LR 4 bar location

[sidewinder69]

Have always wondered what kind of effect you would see if you dropped your lower 4 bar rod on the birdcage to a hole 1" lower and also lower it on the frame the same amount so the bar angle stays the same? This something that caters to the slick or heavy condition?

[Mr.Kennedy777]

It would index less.

[Mr.Kennedy777]

And very slightly more drive angle. Like a couple degrees more inclined. Thats about it. The indexing change would be so small, and the difference in steer or hike would also be so small, the largest of them would be the net work of the links would be pushing slightly more on an incline on the chassis.

[Kromulous]

What would indexing both bars on the cage, up a 1/2" , away from axle CL on top, and towards axle CL on the bottom.

Index more, and traction come on faster? Something i have never done, just wondering.

[MasterSbilt_Racer]

It would index less.

It would index more. The bottom bar removes index during hike. Move it away from the pivot point, the cage rotation is reduced.

Steer would be removed as well.

[MasterSbilt_Racer]

What would indexing both bars on the cage, up a 1/2" , away from axle CL on top, and towards axle CL on the bottom.

Index more, and traction come on faster? Something i have never done, just wondering.

Less LR index. More thrust load in the bottom bar which has less angle. Not a good move, IMO.

[Mr.Kennedy777]

It would index more. The bottom bar removes index during hike. Move it away from the pivot point, the cage rotation is reduced.Steer would be removed as well.Go map it out man. Moving both birdcage mount down 1” AND mounting point on frame down 1” it would index less. And almost a negligable amount of difference between steer and hike. The change is indexing and that would effect the final drive angle between the two bars with a slight increase in inclination of work on the chassis.

[Mr.Kennedy777]

Less LR index. More thrust load in the bottom bar which has less angle. Not a good move, IMO. That I will agree with ^ 100%

[Matt49]

If by "indexing" we mean the dynamic rotation of the birdcage, if you move both ends of a bar further away from the birdcage, you will have less indexing. Not much less at the distances we're talking about but less. Think in extremes. What if you moved that bar 40 feet away. It would have very little affect on the rotation of the birdcage as it moved because of how far it is from the center of rotation.
General rules on bar moves and the things it affects:
1) Moving any bar up on the chassis or down on the birdcage increases thrust angle.
2) Moving any bar up on the chassis or down on the birdcage increases dynamic roll steer.
3) Moving bars further away from each other on the chassis or closer together on the birdcage increases indexing.

[Mr.Kennedy777]

In my map I used a 16” upper at 22 degrees, with a 14” lower @ 5.5 degrees, 6” seperation of mounts on birdcage, dropped the bottom mount 1”, and frame mount 1” to keep exact same angle and length.At 6” of vertical wheel travel which would put the upper link is in the same spot in both scenarios, the birdcage with the mounts at 6” indexed more than when I dropped the bottom bar 1” as well as at the frame. With almost no change in steer or hike.

[Mr.Kennedy777]

On the 1/4 scale print it was about 1/64” difference in steer, and even less for hike, so likely a 1/16th of an inch more steer, better thrust angle by like two degrees and less indexing by one degree. So very little change realistically.

[MasterSbilt_Racer]

A typical setup would be 9" separation on cage, 17. 5 upper and 15.5 lower. The upper birdcage bolt will be in the same point in space with the same hike. The difference comes from the lower. If it is moved 1" at both points, it will have the same angle at droop. The distance the bottom birdcage bolt moves closer to the 4 link mount stays the same. It now happens at a greater distance from the axle centerline. This means less angle change (in the unindex direction). It is also a bit less steer for the same reason (farther from the centerpoint of cage).

I have simulated this on Solidworks many times. I used to run that setup a lot.

As Matt pointed out above, if the lower bar was 40" from the axle centerline, the top of the cage would pull forward massively when the car hiked up.

[Mr.Kennedy777]

A typical setup would be 9" separation on cage, 17. 5 upper and 15.5 lower. The upper birdcage bolt will be in the same point in space with the same hike. The difference comes from the lower. If it is moved 1" at both points, it will have the same angle at droop. The distance the bottom birdcage bolt moves closer to the 4 link mount stays the same. It now happens at a greater distance from the axle centerline. This means less angle change (in the unindex direction). It is also a bit less steer for the same reason (farther from the centerpoint of cage).I have simulated this on Solidworks many times. I used to run that setup a lot. And drive angle would be better because the same angle lower puts that intercecting point further back down the slope of the upper, showing a slight incline in drive angle.

[Mr.Kennedy777]

So even with using 2” different bar lengths both upper and lower, and using a 1/4 scale we’re getting the same numbers even at different birdcage seperation, were talking an error % of 1/16” steer difference to less steer difference let’s say that’s 1/16” less from your scale, with our indexing in agreement, I think with either scenario that isn’t a drastic change by any means though. The amount of difference this would really have is almost in detectable by most drivers.

[Mr.Kennedy777]

Undetectable* man. Lol can’t even spell.

[Kromulous]

Care to explain drive angle more? between the 2 bars.

Also would anti-squat be purely calculated from the lower bar only?

[Mr.Kennedy777]

Care to explain drive angle more? between the 2 bars.Also would anti-squat be purely calculated from the lower bar only? Drive angle is also known as thrust angle or the slope created by the instant center pointing towards the axle center line. The instant center lines for the most part, project backwards from the chassis into the link and extend beyond, and where the top slope and bottom slope intersect, where these lines intersect above or underneath (or level with) the axle center line, creates the slope for the thrust angle which is pointing towards the direction of thrust always, hence the term thrust angle. If the slope points uphill from the axle center line into the chassis this creates thrust that pushes up on the chassis, if it’s level it means there is a straight forward push done due to the combined work of the links. This thrust angle would be the bottom slope of your anti squat instant center map. It is different on each side, as each side will either squat or not, what happens on one side does have an effect on the other, and the combined configuration does have an effect on the overall net component and I think this starts to use the same force based application point physics as the front end suspension uses with force based moment center, but dealing with longitudinal force transfer.

[sidewinder69]

So trying to simplify, I would notice less initial roll steer and more forward traction ?

[Mr.Kennedy777]

So trying to simplify, I would notice less initial roll steer and more forward traction ?Very subtle change yes. But with less indexing into the spring than before you move the bar, also, a subtle change in dynamic wheel load.

[Mr.Kennedy777]

This would be a really good change to make if you were really close to ideal and needed just a hair of an adjustment to correct the handling a bit.