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"Bumpsteer" spacers

Old 02-22-2005, 09:54 AM
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"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.
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Old 02-22-2005, 03:38 PM
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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.
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Old 02-23-2005, 10:03 AM
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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.
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Old 02-23-2005, 01:16 PM
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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.
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Old 02-23-2005, 03:32 PM
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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.
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Old 02-23-2005, 05:57 PM
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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.
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Old 02-23-2005, 09:01 PM
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I still need to check clearance, I'm running 16" wheels, and exact height of spacer needed, but here it is.

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Old 02-23-2005, 09:11 PM
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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.
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Old 02-24-2005, 05:54 AM
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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.
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Old 02-24-2005, 07:20 AM
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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.
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Old 02-24-2005, 07:38 AM
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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.
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Old 02-24-2005, 09:43 AM
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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.
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Old 02-24-2005, 05:01 PM
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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.
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Old 02-24-2005, 05:03 PM
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Originally Posted by FPguy
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.
Welcome to scrubsville. Get used to it. I flip the tires on my wheels every three events to get around this.
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Old 02-24-2005, 06:12 PM
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Whats the front look like?
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Old 02-24-2005, 06:49 PM
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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.
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Old 02-24-2005, 07:20 PM
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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
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Old 02-24-2005, 07:43 PM
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Originally Posted by zlalomz
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.
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
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Old 02-25-2005, 06:01 AM
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Originally Posted by tube80z
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
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.
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Old 02-25-2005, 07:45 AM
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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
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Old 02-25-2005, 08:45 AM
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Originally Posted by tube80z
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.
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.

Last edited by jburge01; 02-25-2005 at 08:53 AM.
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Old 02-25-2005, 09:03 AM
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Originally Posted by tholt29
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
Good tech. Can't argue with numbers like that!
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Old 02-25-2005, 09:09 AM
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Originally Posted by tholt29
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
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
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Old 02-25-2005, 09:25 AM
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Originally Posted by jburge01
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.
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
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Old 02-25-2005, 10:12 AM
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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. 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?
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