FWD posi trac with a Wheelie Bar

[cgunn]

The physic's of using a wheelie on a front wheel drive make sence (at the drag strip). I have a friend with a posi trac fwd, who am trying to convince that the use of a wheelie bar will effectively decrease his run time. The arguement I am getting is that when adding wheelie bar (length)to the car, he will not be able to steer to maintain a straight line (the car tends to pull). I do not see how this will create any great impact to the car. Is there something I'm missing?

 

[Retracnic]

The steering problem with traction bars (wheelie bars) on an FWD car do not come into play until the big end of the track (usually past about 800 feet or so). As we travel down the track, aerodynamic forces will tend to lift the vehicle. Since traction bars effectively lengthen wheel base, but do not change the distribution of mass, we end up with a vehicle with an unusually forward set CG.

Normally a FWD drive vehicle with a greatly forwardly biased CG will understeer severely. Yet, with almost all the traction available to the vehicle being at the front end, the vehicle will tend to oversteer dramatically at high speeds. It is quite common to see very fast FWD drive drag cars wiggling the back-end back and forth as they approach the traps. In many memorable cases the vehicles have even spun complete 360s! Not a lot of fun at 140+ MPH.

Unfortunately the only real solution is retractable bars. I say "unfortunately" because retractable bars have been banned by every governing body (here in the US at least). All-in-all, it's not an issue for a vehicle that has trap speeds below 130, or so. Or an E.T. higher than about 10.20. In those cases, the addition of wheelie bars will not noticeably impact steering. Then again, with times like that there's no reason to be running the bars in the first place.

It's all a juggling act between enough traction bar/spring tension to keep 60 foot times low, yet maintaining steering control at the big end.

Good Luck,
Bryan Carter

 

[cgunn]

Right now he is running approx. 11.10 sec, so yes, the wheelie bar shouldn't have a major impact on his handling capibility. At the moment he is considering building pneumatic upper arms (to swap with the rigid arms), just to see how low he can drop his times, how ever he realizes the reality of never being able to legally race with it. Well, I better get started juggling, your advice is much appriciated.

Curt