with some KW shocks. Mostly on a few slower / tighter turns. Played around with quite a few things trying to discover and fix this issue. In the end we replaced the KW adj camber plates for the Racers Edge version which are designed in such a way as to increase droop. Pretty much fixed the situation instantly. We figured that I was just into the bump stops and ran out of travel which inhibited the amount that the nose could go down to increase frontal grip. I would agree that this is a relatively simple place to start. Not sure what options are available to the 928 though?
I noticed all the steering angle you had in that recent thread. Seemed too much just on a visual sense.
What you're describing sounds like something I went through a few years ago with some KW shocks. Mostly on a few slower / tighter turns. Played around with quite a few things trying to discover and fix this issue. In the end we replaced the KW adj camber plates for the Racers Edge version which are designed in such a way as to increase droop. Pretty much fixed the situation instantly. We figured that I was just into the bump stops and ran out of travel which inhibited the amount that the nose could go down to increase frontal grip. I would agree that this is a relatively simple place to start. Not sure what options are available to the 928 though?
#20
Rennlist Member
Thread Starter
yep... its kind of a problem with the 928 steering rack. the good news, is that it desensitizes any knee jerk movements so it's a tame car for DE guys, but a little more work to race. (and more movement than i like for sure. a contrast to something like a Vantage, that has about half the steering input for the same wheel movement)
so, you are saying that more droop on the opposite side, allows for that side to be more involved in the turning forces? from the "fender cam, i dont think we are getting near full droop, even though that the droop of the Koni, is much less than a stock set up.
go to 12:37 on the video and see one of the pushiest, left turns, that doesnt show the inside tire needing any more droop on that side.
Did you mean , to increase compression range? like , getting a shorter shock body to keep from hitting the bump stop? Just want to be clear with what you did to improve the situation. again, i think you might have a strut suspension, so there are no camber plates that would or could work.
so, you are saying that more droop on the opposite side, allows for that side to be more involved in the turning forces? from the "fender cam, i dont think we are getting near full droop, even though that the droop of the Koni, is much less than a stock set up.
go to 12:37 on the video and see one of the pushiest, left turns, that doesnt show the inside tire needing any more droop on that side.
Did you mean , to increase compression range? like , getting a shorter shock body to keep from hitting the bump stop? Just want to be clear with what you did to improve the situation. again, i think you might have a strut suspension, so there are no camber plates that would or could work.
Mark
I noticed all the steering angle you had in that recent thread. Seemed too much just on a visual sense.
What you're describing sounds like something I went through a few years ago with some KW shocks. Mostly on a few slower / tighter turns. Played around with quite a few things trying to discover and fix this issue. In the end we replaced the KW adj camber plates for the Racers Edge version which are designed in such a way as to increase droop. Pretty much fixed the situation instantly. We figured that I was just into the bump stops and ran out of travel which inhibited the amount that the nose could go down to increase frontal grip. I would agree that this is a relatively simple place to start. Not sure what options are available to the 928 though?
I noticed all the steering angle you had in that recent thread. Seemed too much just on a visual sense.
What you're describing sounds like something I went through a few years ago with some KW shocks. Mostly on a few slower / tighter turns. Played around with quite a few things trying to discover and fix this issue. In the end we replaced the KW adj camber plates for the Racers Edge version which are designed in such a way as to increase droop. Pretty much fixed the situation instantly. We figured that I was just into the bump stops and ran out of travel which inhibited the amount that the nose could go down to increase frontal grip. I would agree that this is a relatively simple place to start. Not sure what options are available to the 928 though?
#21
Rennlist Member
Smooth, meaning without bumps. I should have said "flat", or "consistent". rough vs smooth would make no sense to talk about. If you understood physics, you might have realized that. That's a friction coefficient factor. not really the question here. But you have a hard time reading between the lines... i get that..... winders got it, based on his response saying "even on a smooth turn, the effects......" it would make no sense to be talking about surface quality here. so, what "physics " doesnt change. If the car is going over bumps vs it being flat or smooth (no bumps..... nothing to do with surface quality), the physics dont change... physics doesnt ever change! (the factors can though. ) so, what are the effects on the handling?
I am trying to help you here . No reason to get pissy. Smooth without bumps is what I am talking about. The benefits of camber and toe are there irrespective of the surface characteristics. Which is what I said.
#22
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Handling issue discussion.
There is no such thing as a smooth surface. You might not see or feel the bumps, but they are there.
I work with cars that run on bump stops. They are not easy to set up or a set and forget kind of thing. You have to do a lot of work and be experienced with them to make it work.
I work with cars that run on bump stops. They are not easy to set up or a set and forget kind of thing. You have to do a lot of work and be experienced with them to make it work.
#24
Rennlist Member
yep... its kind of a problem with the 928 steering rack. the good news, is that it desensitizes any knee jerk movements so it's a tame car for DE guys, but a little more work to race. (and more movement than i like for sure. a contrast to something like a Vantage, that has about half the steering input for the same wheel movement)
so, you are saying that more droop on the opposite side, allows for that side to be more involved in the turning forces? from the "fender cam, i dont think we are getting near full droop, even though that the droop of the Koni, is much less than a stock set up.
go to 12:37 on the video and see one of the pushiest, left turns, that doesnt show the inside tire needing any more droop on that side.
Did you mean , to increase compression range? like , getting a shorter shock body to keep from hitting the bump stop? Just want to be clear with what you did to improve the situation. again, i think you might have a strut suspension, so there are no camber plates that would or could work.
so, you are saying that more droop on the opposite side, allows for that side to be more involved in the turning forces? from the "fender cam, i dont think we are getting near full droop, even though that the droop of the Koni, is much less than a stock set up.
go to 12:37 on the video and see one of the pushiest, left turns, that doesnt show the inside tire needing any more droop on that side.
Did you mean , to increase compression range? like , getting a shorter shock body to keep from hitting the bump stop? Just want to be clear with what you did to improve the situation. again, i think you might have a strut suspension, so there are no camber plates that would or could work.
#25
Rennlist Member
Thread Starter
("sure you were")
Again, the discussion isnt talking about surface quality, we are talking about the effects of suspension compression at the end of travel, and roll couple distribution changes.
The question im acting, is that if the surface is perfectly smooth, would you even need a suspension. (i.e. running on the bump stops during braking or corning) if you are at high g loading , does toe really matter that much. after all the inside tire is barely touching the ground. and yes, camber is important, but ive already shown there are no hot spots on the tire. very well distributed and wear characteristics.
the real question is there a way to really get rid of the push. easy to make the rear loose. thats not what i want. I want to fix the push, without having to buy a new set of front tires every 2 races.
maybe as Scott mentioned, i could stiffen the rear bar and change the roll couple distr. thats what im leaning toward first.
#26
Rennlist Member
Thread Starter
There is no such thing as a smooth surface. You might not see or feel the bumps, but they are there.
I work with cars that run on bump stops. They are not easy to set up or a set and forget kind of thing. You have to do a lot of work and be experienced with them to make it work.
I work with cars that run on bump stops. They are not easy to set up or a set and forget kind of thing. You have to do a lot of work and be experienced with them to make it work.
Its not hitting the bump stops on the corners in question.
you are advising or trying to help when you haven't asked any of the right questions. one thing that sticks out, is that the 928 has a weisache rear end. it fights turns and rotation because it has an auto-toe-in functionality. i could counteract it by pinning the rear end or adding more rear toe.
#27
Rennlist Member
Thread Starter
Well essentially I just mean that if you were going into your bumpstops and reducing travel this would/could have a detrimental effect on the steering. I have a vague recollection of the front end suspension on a 928 but am not sure what mods are available to it? How are your other 928 race buddies setting up their suspension? Is there any aftermarket suspension product available for it? You'd think that someone else has run into a similar problem even though there's not a lot of 928s running around hard on the track.
#29
Rennlist Member
Thread Starter
#30
All arm chairing aside. isn't the only way to ferret out this bump stop thing is to raise the ride height to ensure full suspension travel at all times and see what that does to laptimes? Who cares if it is tight or loose if it is fast?