Bumpsteer spacers

[XYZ]

I'm going to be replacing my existing springs and struts next weekend with Eibachs and Tokiko struts. I read quite a bit about developing negative camber from the use of the Eibach's (in general, lowering springs) as it lowers the CG 1" +/-. I know a lot of the members have Eibach's on their cars and I'm wondering if the use of this bumpsteer spacer is prevelant or basically ignored? If the spacers where ignored did you do anything special to the alignment as far as camber adjustments etc.. to counteract the lower CG? I believe I read somewhere that increased bumpsteer detracts from cornering ability which is what I'm trying to increase. If I need the spacers to get the most out of this upgrade I would like to order them so I can install them when the car's torn apart. Thanks in advance for feedback.

[2ManyZs]

The bumpsteer spacers are for regaining the proper geometry in the front suspension but its not the camber, it's the roll center. They do decrease the bumpsteer also but at the same time the move the roll center of the car back into its proper place. Lowering the center of gravity that much puts the roll center of the car below ground. The spacers bring it back above ground where it is supposed to be. The stock suspension has a very low CG to begin with and lowering the suspension will lower it too much.

Wish I could find the diagram I had that explains it. Have to look around here and see if I can post it.

[hmsports]

Again, 2Many is right on with his knowledge... You know, I'm looking for a new crew chief :classic:

Anyway, here's a very good explanation from LongAcre (at the Racer Parts Wholesale site). It explains what it is, how to measure it, how to trouble shoot it and how to correct it. It also has a great picture at the bottom.

[XYZ]

I've got that book about "how to make you car handle" with some explinations and diagrams (not specific to the Z, but I understand the geometry your talking about). I think what your recommending is to use the spacers to get the CG back above the ground. What are the ramifications for not using the spacers? or is that not a reasonable option?

[hmsports]

I think what you will find without them is that on hard cornering, when your suspension loads, you will get an undesirable amount of excess toe in on the front wheels because as the control arm moves up, the tie rod in essence gets shorter. This will make your car understeer (push) through the corner. By adding the spacers and getting the steering geometry back to normal, you will keep the amount of bump steer to a minimum.

On the rear, what you want to avoid is excess toe out as this will give you an oversteer (loose) condition. Since you don't have tie rods on the rear, it isn't a problem that gets worse with lowered suspensions. Just make sure the rear is even or about 1/16" to 1/8" toe in to help tracking.

For racing, I run my rear toe even. The front I usually keep even for long tracks (fewer turns) or add a tiny bit (1/16" to 1/8") of toe out if there are a lot of corners - helps with getting the car to turn in and follow through.

BTW - I ran for three years without spacers and my car is lowered to 5" ride height (measured at the lowest part of the rocker panel) and I had a lot of problems with understeer - even after working on all other variables.

[XYZ]

Sorry to be so redundant here, but I want to be absolutely clear on my terminology so I don't ask the wrong questions. I realized that what I asked might be considered the urethane strut shaft bump stop at the top of the strut. I was not talking about this part but a bump steer spacer set that mounts on the lower end at the control arm. It's a part I've seen in VB and Zcarparts. Sal at motorsports suggested cutting down the urethane strut shaft bump stop by 3/4" (at the top of the strut) to allow more vertical travel. I'm wondering if this allows the control arm to be lowered by only a small amount rather than the 1" +/-. I believe (and I'm going to call motorsports again) that they recommended against the spacer at the control arm. Thanks for the patience.

[2ManyZs]

Cutting the bump stop on the top insulator only does one thing. It increases the amount of suspension travel available. When you put on lowering springs such as these, you only reduce the distance between the spring perches with a shorter spring, therefore you have less available travel. By cutting a small amount of the bump stop on the top, you increase the distance the strut cartridge can compress before the strut housing hits the bump stop. It has nothing to do with the amount of lowering you get, that is all dependant on the type of spring you choose.

The only other way to increase the amount of wheel travel is to shorten the strut housing and use a shorter strut insert and move the lower spring perch upwards or use coil-overs.

The bottom bump steer spacer may not be as critical with a small 1 inch lowering as it is with a large amount of lowering such as you would get from other lowering springs or coil-overs. I believe since the tie rods and rack are in front of the control arm it affects the Z more than cars where the tie rods or rack are behind the control arm.

hmsports is correct in his assessment of why you need to use the bump steer spacers. You could try a one inch lowering without them to see if the handling is affected in such a way as to make the car a handful. The understeer problem will be exxagerated by the sway bars you choose also, so with or without the bump steer spacers is likely to need two totally different sway bar set ups.

Unfortunately after an hour of searching I still can't find the drawing of the suspension geometry and how it is affected by lowering. I think it may have been in an old parts catalog, perhaps one of MSA's old catalogs.

[XYZ]

I appreciate the feedback, thanks. Sounds like I should get some spacers before the weekend. I've got to think a little about cutting the insulator stop. BTW, what is the CG height on a stock Z?

[2ManyZs]

Well, can't answer the CG question unless I find the diagram.

As far as whether or not to cut the upper bump stops, that depends on how you plan to use the car. If it's a street only car, I wouldn't bother. If you plan on the occasional autoX I would go ahead and trim off 1/2 to 3/4 inch, especially if you are using the Eibach progressive springs. The progressives get stiffer the more they are compressed, so by increasing the travel available you will get to use the springs the way they are designed. If they are the single rate it might not be as important, since they will be the same rate through the whole travel.

[XYZ]

Hi mperdue-

Everything turned out really well. I'm very happy with the set up and have become an even more aggressive driver! Half kidding.

If you haven't started the install yet, as I have mentioned before, be sure to get the springs in the right spots. Each spring has a part # on it that ends in either XXXX.100 or .010 and .200 or .020 or some combination thereof. The point is the part # with the .100 goes in the front and the .200 series in the rear. That was my one hangup. I had switched the two spring sets and the result wasn't good so I did it again.

Other than that everything went together pretty well. I would recommend airtools if at all possible or it will take a lot longer. The impact wrench was invaluable when it came to compressing the springs.

I did use the spacers and I'm glad I did. The more I thought about it, it made no sense to push the camber out anymore than necessary. The spacers are real easy to install and bring everything basically back to original configurations. The one thing I have wondered is whether to install the camber kit to help with the overall adjustment.

I also cut down the bump stops about 3/4" ( a little off the top please) on recommendation from MSA. I did not grease these parts and wish that I had although it's not a big deal.

I think what you will find with this setup is that it's an absolute blast to drive the twisties and I look for corners and accelerate through as many as possible because I can! I'm not the fastest off the line but I will kill alot of cars in the curves. You will also realize just how bumpy most roads are out there. I spend a lot of time avoiding bumps and things in the road as it is a bit rougher but well worth it! The performance, for me, far outways the rougher ride and the car looks a lot better in its stance.

Good luck and have fun!

[XYZ]

Here ya go. It's kind of hard to get a good picture without lifting the car but this will give you an idea of where it goes. It's the shiny aluminum plate you see in the center. I think it's about an 1" thick +/- and gets sandwiched between the strut tower and the wheel spindle (?). Not sure of the terms here, but it's real easy.

The bump stops are in the strut tower and I can't get a shot of those without dropping the strut assembly but basically you stick those things in a vice and cut the top off which I believe is the narrower end. I'm trying to remember if they're tapered - I think they are. I used a hack saw to cut the stop.

I do have the non-adjustable tokico's. I previously had KYB's (unknowingly) and they felt sloppy in comparison but that was also with stock springs.

If I can remember, I'll get my car up on a jack and take a better pict. of the bumpsteer spacer for you this weekend.

[XYZ]

Another angle of the spacer.