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Miatav8,MstrASE,A&P,F
PostPosted: December 14, 2023, 8:21 pm 
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blownmiata91 wrote:
What I did was to attach a laser level to the brake rotor, pointing to the wall. I moved the upright through it's range of motion, marking the high and low spots on the wall. I experimented with the steering rack location, until the high and low spots were exactly perpendicular to each other. This shows that there is no bump steer through the range of motion. Mount the rack there, and you'll be golden.
cheers
Doug


It isn't clear what you are trying to describe.

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Miatav8,MstrASE,A&P,F
PostPosted: December 14, 2023, 8:29 pm 
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tibimakai wrote:
Like this?
https://www.youtube.com/watch?v=dXLgh-jkwT4&t=1803s


Doug is talking about bumpsteer, not ackermann.

Think about it this way. A car is sitting on a 30 ft circle painted on the ground with the tires on one side of the car sitting on the line that forms the circle. Turn the steering to where the tire on the line will follow the circle and keep the rear tire on the line as it rolls. The front wheel not on the circle line must turn more since it must follow a smaller circle to prevent scrub (slip angles are another subject). If it does not, it plows and is dragged around the circle versus simply rolling. The drag is most obvious when pushing a car.

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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
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tibimakai
PostPosted: December 14, 2023, 9:44 pm 
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Yes, I know that he is talking about bump steer.

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KB58
PostPosted: December 14, 2023, 10:54 pm 
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blownmiata91 wrote:
What I did was to attach a laser level to the brake rotor, pointing to the wall. I moved the upright through it's range of motion, marking the high and low spots on the wall. I experimented with the steering rack location, until the high and low spots were exactly perpendicular to each other. This shows that there is no bump steer through the range of motion. Mount the rack there, and you'll be golden.
cheers
Doug

How can two dots on a wall be perpendicular to each other? What am I missing?

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blownmiata91
PostPosted: December 14, 2023, 11:09 pm 
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Hello.
Instead of jacking the upright up and down, I made 3 spacers, one to position the upright at ride height, one to make it 1" lower, and one to make it 2" higher. When you position the upright at each position, mark the crosshair or the dot on the wall (I used a piece of drywall) Draw a line through them, it should be straight. If the line is vertical, 90 degrees from the floor, there is no bumpsteer. The wheels are still pointing straight ahead at each position. If they are not, then move the steering rack and try again. I will attach a photo.


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tibimakai
PostPosted: December 14, 2023, 11:20 pm 
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That looks pretty simple. Thanks for the photo.
So the video that I have posted, shows almost the same thing.
Somewhere, somebody mentioned that the distance to the drywall has to be 5x the tire diameter radius?

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KB58
PostPosted: December 14, 2023, 11:40 pm 
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1. With a short/long arm suspension, a laser mounted anywhere outboard will move inward in bump.
2. Bump steer is just that, the hub "steers" left or right in bump.

The problem is that the laser dot on the wall doesn't differentiate between turning sideways and moving sideways, and the above two factors get added together, so you don't know how much is one versus the other.

One way is to bolt a board to the lug nuts, set another board on the ground and lean it against the hub-mounted board. The vertical board has a pin on one side to maintain a fixed distance to the hub board, and on the other side is a dial indicator. Only this separates out bump steer from sideways suspension translation in bump. Being out of the car-building game, I just tossed out my bump steer setup...

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Miatav8,MstrASE,A&P,F
PostPosted: December 15, 2023, 6:53 am 
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Tibor, why are we putting more effort into this than you?

Learn how to perform and understand the purpose of basic wheel alignments, then all these lengthy posts will probably make sense. But asking the same question again after it has been answered, two word replies, and just saying you don't understand an entire paragraph response indicates this is a waste of time for everyone.

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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
Top
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Board index » The North American Locost Forums » Running Gear - Suspension, Brakes, Steering, wheels and tires

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