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 Post subject: Alignment adjustments?
PostPosted: August 22, 2014, 12:22 am 
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I'm working on designing my frame right now and have gotten to the point I'm setting up the suspension attachments. This has lead me to a problem. I'm a professional auto tech, and as such I've done alignments on a number of vehicles. A lot of cars these days are running only toe adjustments, some allow camber, and rarely will I see caster. All front toe is done through steering tie rods, rear toe is often through a dedicated link usually with an eccentric bolt, most camber adjustments are done through an eccentric as well. I really like eccentrics because they're fairly easy to deal with, settings don't change on me when I tighten them, and I can get them on the dot to .01 degrees. I can do the same with a tie rod, but it will move a bit and I have to adjust accordingly.

The problem I've run into is the Caster. In the few cars with adjustable caster it's done on the same member as camber, take an early Miata, the front LCAs look like a sideways or upside down L, caster is adjusted at then end of the leg of the L, camber at the joint, and the wheel is at the end of the foot. Because of this caster adjustments cause slight changes in camber adjustment, and vice-versa. I've seen a lot of adjustable length arms here, but I want to stick with fixed length so I know how my camber is changing through bump and roll. I have a hobby rc truck that uses shims to adjust caster by moving the top arm forward and back, but shimming a full size car is much more difficult and could require resetting the alignment machine every adjustment, so that's unreasonable to me. So what I seek is a way to adjust Camber, Caster, and Toe all independently and easily, preferably with eccentrics on the arms and the tie rods for the front toe.


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PostPosted: August 22, 2014, 1:31 am 
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The voice of reason
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For caster on the front you can adjust the top arm back and forth with shims in the brackets. If you look at stock car parts they mount the upper arm to the frame with little slugs that have offset holes in them. You can buy a set of slugs with different offsets for the mounting holes.

You have to take all of this into account when you design your frame.

I don't think changing the length of the arms a bit for camber will change your curves all that much. It's just hard to get everything you want. You also probably need the adjustments to make up for accuracy in making your frame. Not to mention if you hit something.

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PostPosted: August 22, 2014, 6:49 am 
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Aside of the above there may be other factors to consider. If you are using the manufacturers hubs on your build you will need to allow for the possibility of there being negative trail built into the hub which can wipe out the effect of the caster you dial in. The mazda hub below has about 20mm of this so to get adequate self centering and straight line stability you may require more than the intended amount of castor. Worth checking at the design stage.

Bob

Image


To correct a hub like this the lower swivel would need re engineering to bring it inline or some cleverness applied to the geometry to compensate. Its stuff like this that goes unchecked that causes problems later in the build, normally a lack of self centering or lack of feel.

Image

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PostPosted: August 22, 2014, 9:52 am 
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The other thing to watch out for is when you setting up the frame rake, you also loose caster.
If I had to make rate setting up locost front suspenison, I'd be standing on the corner with a tin cup. Dave W


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PostPosted: August 22, 2014, 11:32 am 
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Also, adjusting caster with the upper link tilts the upright fore or aft, raising and lowering the steering arm, which affects bumpsteer.

Everything is connected to everything else...

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PostPosted: August 24, 2014, 7:08 pm 
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I have double "A" arm. The upper is fixed and both legs of the lower are adjustable. If I move both lower adjustments out it adds camber if I adjust one more than the other it will adjusts caster and or camber. It is not easy to adjust as I need to take the "A" arm off the car and does not really solve you problem of independent adjustment. It might give you more ideas though. Toe is done through the tie rods.

You can see more photos on the 8th page of my build log.
Image

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Last edited by wrightcomputing on August 26, 2014, 7:01 am, edited 2 times in total.

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PostPosted: August 24, 2014, 7:47 pm 
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wrightcomputing wrote:
Sorry for the huge photo.
I had a minute, so I shrunk it <snip> [Dang, it appears I can't delete my message, or the photo from my message, without removing the photo from the site, so I'll leave it for now.


Attachments:
FrontSusensionWrightC.jpg
FrontSusensionWrightC.jpg [ 34.17 KiB | Viewed 8464 times ]

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PostPosted: August 26, 2014, 7:01 am 
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Thank you and done

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PostPosted: August 26, 2014, 3:31 pm 
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bob wrote:
which can wipe out the effect of the caster you dial in.


Can you explain this?

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PostPosted: August 26, 2014, 6:36 pm 
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I think he is saying that you have less effective trail per degree of caster when the axle pin is mounted forward like that. So it doesn't wipe out the caster you dial in, but you would dial in more caster than a comparable upright which had the axle pin in line wight he pivots....

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PostPosted: September 1, 2014, 3:17 pm 
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Always Moore!
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I don't see this relationship between the two. Caster is kind of like dynamic camber when the front tires are seeing higher lateral loads while turning. Trail is what creates a moment about the steering axis created by caster to help center the steering wheel. Unless you make some crazy combination, trail shouldn't have an effect on handling like caster will; just make the steering feel heavy or light.

Are we talking about the jacking that happens from more caster?

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PostPosted: September 1, 2014, 3:38 pm 
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I used heavy wall dom tube and spent hours on a lathe drilling and threading so every pivot point except the front
Lower outer bjs are adjustable, using chrome moly heims everywhere,24 of them, i can adjust it everywhere now.


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PostPosted: September 1, 2014, 8:21 pm 
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Wayne
I'm really interested in what development you've done, now that everything adjustable to the max.
How have you gone about meauring the effect of changes?
What have you found?
What have you adjusted the most?

Cheers - Gavin.


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PostPosted: September 1, 2014, 9:21 pm 
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Im still building it but there is a ton of adjustment everywhere.


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PostPosted: September 1, 2014, 10:49 pm 
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a.moore wrote:
bob wrote:
which can wipe out the effect of the caster you dial in.


Can you explain this?


On the british Sierra based Haynes builds part of the test prior to getting a road worthiness certificate is the the self centering of the steering wheel which predominantly comes from caster . The cars front suspension set up was designed with approx 6 degrees of caster through the top and bottom balljoint axis , it was overlooked that the hubs had this negative trail built in so the cars never self centered. The fix was an offset bush in the top of the strut to dial this out which in effect put an extra amount of unseen caster in to solve the problem but all it is really doing is putting the axle centerline back where it was thought to be in the first place. These bushes at the top of the page are fitted with the hole forward in the hub to counteract this. It was fortunate that the strut based upright had the room to fit these offset bushes or the fix would have to be an adjustable top wishbone. Really all I am saying here is look before you leap because some things that get taken for granted can come back and bite :)

If you check out the drawing of the upright in the link below you will see it has negative trail.

http://www.super7thheaven.co.uk/Sierra_Upright

Typical topic over here where they just go round in circles .
http://www.locostbuilders.co.uk/viewthr ... ?tid=72825

Bob

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