New Product: 928 Bump Steer Kits
05-15-2013, 11:04 AM
#46
Developer
Thread Starter
Nicely done. Unfortuantely a one-of, not a kit piece you can mail to anyone because of your modified spindles.
We used the 7 degree cone taper (self-tightening taper) which is what Porsche called for and is used in the stock tie rod end. Again, Porsche engineering.
We used the 7 degree cone taper (self-tightening taper) which is what Porsche called for and is used in the stock tie rod end. Again, Porsche engineering.
05-15-2013, 11:12 AM
#47
Actually English engineering as the 944,928 spindle/hubs/bearings are all ENGLISH not metric. I made enough of those kits and got tired of drilling and reaming spidles (the mailing part of it) and decided to post my method, same goes for the 928 crew. When you have to trust USPS with a set of M030 spindles, and insure accordingly, it gets old.
05-15-2013, 11:27 AM
#48
Administrator - "Tyson"
Lifetime Rennlist
Member
Lifetime Rennlist
Member
05-15-2013, 12:00 PM
#50
Administrator - "Tyson"
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Back to lowered 928's - why doesn't someone make a set of drop spindles? 
05-15-2013, 01:33 PM
#53
Rennlist Member
Lets look at this in a little more detail.
While the bump steer kit isn't a horrible idea. The math it takes to actually determine the spacing, is substantial.
As the suspension compresses on a unequal length dual a-arm suspension the rate of camber increases, this is not a linear rate either. So first you must determine this ramp.
Then you need to determine exactly how much compression you will achieve in the corner with the rest of the setup you have, and again calculate what the camber rate is at that time.
You then have to determine how the angling of the tie rods will affect the toe in relation to the camber of the hub. Before you can adjust the spacing and therefore the arc of the tie rod to keep your correct suspension geometry.........
No offense to most people on this list, but I seriously doubt that most of the board could figure this out.
Now lets look at the last statement of Mike's posting.
If you look at the pictures posted by Carl in the first post, you can clearly see that the heim joint in the picture, that the threads have been rolled in and are not cut with a tap/die/CNC tool. Then you look at the part that Carl has made, and you can clearly see that it has had cut threads, not rolled. Each sharp edge created when you "cut" threads leads to a stress riser. Rolled threads do not have nearly as many and in ALL cases leads to a much stronger part.
Now if you go back and look at the picture that was posted (Rob Edwards), of the bumpsteer kit mounted on the white zombie, you can clearly see that instead of a setup like Carl's the person who made this likely put a tapered sleeve into the factory tapered hole, and then put a bolt with rolled threads through the entire assembly. They also did one other thing that is a very wise idea. Put a nice thick heavy washer on the bottom so that if the heim joint wears to the point of failure, it likely will not be able to fall off 100% and will enable the driver enough control to be able to get off the track safely.
Personally, I would take the setup on the white zombie over the other as far as safety is concerned.
I cannot comment on the bump steer kit's requirement as I have never lowered a 928 to worry about this. Though I would imagine that a slight change to the tie rod angles would not be a bad idea. But again there is lots of work to determine as to how much and what is needed!
While the bump steer kit isn't a horrible idea. The math it takes to actually determine the spacing, is substantial.
As the suspension compresses on a unequal length dual a-arm suspension the rate of camber increases, this is not a linear rate either. So first you must determine this ramp.
Then you need to determine exactly how much compression you will achieve in the corner with the rest of the setup you have, and again calculate what the camber rate is at that time.
You then have to determine how the angling of the tie rods will affect the toe in relation to the camber of the hub. Before you can adjust the spacing and therefore the arc of the tie rod to keep your correct suspension geometry.........
No offense to most people on this list, but I seriously doubt that most of the board could figure this out.
Now lets look at the last statement of Mike's posting.
If you look at the pictures posted by Carl in the first post, you can clearly see that the heim joint in the picture, that the threads have been rolled in and are not cut with a tap/die/CNC tool. Then you look at the part that Carl has made, and you can clearly see that it has had cut threads, not rolled. Each sharp edge created when you "cut" threads leads to a stress riser. Rolled threads do not have nearly as many and in ALL cases leads to a much stronger part.
Now if you go back and look at the picture that was posted (Rob Edwards), of the bumpsteer kit mounted on the white zombie, you can clearly see that instead of a setup like Carl's the person who made this likely put a tapered sleeve into the factory tapered hole, and then put a bolt with rolled threads through the entire assembly. They also did one other thing that is a very wise idea. Put a nice thick heavy washer on the bottom so that if the heim joint wears to the point of failure, it likely will not be able to fall off 100% and will enable the driver enough control to be able to get off the track safely.
Personally, I would take the setup on the white zombie over the other as far as safety is concerned.
I cannot comment on the bump steer kit's requirement as I have never lowered a 928 to worry about this. Though I would imagine that a slight change to the tie rod angles would not be a bad idea. But again there is lots of work to determine as to how much and what is needed!
Awesome Colin...certainly beats the **** out of "I know, but Im not telling YOU guys...".
05-15-2013, 02:30 PM
#55
Developer
Thread Starter
Bump steer is a bigger issue on cars with strut-type suspensions, without question.
But that is not to say that the 928 with its dual unequal length a-arms doesn't have any, as this data shows. We just have less than they do.
Good resources on this topic are Carroll Smith's "Engineer to Win", or "Tune to Win" or Allan Staniforth's "Competition Car Suspension"
Carroll Smith focuses largely on open-wheel racers, but as our car has dual-arm suspension too, his information is directly applicable to the 928.
But that is not to say that the 928 with its dual unequal length a-arms doesn't have any, as this data shows. We just have less than they do.
Good resources on this topic are Carroll Smith's "Engineer to Win", or "Tune to Win" or Allan Staniforth's "Competition Car Suspension"
Carroll Smith focuses largely on open-wheel racers, but as our car has dual-arm suspension too, his information is directly applicable to the 928.
05-15-2013, 03:08 PM
#56
Rennlist Member
bumpsteer is not all that bad. if you think about it, a fully compressed suspension in a high G turn will only have the inside tire in full droop, and the outside tire is doing the steerinig. in this case, bump steer desensitizes the turn which is probably a good thing in most cases, especially with non-pro drivers.
the only real downside is possible extreme toe out under hard braking with sticky tires, but if the car is sprung tight, that shouldnt be a huge deal. the other is that the inside drooping tire will scrub of the inside edge of the tire in long duration, constant radius turns.
mk
the only real downside is possible extreme toe out under hard braking with sticky tires, but if the car is sprung tight, that shouldnt be a huge deal. the other is that the inside drooping tire will scrub of the inside edge of the tire in long duration, constant radius turns.
mk
05-15-2013, 03:11 PM
#57
The Parts Whisperer
Rennlist
Site Sponsor
Rennlist
Site Sponsor
http://erpparts.com/instructions/481...er_install.gif
I believe Cary is well know for his high quality
http://www.stableenergies.com/911_91...ERP-911-008-L/
05-15-2013, 03:48 PM
#58
Addict
Rennlist Member
Rennlist Member
Join Date: Feb 2004
Location: Monterey Peninsula, CA
Posts: 2,374
Likes: 0
Received 16 Likes
on
12 Posts
curiosity.......
Hi Carl,
Can you also provide the vehicle's alignment settings in example 1, 2, & 3?
Settings for Ride Height (mm), Camber, Caster & Toe (Degrees)? (I can see the toe reading/deflections from the post, but what was it set at in degrees from which you measured the deflected settings?)
When you lowered the car in the example posted, was there an alignment recalibration after lowering the vehicle 1" but prior to taking the deflection measurements posted?
If the alignment recalibration was not done after lowering, then how was the measurement done for the data posted with the previous unlowered settings?
Thanks
Can you also provide the vehicle's alignment settings in example 1, 2, & 3?
Settings for Ride Height (mm), Camber, Caster & Toe (Degrees)? (I can see the toe reading/deflections from the post, but what was it set at in degrees from which you measured the deflected settings?)
When you lowered the car in the example posted, was there an alignment recalibration after lowering the vehicle 1" but prior to taking the deflection measurements posted?
If the alignment recalibration was not done after lowering, then how was the measurement done for the data posted with the previous unlowered settings?
Thanks
05-15-2013, 03:54 PM
#59
Developer
Thread Starter
My kit came from ERP and was intended for a 911 but I modified it for my car.
http://erpparts.com/instructions/481...er_install.gif
I believe Cary is well know for his high quality
http://www.stableenergies.com/911_91...ERP-911-008-L/
http://erpparts.com/instructions/481...er_install.gif
I believe Cary is well know for his high quality
http://www.stableenergies.com/911_91...ERP-911-008-L/
Our kit is $364 and fits right out of the box.
Ours is made for us by Coleman Racing products and I believe they are well known for their quality also.
http://www.colemanracing.com/
Eckler's/Automotion/Perfromance Products sells a similar kit for $345 (for the 911) but I could not find anybody who
offered a 928 kit. That's why i made it.
Pleased that we were able to hold our quality high and still come in similarly priced, even though our production numbers are quite a bit lower.
05-15-2013, 04:02 PM
#60
Developer
Thread Starter
Richard, I'm not sure I understand your questions. The caster, camber and toe on the test vehicle was set to the WSM factory settings before proceeding.
As we were only testing bump-steer, I did not check changes to camber or caster. It wasn't part of my study for this.
I'm also not sure what you mean by "recalibration" when the changes were exactly what we wanted to measure. If we would have re-aligned the car after the changes, then we would have lost our delta.
The stock rubber suspension bushings were challenging in this study. Whether raising the spindle an inch or lowering it an inch, we had to wait for the a-arms to "settle" as it kept slowly moving against the resistance of the rubber bushings.
We did not record the change in toe until the spindle had time to stop moving. Tapping the car with a finger was enough to make the indicator jump!
As we were only testing bump-steer, I did not check changes to camber or caster. It wasn't part of my study for this.
I'm also not sure what you mean by "recalibration" when the changes were exactly what we wanted to measure. If we would have re-aligned the car after the changes, then we would have lost our delta.
The stock rubber suspension bushings were challenging in this study. Whether raising the spindle an inch or lowering it an inch, we had to wait for the a-arms to "settle" as it kept slowly moving against the resistance of the rubber bushings.
We did not record the change in toe until the spindle had time to stop moving. Tapping the car with a finger was enough to make the indicator jump!