Upper Link Geometry Question
 

I need someone smarter than I (which is pretty much anyone when it comes to suspension geometry! :mrgreen:) to help out with this upper link scenario.

The blue upper diagram represents a current upper link setup on a berg.

The lower red portion is a possible change a buddy is considering to make a steering solution work.

The upper links stay the same in both situations. What changes is the actual upper link mount is pushed to one side and different size spacers are used to keep the upper link spacing the same. The shift is less than 10mm.

http://htubayarea.com/pics/Temp/geometry.JPG


What are the adverse affects if any of the scenario above? The pivot point changes , correct? Or really nothing to be concerned about?

Thanks in Advance.

-Mike

The pivot on the link end is the action point. If the mounting location of the link end does not shift relative to the axle or the chassi, the geometry can be considered the same. In other words, if the spacer used has no (or negligible) movement, then the suspension will perform the same. "thumbsup"

symmetry is a good thing when putting together a suspension.
Basically from what I understand in the pic is that the suspension isn't symmetric anymore.

What this will do is shift your axle and it won't be parrallel to the other axle.

You'd need to adjust the length of one of the links to compensate for the change in mounting position. But this has it's problems too, the suspension will act differently from left to right because of the different lengths/angles.

My suggestion is to keep the angles and lengths the same on both sides. Can you get away with both short or both long spacers and still fit the steering in?

The answer is C. There will be no change in the pivot. You are not moving the link location just how the link is mounted to the axle. None of it maters anyway if it is on the front axle it will have little to do with how the rig drives.As long as it does not bind."thumbsup"

X2 no difference. 8) Like a plane taking off on a rolling runway.:-P

Thanks, MythBusters"thumbsup"

What are you guys smoking?

Changing the mounting locations of the upper suspension links to be asymmetrical (relative to the axle) will definitely change the characteristics of how it handles. This is why the axial guys do it to reduce torque twist. You guys are forgetting to take into account the lower link lengths

Try it and measure the wheelbase on both sides. I guarantee they won't be the same.

Am I looking at the drawing wrong? to me it looks like he is shifting the axle to the side by ~10mm

that was my first thought..... after another look he is moving the upper mount off to one side and compensating the movement with offset spacers. thus keeping link length and location the same at the action point (rod ends)

But...the pivot point is moving. Even though the link is spaced back to its original position, it is going to move differently than the other as it is further away from the actual axle mounting point. When the axle twists, the shimmed link will move further than the non-shimmed link...its moving in a larger arc.

Instead of looking at it from the top down, look at it from the front.

Both links need to have a compensation for the movement of the axle, in order to have no affect on suspension behavior. I made the assumption that if he was putting a spacer on one, he would take care of the other as well. My bad.

mannOmann, if you could mark the actual pivot points (link balls) on your drawing, I think it will be much clearer.

Assuming the balls at the axle end of the upper links are in the exact same position in both drawings, and only the link mount and spacers between the balls and the axle has been changed, the set-up will work the same for both.

Cheers.

If the links end up in their exact same positions after the mod, nothing would change. Mike is not moving the links, he's just bolting them up in a different way. As long as the axle is centered, and the ends of each spacer are equal distances from the centerline of the axle, it will flex the same on each side.

if you change the link point on the axle without shifting the axles' center point it will affect the axle steer..one direction will increase while the other side decreases,,,it will also affect axle swing again increased to one side over the other. the affective way to shift the axle is to shift everything not just the links..better yet move the differenatil to one side to decrease TT,,what you are thinking here is basically the same thing that sprint drivers do,,but it stiffens one side of the suspension but it changes squat and anti squat and articulation dramatically....

EDIT: i just looked at his drawing again,,if the mount itself mounts to one side being offset where it mounts to the axle but the points of arc return to neutral then articlation wont change,,look at Bully axle upper link mounts,,they are offset as is the GEARCASE Link I use on my GX2 chassis. The gearcase link mount center is 30mm from center line of the axle but the link offsets to the center of the axle where it meets the chassis bringing the axle pivot point back to center,,,the offset link will work, but the amount of offset to the one side has to compensated to the opposite side to bring the pivot center back to neutral. in affect the mount could be mounted all the way to the end of the axle tube as long as it is square and centered,,now with all that said it will affect balance but only slightly.

Yes, remember, Mike is moving the original berg mount over, as long as the spacers center up the links again and compensate for the move, it will work fine.

You know it's a good question when the first three responses are different. :mrgreen:

To clarify further - I've updated the picture with where the pivot balls and attachment points are of each upper link.

Also, the axles will still remain centered.

Only the link mount and the spacers used on each side will have changed. between each two setups.

These are not real measurements, I don't have anything in front of me...but an approximation would be lets say the total width spacing between the two upper links is 40mm at the axle side. The original setup would have a 20mm spacer on each side. The altered one would have a 10mm one side and a 30mm on the other.

My personal thought is similar to Duuuudes. I'm thinking that with the change there will be a change in the arc of movement and one side would flex higher than the other. My reasoning is pinch a pencil at it's center point in between your pointer finger and thumb. flex it up and down. Now move where your pinching/holding it over to the left an inch and twist.

Isn't that what's happening here? The real question if it is...is 10mm really enough to translate to much difference? I'm thinking no..

Thank you for all the responses. I hope this helps out more.

But if everything is re-centered, wouldn't the arc be the same on each side? As you said, the links remain in their original positions, your just moving the mount over, and fixing it with the spacers. I would think the arc would change if you had a longer link on one side, or the mount was off-center.

That change shouldn't cause any significant change in the axle movement. Reason: He is not changing the point of intersection of the cross bracing links in relationship to the axle, i.e. he is in not charging the point that the axle rotates around in relationship to the chassis. If you extend the cross braces out to there point of intersection in both drawing they are the same.

where the mount is in relation to the center of the axle wont affect the arc as long as the link ends are back at neutral center

Correct