LocostUSA.com

Not wrong, I was just about to post it looks like a reverse ackermann setup to me, the steering arm centerline looks to be inside of the steering axis to me.




In bump you should have a little toe out, not zero that many try to achieve.

The reason is very simple, slip angle. If you are cornering at maximum slip angle, and you hit a compressing bump, then you will exceed the slip angle and lose traction. Having a little toe out relaxes the slip angle at the same time as the pressure of the bump increases it.

Too much toe out will increase braking instability, but some people like that for turn in, and then some don't.

After reading all this and watching a bunch of confusing videos, I'm still confused. Some point the laser at the front of the car, some perpendicular to the rotor. Mazdav8 explained it that the perpendicular is better, because the camber gain is not introduced in the measurement.
Why nobody has a nice video, where it is properly explained how to do it correctly?
I'm looking at these bump steer gauges with a plate, which have on one side the dial gauge, and on the other a fixed roller bearing follower. Why that follower is needed? Some have two gauges.
I'm using a 3" travel gauge and magnetic base mounted to some steel tubing, with counterweights on it. I'm placing the dial gauge against the rotor(braking surface). Using a 2" bump and 1" droop, and I can bring it pretty close. In some portions goes in positive, then goes into negative area, but not by much.
But, if I use a laser beam mounted perpendicularly at the edge of the rotor and pointing it at a cardboard(don't understand why I would need a mirror), where I have a vertical line, it is way off from the vertical line.
If I manage a very nice vertical laser beam trace(using the vsusp height for the rack), then the dial reading is horrible.
Any help would be appreciated.

_________________
Tibor


'20 Alfa Romeo Stelvio daily
Locost/442E in progress

Here are some pictures, cardboard is placed at 7' not perfectly aligned:

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Tibor


'20 Alfa Romeo Stelvio daily
Locost/442E in progress

Most videos are made to get views/money over being true/accurate. Lots of folks prefer privacy/security to sales.

There is error in everything we try to do; multiplied by each gadget added. The dial indicator has the least setup error to worry about. I suggest moving it as far away from the spindle center as practical and adjusting the rack height to minimize toe change in bump more than droop, then call it good.

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Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

I've ranted about this elsewhere, but quite a few alignment setups that use lasers are, well, wrong.

The problem is that a laser dot on a wall moves due to rotation and/or translation of the emitter. Said another way, with the laser mounted to the upright, the dot appears to move sideways when the upright turns. The dot also moves sideways if the upright moves forwards or backwards during bump and droop (caster effect). The problem is that the two can't be differentiated. Using a board, hinge, and dial indicator is best because it only measures toe change, ignoring the upright motion moving forward or back.

_________________
Midlana book: Build this mid-engine Locost!, http://midlana.com/stuff/book/
Kimini book: Designing mid-engine cars using FWD drivetrains
Both available from https://www.lulu.com/

And there is a camber change. The toe change might be zero, but if the wheel cambers negative on bumps, it will look like you have a toe change, and correcting that will produce a toe change.

Boards on a piano hinge eliminate this problem. It doesn't matter what the measured number is (via dial indicator, for example), just that there is no toe change.

I did air ride on my '61 Chevy pickup, and have zero toe change from 5" ride height to sitting on the ground (above that it goes pretty drunk), but despite a wild camber change, there is no toe change.

(Ever measure bump steer on a factory car? The are pretty amazingly awful)

_________________
The Lethal Locost
The Lethal Locost 2 - Even More Lethalerer

Nailed it! I thought I was the only one that thought that,lol.
I have a 2005 Dodge Nitro, go over some rough railway crossing at 50mph, you'd think you were in a boat slewing back and forth.
It's all about compromise

_________________
Perry

'If man built it, man can fix it'
"No one ever told me I couldn't do it."
"If you can't build it safe, don't build it."

Perry's Locost Super Che7enette Build
Perry's TBird Based 5.0L Super 7 L.S.O
Perry's S10 Super 7 The 3rd
Perry's 4th Build The Topolino 500 (Little Mouse) Altered
Perry's 5th Build the Super Slant 6 Super 7
Perry's Final Build the 1929 Mercedes Gazelle

Tibor, you can setup a second dial indicator and snake mount on the rotor face aft/behind of the spindle and rotate the dials for the same indication at ride height. Zero bump will have matching indications depending on how evenly you place the dial indicators.

It has been said many times over the years that a square, hinged loop or panel can do the same thing. Attach two, flat, 24x24x1/2" mdf panels to each other with small gate/door hinges near the corners of one edge. Install the wheel and tire and set at ride height. Place the mdf against the tire sidewall bulges and sloped at about 15 degrees from vertical, with the other panel against the floor. Put some weight on the floor panel so it won't move easily. Swing the suspension to see the bump steer in the form of a gap created at either tire bulge.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

I will try first with another indicator.
What kind of deviation should I shoot for?
What do you think it means, when from 0(ride height) to 1" goes into positive .030", then after 1" toward 2", goes back to zero and even goes into -.030?

Thanks

_________________
Tibor


'20 Alfa Romeo Stelvio daily
Locost/442E in progress

I am going to suggest that your rack height is pretty good but the tie rod length is too short. I am sure not something you want to hear. Try lengthening the tie rod adjustment a few turns and compensate for the adjustment by turning the steering wheel to the right. The laser dot should have less of an arc. Keeping the dot on the line is the goal for "0" bump steer.

The length of the tie rod changes toe pattern in an arc and the rack height in relation to the steering arm will be a diagonal pattern in reference to a vertical line. A lot of fun working with both factors.

Discussion here -> viewtopic.php?f=5&t=20946&p=262503&hilit=bump+steer#p262503

Chassis should be level (road level)
I have a mirror (about 8" tall and 4" wide) that is stuck to a piece of aluminum with holes that I can attach to the wheel hub. I put my laser level on top of a box with a vertical line on face of the box. The top of the box is higher than the top of the mirror when the suspension is in bump. I usually have the box about 4' to 5' away from the hub. Point the laser at the mirror and tilt it down so the dot stays on the mirror thru the range of suspension movement. Move the box the dot should be on the vertical line on the box. The laser can be to the side of the box also. I use a box as a simple way to have a vertical line for reference.

I used to put a long aluminum bar against the rotor that was parallel to the floor. Another "bar" on the floor directly under the aluminum bar. I would raise and lower the suspension by hand, noting any visual deviation out of parallel between the 2 bars. My "red neck" bump steer device.

Hope this clears things up. I find the mirror simpler than trying to keep the laser stable on the hub/disc/upright.

_________________
When you're racing, it's life. Anything that happens before or after is just waiting -- Steve McQueen from LeMans

My build log viewtopic.php?f=36&t=10658&start=0 NOW NAMED =The Wycked 7

My other build log viewtopic.php?f=18&t=15162 The Skayt'R6

What I have just mentioned above, that with the laser I'm getting a straight nice vertical line, but with the gage I have around 1/2" movement(-1" to +2" range).
The rack length could be to short. I have tried adding a spacer behind the inner tie rod and it made it much worse. Mabe a 1/4" spacer is to much, I will try with different widths.
Could you please explain to me, why we need a mirror? I can mount the laser on the rotor, and point it at a cardboard, which has a vertical line.
Thanks

_________________
Tibor


'20 Alfa Romeo Stelvio daily
Locost/442E in progress

I used Kartracer's mirror/laser approach. It's easy and works well. To save my back while raising and lowering the suspension (shock removed) I used a cheap scissor jack driven by a battery powered drill. That allowed more precise suspension movement than my hydraulic jack and gave me time to mark the laser-dot track on the vertical line.

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Cheers, Tom

My Car9 build: viewtopic.php?f=35&t=14613
"It's the construction of the car-the sheer lunacy and joy of making diverse parts come together and work as one-that counts."
Ultima Spyder, Northstar 4.0, Porsche G50/52

Looking for minimal deviation from ride height to bump and everything else is secondary.
I've not read the other recent posts yet but it sounds like the rack is too high and the tie rod length too short (i.e., the rack is too wide for the lcap and ucap locations on the chassis).

EDIT: looking at your pics just now, You can't go any lower with the rack because the lca fwd leg is in the way. That leaves flipping the outer tie rod pin on the spindle and probably raising the rack to level the tie rod link at ride height.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

Where are you measuring the "toe change of 0.030"? Is this 0.030" over 7'?

The mirror method of checking toe change is very accurate as the laser dot is reflected off the plane of the mirror. This compensates for any fore/aft movement of the hub exactly as the board/dial indicator/hinge does. The laser attached to the rotor is mainly showing the castor angle with a delta of toe change against a vertical line! Remember the chassis must be "road" level with the floor.

Please take a few minutes to vary the tie rod length relationship with the amount of toe change and let us know.

Make your own or here is a racing product with instructions on the page --> http://advancedracing.com/product/laser ... eer-gauge/

I would be concerned the the amount of ackerman you have as the rack is pretty far back in the chassis in relation to the steering arms (hard to tell with the pictures).

Might be easier to raise the outer tie rod end than trying to lower the rack if that is what is needed.

Good luck

_________________
When you're racing, it's life. Anything that happens before or after is just waiting -- Steve McQueen from LeMans

My build log viewtopic.php?f=36&t=10658&start=0 NOW NAMED =The Wycked 7

My other build log viewtopic.php?f=18&t=15162 The Skayt'R6

I prefer the "red neck" gauge but the laser off the car and mirror is more accurate and not much to go wrong setup-wise. The critical part is to use glass versus plastic mirror that is flat and parallel to the rotor disc or wheel hub face.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12