"Bumpsteer" spacers
 

Who makes 2" to 3" "bumpsteer" spacers for the front LCA's? Any idea how tall the MSA's spacers are?

I want the outboard ends of my front LCA's to point to the ground instead of the sky.

Have some made and see if the bolts break! The biggest I have seen are Panchovisa's custom one's on Classic Z. I think they were a little over an inch. I was thinking of stacking two of my 3/4 inch ones together and having them Tig welded together for a 1 and 1/2 inch spacer.
Which brings up a question I have been wanting to ask for awhile.
While talking to Jay Morris of Ground Control about 5 years ago at an autocross he said I should lower my Z as far as I could. When he was driving his I.T. Z he said it was the only car he had ever set up that would keep getting better the lower he made it. He said it was almost boring to drive because it was so predictable.
I know this sends your roll center underground and screws up your camber gain curve. But then all of the EP 240's on slicks are much lower than many on Hybrid Z would say is a good ride heigth. I would like to see the angle of their control arms.
Anyway back to spacers. The biggest I have seen for sale are 1 inch thick. I bought a set of those years ago from Jim Cook Racing. I just read a thread from Dan Juday who just bought some 1 inch from Motorsport Auto but they were too big for his rims. Maybe you could see if http://www.designproductsracing.com/DesktopDefault.aspx could make you some.

I found his post on HybridZ. I think I'll mock something up first just to make sure everything clears.

I found some interesting pieces while looking around on the Net. Here is an interesting piece that adds camber and adjusts roll center at the same time.

http://www.technotoytuning.com/t3_si...cts/ncrca.html

Hmmmm.

I'll keep looking though.

When I had 14 inch wheels I found when I moved the suspension through it's travel, the zerk grease fitting whould hit the wheel. I replaced it with the screw in plug the ball joint came with for the needed clearance. Just a thought for when you are reaching the limits of clearance with your spacer. I will take some pics this weekend with different spacers and a 16 inch wheel and 5 inch backspace to find the clearnce limit on mine.
Have you re-drilled your crossmember and moved the inner pivot up? There is a little angle change for the LCA.

I looked at moving the inner pivot up and it seemed like that would cause more potential problems than it would cure, like the frame rail interfering with the sway bar and LCA. The spacer seems to me to be the right way to go about it. I ball parked some dimensions into emachineshop today and it looks like I can have some 2.5" spacers made for about $100 each, probably less. I'll take some real dimensions tonight and see if that brings the price down at all.

I've taken both approaches - 3/4 inch spacers AND moved the inner pivot point up by about 1 inch. One thing to consider is the size wheel you're using. Make sure you have enough room between the bottom of the control arm and the wheel to use a 2.5 inch spacer. I don't believe that would work with my 9 x 15 inch wheels.

I still need to check clearance, I'm running 16" wheels, and exact height of spacer needed, but here it is.

https://www.zdriver.com/gallery/data/571/4650rca.jpg

Let me know if it works. If I make the move to 16 inche wheels I might do the same with the bump steer spacers. With the changes I've made the lower control arms are level at the current ride height - but if lowered (as in leaning in a corner) they move up and the roll center drops below ground.

Have you guys experimented with the tie rods at all? I plan on swapping mine out with rod ends and using different height spacers off the steering knuckles.
This is strictly for bumpsteer and not roll centers though.

We've considered it - but have not gone that route yet. With the 3/4 inch spacers we don't feel it's really needed. But then again - this is a back yard project. It would be nice to have someone with a computer program do an analysis. A complication for us is the custom control arm and TC rod. Both are completely adjustable so we can get any caster/camber we want. We're currently running -1 camber and +6 caster. The tire temps are pretty even all the way across - but the inside edge wears faster than the outside.

I can't say I have ever actually noticed bump steer on my car, but that could be because other issues are covering it up. Once I get my LCA's back to a reasonable position, I'll look for it.

Perhaps Drivesideways will chime in. He did a very nice job of conversion to tubular
tie rods and bumpsteer correction with a spacer between the steering arm and outer tie rod bearing.

Hi John,

Having the control arms point up isn't necessarily bad, neither is pointing down. But if it is a lot then it might be an issue. I know a lot of people talk about camber gain and how important it is. If you're running bias ply slicks and your car doesn't roll too much then I wouldn't worry about it. In our strut based cars we can't really get an adequate level of camber gain without causing too much scrub.

For autocross a below ground front roll center isn't really bad and may help. We tend add input to the car much quicker than road racers and a below ground roll center helps to load the tire contact patch not as quickly and this tends not to heat up the rubber as quickly. Below ground roll centers generally are more stable and the car reacts slower. When you think about how quickly we ask it to transistion then you can see why this might work. What you don't ever want to happen is have the RC move through the ground as you're cornering. If this happens the car will have a moment of instability where it feels like it hopped sideways.

One thing to consider is the Z has bumpsteer built into it. And when you get the arms at either extreme you'll find that is when the bumpsteer is usally worst. You don't really realize how much until you get rid of most of it. On a 50 second course I picked about about a three tenths from bumpsteering the car. It made it easier to drive and inspired more confidence. It's entirely possible that my car had issues much worse than yours.

I have Susprog3D and I'm willing to input a few peoples numbers. It's not easy and takes a lot of work to measure everything. You need to be accurate to a tenth of an inch (and probably more) for all the hardpoints and 0.020 for the steering components. Each car will have differences and this is one of the first steps to figuring out what you have and where you might make some changes.

Welcome to scrubsville. Get used to it. I flip the tires on my wheels every three events to get around this.

Whats the front look like?

Hi Cary, I deleted my idea cause I just figured out changing the angle of the arm without changing the pivot don't work. Brain fart. I was trying to figure out a poor man's version of Panchovisa's well engineered and machined rear spacer that lowers the outboard pivot point. (Look in his photo gallery on Classic Z). Here is the original pic of the Red Frog rear suspension. I do no have one of the front.

Hey Steve,
Randy is still around . I need to get a hold of him and see what happened to
to his GT2 car aka Red Frog . He had a few suspension ideas that were a bit out
of the norm :)

Mike

I am following this whole thread trying to figure it all out :)

There's some cool stuff in his gallery but some really has me scratching my head. If you were going to that much trouble why didn't they simply cut the arms off the strut and build a nice tubular arm with heims that mounted in double shear.

I wasn't going to give you guff about the pickup points not moving, at least not for a while :p

My thoughts too. It seems like too many guys hack up the stock arms to death, including the front ones, and put more time and energy in than what it's worth.

EDIT: nice to hear from you again Cary.

Hey John,
I had the bumpsteer worked over in my car late last summer. Like you, I never really noticed it (payed attention to it is probably a better term) but once it's gone you realize how much less the wheel is moving through the turns. The only mods were to the tie rods, switching to heims and spacers, and the change pretty huge. Initially, I had .23 total toe change at 2" compression and -.32 at 2" droop. That's .55 total over 4" of travel. Now I -.045 at 2" compression, and -.062 at 2" droop. So we eliminated nearly 1/2" of toe change over 4" of travel. I do have the bumpsteer spacers (I think they are 1"). We did also switch to heims on the inner front pivots, just to eliminate slop, but that didn't really impact the bumpsteer. I'll post some pictures of the new tie rods when I get home. It's pretty simple stuff.

Tom

My thoughts:

I thought that perhaps the Susprog3D would be a good start, but as you say, measuring everything accurately is difficult, plus you really need a level platform to measure from, something I don't have. My experience with with the computer analysis is that I'm not sure how usefull the information gained would be unless you coupled the analysis with a lot of field testing to help sort out what is good, what is not so good with a complex system like a race car chassis.

I've got quite a large upward angle on my front lca's (I'll take a pic and post tomorrow) and with good sticky new bias ply slicks, everything seems pretty well glued to the pavement. But I suspect that those sticky tires can mask some weaknesses (both in the car and the driver).

Like you, I agree that camber changes are nominal. But it would seem to me in a corner, having the lca's angled up (mine have got quite an angle too) would push/wedge the sprung chassis into the ground on the outside, lift on the inside. (I guess that is the result when your roll center is below ground). Good/Bad? I think bad, but I need the real world experience to convince me completely. Additionally, there would be an ever so slight reduction in track width from the compression of the suspension, causing the tire to slide insward a smidge. I'm pretty sure that is bad, I wouldn't think that would be good feedback to the driver or facilitate high grip.

Good tech. Can't argue with numbers like that!

Your numbers were a little better than mine. In all honesty going to stiffer springs will help as you won't be going through as much suspension travel.

In a race car engineering class I took they showed us a data trace of how much turning the steering wheel costs on a slick based car. Turning alone accounted for .3 gs of deceleration. I figure most of the time I have saved from bumpsteer is probably from this as I don't have a really powerful car.

Cary

My initial use of Susprog was to determine what issues I had. Where were my roll centers and when I change things what am I doing.

Here's an example. When I add an 0.125 degree of negative camber to the front of my car the RC drops a tenth of an inch. If I drop the ride height one turn of my spring collars I get a similar drop in the RC but much less camber change.

I had an issue of the rear of my car hopping that I couldn't figure out. I played and played with rear camber and tire pressure but the rear hopped in certain corners. Using susprogrg I could see that under certain conditions my RC would pass through the ground. While I don't have sophisticated enough data collection to know for sure when I fixed this by increasing the rear ride height the problem disappeared.

What I really wanted to understand was a little better how everything is related. This is how I learned the Z steering is almost parallel and how hard it is to seperate changes in with a strut based suspension.

One area where the program was very useful was determine scrub and where I needed to position the lower ball joint to have my caster trail around a half inch. I'm runing 7 degrees of caster (a rule of thumb to run half of the KPI). This required changes to where the balljoint is mounted and is dependent on the radius of your tires. This is where susprog really shines.

I also used the program to eliminate as much antidive as I can get from the suspension. Antidive has no place on an autocross car (or probably a road racer either).

Cary

Hi Mike, is Randy's website still up? I lost the URL and Cary, thanks for letting me off easy. But then if it is so simple to change the outboard pivot points in the rear how come no one has done it? I would love to see some ideas on how to do it so I don't have to chop up the unibody to raise the inner pivots. Are we talking about cutting off the arms in the picture below and adding tubular extensions? I will let you try that first since you already know my engineering skills. :rolleyes: From what I understand you want the rear roll center higher than the front and it seems we are doing the opposite with a low car and front spacers. Is it not worth chasing a rear spacer idea?

Steve,
Randy's site isn't up anymore . Remember they threatened to sue him for using
the dinosaur and the name GTZilla ? He also ran in to some bad luck and was going
through some issues . I need to grab his phone number and give him a call this weekend , and see what is going on .

Cary,
You are coming up with some way cool stuff here :) I am trying to follow the what all of you are saying and the funny thing its all becoming clearer on what is working for all of you. One nice thing is my car is sitting and I have done nothing to it over
the past year , so no waisted time or money yet :)

Mike

I think rear spacers make a lot of sense for you big wheel guys. But those of us that decided smaller is better look at the other end to make changes 'cause we have no more room.

The idea that I was thinking about was to mill the arms in your pic down a bit so they were flat (on the bottom) and then put a box section on it that held heims on the outside in double shear. I'd use spacers under the box section to allow for spacing needed to change roll centers (take a look at a 956 porsche front suspension's steering arm for a pic of what the piece would look like -- I can't seem to find a pic no my PC). Connected to this box would be tubular arms similar to what I have for my EMOD car (I think you've seen a pic of those). If you make custom tubular arms then you can make a custom inner pickup at the front of the diff that should give you a few inches to play with and the back is easy.

Since the SCCA has decided to mess with the MOD rules again I'm thinking I may spend the majority of this year playing with the unibody car. So as I move more of the MOD car's suspension over I can show you pics of this in real life.

I'm also on a mission to try and convert as much of the car's alignment to shims as possible. I know this sounds silly but I actually make adjustments to my car between runs at an autox and I need a faster way of doing it.

Cary "we do this for fun, right?"

I like the milling idea. Here is a pic from a 962. Something like that with the control arm heim joints in double shear?

I just ordered a couple chunks of 3"X3"X6" chunks of 6061 and a buddy has a buddy with a mill I can use for making these. I'll keep you posted!

Yep, something like that long the bottom with the heims properly mounted flat and in double shear.

I found a couple of pics of from the back of a JGTC Z. Turn it upside down.

https://www.zdriver.com/forum/attach...tid=1857&stc=1
https://www.zdriver.com/forum/attach...tid=1858&stc=1

Over the weekend I tried two BS spacer combos. Two 3/4 inch spacers stacked (the black ones) and a one inch combined with a 3/4 inch. I had to remove the zerk fitting and file down a sharp edge from the bottom of the ball joint to clear the 1 and 3/4 inch combo. I am not sure how much room is left in the second one for actual bumpsteer correction with heim joints at the rod ends. I will just have to try. The last pic is where the ride heigth is with 1 and 3/4 spacer and 1 inch inner pivot raise(haven't done it yet) and the LCA level. The wheel is a 16 with 5 inch backspace. And yes Cary, that is the driver side strut on the passenger side. Oops! :o

The car looks really good. From the pic it looks like you have it set to just clear the ground on the wheels?

For bumpsteer you can move the inner rack point as well as the outer. Ideally you should be able to shim the rack as needed, which probably means a different mounting than stock. You might consider a shorter steering arm to get you quicker steering and more room. Generally the outer arm needs to go down. I have some pics of one of my old steering arms made out of flat plate that I used instead of the stock arms. I just need to find it.

I'm still trying to figure out how a 2.5 inch spacer is going to fit on John's car.

BTW, take a look at http://www.susprog.com/tutorial/tuto...tutorial02.htm. It has good info on how on what needs to be moved when you plot out what you have.

Cary

With the biggest 1 3/4 inch spacer the wheel is level to the bottom seam. So with a tire of 23.8 diameter it would be 3.9 inch clearance without the tire "squish". I am guessing 3 1/2" ride heigth.

A 2.5" spacer is not going to fit on my car. I stuck some measuring tapes under there this weekend and took some pics, and it looks like a 2.25" _might_ fit, but the steering arm will probably hit the wheel first. Heating and bending the steering arm could help to make it clear.

I am cleaning the place up before I continue, figuring I will be more motivated if I don't have to lie in metal shavings from the drill press and other stuff to get under the car. Plus I can't find any tools or move around in there because everything is strewn about the garage, and stuff left over from last summers projects are still in the way!

A bonus was I found the new pilot roller bearing I lost last fall for the new motor build!

Now that I am totally lost on this one . Let me ask a few questions here :D

When the car is lowered , the outer part of the control arm would move
up . What angle is prefered ? I take it that the angle of the steering arms plays a key role in all of this as well. Severe changes will bind the steering tie rods, since the
rack has a fixed point and the changes to the control arms would effect this. it has been mentioned that you can redrill the cross member hole 1" up for inner control arm mounting . With this and lets say a 1" spacer is the net gain about the same as
a 2" bump steer spacer . Is the steering rack design in effect during all changes of suspension angles ? I was thinking that it was with that desing steering and strut assembly .

The RC and CG are what is going to take me a bit to figure out :) The hard thing is the RC being below ground . What does this actually fill like ?

Mike
More questions to come

"I take it that the angle of the steering arms plays a key role in all of this as well."

Severe changes here. No binding on the tie rods/steering arms. Of course toe changes when the car is lowered, but that is adjustable to suit your taste. Ballpark, the bottom of my control arm is 2.5" off the ground on the inside and 4.75" off the ground on the outside. No steering interference that I can tell, except I do think the top of sway bar may be touching the bottom of the frame rail in full bump.


Raising the inside or lowering the outside should have the same effect, I don't see why moving the hole up 1" would be any different than moving the ball joint down 1 inch.
Whats the RC being below ground feel like? It feels normal to me. I've been driving the car for 3 years like that. I hope there is a change in the way it feels when I move the RC up. Like maybe I am feeling that I am getting closer to catching Tom!

The advantage of moving the outside with a spacer is that if you set bumpsteer you shouldn't be changing the relationship -- just where you are on the curve. While moving the inside pivot would have a similar effect for the RC it will change the relationship of the steering, which will introduce bumpsteer.

For a stock length set of control arms flat or slightly drooping down (towards the outside) would be best. What you want to avoid like the plague is a RC than passes through the ground when you have significant lateral load. It feels like someone kicked the and end of the car. Very unsettling.

My EMOD car will have a front RC below ground. I chose this because it helps to slow the loading of the tire contact patch and has lower jacking forces. I can get away with this because I have extremely long arms and I don't have to worry about lateral track changes due to suspension movement. This is almost the opposite of the argument many people have for wanting a steep angle on the arms to give them camber gain. The lateral displacement causes more issues than any potential camber gain does, hence my claim of not worrying about this.

If you rasie the RC it should make that end of the car react quicker. You may also see a rise in tire temps and will most likely need to change other settings to achieve balance again.

Should I mention there are three roll centers :-)

Cary

agree.

Yaw maybe?

Three RCs.

1. There's a geometirc roll center. This is what most of us talk about when we talk of RC changes.

2. Forced based roll center.

3. Datum roll center. This is the actual point about which the car rolls.

Additional reading on RCs can be found at http://www.auto-ware.com/ubbthreads/...=knowledgebase (Mark Ortiz chassis newsletters)

Cary

String theory, UhHuh.

Took some more measurements lastnight. It looks like a 2.25 to 2.5" spacer will just fit inside the wheels, BUT the steering arms/tie rod ends will hit the wheel even with a 1.5" spacer UNLESS I move the tie rod rod mounts to the top of the steering arm. That may require rearranging the sway bar and raising the steering rack to compensate for screwed up tie-rod geometry. Opinions?

That would work. Take a look at the attached pics of a similar option to what you're talking about. This is from a national winning GT car. I also included some spring mount pics for a swaybar but I can't remember if that was this thread or a different one.

Cary

So you could do the bumpsteer correction at the steering rack end rather than the steering arm end, correct? You size the spacer to put the tie rod above the steering arm and to make it parallel with the lower control arm, right? The heim joints in single shear seem no more of an abomination than doing it at the other end.

Thats what I was thinking.....

You may need to move both ends. The GT car in the picture required a few small spacers at the arms but much of the work was done on the inner end. Sorta similar to the JTR modification of moving the inner suspension pivot up to match the rack. If you read the info on the link I posted up above it tells you based on the bumpsteer curve you get which end has to move.

I have some parts I'm playing with tonight that I'll try and take some pictures of. It's a fabbed steering arm that uses a boss on the bottom for a heim joint instead of the usual ball joint. On my car I'm trying to get more ackerman by moving the outer pickup higher and closer to the brake disk. Its made from half inch T1 structural plate.

Cary

If I went with tubular LCA's it seems the spacer would be huge. The steering arm looks to be the first to hit the wheel. I added spacers over the existing picture leaving the LCA in the same place and guessing where the tubular arm would be with the rod end "ball joint" and the inner pivot point raised. I will try adding spacers in my garage till the steering arm hits. I also added the raised inner steering rack heim joint from Cary's picture. A big spacer scares me with the thought of the bolts breaking though.

What about welding in some strut tube to the bottom making something that looks like a dropped spindle. The steering arm would need to change as would the ball joint arrangement .

In prepared there isn't any reason you can't clearance the frame rail or poke holes in the inner fender to avoid the really large stack of spacers.

Cary

Add more tube! Great idea. I wonder if a 1/4 inch plate in the silhouette of a bumpsteer spacer, welded to the bottom of the tube with gussetts and bolted to the stock steering arm would be strong enough. Bend the steering arm up and have it re-heat treated (like in the "How to Hotrod your Datsun" book) for more wheel clearance.I guess I should have paid attention in math class years ago.

I don't think you'd want the steering arm on the bottom in this case. You can have it mounted where the original arm would be (further up the strut). If you fabricated an arm (I've used 3/8 T1 structural steel) and put a hole in it for the new section of tube you might be able to slide it on the bottom and then bolt it onto the original mounts. You'd also want to move the outside closer to the brake disk to add ackerman. If you use a heim on the bottom you should be able to get a little more clearance than a balljoint (use a 3/4 to be safe). If this isn't strong enough in bending then we'd need to treat it like a truss. When you stack all those spacers I'd get a little worried about the stress on the bottom of the original strut.

I think John should be the guinea pig :-)

Cary

You so smart! A Ford Truck rod end can be used on tube arms to replace the ball joint. Definately more clearance than a ball joint. So what do you think John. You wanna do some testing?

How 'bout the spacer tube is welded to the steering arm slipped over the tube like you said, which bolts to the spindle area. So the steering arm-spacer tube is a seperate boltable piece to the original strut bottom.Then you could tighen the nut holding the "ball joint" on the plate on the bottom by unbolting the spacer steering arm combo and put a socket down the spacer tube.

I don't know about T1 structural steel. Would welding soften it?