[84Z]

Probably a really dumb question but I've heard so many different things I just have no clue. Does a thicker REAR sway bar help with 1/4 time? I always though it helped out, but not sure anymore. Thanks.

[bracketeer]

It actually makes it harder for the car to get traction.

[84Z]

hmmm, alright thanks.

[jimfulco]

Some of the later-model Fox Mustang racers have had good luck with rear bars at the strip.

[BillyShope]

I'll have to disagree with "bracketeer" on this one. Perhaps he inadvertently changed something else while he was increasing the size of the rear sway bar.

Yes, increased rear roll stiffness will help a car with a beam rear axle. More accurately, increasing the ratio of rear roll stiffness to front roll stiffness will help a car with a beam rear axle.

The reason: Maximum traction performance, from the rear tire pair, will be achieved when the loading is equal. Driveshaft torque tends to unload the right rear. The reaction to that same torque is taken at the engine/transmission mounts, where it is distributed, front-to-rear, in proportion to the relative roll stiffness of the front and rear suspensions. The worst case scenario...for traction performance...would be if all the roll stiffness was at the front. All of the reaction torque would then act to unload the left front and there would be a maximum imbalance at the rear.

So, for maximum traction performance, you want as much of that reaction torque to find its way back to the rear axle assembly as possible, so that it can act to cancel that tendency to unload the right rear. To that end, you want to minimize the roll stiffness at the front (i.e., disconnect or remove the front sway bar) and maximize it at the rear (a larger rear sway bar).

[84Z]

Ok, I'm confused once again. Anyone else?

[bracketeer]

What BillyShope is referring to is the rear end acting like a propellor. You use a panhard bar on top of the rear end to counter act propelling. Not a traction bar under it.

[k-star]

I am with billy on this one... Most cars will race better with a rear sway bar. It will act like a anti-roll bar to some extent. Of coarse a anti-roll bar would be a better piece but on a slower car the rear sway bar will help out..

Keith

[BillyShope]

Boy, are we having trouble communicating!

When I say "sway bar," I mean what others might call an "anti-sway bar" or an "anti-roll bar." As far as I'm concerned, it's all the same thing.

Bracketeer, thank you for alerting me to another communications problem. When you started talking about "propellers," I had no idea what you were talking about! Then, I realized, for the first time, that I'm talking to a generation that grew up, for the most part, with FWD vehicles and are not really all that familiar with the problem of the unloading of the right rear to which I was referring.

When I was, say, 14, my buddies and I realized that if we sneaked into our dad's car, put it in 1st, revved up the engine, and popped the clutch, the car would just sit there as the right rear tire spun ineffectively. The cars were all RWD and beam axle, of course. This is still the common configuration at the dragstrip, so the problem still exists, though LSD's and welded spiders (or spools) have made the problem less obvious. But, this can't be fully appreciated by those who drive FWD cars or RWD cars with IRS.

(Incidentally, the Panhard locates the axle assembly transversely and has nothing to do with this "propeller" problem.)

[OneMoreTime]

This rang my ole chimes and propelled me to think of why the ladder bar suspension is so effective on a drag car..with the ladders being solidly attached to the rear housing there is now no way that thing is going to twist and unload the right rear..the ladder bars and rear housing are acting like the biggest anti-roll bar one can think of..Of course there are some issues with ladder bars that are unique to that setup..

OMT

[BillyShope]

Originally Posted by OneMoreTime

This rang my ole chimes and propelled me to think of why the ladder bar suspension is so effective on a drag car..with the ladders being solidly attached to the rear housing there is now no way that thing is going to twist and unload the right rear..the ladder bars and rear housing are acting like the biggest anti-roll bar one can think of..Of course there are some issues with ladder bars that are unique to that setup..

OMT

Good example, OMT, of how increased rear roll resistance can help at the strip.

Since the dragsters don't have a recognizable suspension, we might not consider them, but they actually provide another excellent example of the same principle. The rear wheels are tied rather solidly to that portion of the frame which picks up the engine and transmission mounts, but the front wheels are a whoop an' a holler up the road, connected by a frame with very little torsional stiffness. Yes, that long wheelbase adds to the directional stability at speed, but perhaps the greater benefit is the decoupling of the front wheels, allowing the rear tires to be more equally loaded.