Changing Slider Mounting Point Birdcages

[DirtRacer9x]

What happens when you move the mounting point further away from centerline of axle vs closer to it maintaining the same ride height? Thanks

[keeks]

I'm not sure what you mean by slider. Do you mean indexing the top bar on the cage?

[DirtRacer9x]

I'm not sure what you mean by slider. Do you mean indexing the top bar on the cage?

On the birdcages where you can raise or lower the mount on birdcage for the slider to clarify.

[Brian Gray]

A number of things happen but I'll Focus on the 3 I feel are most important. First probly most important if your talking about the top link increasing the distance will lower the rate of indexing. Secondly it will change roll steer. 3 you increase the ratio of leverage which increases rotation control but lowers the loaded force during indexing.

[TALON75]

A slider is a LR spring assembly without a shock, commonly found on modifieds that can't have more than one shock per wheel, some limited LM'S also have a similar rule. By moving it down you will achieve more indexing into the spring which "should" also give more drive.

[DirtRacer9x]

So lower on the birdcage will create more indexing into the spring? Will it affect the way the car gets onto the bars at all? Meaning does it think a heavier spring is on the birdcage he higher or lower it goes? Thanks!

[TALON75]

I personally don't think there is much there, we move ours to achieve more drop sometimes and it doesn't seem to have much effect elsewhere. It will slow the reaction down a little, but not sure if it thinks it has a heavier spring or not.

[TheJet-09]

Out of curiosity, are you thinking/talking about lowering the coil-over assembly's upper mounting point as well, or just increasing its overall length when lowering the bottom?

[keeks]

A slider is a LR spring assembly without a shock, commonly found on modifieds that can't have more than one shock per wheel, some limited LM'S also have a similar rule. By moving it down you will achieve more indexing into the spring which "should" also give more drive.

OK. Now I understand. Thanks.

[DirtRacer9x]

The upper is fixed on this chassis as far as moving up and down. It can only tilt in or out from 0 degrees to 25 degrees inward. But the birdcage has multiple mounting locations up or down. Right now I just picked the center holes but it has about 6" of adjustment from mounting lower part of slider even with axle tube to dropping it down 6" below axle centerline. So right now I'm sitting at about 3" below centerline. I don't see how it would affect indexing overall though. I can only see a change at a leverage point perspective.

[Matt49]

Moving it further from the center changes the motion ratio. So with the same amount of birdcage indexing, you're going to have increased motion of the mount which will in theory give the car a little more drive.

Most late models have their lower shock mounts from 5-7 inches below the centerline of the axle.

[DirtRacer9x]

So it will create more drive lower down? So possibly this can be an adjustment for when track slicks off?

[Bcollins82]

So it will create more drive lower down? So possibly this can be an adjustment for when track slicks off?

Yes, it will drive harder, but not a good adjustment unless you like resetting wedge at the track after you change it, and you can do basically the same thing by lowering your upper on the birdcage. There are better adjustments to utilize at the track than changing your lower shock mounting position. Also, if you go too far, and your spring indexes upward faster than your axle drops (this can happen at the end of your downward travel) you can lose forward drive.

[JTSjet]

i've messed around with this a fair amount this season. this is what i learned so far:

- watch your scrub line. if you get the lower shock mount below the wheel rim and you get a LR flat.....bent birdcage. murhphy's law

- increasing the motion ratio does seem to help drive HOWEVER just use caution when making an adjustment that will increase birdcage indexing. it exaggerates the change you made

- in some cases you are reducing shock angle (increasing effective spring rate) which may be counter productive.

[DirtRacer9x]

i've messed around with this a fair amount this season. this is what i learned so far:- watch your scrub line. if you get the lower shock mount below the wheel rim and you get a LR flat.....bent birdcage. murhphy's law- increasing the motion ratio does seem to help drive HOWEVER just use caution when making an adjustment that will increase birdcage indexing. it exaggerates the change you made- in some cases you are reducing shock angle (increasing effective spring rate) which may be counter productive.

Best answer so far and actually tried it. Thank you. Any other input you have would be great! Also find any sweet spot and just leave it? Shock in front higher or lower than the slider behind? Thanks!

[Matt49]

Best answer so far and actually tried it. Thank you. Any other input you have would be great! Also find any sweet spot and just leave it? Shock in front higher or lower than the slider behind? Thanks!

Not to answer for him but usually your shock in front is going to be a little higher on the birdcage. If it's not, you usually run out of shock travel before the chain grabs (not a good thing).

[DirtRacer9x]

Even shock height I believe would matter for valuing higher or lower right?

[JTSjet]

i forgot to mention that i run a left upper shock mount that is 1-1/2" LOWER than standard.

if you are only changing the lower mount on the rear shock you shouldn't have to change anything about the front shock lower mount. you won't be changing the amount of birdcage index, you will simply be changing the distance-traveled of the rear lower shock mount for the given index. definitely important to pay attention to all shocks extended though as matt said.

this setup is NOT something you would change at the track. it belongs in the shop

to sum everything up, i would say that if your LR setup allows you to have your left rear spring to be loaded at all times, increasing the radius of the rear left lower shock mount will "enhance" your drive and will probably have good results if that's what your car needs.
if you are typically unloaded and might become loaded with a possibly adjustment throughout the night (dropping left lower bar on frame) vice versa, i do not recommend it.