Help on Ladder bar car
03-04-2009, 05:08 PM
#21
Junior Member
APPRENTICE
Join Date: Jul 2004
Posts: 24
chassis
altune i have a 2/3 chassis vega does the same thang mine goes to thr right every time unless i can kept the wheels down mines my not be right but i ended up with preload and right shock ajusted abought 1 1/2 inches higher on the shock has done good like that like i say my not be right but it works good luck
03-30-2009, 10:31 AM
#22
Member
CRAFTSMAN
Join Date: Jul 2007
Location: Orlando
Posts: 58
Actually Dparker, a high powered car will go left, not right. The turning condition he has is no doubt, due to the rear pointing that way or random preload, old tires, shocks with unequal adjustment etc. He said that they just made an adjustment in the squareness of the diff in his first entry prior to testing the new engine, that fact may have eluded your prognosis. When you make real power in a door car like 1200 or so you will find that negative preload is your friend. I have a car that I built and drive that needs no preload at all, in fact I use 1/2 flat negative to keep from going left. But I'm only running My crap in a door car at 7.62 ET at 187.22 MPH for what it is worth.
Yes, a high powered door car will veer left on launch, and, yes, negative preload (adding static load to the left rear) will straighten it out.
But, we have to consider both transient and steady state effects. On launch, a good portion of the reaction to the driveshaft torque goes to the front end, where it does a good bit of twisting. When that left front fender pops into the air, that corner of the car acquires some inertia. To slow its upward flight, increased loading appears at the right rear tire. The result is that veering to the left. (Actually, the whole front end acquires a rotating inertia, but it's easier to think of that left front corner by itself.)
This is, however, only a transient effect. After the car has twisted as much as its going to twist, steady state effects take over. As we know, the driveshaft torque tends to unload the right rear. So, for the rest of the run down the strip, that negative preload is helping the driveshaft torque to cause unequal rear tire loading. And, unequal loading of a tire pair results in a loss of traction performance.
What's a fella gonna do? With negative preload, performance is lost and, with positive preload, the leftward turn is worse. (Actually, enough positive preload will fix the problem, but we're talking hundreds of pounds difference between right rear and left rear.)
A reasonable approach is to somehow cancel that torque which is twisting the front end. There are various ways of doing this, almost all of which involve some form of asymmetric rear suspension setup. For instance, the problem goes away when different antisquat values are used for left and right sides of a 4link. With the proper ratio, the car can have equal rear tire loadings statically and maintain that equality throughout the run. And, since the rear tires remain equally loaded, that means the fronts also remain equally loaded.
I cover a few of the possibilities at my site:
http://home.earthlink.net/~whshope
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