SAI Mod & Bump Steer

[rlampman]

I have been researching and reading all I can about the SAI mod and how I want to change my suspension setup to get the best handling manors that I can. I will first state that I am not planning any racing or autocross with my car. Just street driving but I know how a good driving car is more fun to drive and well I like to work through these kind of things to learn what I can. So far I have learned to do my own alignment on the front as well as the IRS. Still learning but I think I have a handle on it to at least get repeatable results. In addition to the handling I want to be able to have the tires inside the fender and have a deep dish for a better look. With all this I am only at mock up in my build so all of this is only theory for quite a while before I get any road time.

I have a MKII with standard width IRS and front pin drive. I did this to allow the front tires to stay in the fender but have a deeper dish look. The rear will already have a deeper dish as I have a TriStates body and the rear fenders are 1.5" wider than a standard MKII. I have manual steering and I will be using 15" wheels with a custom offset.

Today I started the SAI mod install. The standard mod includes the spindle adapter which I used and a frame adapter which I chose not to use. The frame attachment for the UCA was inspired by this thread by skullandbones, thanks WEK!
Changing MKIII Front Steering to Resemble MKIV Level

By mounting the UCA below the frame mount and changing the angle it matches the SAI mod frame bracket location but keeps a longer arm and leaves clearance for the coil spring.

Because I have the wider pole position UCA's I needed to clearance the 3/4" cross member. After I have the body back off and I can get better access I will clean up the cut and weld reinforcement by boxing it back together and adding additional support below.


I used a 4 degree pinion shim which I cut in half and drilled for the UCA bolts. I also had to clearance the bolt holes on the frame to bring the UCA out just a little to clear the 2X3" frame member below the mount. I ended up making a shim for the bottom and the top of the frame to give the bolts and nuts a flat surface to torque too. makes a sandwich around the frame mount and changes the angle. Seams to be a good plan to me but I'm not sure if the fact that the spacers/shims are made of aluminum instead of steel.






I installed the SAI mod spindle bracket per the instructions. The instructions where great but pictures would clarify a lot. One thing I noticed but didn't read on other posts is that with this mod installed in order to remove the caliper bracket or with the PBR brakes to remove the upper caliper bolt you have to remove the spindle bracket first. That means to service the brakes you have to remove the spindle bracket. Not to hard and you can leave the ball joints in place but a pain.

In the kit I had two left spindle brackets so only one side for now. They are sending a right one out to me. So if you just received your SAI mod kit look for two right brackets. Also for the PBR calipers you have to use a button head bolt for the upper caliper attachment. The ones I received where the wrong thread so had to go the the hardware store and get the correct ones. With that there is just enough clearance. Tight but it works well. Pictures are with the brakes removed for alignment but you can see where the caliper bracket bolts on. It is behind the upper ball joint nut so you have to install before the bracket is installed. Also the lower ball joint has to be torqued before the bracket is installed because it is covered also.

[rlampman]

Now to measure my bump steer and correct what I can. I installed the Breeze offset rack mounts moving the rack as low as I could. I centered the steering and measuring from the inner tie rod ends I adjusted the rack to the passenger side to center it. After that I completed the alignment. Camber 0.7 degrees, Castor 4 degrees, toe 1/16" per side.

I clamped on a 90 degree angle to attach my laser to the rotor and clamped the rotor to keep it from moving.


With a paper about 3 feet away I have a fairly linear line but it moves to the rear on bump and front on droop. I measured from a 2" droop to 2" compression. Marks are at ride height (0) and 1", 2" rise, 1", 2" droop.


Pictures of my setup at ride height:


Looks like the LCA is at a slight upward angle and the tie rod is at a slight downward angle. Hard to see in the pictures but the angles are fairly close though. I also see that the inner tie rod could use rack extenders as they are about an inch inboard from the line between the inner pivots of the UCA and LCA. Hard to see from the picture but this is looking down from the UCA pivot showing the LCA pivot and where the inner ball joint sets when centered.


So the question is, what to change? I am thinking I need rack extenders and probably a bump steer kit. Both I will need to order. Any input is appreciated.
Thanks Rod

[CraigS]

A couple of thoughts. 1- I think I understand that you had to slot the holes in the frame piece where your two UCA bolts mount. That would make me a little nervous that it could slide under load. If the shims where steel I would say run a weld bead. Since they are not, my other thought would be to put some weld material in the holes to make them a circle again. OTOH, on a street car they may be fine.2- I think it will go in the wrong direction re; bump steer but it's free so an easy experiment. How about moving the rack up? I am not sure rack extenders will be needed but I would get the Forte bump steer kit. I think you may be moving the tie rod to the top of the steering arm. 3- I tried to figure if you have power or manual steering but couldn't. If PS go for up to 8 deg caster. This is a better caster number and will also raise the steering arm which may help w/ bump steer. Also it's another freeby.

[rlampman]

CraigS - 1- The holes where only opened up about 1/8" and was just enough to get the UCA cross bar to clear the 2X3 frame member below the mount. It is actually against the frame member so it can't move back in the holes. I was only thinking that the aluminum may compress when torquing the bolts or under the stress of the suspension. If that is a real concern I can get some steel wedges but they are about $70 more for steel. Not a lot in the scheme of the hole car but everything helps. Also, that is what WEK used and he didn't mention any issues.
2- you are correct but not much change. See below
3- I have manual steering so not sure if I want any more castor but I may try this just to see the change that it makes in the bump steer.

I tried a few changes and here are the results.

RED line is the original setup with the outer tie rod below the spindle arm as usual and the rack is centered and lowered
ORANGE line is with the outer tie rod below the spindle arm as usual and the rack is centered but raised
LIGHT BLUE is with the outer tie rod bolted above the spindle arm (center is 1 1/2" above the spindle arm) and the rack is centered and raised.
DARK BLUE is with the outer tie rod bolted above the spindle arm (center is 1 1/2" above the spindle arm) and the rack is raised more but not centered.


Looks like the outer tie rod needs to be on top but maybe not as high as I have it now. I hope with that change I can lower the rack again. With the rack raised I will need to modify my radiator fan setup as with it in the stock position I only had about 1/8" clearance rack to fan. From these results I will order Mikes bump steer kit today and some rack extenders. After that I should be able to get it closer to where I need.
Thanks Rod

[rlampman]

Well forward a little. I installed Mike Forte's bump steer kit today. The kit is great and I recommend to anyone! I really like the way the threads are opposite so you can adjust toe by twisting the sleeve.
The rack extenders I receive are not the right ones for my rack. I have a flaming river manual rack. I didn't even ask cause I didn't know there was different threads. These are a little smaller than an inch and mine are either 14mm or 9/16. I need to figure out what mine are so I can get the right rack extenders.


I also need to get some shorter inner tie rods. I know some have cut theirs but I need to shorten mine by at least 2" if I use rack extenders. I was right on the edge before but the bump steer kit is longer than the outer tie rod I have.


I lined them up in the photo based on how far they thread onto the inner tie rod. I could cut the threads down about a 1/2" but after that I would need to start cutting down the sleeve. The first part is the indents for a wrench. My inner tie rods are 11" total. Anyone know if I can get shorter ones?

Even with the longer tie rods the bump steer is better. I turned the rack to the drivers side so the passenger side lines up with the right toe in. This leaves the pivot point 2" inboard of the A arms so I think there is still more improvement. This is from 2" above and 2" below ride height.


Rod

[skullandbones]

Hi rjampman,

I'm curious to see what a perfect bump steer graph looks like. If I am interpreting your last one correctly you only have some change in the toe at the extremes (compression and rebound)? I would think a perfect graph would be very close to yours but with no tails at each end. It's an interesting quest whether you get there or not. I haven't even begun to attack the bump steer issue. I recently went on a long trip and didn't experience any violent bump steer over several varieties of terrain. There were cattle guards, bumps, dips, a few pot holes and a lot of uneven pavement. I'm hoping that I lucked out on that aspect of the suspension but I'm waiting for a comparison with yours when you get to that "sweet spot" you are looking for.

Thanks,

WEK.

[CraigS]

WEK, I found that the fact that I can't feel any bump steer doesn't mean anything. To cut out a lot of detail, I can say that, when I got my MkII in 07 I had very noticeable bump steer. Some changes later, mostly going from 2 deg caster to 8 deg when I went to power steering, I didn't feel any bump steer so I let that upgrade ride till about a year ago. Then I actually measured it. Wow, plenty there. So I got a Forte kit and reduced it to reasonably close to zero. To me this is one of those things that may not make a huge difference, but every small improvement to our front suspension geometry, that brings it closer to accepted norms, makes the car drive a little better.

[rlampman]

Yea WEK I don't know what a perfect bump steer line would be either but I am pretty happy with what I have with only 1" of suspension movement. You are right on the extreme is where it swings out. I think if I can get the inner tie rod pivot point moved in line with the upper and lower control arms I may be able to get closer. The bump steer kit really helps dial in and you can see the changes quickly.
Rod

[rlampman]

I have been doing other things while waiting for parts and trying different combinations.

I needed to go to a shorter inner tie rod. That created a problem as the one I have is the shortest one with the threads that I have. 14mm 1.5 threads on the rack and 9/16 threads on the outer tie rod (or Forte bump steer kit). In order to go shorter with my rack I need to change the outer tie rod to 14mm threads. I found new sleeves from RaceCraft that have the same threads for the heim joint but 14mm threads for the inner tie rod. Then I got new inner tie rods that are shorter. In this thread combination there are many choices for length.

I also found the best results with the 99' spindles (strait arm) with the tie rod above the spindle. In order to use the 95' spindles (dog leg arm) I would need to do modifications and drastically lower the rack or drastically raise the rack. Finding the same thing that Todd Buttrick found, the tie rod needs to be right where the spindle arm is for the 95' spindles (dog leg arm).

The other item I still need to work out is the rack extenders. I bought some from a member here not realizing or asking about threads and they don't work with my rack. The only one's I can find in 14mm threads are 2" long. I will probably have a machine shop build some for me. For now I will adjust the rack to one side until I find exactly what length extenders I need.

So here is where I am: Rack lowered all the way with Breeze mounts. Bump steer kit installed above the 99' spindle with one large and one small spacer.


This is what is measured on the passenger side so far and looks really good. I went from a 3" compression to a 3" droop. The paper is 4 feet away from the rotor so nothing drastic.


The only area that still needs improvement is past 1" of droop. I'm not sure realistically how far the suspension will droop but I would like to get it linear to at least 2" of droop. From the changes I see so far I think I still need to go shorter with the tie rods (longer rack extenders) to move the inner pivot point in. The threads in the sleeves I have don't go all the way through so I plan to get a 14mm tap and run the threads all the way. Then I should be able to use all the threads of the inner tie rod and gain another 3/4". Should be plenty.

Any other ideas to help improve the droop side of my bump steer would be appreciated.
Rod

[CraigS]

That is going towards toe-IN at both ends correct?

[CHOTIS BILL]

When dealing with bump steer having a small change in droop is not a real concern because in order to have droop there is weight removed from the front springs and you have less traction and less of a chance of it causing a problem unless it causes substantial toe out. The big concern is in bump which means add weight to the springs like when you are breaking and again going into toe out under breaking can cause major instability. I have FFR spindles so not a direct comparison but I was able to get the bump steer down to .000” in 2” of bump and 1” droop and then .005” toe out in the last inch of droop.

Bill Lomenick

[skullandbones]

When dealing with bump steer having a small change in droop is not a real concern because in order to have droop there is weight removed from the front springs and you have less traction and less of a chance of it causing a problem unless it causes substantial toe out. The big concern is in bump which means add weight to the springs like when you are breaking and again going into toe out under breaking can cause major instability. I have FFR spindles so not a direct comparison but I was able to get the bump steer down to .000” in 2” of bump and 1” droop and then .005” toe out in the last inch of droop.

Bill Lomenick

Are the tails on your last graph indicating "toe-in"? I think they are but not sure. Thanks, WEK.

[rlampman]

That is going towards toe-IN at both ends correct?

No, this is the passenger side so it is "toe out". With the inner tie rod longer (smaller rack extender) I still have the same graph but the top and bottom are more pronounced.
Rod

[Jim Schenck]

Rod,

If you are measuring bumpsteer the way it looks to me I think your results are being skewed by the suspension scrub. As the suspension moves up and down the wheel travels in an arc even if the steering angle was completely fixed, so when you are trying to get a straight line up and down you are actually adding bump steer in that is masking the normal wheel movement. In order to measure true steering angle you have to measure out the rear of the rotor mounting surface as well and then compare the two lines, when they are the exact same curve then you have zero bumpsteer. (we usually intentionally go for slight roll toe-out to help stabilize the short wheelbase car under turn in but starting from zero makes that an easy thing to tune in)

[rlampman]

Rod,

If you are measuring bumpsteer the way it looks to me I think your results are being skewed by the suspension scrub. As the suspension moves up and down the wheel travels in an arc even if the steering angle was completely fixed, so when you are trying to get a straight line up and down you are actually adding bump steer in that is masking the normal wheel movement. In order to measure true steering angle you have to measure out the rear of the rotor mounting surface as well and then compare the two lines, when they are the exact same curve then you have zero bumpsteer. (we usually intentionally go for slight roll toe-out to help stabilize the short wheelbase car under turn in but starting from zero makes that an easy thing to tune in)

Thanks for the input Tim. I have not heard of that. What I have is a laser level clamped to the rotor pointing to the side. 4 feet away to the side of the car is where my paper is. That way the point on the paper moves to the side as the toe changes.
So you are saying to put my laser on the back and then the front of the rotor and try to get both arcs the same even though they are not strait? Not sure if I follow how the front of the rotor would have a different arc than the rear..
Rod

[Jim Schenck]

If you are pointing out to the side then the issue would be that the upper and lower control arms are not in the same plane (unless you have made them the exact same with your shims) The upper ball joint normally tracks backward under compression and the lower is perpendicular to the ground which gives the front end some anti-squat under braking.

[CraigS]

Jim, so picturing this in my mind, zero bumpsteer would actually be a line that moves rearward at the top of the travel because that is what the upper ball joint is doing. I suppose, if the UCA is mounted at a 6 degree angle, while the LCA is at zero degrees, the track of the laser would be at about 3 degrees from vertical to indicate zero toe change. Am I picturing this correctly?

[Jim Schenck]

Craig that is pretty much it, the tie rod would be a little less than half the travel of the upper though because of it being located closer to the lower ball joint. So maybe closer to 2 degrees than 3 in your example.

[CHOTIS BILL]

One way to double check the bump steer is to mount a flat plate on the disk in place of the wheel and mount a dial indicator at the front and one at the back of the plate. Moving the suspension through its travel and comparing the dial indicators will give you the toe change that compensates for the tire scrub. There are several companies that sell the tools to do this such as Longacre. http://www.longacreracing.com/produc...p+Steer+Gauges I use aluminum plates machined to fit the hub and 2 dial indicators mounted on magnetic bases that attach to the frame.

Bill Lomenick

[skullandbones]

Is it possible to use the toe plates for the purpose of measuring with the dial indicators? I'm not seeing how having the tire/wheel on or off will affect or change the measurement. Personally, I don't want a garage full of alignment tools. Also, is there value in comparing the graphs to the direct measurements. It seems to me that the direct measurements would help you to translate the graph. Can't seem to find what a perfect graph would be. Don't remember seeing anything like it in other literature to compare. WEK.

[CraigS]

WEK, my experience says it is not necessary to get this perfect. If you look at Rods curves in post #4 compared to post #9, you see a tremendous improvement. When I first measured mine it looked something like the light blue line in post #4 and I couldn't feel any problem at all. I was very surprised it was that bad. The reason I had never measured it was the old school method of using at least one, and often two, dial indicators, plus needing a flat plate to replace a wheel was way more than I wanted to spend. When I first saw the side pointing laser technique in David Borden's build thread, I knew that was something I was willing to do. I think Rod is done at this point but will be interested to see if he gets rid of that curve in droop.

[rlampman]

Thanks everyone for the info. Some great information. I really agree that the more you understand about suspension the more you know that you don't know.
I may try making a real bump steer guage to see the difference but for now I will see what I get with the current method after shortening my tie rods a little more.
Rod

[rlampman]

Well MUCH better today. After shortening the tie rod length (longer rack extender) my curve is gone. I slowly moved the inner tie rod out, adjusted the height of the outer tie rod, measure bump steer, repeat. Ends up I need 2" rack extenders which are available.


Red is what I had with about a 1" rack extender and Blue is what I have now with a 2" rack extender. I found that as the inner tie rod pivot point moved out the swing that I started with at droop moved lower (reduced) and if I went farther out than 2" the top (compression side) then started to curve out but not as drastic.

I would still like to see how this compares measured with a real bump steer gauge. For now I will just stick with the laser method but I am still a long way from being on the road. At least now I know I am close and I can adjust the curve around as needed.
Rod

[spino]

Is there some benefit to performing this Modification work over installing a MK 4 spindle kit. I am debating what to do to my MK2 for the best performance. Any advice would be appreciated.

[CraigS]

Spino, I am making an assumption here since I see you have a MkII like I do. IF you have Fox spindles, to install the FFR spindle, you will need all new brakes, rotors, hubs etc since none of the Fox stuff fits. I feel that the FFR spindles are the best setup as long as you also do the frame mod to move the mounts of the UCA. But it's an expensive upgrade due to all the other stuff needed. That is why I have a 1/2 SAI mod on my car. IF you are running 17 inch Bullitt wheels, Whitbys can machine the hole in the SAI spindle adapter 5/16 deeper which will allow it to fit inside of the wheel. I have had this on my car for several years now. It definitely helps, but, of course, doing the whole thing would be even better.

[rlampman]

Is there some benefit to performing this Modification work over installing a MK 4 spindle kit. I am debating what to do to my MK2 for the best performance. Any advice would be appreciated.

If you change to SN95 or to FFR spindles you should measure bump steer. Unless you measure you don't know what you have. There is to many variables to say bolt on these parts and it eliminates bump steer. Either way it doesn't mean you have to do all the modifications I have. If you have standard width there is more length to the arms and simplifies some things. You may want to update your signature line with your setup. I think either the SN95 spindles with the SAI mod or the FFR spindles by themselves will get you better SAI and then you can measure your bump steer and see what you have. The FFR spindles will cost more but are really nice. Not sure about the exact difference in set up between the two but with the FFR spindles you may not need to unbolt the spindle to remove the caliper. You do with the SN95 w/SAI mod.
Rod