Pinning rear Weisache (how do you do it)
07-29-2009, 09:14 PM
#31
Rennlist Member
Thread Starter
adding front pressure often will create a push and front rebound as well, as that inside tire of a turn cant keep contact with the ground under a quick trail brake turn. after a second or so, it should be in contact to the extent of the g loading you are able to apply. you want to get rid of the push in a 928, reduce the toe in , in the rear, and use bigger tires up front, along with loosening the swaybar, and stiffening the rear bar.
mk
mk
07-30-2009, 12:25 AM
#32
Instructor
http://928frenzy.com/Downloads/928_Tech_Forum_4.pdf
I'm sure we have all seen this article before at some stage. A back to basic theory read, hopefully it's relative to this thread Mark.
Glenn
'81 928
AU
I'm sure we have all seen this article before at some stage. A back to basic theory read, hopefully it's relative to this thread Mark.
Glenn
'81 928
AU
07-30-2009, 12:27 AM
#33
Instructor
07-30-2009, 01:07 AM
#34
Rennlist Member
Thread Starter
great reads, but what is the issue with power? from the second link, devek seems to talk about the power on changes, which from the earlier links, talk about only toe in with braking, not accel. devek talks both accel and decel being effected. Is the change they are talking about toe in under decel and towe out under accel, which I would like, as i have NEVER seen any power on issues at any track anywhere with up to 335 size tires and power from 295rwhp to 373rwhp with up to 420ft-lbs of torque.
rear tire wear is actually very good and comparable to others I race with at the track. maybe what i need to do is get more rear brake bias, pin the rear weisache to counteract rear end wiggle that could be caused by trailbraking with more rear brake. so am I understanding it correctly. weisach only works by causing toe out under accel and toe in under braking?
rear tire wear is actually very good and comparable to others I race with at the track. maybe what i need to do is get more rear brake bias, pin the rear weisache to counteract rear end wiggle that could be caused by trailbraking with more rear brake. so am I understanding it correctly. weisach only works by causing toe out under accel and toe in under braking?
07-30-2009, 01:29 AM
#35
Race Director
MK
it seems the "push" is getting worse right? Over the past season or so you increased the front tire size quite a bit and added more HP (but not weight).... you would think that will make the car MORE loose..not tight...odd
Under power it pushes....how good is the LSD?? Maybe its acting like an open diff?? Not letting the power rotate both tires? I keep thinking in terms of three "zones" of the corner....entry (fine but easier to correct with driving style) mid-apex (problem) and exit (slower due to speed lost mid corner)....since the steady state mid corner is the problem.....& more HP (you do have lots) doesn't help....can you stiffen up the rear shocks?
Its going to be fun to see the handling differences between our 928's.....I think my setup would be MORE understeering than yours...due to the huge rear tires and soft springs...but we will see...it seems to turn fine for me, but my times are quite a bit slower too
it seems the "push" is getting worse right? Over the past season or so you increased the front tire size quite a bit and added more HP (but not weight).... you would think that will make the car MORE loose..not tight...odd
Under power it pushes....how good is the LSD?? Maybe its acting like an open diff?? Not letting the power rotate both tires? I keep thinking in terms of three "zones" of the corner....entry (fine but easier to correct with driving style) mid-apex (problem) and exit (slower due to speed lost mid corner)....since the steady state mid corner is the problem.....& more HP (you do have lots) doesn't help....can you stiffen up the rear shocks?
Its going to be fun to see the handling differences between our 928's.....I think my setup would be MORE understeering than yours...due to the huge rear tires and soft springs...but we will see...it seems to turn fine for me, but my times are quite a bit slower too
07-30-2009, 02:00 AM
#36
Rennlist Member
Thread Starter
I can back off the car by 1 second a lap and its a differnt car. Im overdriving the tires a bit, but thats what you need to do to go faster! 
Hey, I know what a one legger feels like, remember, I ran a 79 at laguna with my tires and wheels. Not an issue at all. initial turn in under trail braking is ok, once the brakes are released, there is a push at the limit. power on doesnt help things at all through out the turn. turn 2 for example, got a little better with the hoosiers and could get a little wiggle with the power, but it wasnt like you want, where the power can really rotate the car. the only time the diff lets me down, is out of turn 5 from the eagle's nest, where the hoosiers really lean the car over and the inside rear gets a little spin-eee. in that area, there is no push.
I have a feeling that changing the rear toe setting to something other than bone stock setting, might be the answer. I remember my old 84 part euro 5 liter handled much better,but it was a lot slower too. I guess this is the fun part of setting up a race car. Ill change tha toe by 1/8" and see what it does.
shock settings are good for exit, entrance, etc, but during a constant turn, its kind of a swaybar , spring, or alignment setting issue I think.
mk
Hey, I know what a one legger feels like, remember, I ran a 79 at laguna with my tires and wheels. Not an issue at all. initial turn in under trail braking is ok, once the brakes are released, there is a push at the limit. power on doesnt help things at all through out the turn. turn 2 for example, got a little better with the hoosiers and could get a little wiggle with the power, but it wasnt like you want, where the power can really rotate the car. the only time the diff lets me down, is out of turn 5 from the eagle's nest, where the hoosiers really lean the car over and the inside rear gets a little spin-eee. in that area, there is no push.
I have a feeling that changing the rear toe setting to something other than bone stock setting, might be the answer. I remember my old 84 part euro 5 liter handled much better,but it was a lot slower too. I guess this is the fun part of setting up a race car. Ill change tha toe by 1/8" and see what it does.
shock settings are good for exit, entrance, etc, but during a constant turn, its kind of a swaybar , spring, or alignment setting issue I think.
mk
MK
it seems the "push" is getting worse right? Over the past season or so you increased the front tire size quite a bit and added more HP (but not weight).... you would think that will make the car MORE loose..not tight...odd
Under power it pushes....how good is the LSD?? Maybe its acting like an open diff?? Not letting the power rotate both tires? I keep thinking in terms of three "zones" of the corner....entry (fine but easier to correct with driving style) mid-apex (problem) and exit (slower due to speed lost mid corner)....since the steady state mid corner is the problem.....& more HP (you do have lots) doesn't help....can you stiffen up the rear shocks?
Its going to be fun to see the handling differences between our 928's.....I think my setup would be MORE understeering than yours...due to the huge rear tires and soft springs...but we will see...it seems to turn fine for me, but my times are quite a bit slower too
it seems the "push" is getting worse right? Over the past season or so you increased the front tire size quite a bit and added more HP (but not weight).... you would think that will make the car MORE loose..not tight...odd
Under power it pushes....how good is the LSD?? Maybe its acting like an open diff?? Not letting the power rotate both tires? I keep thinking in terms of three "zones" of the corner....entry (fine but easier to correct with driving style) mid-apex (problem) and exit (slower due to speed lost mid corner)....since the steady state mid corner is the problem.....& more HP (you do have lots) doesn't help....can you stiffen up the rear shocks?
Its going to be fun to see the handling differences between our 928's.....I think my setup would be MORE understeering than yours...due to the huge rear tires and soft springs...but we will see...it seems to turn fine for me, but my times are quite a bit slower too
09-02-2009, 11:16 AM
#37
Rennlist Member
Thread Starter
I mounted a video camera in the rear of the car, watching the action of our rear Weisach suspension. it clearly shows toe-in movement under compression. (doing aggressive "S" turns where the compresson of the spring, shows the rim toe-ing in.). This clearly could be one of the issues of getting the car to rotate. Is this possible, and independent of the Weisach function, which seems to move on thrust forces longetudinally, (i.e. accel and decel ) where it basically toes under rear braking and toes out under accel?
I can do a test of accel and decel with the same camera position to see if we get any toe change. wouldnt that be interesting!!!
mk
I can do a test of accel and decel with the same camera position to see if we get any toe change. wouldnt that be interesting!!!
mk
I understand the Weisache to be thrust sensitive not lateral load sensitive.
My understanding of the Weisache geometry is that it is designed to adjust toe due to tire thrust not lateral loading. The flat vertical plate is designed to allow the hub (outboard end) to be able to move fore and aft, flexing the plate, while maintaining the hub in its lateral location since the plate is essentially rigid in compression. The small link at the front of the arm is used to control the toe change. Under decel the hub is pulled slightly aft by the "braking" force at the rear tire. This aft movement causes the small front link (mounted at ~45 degree angle from inboard chassis end aft and back to outboard control arm end) to rotate about it pivot end mounted to the chassis. In turn the link end attached to the control arm moves aft in inward which increases toe in. The converse of this happens under acceleration. The movement is controlled by the rubber sleeve on the control arm end of the small link, allowing for this rotation. To pin the link a second bolt is installed through the control arm into the small link forming a rigid member and eliminating then relative rotation of the small link relative to the control arm fixing the toe angle.
So to Marks question about pinning the Weisache and whether pinning will help: If under steer is occurring under decel then pinning may be helpful, as it will eliminate the toe in generated by the Weisache suspension. If it is occurring during accel pinning will work against the desired result, as the Weisache geometry adds toe out and aids in rotation.
My understanding of the Weisache geometry is that it is designed to adjust toe due to tire thrust not lateral loading. The flat vertical plate is designed to allow the hub (outboard end) to be able to move fore and aft, flexing the plate, while maintaining the hub in its lateral location since the plate is essentially rigid in compression. The small link at the front of the arm is used to control the toe change. Under decel the hub is pulled slightly aft by the "braking" force at the rear tire. This aft movement causes the small front link (mounted at ~45 degree angle from inboard chassis end aft and back to outboard control arm end) to rotate about it pivot end mounted to the chassis. In turn the link end attached to the control arm moves aft in inward which increases toe in. The converse of this happens under acceleration. The movement is controlled by the rubber sleeve on the control arm end of the small link, allowing for this rotation. To pin the link a second bolt is installed through the control arm into the small link forming a rigid member and eliminating then relative rotation of the small link relative to the control arm fixing the toe angle.
So to Marks question about pinning the Weisache and whether pinning will help: If under steer is occurring under decel then pinning may be helpful, as it will eliminate the toe in generated by the Weisache suspension. If it is occurring during accel pinning will work against the desired result, as the Weisache geometry adds toe out and aids in rotation.
09-02-2009, 01:30 PM
#38
Rennlist Member
The original pin position was designed for 225 wide tires and offered considerable toe change.
two positions for the factory set pin were considered and the one that allowed the most/fastest toe adj was choosen and never changed.
By revising the pin location, you are adding "Stiffness" to the rate of toe change in the rear.
Try it , you might like it and it is reversable.
two positions for the factory set pin were considered and the one that allowed the most/fastest toe adj was choosen and never changed.
By revising the pin location, you are adding "Stiffness" to the rate of toe change in the rear.
Try it , you might like it and it is reversable.
09-02-2009, 03:23 PM
#39
Rennlist Member
Thread Starter
Thanks Marc!
Dont know what it looks like or what im looking for, but Ill take a look.
From the infomation posted, and the way the car is handling, im surprised i have a problem under acceleration out of turns. trail braking response is a little muted, so that might be the problem. however It was curious to see the rim toe in with the video under the car, in the wheel well. as it compresses, it toes in. Ill have to do some power on and braking video to see if the action changes at all.
Dont know what it looks like or what im looking for, but Ill take a look.
From the infomation posted, and the way the car is handling, im surprised i have a problem under acceleration out of turns. trail braking response is a little muted, so that might be the problem. however It was curious to see the rim toe in with the video under the car, in the wheel well. as it compresses, it toes in. Ill have to do some power on and braking video to see if the action changes at all.
The original pin position was designed for 225 wide tires and offered considerable toe change.
two positions for the factory set pin were considered and the one that allowed the most/fastest toe adj was choosen and never changed.
By revising the pin location, you are adding "Stiffness" to the rate of toe change in the rear.
Try it , you might like it and it is reversable.
two positions for the factory set pin were considered and the one that allowed the most/fastest toe adj was choosen and never changed.
By revising the pin location, you are adding "Stiffness" to the rate of toe change in the rear.
Try it , you might like it and it is reversable.
09-03-2009, 01:31 AM
#40
Rennlist Member
Thread Starter
Here is the video of our rear ends in action. I think what i was seeing was the tire movement, not the rim toeing in or out. Ill have to do some more testing.
http://www.youtube.com/watch?v=KHm8kIu5S8U
http://www.youtube.com/watch?v=KHm8kIu5S8U
09-03-2009, 10:19 PM
#42
Instructor
This could provide some interesting and perhaps also useful information.
I hope you will continue testing and provide more videos.
As for camera location - it would be desirable to get a view at as many of the links as possible, and the wheel rim.
Also, one needs to have acccess to information on what is going on at what time in the video - i.e. side forces, accel - decel, combination of forces and so on.
09-04-2009, 11:21 AM
#43
Developer
Will these help?
One nice thing is that its reversable. If you dont like it, take the bolt back out. No harm, no foul.
It is not an issue of just having more HP or wider-than-stock tires. Higher wheel offsets that widen the track are the largest single factor (IMHO) in changing this geometry such that the amount of movement allowed by the stock Weissach is now too much because you have now lengthened the torque-lever arm on the suspension member.
I happen to like it, but my rear track is now 66" (measured at he centerline of 315 rear tires)
One nice thing is that its reversable. If you dont like it, take the bolt back out. No harm, no foul.
It is not an issue of just having more HP or wider-than-stock tires. Higher wheel offsets that widen the track are the largest single factor (IMHO) in changing this geometry such that the amount of movement allowed by the stock Weissach is now too much because you have now lengthened the torque-lever arm on the suspension member.
I happen to like it, but my rear track is now 66" (measured at he centerline of 315 rear tires)
09-04-2009, 11:23 AM
#44
Rennlist Member
Thread Starter
Thats why i put the title on the video when I started "S" turning. (side to side turns). The beginning is just straightline acceleration in 1st. Overall, it was a 1st try at some suspension cam video. 
. next time, Ill try and get more areas, but its tough as Im limited to a camera with no view finder, and the suctioncup mount, along with limited light.
But, ill try some hard, fast 2nd gear turns to see the action of the wheel and suspension next time.
mk
. next time, Ill try and get more areas, but its tough as Im limited to a camera with no view finder, and the suctioncup mount, along with limited light.But, ill try some hard, fast 2nd gear turns to see the action of the wheel and suspension next time.
mk
Very interesting, how do you get those ideas..
This could provide some interesting and perhaps also useful information.
I hope you will continue testing and provide more videos.
As for camera location - it would be desirable to get a view at as many of the links as possible, and the wheel rim.
Also, one needs to have acccess to information on what is going on at what time in the video - i.e. side forces, accel - decel, combination of forces and so on.
This could provide some interesting and perhaps also useful information.
I hope you will continue testing and provide more videos.
As for camera location - it would be desirable to get a view at as many of the links as possible, and the wheel rim.
Also, one needs to have acccess to information on what is going on at what time in the video - i.e. side forces, accel - decel, combination of forces and so on.
09-04-2009, 11:28 AM
#45
Developer
I think I used a M8 bolt (5/16" in diameter) so as not to need to drill too big a hole and hopefully not weaken the inner link. Went through Pikes Peak this year just like you see here with no issues.