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Author Topic:   Another pullbar idea..
posted January 16, 2001 12:37 AM
I was driving to work a few days ago, and I had a bit of a brainstorm. I was wondering how a guy could build a pullbar that would make dynamic changes in anti-squat through different points on the track. I think I've come up with a pretty nifty concept, although there's still a lot of geometry that needs to be drawn out. I'll do my best to describe it here.

The pullbar would mount on the rear end housing the same way it does now (call it conventionally?). Where it would normally mount to the chassis, I would have it mounted to a short rod (3-4"???)that would extend rearward and up to where it would mount to the chassis. Also from the leading end of the pullbar would be mounted a shock extending straight forward from there. Here's how I see it working:

As the car enters the turn, the short bar is extending back and up (45 degree angle?) from the front of the pullbar. As throttle is applied in the middle of the turn the short bar would try to swing through an arc to the rear, bringing the leading end of the pulbar downward, thus increasing antisquat. The shock rate would control the amount of time it would take for this short bar to arc, so this process could be timed such that your car could be free enough entering the turn to allow it to turn, but tighten through the middle and off as the anti-squat increases. As the car straightened out on the straightaway, the short bar would pass center to where it would be angled toward the front off the front of the pullbar. This last action would flatten it out again allowing the car to settle near the end of the straight to enter the next turn, where the whole thing would reset itself under drag braking. This whole process would be timed by the dampening force and/or angle of the shock attached to the front of the bar.

I hope this is close to understandable, and not too convoluted for you guys to respond to... Your input on this would be quite helpful as this design evolves.


posted January 16, 2001 06:17 AM           

This concept is very similar to the fulcrum (6th link) system I described on the other post. You truly have the concept and the basic understanding of the geometry.

I would like to comment on a few things though. Rethink the angle of the rear bar. We have been using this same system for 2 seasons and have found that the up angle on the rear bar causes a bind on chassis & actually hold it up. The suspension becomes rock solid under power. The decrease in pinion angle (rearward movement of the top of the rear end) causes a bind to occur during this transition. Add any chassis movement to this (body roll) and it gets stiffer.

Think about placing the rear bar downward at about 10 deg from the top of the center birdcage. This will keep the bind completely out of the picture. If the rear arm is too short the car becomes extremely erratic due to the short arc radically changing angles.

Picture it in your mind as a Z-Link on the top of the rearend and you will see what I mean.

I like to see someone really think about how something will work and then create it. I really admire that. Really think about how it works and then sketch it out.

If it doesn't make sense after that, let me know and I will give you some input. KUDOS TO YOU. You are my kind of racer!


posted January 16, 2001 08:19 PM
While fighting for forward bite a couple of years ago I considered a similar deal. This sort of rocker deal is used on BMW motorcycles, and Harley soft-tails too. If you check them out it might help with the complex trig. I wasnt smart enough to figure a way to install it on my car. I got a new chassis to cure my forward bite problem....

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