Drag racing and sway bars

[Ghoste]

I can understand easily enough the effect a front sway bar could have in a hard launch but I'm having a hard time getting my mind around the dynamics of a rear bar under those conditions.  How would it affect hard launch characteristics?

[charger1972]

Wow , that`s a great question . I was going with the cal tracks traction bar set up , and think I have to remove it anyway . But never thought about it .

[Back N Black]

Putting a large rear sway bar on a drag car helps plant the rear end which aids traction.  Front sway bars are different. While they are invaluable on the street for reducing body roll and aiding in cornering, at the strip they prevent the front suspension from unloading quickly and completely. Disconnecting them aids in weight transfer to the rear wheels, where a large rear bar helps get the power to the ground.

[Ghoste]

How does the rear bar help though?

[HPP]

The same way a front bars helps in a corner by equalizing the load on the tires.

In a drag launch, the body rotates. This is why SS springs have a bias on the passenger side spring, to absorb the additional torque load. With a sway bar, it uses that torque to leverage the body to a more neutaral position which reduces load on the passenger side and increases it on the drivers side.

[Ghoste]

It isn't an item typically added to a drag car though, correct?  This is more of a situation where a street part is beneficial?

[Mike DC]

Yeah, it does help. 


Dedicated drag racers aren't big into rear swaybars because they tend to go all-out to solve the problem.  They just put way different rear spring rates on the two sides.  It's also more fine-tunable that way. 

It's like the way NASCAR racers have not relied too heavily on swaybars to keep the RF corner off the bumpstop in the turns.  They have mainly combatted the problem with ridiculously heavy springs on the RF corner.

[Cooter]

If one has ever actually watched a Chrysler leaf spring suspension "lift" the rear to plant the rear tires, an anti-sway bar does nothing to promote this in the rear as one on the front doesn't allow for transfer.

[Ghoste]

So it would really only be of benefit to a coil sprung car or one with symmetrical leaf springs?

[Mike DC]

   
It doesn't matter about the spring type, so much as whether the rear spring package was chosen for drag launches or not. 

I don't see a rear swaybar ever hurting a dragstrip launch.  But some cars would benefit more than others.  And swaybars are not the ideal tool for the job (unless you are one of those weirdos who cares about something besides going straight ahead.)

 

[Cooter]

So it would really only be of benefit to a coil sprung car or one with symmetrical leaf springs?

Then you get the "G body shuffle" as it's called today.

[Back N Black]

This is what you do not want to happen

[Cooter]

   yeeeup!

[firefighter3931]

Wow , that`s a great question . I was going with the cal tracks traction bar set up , and think I have to remove it anyway . But never thought about it .

James,

With the caltrac setup you can individually adjust the pre-load on each side independantly so a rear swaybar is not required or needed. Once you start tuning it's very simple to correct a pull to one side or the other. Typically, the passenger side requires slightly more preload to get the car launching straight. 


Ron

[charger1972]

Don't want to highjack the thread but , you shouldn't run a front sway bar ? Never thought about it but with the looser shocks the sway bar would bind it up ?

[Cooter]

Don't want to highjack the thread but , you shouldn't run a front sway bar ? Never thought about it but with the looser shocks the sway bar would bind it up ?

Two different suspension actions. Sway bars limit front end travel up/down. Wants to keep it stiff.
this is typically why 'canyon carvers' like to call drag raced suspensions single purpose as it allows full travel upwards for weight transfer to rear. A vehicle set up for road racing will not fair well at the drag strip, just like a drag suspension will not fair well at the road course. Two totally different actions being requested. One could mix and match by simply unhooking sway bars for drag testing, but does nothing for the extra wieght, and rehook up afterwards.

[charger1972]

So, just run no sway bars on the street ? My car will hopefully see some track time soon , better to unhook at the track and re hook when i leave ? Just wondering how much it would adversely effect handling not running one on the street . Not that i do any high speed cornering or anything .

[JB400]

It's better to run one on the street, and just unhook it at the track.  Otherwise, you'll notice a little extra lean when you do turn.  It could make for uncomfortable feeling around town.

[charger1972]

It would be cool if they made a quick disconnect like the ones for rock crawler jeeps .

[Ghoste]

For the typical street car I don't know that unhooking the front sway bar for the drag strip would make a huge difference anyway would it?

[HPP]

IMO, no its isn't a huge difference. In my experience, you are giving up a full second with a heavy duty street suspension compared to a drag race specific suspension. I ran the exact same engine/trans combo in two cars, one a canyon carver with big t-bars and s-bays and gas charged shocks, one a bracket racer with light t-bars, no s-bars 90/10 shocks and SS springs. The canyon carver would click off 13.2 e.ts and the bracket car would run 12.2.

One possible drawback of a very loose, drag race specific suspension is that it becomes much more sensitive to track conditions and ambient atmosphere. On the two cars above, the canyon carver suspension was so repeatable it would rarely vary more than 2/10. By contrast, the drag suspension would vary half a second or more if it wasn't dialed in right.

So to your average bracket racer, the street suspension is going to be more repeatable even if it is a tick or two slower.

[Ghoste]

Interesting, nice to have the comparison.  I assume the rest of the two cars beyond drive train was similar as well?

[HPP]

Aside from being RWD mopars, no, not entirely. I did use the same wheel/tire combo between them. The canyon carver was a '67 Satellite, 3250# with a full interior and a basic street car. The bracket car was an '80 Aspen, 2900#, totally gutted, and built specifically for drag racing.

Assuming .1 second per 100#, the weight differences only accounts for 3 to 4 tenths of e.t. reduction. The rest of the difference was the efficiency of suspension action. So the actual difference because of suspension is more like half a second. However, the feel of the drag suspension vs the heavy street suspension was drastic. While the drag suspension could have been run on the street, I would have done so regularly. The heavy rear spring rate, quick rise rate, and no sway bar combo was not particularly confidence inducing when taking corners.

[HPP]

So it would really only be of benefit to a coil sprung car or one with symmetrical leaf springs?

Then you get the "G body shuffle" as it's called today.

...and since most super class cars are using coil overs, they also tend to use rear sway bars as a tuning device to avoid the G body shuffle.