Reverse 4 bar RR is it legal?

[backwaterusa]

Checkout the video

[Austin34471]

Checkout the video https://usdirt.com/viewtopic.php?f=23&t=24&p=105#p105
As long as the 4 link bars are separated by more than 6" on the frame, I don't see how it would be illegal... But techmen/series do have a way of making things illegal that are in no way, shape, or form illegal according to the written rules, if they don't understand what the new gizmo is.

Not sure I understand it either.. the way this is currently configured, the suspension has "pro-squat" or downward thrust on the RR corner of the car when accelerating. In my opinion, I would think this would be undesirable as you are unloading the tire when accelerating, you are pulling the RR spoiler down instead of pushing it up, and the rear steer curve would be funky. Would like to hear the creator's logic for why he did it.

[Kromulous]

Thats really cool, there is almost no / very little indexing on that RR birdcage. That alone i think would be very desirable, you can get a nice soft rate to keep the RR from gaining to much spring rate to fast. The rod ends are very close to the axle CL as well. I would like to see how its mounted on the frame.

I would have to think about the what the bars would do squat wise, but pro squat like the post above says is right, i tihnk LOL.

[dirtrace09]

It appears the the birdcage is locked which adds another factor into the equation. Think about what the rotating axle is doing (or not doing) to the car through the rearward facing bars. I would like to see the attitude of the car from different angles compared to a more traditional setup.

[Austin34471]

Thats really cool, there is almost no / very little indexing on that RR birdcage. That alone i think would be very desirable, you can get a nice soft rate to keep the RR from gaining to much spring rate to fast. The rod ends are very close to the axle CL as well. I would like to see how its mounted on the frame.

I would have to think about the what the bars would do squat wise, but pro squat like the post above says is right, i tihnk LOL.
Could do that with the 4 link bars pointed forward too. Move the bottom bar up to the top hole on the lower set of holes and move the top bar to the bottom hole of the top set of holes and see how much it indexes. If you run both bars at the same angle and at the same length, there will be 0 indexing through travel.

[Kromulous]

That birdcage isn't locked i don't think, it couldn't be the shock mount never moves vertically, once he gets on the gas it would move up an inch or so i would guess. Also with 2 bars connecting to the BC it wouldn't be able to move either, mechanically locked out.

Most 4 link brackets wont allow a parallel angle do they? i guess close, and i have tried to run them this way before.

Wouldn't this type of set up be similar to a spear rod set up like back in the old days?

[JustAddDirt]

That birdcage isn't locked i don't think, it couldn't be the shock mount never moves vertically, once he gets on the gas it would move up an inch or so i would guess. Also with 2 bars connecting to the BC it wouldn't be able to move either, mechanically locked out.

Most 4 link brackets wont allow a parallel angle do they? i guess close, and i have tried to run them this way before.

Wouldn't this type of set up be similar to a spear rod set up like back in the old days?

I would think it does act like a spear rod, but not one with a centered front pivot. I would think you would have to have the front mounting point way down on chassis to shorten wheelbase sweep to have it act like that one.

Sounded like a crate car too. I would think that would load the bars pretty hard (especially the long bottom one) with a super motor and a cushion.

[Kromulous]

True on that bottom bar, it would have a lot of force on it. Its wild how he has the bars mounted, almost looks like there inline horizontally, fwd to aft on the car. I keep watching the video over n over LOL.

That RR spring is big too i would say a 300lber by the looks of it. Just a guess. That would make since thou, all the force pulling down on the chassis.

I noticed something else too, all the force when he picks up the gas, not a lot (force) i guess with a crate, is being applied to the LR, the axle doesn't wrap axially much at all. Soon as he picks up the gas you see the LR travel down. almost like he is using that RR spring as a pivot, I bet that cars is seriously snug off the corner, which may or may not be a bad thing.

[CCHIEF]

A positive pregnancy test may or may not be a good thing too!

[MasterSbilt_Racer]

I don't think you want the prosquat. It should be legal. But so should a brake floater. By some rules, it is not legal for sure.

[Matt49]

The mounting on the frame is visible in the video if you look close enough. It's a single long bracket mounted parallel to the frame rail with both bars mounted in holes equal distance (apparently) from the frame rail. Very short top bar, very long bottom bar.
This is going to index the birdcage in the opposite direction as a typical 4-bar setup. This will make the wheel rate digressive which is probably the reason for the apparent heavy spring (I'm guessing a 400) to make it work at all.
Rear steer (from the RR alone) is minimal and thrust angle is mostly negative.
Stop looking at the suspension and watch the slip angle of the ground moving past the tire as he goes through the corner. That car is yawed out and loose as hell which would completely be expected with this setup on the RR.
And I'm guessing it is NOT a crate motor. Oil filters are visible in the video so I'm guessing dry sump setup.

[Lizardracing]

Seems to me to react much like 4/Z on a dirt modified. (RS watts link). Those have been around a minute. I'd venture a guess that theres some chassis flexing there too with the overall assuming the loads.

[a25rjr]

I have watched the video twice and have not seen the birdcage move....it appears locked down to me!

[Lizardracing]

Has a lift arm so it kinda has to be floating right?
Something has to be giving...

[fastford]

i would think if the cages are locked the bars running back to the frame are mounted at the same point or you would have some sort of suspension bind with the amount of movement going on under there.

[a25rjr]

Has a lift arm so it kinda has to be floating right?
Something has to be giving...

Not really. It was common many years ago to lock the lr down. Made a ton of forward bite!

[MLR19]

I think you are talking about clamping the LR shock to the axle tube, not locking the birdcage.
I have seen the LR birdcage locked, & the upper bar removed on a swingarm car, (basically 3 link ) it was really fast in the right track conditions.

[a25rjr]

I think you are talking about clamping the LR shock to the axle tube, not locking the birdcage.
I have seen the LR birdcage locked, & the upper bar removed on a swingarm car, (basically 3 link ) it was really fast in the right track conditions.

No, Im talking about locking the birdcage to the axle. Pretty common a few years ago.

Put 150lbs of bite with it and have tons of forward bite!

[MasterSbilt_Racer]

No, Im talking about locking the birdcage to the axle. Pretty common a few years ago.

Put 150lbs of bite with it and have tons of forward bite!

If the birdcage can't rotate, the wheel cannot move vertically?

[MLR19]

Locking the birdcage & leaving both 4 bars connected would result in a rigid arrangement, any movement would be from something flexing or bending. Clamping the shock bracket to the tube with shock & spring in front but floating birdcage was very popular at one time.

[a25rjr]

Look at some of the earlier TWM birdcages. They had a built in clamp bracket to lock down the birdcage. I believe GRT was the first to use them.

[MasterSbilt_Racer]

Look at some of the earlier TWM birdcages. They had a built in clamp bracket to lock down the birdcage. I believe GRT was the first to use them.

I remember the bracket. You took a bolt out that connected the shock bracket to the cage. You then put the bolt thru the clamp bracket and the shock mount.

To lock the cage, the top and bottom of the cage would have to connect to the same point on the chassis. Otherwise there would be zero degrees of freedom in the system. Or, you would have to remove a link. (3 link type deal)

[a25rjr]

In the mid to late 90's, the top grt teams, were running the clamp bracket with a long bolt through the lower trailing arm mount, on the birdcage. The birdcages were 1 piece twms, so essentially the cage was locked down. This was before the lr behind setup, and grt found this really increaded drive at the super-slick tracks, like Dixie!

[billetbirdcage]

In the mid to late 90's, the top grt teams, were running the clamp bracket with a long bolt through the lower trailing arm mount, on the birdcage. The birdcages were 1 piece twms, so essentially the cage was locked down. This was before the lr behind setup, and grt found this really increaded drive at the super-slick tracks, like Dixie!

What your talking about had the spring clamped to the axle not the entire cage, the cage still rotated on the axle.

If you watch the video, the spring doesn't seem clamped to the axle as I don't see any indexing upon throttle or deceleration out of the spring. I'm certain it isn't locked (cage or spring), watch at 47 seconds noting the torque arm link that lowers when off the gas. If it was locked you'd see the cage rotate downward in front with the axle rotation and I see no sign of that at all. The way the bars are set, there would be very little indexing so probably just can't see it moving that slight amount.

[a25rjr]

What your talking about had the spring clamped to the axle not the entire cage, the cage still rotated on the axle.

If you watch the video, the spring doesn't seem clamped to the axle as I don't see any indexing upon throttle or deceleration out of the spring. I'm certain it isn't locked (cage or spring), watch at 47 seconds noting the torque arm link that lowers when off the gas. If it was locked you'd see the cage rotate downward in front with the axle rotation and I see no sign of that at all. The way the bars are set, there would be very little indexing so probably just can't see it moving that slight amount.

No billet, we copied what Frye had. The hardest part was finding a long 5/8 bolt to hook the clamp bracket to the 1 piece birdcage. Since this was the latest/greatest we had to put this together at the motel parking lot! lol

I believe the year was 96 when Frye came from the back to win the hat shootout!

fwiw....we ran the same setup on a limited, on a sandy slick paperclip track, and won a bunch of races with it!

[MasterSbilt_Racer]

No billet, we copied what Frye had. The hardest part was finding a long 5/8 bolt to hook the clamp bracket to the 1 piece birdcage. Since this was the latest/greatest we had to put this together at the motel parking lot! lol

I believe the year was 96 when Frye came from the back to win the hat shootout!

fwiw....we ran the same setup on a limited, on a sandy slick paperclip track, and won a bunch of races with it!

You are leaving something out. As you describe, this would not move til you broke something.