Strut spacers
 

Hey all,
My car is now sitting about 5 1/2 from the ground measured around the bolt of the lowest point on the front fender . I was wondering if I should be running the 3/4 " strut spacers . Would this help a bit of the understeer problem I have ? Any help would be appreciated :)

Whether strut spacers will help with understeer depends on a number of factors. They won't hurt that's for sure. If you have lowered you car with shorter springs or a coil over set-up, what the spacers do is lower the outboard side of the swing arm, thus placing the arc it travels through closer to the middle. Looking at the driver’s side of the car from the front, picture a clock face as the arc. If you have lowered your car, the outboard end of the swing arm is at 3:00. As it raises it swing past 2:00 and ends up at 1:00. The sine angle of the arc brings the swing arm and the tie rod (since it is attached at the same place) back towards the inside as it moves up. This is bump steer. If you lower the end of the swing arm back down to 4:00 as it moves up the sine angle change is less through the same range of motion, thus lowering bump steer. Bump steer can never be eliminated in a strut suspension.
Z cars understeer. Making them oversteer is possible but I don't think it makes them faster in autocrossing. A couple of things that I have found (and these are all just my opinion) is that too much spring and too much shock does not a happy Z car make. Same with bars. If you have adjustables, 1 1/8" front and 3/4" rear seem to work well. In a BSP car about
-2.5 degrees camber in front is the most you can get. About -1 camber in the rear is good. Too much rear camber = too much toe change in the rear, which is bad. About 1/8 total toe out in front and 1/16" total toe in rear.
Once again, this is what worked for us, your mileage may vary. One other thing that works, is adjusting your driving style to cope with it. Sometimes one most go slow to go fast. ;)

Randy

Thanks Randy !!

I am going to cheak everything out on the front end tomorrow . I need to get busy on the car though . We have a two day autocross coming up the end of June.


Did you get any photos of the Mac's GT3 350Z from last weekend ? If you did could you post one to the photo album ?

Thanks,
Mike

BTW... it helps to have a spouse who is a math teacher :)

A math teacher is good to have handy! When I bought my lathe, I realized that I should have paid more attention in trig class!
Sorry, I didn't get any pictures of Mac's car lat week. I may have got some from Portland, I'll check.
I took a look at Tom Holts alignment set up. Now that's the way to go. Much easier than jack stands, and you can roll the car back and forth to settle the suspension. Hope Tom doesn't mind if I copy his set up. :p Thanks Tom! Mine will have to be different in the way it attaches, but I think I can make a "indexable" type attachment that can be mounted for quick changes.

Randy

Is this the alignment set up you are talking about ?

Yep, that's the one! One more of Tom's speed secrets unvailed on the Internet. A company called Sherline makes a fixture for aligning race cars, but it works best on open wheel cars. Pretty spendy too. Tom's looks like about $20 in parts, tops. Less if Guy can bring you some conduit from work LOL...

Randy

Hey! Did I mention the copyright I have on that setup? I think you guys are going to have to send me $20 or so to cover my intellectual property! ;)

I basically bootlegged the idea of mounting the strings on the car from the Sherline setup. It makes too much sense. It's especially easy if you get rid of those pesky bumpers.

A few of tricks I learned making this setup are; make two marks 72" apart on the horizontal tubes (or whatever measurement works with your outer track width). This will ensure your strings are parallel. Measure from the vertical center of each hub to the string and move the tubes to get it centered. For measuring toe, since my rims are actually wider than my tires, I place a carpenters framing square against the rim with the short leg on the front tread surface and measure from the string to the inside corner of the square. Then I flip the square to the rear tread surface and measure to the inside corner again. The difference is your toe. Repeat at all four corners. I recommend using a machinist scale to take the measurements or at least something that reads to the 1/32nd". Also, the finer the string the better.

I remember reading in the old book "How to make your car handle", their recommendation for toe measurement... First they suggest you mark a chalk line down the center of your tread and make a square out of plywood and measure with a tape measure at the front and rear of the tire... That kind of reminded me of the old machinist joke of "Measure it with calipers. Mark it with a pencil. Cut it with an axe", or something like that! :) I think my setup is a little more repeatable.

Tom

The only problem that I have doing that on my car, is that I have crash structures both fron and rear, and I don't have a suitable place to attach the fixture. Looks like I'll have to break out the welder and put a couple of brackets to support the fixtures. The front has a something I can us, but the back will be a issue. Tom, I assume that you are using a camber gauge like the Smart Camber digital for setting the camber?

Randy

I usually use a SmartCamber gauge. I have also used the framing square and measured the angle of the wheel relative to my garage floor (which is very level across the width of the car (I checked it with a water level)). Either way seems to give about the same degree of accuracy.

Tom