rayburn swing arm/pullbar

[Stede Bonnet]

I get that. I was just trying to point out they have the same job to do.

Riddle this for discussion purposes.

If you were remove the Sixth Coil on a Lift arm, remove the spring from a pull bar, mount them to the car in the same place, (basically remove the adjustable part of both) would they not act the same?

No, they wouldn't.

Would the measured amount of anti-squat come out the same?

No. I'm guessing your exposure to pullbars is all theoretical, is it not?

[Lizardracing]

No it's not. I race a USRA Modified and never even drove a lift bar although I've drawn up designs while contemplating trying it. I haven't yet. Not sure if I will.

I am being theoretical however for discussion purposes. I try not to speak on the internet forums in absolutes because too many variable exist and the limited amount of info I think might steer people in a direction not intended when they seek advice. How would you calculate Anti-squat on a lift arm?

[zeroracing]

Anti-Squat is a function of the rear linkage arrangement as well as the lift arm or pull bar, or any other torque absorbing device. The most popular anti-squat for 4 bar theory/literature has a flaw in it and is not 100% in my opinion, it is a close approximation but needs to be taken further to be accurate. Anyways back to the purpose, your line that you usually use for the pull bar in your anti-squat drawing is a line from the top to bottom of the 5th coil spring.

All of that said they react differently in the car and a driver could easily tell if you changed one for the other. The pull bar can get you more instant bite, but it wears off quickly and is violent! The 5th arm is much smoother and has more down track traction.

[Lizardracing]

I think we are agreeing that the pull bar comes on faster but falls off faster and the lift arm comes on slower and last longer. I could agree if one were to graph the dynamic Anti-squat, they two types would look different thereby explaining why they would act different. However, and the big butt, is they both are controlling axle wrap by lifting the front end and and if the axle is allowed to rotate within the birdcages than the old theory's of calculating the anti-squat via linkages has to be looked at. Is this the flaw you speak of? If so, the flaw would be that assuming the links were solid in both configuration the axle wrap is independent of the calculation yes?

[billetbirdcage]

One of the big differences in the two the is overlooked is the forward thrust on the rear end with a pull bar. It can radically change the thrust seen on the links to promote hike/lift. Torque arm you basically only have the forward drive of the rear end against the mass of the car (resisting acceleration) to apply thrust on the links to promote lift, where the pull bar also has this but adds the thrust of the pullbar trying to shove the rear end forward also.

That is part of the reason a typical older swing arm car doesn't get up with torque arm like it will with a pull bar unless some of the links are changed angle/length/etc wise.