Changing MKIII Front Steering to Resemble MKIV Level

[skullandbones]

My MKIII roadster handles pretty well as it is but I wanted the steering geometry to look good on paper to optimize my potential setup attempts. It is rather complicated with the upper adaptor that FFR created. So after some research, I found a u tube video of some changes made by one of the vendors.

http://www.youtube.com/watch?v=sNy7XHjtu4w

This video has been out since July of 2012 and was created by Breeze Automotive. It helped me to make a decision I have been contemplating for some time (before I had even heard of the SAI mod for my roadster). I really wanted to see someone do it to see if it could be done. The problem is I haven't seen much discussion about it but I haven't done a serious search on FFcars.com. So I decided to do the necessary operations to reach the goals of improving the geometry which are 1) to get the SAI (steering axis inclination) also called KPA or KPI (king pin angle or inclination) to the standard of 9 degrees and 2) to reduce bump steer potential from the initial setup.

My plan involves using two of Breezes changes which are to move the LCA to the SN95 hole positions on the FFR chassis (done). The other change is to move the UCA from it's stock MKIII position on top of the FFR UCA mounting bracket to underneath the bracket. My modification to this task is to angle the UCA down in front so it will clear the 3/4 inch frame rail that Breeze partially cut for clearance. It creates a very close tolerance but it does clear. My modification will include a 6 degree pinion shim installed to allow the front of the UCA to droop down instead of mount flat against the bracket. The wedge will create a flat surface for the UCA to rest on. I am also installing the Breeze offset aluminum bushings on my power rack to lower and center it to make the steering more symmetrical regarding things like bump steering. Of course, the most drastic change is that a portion of the SAI mod has to be incorporated into the mod or it will not improve the SAI to the standard needed. I did this by chopping up the FFR spindle adaptor and creating a new ball joint attachment point for my upper ball joint. I attached the ball joint mount portion of the FFR adaptor to the UCA and the lower part cut off to the spindle and lined them up. After tacking the pieces in place, I removed the new adaptor and had it welded. Now the upper ball joint is in a much more normal position relative to the rest of the suspension. I realize many will use the SAI mod offered by Whitbey Moter Cars to simplify the process. In the Breeze version, they are only using the ball joint adaptor from the SAI mod, too.

So in summary: I hope to get an SAI of about 10 degrees (preliminary measurement) which will meet the standard when I induce -1 degree of camber into the alignment. The bump steer should be reduced to almost zero as the outer tie rod end is in alignment with the upper and lower ball joints. I also have the rack adaptor kit which moves the rack forward a little to also help properly align the rack with the steering setup. The UCA is in a good position (lower and inboard) to allow for longer adjustment arms on the UCA to create a more similar arc for the UCA and LCA to travel in. There are some tight tolerances to deal with including the upper caliper bracket bolt which I made allowances for on the new adaptor. If it hadn't been for that bolt, I would have lowered the ball joint even more than I did. The grease fitting on the upper ball joint is close (I got a low profile one). The brake line had to be rerouted a little. I will be inducing several degrees of castor into the setup (6 to start with) as I am using a power rack and want the castor. This is all being modeled using a 17x9 Cobra R wheel. So I will report how the steering mod changes the steering characteristics and road feel. Thanks, WEK.:cool:

Note: pics of the original setup and two shots of the modified spindle adaptors.

[skullandbones]

I think I forgot to mention that another reason for doing the mod is to move the wheel/tire in under the fender. I have the SN95 spindles that add about 8 mm of width per side to the front track so the mod tucks the edge of the wheel neatly under the fender. I've already checked with a straight edge. I also did some more reading on the ffcar forum. I still didn't see much about using the info from the Breeze video. Has anyone out there tried this? I promise there will be no hard feelings for comments or criticism. I'm curious to see what's happening out there. I know you MKIV guys are pretty much immune to the issues but there are still a lot of other MK versions that are not. Thanks, WEK.

[Jeff Kleiner]

Not to gloom & doom on ya' but a couple of things for you to consider:

1) In the photo above it does not appear that you have sufficient thread engagement on the forward UCA adjusting link. See THIS (http://www.ffcars.com/forums/17-factory-five-roadsters/244160-lots-caster-warning.html)

2) Regarding the alteration to UCA mounting:


My modification to this task is to angle the UCA down in front...

By doing so you may find that you have reduced or eliminated the "anti-dive" built into the front geometry with the end result being that the car will want pitch nose down under heavy braking, loading the front tires and unloading the rears. We all know that a lack of enough rear braking can be an issue with these cars and it is quite possible that this will exacerbate that condition. Taking it further the possible scenario while cornering under braking is that the heavily loaded front end will cause the car to push until the front finally bites and when it does the light rear will snap around...

Remember, any suspension change generally affects other areas of the dynamics as a whole, sometimes positively and other times negatively. I suggest you study and research your proposed mods carefully and thoroughly considering the "trickle down" effect they can have.

Good luck,
Jeff

[CraigS]

I also thought about the antidive aspect of the uca mount but I think you will be ok. If you look at the SAI kit chassis mount, you will notice that the holes for the new position do something similar to what you are doing w/ the wedge. I always wondered why they did that.
http://www.whitbymotorsports.com/UInvDetail.asp?inventoryid=1604
You can see what I mean in this pic looking at the left top piece. Notice that the gold washers are not the same distance from the 'bend' line of the angle iron. Later today I will get my mounts out of the attic and try to determine what the angle of the holes is.

[skullandbones]

Hi Jeff,

It may have been misleading that I said I had not done a serious search of ffcars.com because I have been reading posts that you and others have been discussing for anything front suspension related. So I had already purchased the 5 inch adjustment arm for the UCAs. It is very hard to measure the length needed at this point in my mod but I think it may even require another set of 5 inch ones or something longer. I will have to set it up when I have the components completely mocked up which will entail putting pressure on the LCAs and putting it in a static driving position to see approximately where the UCAs and upper ball joints end up. At this point, I can get some threads on the adjusting arms but it doesn't look like I would have enough to make the system safe (even with the longer arms but too soon to judge). I will probably lean toward the conservative side and get as much threaded contact as possible which could necessitate shortening those longer adjustment tubes some to fit perfectly.

Regarding the anti-dive issue: I have been looking at many models of front suspension and have found that the ones similar to the FFR setup usually don't have as much upper slant to them as the one on the MKIIIs. When I saw the SAI mod (angle iron) portion, it seemed to validate that the angle of the UCA was maybe a little high for the more normal position of the upper ball joint of the SAI mod. As many have noted the UCA is still angled up after the mod but not as much. I don't think I have exceeded the change in angle of the SAI mod. So I think it should be OK. I haven't seen any reports of anti-dive issues with the SAI mod installed, yet.

I really appreciate your time to discuss this on the forum and also appreciate your concern for my safety. I do not go into this area with blinders on so to speak. I just want my MKIII to have excellent steering geometry and see an opportunity to make that happen. So any experience you have had will be helpful, I'm sure. WEK.

Note: I also have the option of adding a smaller "wedge" in the UCA relocation if I experience any bad braking behavior. The pinion shims come in sizes from 2 degrees up to 8 degrees and some even in half degrees such as 2.5 degrees.

[CHOTIS BILL]

I don’t know if you are using a suspension program to analyze where you are starting from and where you are going to or not. I use WenGeo3 and have run the numbers on my Gen2 Type 65 front suspension and it has zero anti-dive and lowering the front UCL will make it go into positive anti-dive which I haven’t know anyone to use so I don’t know what effect it will have but I wouldn’t think it would cause more front dive under braking which will make eliminating bump steer more important and will reduce the tire contact patch due to more camber change. That change will also raise the front roll center which when used with IRS is to high to begin with which is another negative on handling. But changing the UCL will only make about half the change to anti-dive as changing the lower links. Making the UCL longer will decrease the camber gain in roll which on mine is not enough to begin with in my opinion. Another thing to consider is roll center stability which is very important. You want the roll center to remain a constant distance from the chassis and also stable to the center line of the car as the chassis moves up and down. Before I make changes to a suspension I run the numbers to get an idea of how it will affect all the parameter. Don’t be afraid to make changes but make a big enough change so you can tell what affect it has but always know how to get back to where you started just incase you don’t like the change.

Good luck and let us know what difference the changes made.

Bill Lomenick

[skullandbones]

I forgot to thank CraigS in advance for offering to check the repositioned angle of the SAI mod on the inner UCA location. Looking forward to hearing from you.

Looks like I will be "down" for a while as I just ordered the leaf spring or pinion shims as some call them. Also, had to order some more adjusting arms for the UCA (6 inchers). So it will be a couple of days before I can continue with the left side of the car. I still need to move the LCA on the passenger side. I also have the solid adaptors from Breeze to install on my PS rack. I think that is more work than it sounds like.

Bill,

That's a lot to digest! I am so covered up with trying to measure and relocate the static positions of my suspension components, I haven't even gotten to how it will affect the dynamic aspects of the handling. I do not have a WenGen3 program (that's by Wm Mitchell, I think). I am graphing the component locations on paper and have only a few done as I am still without some critical parts. BTW, I read that accurately locating the center of movement of the ball joints is not as easy as you would think so I am researching that, too. However, I will be able to graph the instant center and should be about to determine the ideal location for the tie rod end (inner and outer) based on that number. Hoping I can move the rack enough to bring that tie rod location and angle into the ball park theoretically. That should at least get me on the right track for lowering the bump steer to a manageable level. Is your 65 coupe set up like a roadster or does it have the improved steering geometry like the MKIV (or did you add the SAI mod)? Would like to know if we are apples to apples. Thanks, WEK.

[CHOTIS BILL]

Mine has the new setup without needing the SAI mod. I have no idea what the suspension locations you have and the only information I could get from FFR is the height of my roll centers. I measured mine and got the front roll center to within .002”. It in not necessary to get the steering rod end locations in line with the control arm as long as the length and angle are correct but it easer to visualize if it is. If that makes
any sense. The steering link needs to be certain length and angle at any given location between the upper and lower control arms but the pivots don’t need to line up. The most sensitive location is the height of the outer end of the steering link, that controls the steering link angle, where a few thousands of an inch makes a very measurable difference in the bump steer. I stopped when I got the bump steer to within .008” TIR. in +/- 2" travel.

Bill Lomenick

[FFRSpec72]

FFR made a upgrade for the challenge cars that allowed us to mount the new FFR Mk IV spindles, this was a frame adapter for the UCA mount, this required us to weld on the new mount but they gave us a guide and all went well. The handling has improved and allowed us to remove the bump steer (not eliminate but far better than before). I'm now running about 8.5 caster and could only get 3 before.

[CraigS]

Here is a shot of the bracket for the left side of the car. So the bolt (I stuck thru to make the holes more visable) on the left would be toward the front of the car. this would decrease antidive compared to the original mount.
http://i3.photobucket.com/albums/y91/craig-s/SAIbracket_zpse12abc67.jpg
The left bolt s .760" below the edge and the right bolt is .500" below the edge for a difference of .260". The bolt holes are 5.0 inches apart center to center. I measured the angle w/ a cell phone app and w/ my camber gauge. My accuracy is a little suspect, maybe + or - .1 degree. I get average of 3.0 degrees. Perhaps someone who has done trig less than 46 years ago can check this. So Borden's SAI kit antidive change is about half of what you will get w/ the 6 deg. wedge. While there is a difference, I think that as long as the UCA side view mount is any small amount higher in the front, you will still have some antidive. If you have 'some' you will be OK. The good thing is that front springs up to 750 w/ the correct shocks are still streetable in my experience. So, if the antidive is too little you can bump the front spring rate to compensate. Bill, have you modeled the FFR front suspension in your program so you could check this more scientifically?

[CraigS]

Another thought for you regarding bump steer. My experience is that the older cars need the rack lowered as much as possible. And that it usually isn't enough. Only measurement will tell for sure. I discovered this a couple of months ago on my car. At one point I had obvious bump steer easily noticeable on a bumpy road where the left and right wheels were hitting different things at different times. I had fixed that and thought it was Ok since I couldn't feel a problem. Finally measureing told me I was no where near correct. I got an idea from Borden's MkIV build thread and found a very simple and inexpensive way to measure bumpsteer.
http://i3.photobucket.com/albums/y91/craig-s/IMG_20130428_162158_880_zps1486ee99.jpg
I bought the least expensive laser available at HD that had a flat bottom w/ magnets and was compact. I bought an angle bracket at the same time. I clamp the angle bracket to the rotor and set the laser on it. I didn't realize I had gotten one that projected a line. Bill3422 had one that projected a small dot and was a little easier to use since there was no need to assure the line is vertical. I remove the bolt from the top of the coilover and let the suspension hang. mark the laser position on the box and jack it up. initially the thing moved maybe 3 inches sideways so there is no need for pinpoint measuring. It moves toward toeout as the wheel goes up. I kept messing w/ shims between the rodend and the steering arm until I had about 1/4 inch of movement. you could make a chart w/ careful measurements if you wanted but I didn't even figure out normal ride height for the center of the graph. I jacked from full droop as high as it would go. When you go from 3 inches to 1/4 inch, that's a hell of an improvement. A very unexpected result was that the steering now feels quicker. makes sense though. As you turn left, for instance, the RF wheel goes up. W/ poor bumpsteer it also toed out. So your steering wheel input was reduced. W/ correct bumpsteer, your steering wheel input actually gets to the wheel. It is enough of a change that I am seriously thinking about going back to the 3.0 rack I replaced about a year ago w/ a 2.5 rack. I did that for autocross only and didn't like it on the street. I like it less on the street now.

[skullandbones]

FFR made a upgrade for the challenge cars that allowed us to mount the new FFR Mk IV spindles, this was a frame adapter for the UCA mount, this required us to weld on the new mount but they gave us a guide and all went well. The handling has improved and allowed us to remove the bump steer (not eliminate but far better than before). I'm now running about 8.5 caster and could only get 3 before.

This is exactly what I hope will be the added benefit from the extra castor for my mod too. It should bring the outer tie rod end up with the steering arm on the spindle as everything leans back. Along with the offset adaptors for the rack, it should be enough to correct most of the bump steer. But that will require some measuring to validate that when it is together. Thanks, FFRSpec72

Craig: I measured my UCAs as they hang from the mounting bolts. This should be the approximate location except it may pull a little tighter which will reduce the measurements a very little but some. So I go 0.31 difference in the bolt locations from the original position. When I measured the plane of the original bracket and the angle of the UCA as it is mocked up, there was a 4 degree difference in the locations. So I would say our measurements are pretty close. I was not aiming for a 6 degree change. That was and estimate of what I thought I would need to fill the gap. Now I think I will have some grinding to do to get the pinion shim to fit between the UCA and the UCA bracket (better a little fat than a little too small). My original plan was to get the UCA to mount under the bracket and avoid the frame surgery which this will do. However, after mocking it up like I have it, I noticed that the new position of the UCA was more like the SAI and MKIV UCA locations. So that was a happy accident! Your measurements help verify that. Thanks. I owe you one.

I will have to check out that bump steer measuring technique when the time comes.

Here are some shots of the mock up of the new suspension setup with the UCA repositioned and how close the UCAs come to the 3/4 inch frame rail (close but not binding). Thank you, WEK.

[FFRSpec72]

Here is a picture of the new mount that we had to weld on to fit the FFR Mk IV spindles

19746

[CraigS]

Wow, Tony's mount looks to have no anti dive at all. And WEK's first pic seems to show that he will still have 'some' anti dive.

[Dan Babb]

I recently completed a power steering upgrade on my MK3. After talking with Mark, I moved my lower control arms to the inner hole. I looked at moving the uppers as Mark shows, but on a completed car, it was going to be too much work to get that done.

By moving the lower arms inside, I was able to pull the wheels in a bit and was able to get more caster without having to change the sleeves on the upper arms.

I don't notice any negative effects from making this change...the front end seemed quite predictable at the auto-cross I ran on Sunday. The course had some bumps and the car didn't seem to jerk from side to side when I hit them.

[skullandbones]

I recently completed a power steering upgrade on my MK3. After talking with Mark, I moved my lower control arms to the inner hole. I looked at moving the uppers as Mark shows, but on a completed car, it was going to be too much work to get that done.

By moving the lower arms inside, I was able to pull the wheels in a bit and was able to get more caster without having to change the sleeves on the upper arms.

I don't notice any negative effects from making this change...the front end seemed quite predictable at the auto-cross I ran on Sunday. The course had some bumps and the car didn't seem to jerk from side to side when I hit them.

Hi Dan, I am glad to actually hear from someone who has moved their LCA inward. So do you have the SAI mod? Also, did you get any positive results from you Breeze adaptors like centering, changed rack angle and other location, and steering feel? If you look at some of my pics you will see that I have not cut the 3/4 frame rail with my mod. So you might want to look at that again about moving the UCA. The only thing is you will definitely have to change adjustment tubes on you UCA. I have parts coming in the mail so I will mock up that setup and post a pic as soon as they get here. It's good to hear that you are seeing no "bad behavior" from your change in the suspension.


Wow, Tony's mount looks to have no anti dive at all. And WEK's first pic seems to show that he will still have 'some' anti dive.

I'm glad you saw that and mentioned it first. I thought I was seeing things! That's a great shot. It looks square and level. There may be a very good explanation for adding the extra angle for the UCA for the spec racers. I'd love to hear what it is. Also, Tony, did you add any other components to your setup besides the frame adaptor and the FFR spindles? I guess the rules lock you into whatever is decided by FFR otherwise it wouldn't be called "spec racing".

Thanks for the info, WEK.

[FFRSpec72]

We added 13" front Cobra brakes and a sway bar. With the loss of the anti dive I get better braking now, more even, no 1 wheel lock-ups like I was getting before. I can tell you that with 8.5 caster I get more inside tire wear but have no issues turning in on corners now and comes out of the corners better.

[skullandbones]

Tony,
It looks like I will be running less of an extreme setup than yours but I'm glad you are happy with the way yours is performing.

I still didn't get the pinion shims from Summit but I did get the longer adjustment tubes for my UCAs from Speedway. That's the first time someone has beaten Summit on a delivery to me! So here is what it looks like. I will not be able to do anything else until the other parts get here and I set it up for a rough alignment. At that time I think there will be some cutting to the adjustment tube/s. There is a 6 inch one in the forward position and a 5 inch one on the trailing arm. I have all of the adjustment taken up on the trailing tube and almost all on the forward one. I know I will have to take at least 1/2 inch off the trailing one. Then I will see if that is enough to induce the required 6 degrees of castor. . As you can see from my angle gauge there is a positive camber with no more adjustment. But that is about what it will look like less the pinion shims. See you later, WEK.

[CraigS]

From reading I have done on suspension setup this is my understanding of anti dive. On a street car w/ relatively soft springs a lot of anti dive helps out quite a bit. On a performance car the springs are usually stiffer so less anti dive is needed. At some point anti dive can actually become detrimental. Think about entering a corner under heavy braking. Anti dive has the effect of increasing the spring rate but only while the brakes are applied. If you have a spring/ shock combination that is optimized for cornering it is usually about as stiff as it can be while still allowing the suspension to absorb bumps. So, w/ antidive in place, your perfect spring/shock becomes too stiff under braking only. This thinking seems to jive pretty well w/ Tony's experience. Geez, I may need to move my UCA cross bar too.

[skullandbones]

Still waiting on the pinion shims but after looking at the adaptor I modified from the FFR MKIII adaptor that came with my kit, I have discovered something I had not thought about during this process. The hard fact is that the spindle and adaptor will not be equivalent to the MKIV spindle. You can't put the ball joint on top where it is optimized. I had three choices to place the new upper ball joint position: forward of the spindle, inside, or behind the spindle. I choose behind because it looked like the most normal position of the three choices. What I think after seeing it installed is it may have an added benefit. It appears to have "built in" some castor to the system. If that is the case, I will probably have to adjust the UCA adjustment tubes less to get the desired added castor for my setup. Another way of looking at it is the upper ball joint will be in a more neutral position or center of its range of movement instead of tilted more with a large castor angle. I will be able to verify this at alignment. WEK.

Note: CraigS, got a chance to reread the thing about the laser level. After it sunk in that really looks like a simple way to do an estimate on your bump steer. The regular process is so tedious, this will help to quickly know if you are in the ball park. Thanks a lot for that.

Also, going back to what Jeff said earlier about the built in "anti dive" of the UCA: I can reduce it a little with a slightly thinner shim if I see some bad behavior while braking hard in the corners. All resources say to test, test, test..... You have to verify it or it's just theory. One thing that has stuck with me is reading about how not to brake in corners but accelerate through with a short wheelbase. But if you are going into a corner and have to panic brake to keep from hitting another car or if you do autocross (I believe it requires a lot of braking), you would have to use the brakes in the corners. So you must have some control to keep the car from swapping ends when you touch the brake in a corner. Seems like a real balancing act.

[CraigS]

Quote:
"I choose behind because it looked like the most normal position of the three choices."
That is exactly what the SAI mod piece does. This also makes the spindle more upright even w/ a lot of caster which makes the lower ball joint look a lot better.

[FFRSpec72]

I run 650# front springs with sway bar

[skullandbones]

Doesn't the sway bar effectively make the 650# act like a 700#? Mine are stock for the MKIII 450# in front and 250# in the back. I'm also looking at the sway bar possibility but not yet. Don't want to get to many components changed all at once.

[skullandbones]

I finally got my pinion shims from Summit today. I cut them down as the stock shim is 3 inches wide and a little too long for my use so I used a hack saw to make the two wedges I need from one of the shims. When I put it together and snugged the bolts up, it fits pretty well. I will have to modify some thick washers to use under the heads of the cross arm bolts for the UCA so they will be torqued in flat. Also, one bolt is too short so I will have to get one 1/2 inch longer. So now I will put this together, do an alignment and test it this weekend. I will pass on the results. I am not installing the rack offset solid bushings as I want to test the changes and the rack mod separately. See you later, WEK.:cool:

Note: first pic shows paper between 3/4 frame member (close but clears).
second shows the mocked up changes without the shock.
third shows the wedges before install.
fourth shows the components used to upgrade the MKIII setup to one similar to the MKIV.

[David]

Re the anti dive, I originally designed it to be 0 or new zero. IMHO, with the low cg and rear bias, I felt it wasn't needed and would increase braking feel and compliance to help prevent lockup.. I've had run my car that way for years and was happy with it.

I'm am slightly concerned about your bracket since you don't have something wrapping around the other side supporting the top of the top where the ball joint taper enters since it appears it is a bit cantilevered.

My original prototype was steel and welded up like your part, but did have some more metal supporting the top area and it wrapped around and bolted. I may still have mine if you want a pic. I was never really comfortable with those parts due to the forces involved hence the billet steel Adapter in the SAI kit.

David

[skullandbones]

Hi David,

I've read some of your posts of ffcars but did not get in on any info about the original project (very interested though). I was going to double the bracket like the FFR but needed to install the bolt with head partly cut down (to create the stud) under the tapered ball joint mount so couldn't. I would be interested in seeing your prototype. I did leave some additional metal as a stiffening measure and the ball joint mount is pretty close to where the stud goes thru. I also prepped the weld seams so my welder could get as much surface area as possible. He builds sprint cars and does quite a bit of suspension fabbing. I would not trust too many people I know to weld such a critical part. I asked him about it. He seemed to think it's OK. I will definitely have another look. Appreciate your concern. Thank you very much, WEK.

So you think the anti dive angle is OK with the cross arm? I don't think mine is as radical as the change on the Spec racer cars done by FFR. Like I said before, if it does not behave well, I can put a smaller wedge in the area such as a 4 degree pinion shim.

[skullandbones]

I completed the tasks discussed above this weekend and was able to do an alignment and test drive.

1. Moved lower tubular control arms to the inboard position to allow the 9x17 rims to tuch under the front fender (SN95 2000 GT spindles).
2. Moved upper control arms under the normal MKIII mounting bracket to put it in a more normal position (with SAI type mod).
3. Installed a pinion shim (wedge of 6 degrees) between the UCA bracket and UCA cross bar to change the angle as in the SAI mod (also reduced some anti-dive).
4. Fabricated a new spindle adaptor from the old FFR one similar to the SAI mod to bring the SAI close to standard of 9 degrees. Added benefit was a built in 3 degree castor.
5. Installed new adjustable control arm pieces of 6 inches in front and 5 inches in back (shortened 1/2 inch).
6. Relocated the outer tie rod ends to the top of the steering arms after installing MOOG style tie rod ends. Reason: to reduce bump steer (measurements to follow).

The initial setup for the alignment is -1 degree camber and 7-8 degrees castor with PS.

Trish and I took the first test drive on the new suspension tonight. My first impression is it feels a little more stable and quicker if that is possible. When I moved the steering wheel before there seemed to be a little bit of "wandering" for lack of a better term. Now the movement is quick but more dampened or maybe it's the castor that is just stabilizing it more. When I was doing the toe, I tried moving the wheel by hand and it would not stay turned out. I need to drive some of the same routes I did with the other steering setup to get a more objective opinion on it. The braking seems to be more responsive and what cornering we did was very predictable. I have not done the Breeze rack aluminum bushing install yet. I wanted to see what it felt like without it and then after it's installed. After checking for bump steer, I will see if we need to move the rack any for that and also check to see if it needs centering. From what I have measured so far it will not require much centering. My next task is to put these new geometric positions on paper to document where they are in relation to racing standards. I already know the SAI is better but the roll center, instant center, steering arm and tie rod arcs and their relationships need to be checked.

Below: You can see the aluminum wedge I put in and the brass bushings (shaped to match the angle) under the mounting bolts. Also, the tie rod end is in it's new position.

I would like to continue researching as I go forward with these changes. Hope other have some experiences with them. See you later, WEK.

[Jeff Kleiner]

Interesting stuff. Curious how you dealt with the taper at the interface of the tie rod ends and steering arms with them installed from the opposite direction :confused:

Jeff

[skullandbones]

Hey Jeff,

I started with a narrow step bit and then cleaned it up with a tapered bit. I got one perfect and the other is not quite perfect. I am going to get some steering arm tapered bushings to install as I am not completely happy with the "hour glass" created by the process. I was talking with Mark Reynolds about that. He said he had heard it being done many times. I also read about the old hot rodder trick when I was checking out the ffcar.com threads. I believe it is safe enough. I just don't like it. So that will get changed when I am working on the rack and the aluminum offset bushings.

BTW, I am scratching my head on how exactly to test this and get any meaningful results. I was thinking of AX. So I was just wondering how you got started in AX. I haven't even researched to see how available it is in this area (Firebird just changed management). They have had one track day event this year. I have met three people here with cobras who have found themselves in the ditch or in trees and cactus but I don't think that's the way I want to test it if you know what I mean. Thanks, WEK.

[David]

1. Moved lower tubular control arms to the inboard position to allow the 9x17 rims to tuch under the front fender (SN95 2000 GT spindles).

Just an FYI, that makes a pretty big difference in your front roll center height(makes it higher which isnt good IMHO) since it raises your inner pivot about .75"(from memory)

Depending on where you ended up with your upper pickup points, it may be OK but wanted to give you a heads up. One of things that was accomplished with the SAI mod was lowering the roll center along with the SAI. A high roll center really increases jacking forces and geometric roll resistance. Some is OK... but on a low CG car, you will most likey be giving up front grip by going higher than lower.(as long as it stays above ground)

If the upper control arm is angled back like the earlier cars, that also raises roll center height.

If you are just using the car on the street, you may not notice it. You've made lots of changes, just wanted give you some heads up of what the changes may affect.

David

[skullandbones]

I measured 7.5 mm on the x axis and 22 mm on the y axis so the LCA relocation position may be about what you said (.75 inches on avg). Good observation. That is the only change I made that didn't move the component to a more desirable position. It will make the wheel fit better but may cause a geometry issue. I will have to reserve judgment until I can get a real measure of all the changes together. That may be more difficult than I anticipated. The thing that may at least cancel out any bad effect is that the pickup points on the UCA are lower and may compensate (lower than the SAI mod but not as low as the spec racer mod). I did not get the new setup down to proper ride height yet so that may look a little better when I do that (at 5.25 inches at this time).

I read an article by Curtis Deitzsch about finding the Roll Center. He said he used a paper model method many years ago (referenced a book by Carroll Smith called Tune to Win) but recommended going to suspension software as a second option and then a third option of CAD software. I want to do the measurements but doing them mechanically is very difficult. Would the Roll Center Calculator from Performance Trend, Inc suffice for this task? The base program is $79 and there are some upgrades that do more. CAD is out of the question. What do you think?

Thanks, WEK.

[CHOTIS BILL]

THINK FAST by Neil Roberts covers his list of geometry parameters that produces the foundation of a decent handling car. He found that this set of parameters seems to work well through the entire race car size and spectrum and with either bias ply or radial tires. Some of the parameters are a bit different for very high down force ground effect aero cars, but he didn't cover them. His list is too large to post here but if anyone is interested in them E-Mail me and I will send them to you. Blomenick@deltatau dot com. When the cars I designed and built were brought into his design parameters they handled very well.

Bill Lomenick

[CraigS]

I wonder why you have tire clearance to the body problem and need to move the UCA inward. My self and all my autocross buddies run 275/40x17 and height of approx. 4.0 inches and have no problems. 2.5 deg. negative camber helps though. One guy is running 295s on the front. Most of us run this wheel or similar
http://www.americanmuscle.com/buwh1-9404.html
In the past I have worked out roll centers on paper. The biggest problem I have is deciding where the center of the ball joint is. Last time I did it I got a roll of brown paper, laid it on the floor, and did it full size. Now that I type this, I realize I have never done my FFR.

[skullandbones]

Bill: I would like to see that (never too much data!). I will send you an email. Thx.

Craig: I have the SN95 late model spindles. I have heard different measurements but I think they are about 8 mm wider than the 94-95 version per side (Mark R moved his in for the 94-95 spindles). When I tried mounting the Cobra R 7x19s when I was mocking this setup up, it looks to fit just where I want it. The fellow who had these before me used 1/4 inch spacers to clear the suspension. I don't have that problem after changing a grease fitting out on the top ball joint. I am starting off with 8 inches of tread on a 9 inch wheel. I've read that "stretching" the front tire a little will reduce tire roll over.

As for the measuring, I think it will be difficult because of things you mentioned (getting the accurate rotation point for the ball joint, etc). Also, introducing large error factors in the process with scale model multiples error. So the full size measuring model is less prone to that sort of error. Brown paper roll, good idea! The only problem now is I may have a very long piece of paper as a similar model I saw had a 200 inch instant center which went way outside both wheels. The software wouldn't have a problem with that.

Note: Six sigma adage: if you can't measure it you can't manage it.

[David]

Dont worry about spending money on software I already have it. If you can give me the hieght of the pickup points for the inner and out pivots (front and read mount point on the chassis, I can give you the numbers.

David

[skullandbones]

David, That's very nice of you. I will have to get the measurements and send them to you. I have not re-adjusted my ride height. It moved up to 5.25 inches when I put everything back together.

I was not understanding the relationship of the roll center and it's correct position to the suspension. Then I read an explanation about proper height. It explained on racers like Formula I it was about 1.8 inches and on sport cars between 3 and 4.5 inches. So in order to roll in concert with the suspension the chassis has to roll on that axis or the roll will fight against the suspension (high can cause jacking). It was the first time it made sense to me. Thanks, WEK.

[David]

The challenging thing about suspension geometry... at least what I've learned, is the more you learn, the more you realize you dont know. :D Knowing a little is fairly dangerous. For instance... If I make the upper control angle steeper, I increase camber gain which keeps the tire on the ground when the car leans in a corner... good right? Sometimes yes, sometimes no... IMHO, this is risky on a low COG car. Increasing the upper control arms angle increases the roll center height, causes jacking and geometric roll resistance. In essence geometric bind which locks the suspension up in a corner. Roll center height, both vertical and horizontal migration is a hotly debated topic. With that said, most people in the know throw this out in favor for calculating force based roll centers which Im still trying to learn. Static roll center height is still valuable to use, but its not the whole picture. IMHO, I would target a RCH of ~2 inches or so, keep your roll center height fairly stable vertically and dont pay as much attention to horizontal migration. What you will probably find, is your camber gain will be in the area of approx .7 degree for every 1 degree of roll. That seems to be a fairly decent compromise.

What I am going to do on my new build is to drill two new holes under the pin drive holes and get new lower ball joints with longer shafts. Most likely adjustable and rebuild-able ones. This way I can stuff the 275's I already purchased under the narrower Mk4 front end along with tuning the control arm angles.

David

[skullandbones]

I had not thought of drilling new holes for the inner LCA but I had thought about the adjustable lower ball joint. Saw some on a racing website with multiple adaptor heights to change the ball joint position. Hope I don't have to go to that extent but it's an option. I got a chance to drive the roadster today. It finally cooled off a little (<100). I am noticing a real center feel for the steering now. Before it wasn't real twitchy but it wandered a little. Now there is a definite tendency for it to hold center or near center of the rack. I added enough castor. It had better have some effect! But besides that, I can't tell much difference in the way it drives so far.

Need a clarification: do you mean raising the UCA from it's pickup points to the ball joint or front to rear?

BTW: David, did you get my PM? Just wanted to make sure you got the data I sent. Thanks, WEK.

[skullandbones]

I've always heard that "numbers never lie". However, they can be misinterpreted. I finally have some numbers regarding the suspension mods I made and the front end alignment in general. I did the measurements back in Sept but just haven't gotten around to laying it out and projecting the instant centers and static roll center. I must say that I'm surprised that the roll center is higher than I expected. These measurements are as close as I could estimate with the roadster on a 4 post lift. One reason I waited so long was to do the measurements after I got a professional alignment which was interesting in itself. The fellow who was given the task had many years experience on modified suspensions such as Mustangs. He spent about 75% of the time on evaluating the setup. ~He was one of those guys who does not say much so I didn't get much feed back about it. However, after a few consults with his counterparts, the final alignment was as follows: 1/16 toe in, 0.5 degrees negative camber, and 9 degrees positive castor. The SAI was 10 degrees after alignment. I found that after transferring the measurements I got from the pickup points and ball joints and tie rod ends to an actual size card board and connected the dots, the estimated points were as follows. The instant centers were not as far outboard of the wheels as I thought they would be which resulted in a higher RC than I expected. So my best estimate is the roll center is ~7.25 inches above the ground level. At this time I have my ride height at 5 inches in front and about 5.5 inches in the rear. I plan on doing a track day in January so I will lower the ride height about an inch or more. I can't drive the roadster safely at those lower ride heights for normal driving (at least in this part of the country). I suppose the lowered height will lower the roll center but that will take some additional measurements when we lower the car. I'm not sure what to make of these numbers yet but it would be nice to know the average roll center values for the MKIV to do a direct comparison. Maybe those numbers will be published eventually. This is an interesting process even with limited resources and experience with the suspension changes. Comments are always welcome.

WEK.:cool::cool:

[CraigS]

I just came across this forum a few weeks ago. Read the 2nd, 3rd, and 4th sticky threads by Sutton to blow your mind.
http://www.lateral-g.net/forums/forumdisplay.php4?f=38
I am not 100% understanding the 'long travel' part of the 'long travel low roll' concept although I certainly get the big bars part. I am going to try a 1" Forte front bar (vs current 7/8) next season. I also really like his theory that caster should be 1-2 degrees more than SAI. I have been running 8 or so deg caster for several years now. Once I get the software and hopefully can figure my SAI, I suspect I will be looking for a couple more deg caster.
BTW he sells the performance trends software. I am getting the 'roll center plus' for Christmas. Seems like a really good deal as it includes some rear suspensions including 3 link so it covers us and our FFRs.

[skullandbones]

First I've heard about the castor/SAI relationship. I will have to reread that a few times. It looks like this is the ultimate subject for the "butterfly effect" where if you change one thing it is bound to affect other aspects of the system. I like where I am at this point but it will take some real life testing (track time) to justify what I have. Of course there is also the variable of the driver, also! Thanks, WEK.

[skullandbones]

Curious if anyone is carrying any more than 9 degrees positive castor on their roadster front suspension. I suppose if you are it would be on a PS setup. Also, how you have used it and results.

Thanks,

WEK.

[cobrabit]

CraigS:

You are correct on your measurements and angle estimate: Setting up a Right Triangle with adjacent sides a=.26, b=5 and c=hypotenuse using a few Trig. Theorems for Right Triangles: c=√[aˆ2 +bˆ2] and the Law of Sines: c/sin(90˚) = a/sin(ø) , where ø= Arc Sin[a/c] since the Sin (90˚)=1; Hence ø=2.975˚ or ~ 3˚ for our purposes.

Regards to all, cobrabit Jerry P.E.

QUOTE=CraigS;108508]Here is a shot of the bracket for the left side of the car. So the bolt (I stuck thru to make the holes more visible) on the left would be toward the front of the car. This would decrease anti-dive compared to the original mount.
http://i3.photobucket.com/albums/y91/craig-s/SAIbracket_zpse12abc67.jpg
The left bolt s .760" below the edge and the right bolt is .500" below the edge for a difference of .260". The bolt holes are 5.0 inches apart center to center. I measured the angle w/ a cell phone app and w/ my camber gauge. My accuracy is a little suspect, maybe + or - .1 degree. I get average of 3.0 degrees. Perhaps someone who has done trig less than 46 years ago can check this. So Borden's SAI kit antidive change is about half of what you will get w/ the 6 deg. wedge. While there is a difference, I think that as long as the UCA side view mount is any small amount higher in the front, you will still have some antidive. If you have 'some' you will be OK. The good thing is that front springs up to 750 w/ the correct shocks are still streetable in my experience. So, if the antidive is too little you can bump the front spring rate to compensate. Bill, have you modeled the FFR front suspension in your program so you could check this more scientifically?[/QUOTE]