pull bar location

[JHobbs26]

Just curious what everyone thinks/likes about either a pullbar mounted somewhere off the bottom of the car (driveshaft loop) or one that is mounted higher, like off the dash bars.

Lets say the length and angle are the same, does the car react different if its mounted low or high?

[Anonymous24]

Absolutely it makes a difference where the bar is mounted. I believe that mounting to the driveshaft hoop is best. There are several contributing factors: rear end type, rear suspension type, rear suspension dampering, pull bar type, pull bar length, front/rear suspension travel, pinion angle, etc...Through simulation and proven on the track, I have found that it is optimum to have the pull bar parallel to the track in dynamic. Radical changes in angle during acceleration and braking causes instability, reducing forward bite, and creates a push when entering the corners. Also it alters pinion angle reducing applied horsepower at the real axle. Take precise measurements of suspension travel in dynamic. You want the pull bar to be parallel the race track as possible under full travel of the suspension going down the straightaways, maintaining optimum pinion angle. You must not forget axle wrap due to traction availability. Proper dampening is a must. You must factor in several other actions in achieving this. Using a phone to post this so I have tried to make it short and simple. If you have questions, message me and I will clarify. This information is my opinion and has been track proven. Every racecar is different, and what works for my car may not necessarily work for yours.

[charcoal01]

Perpendicular? Did you mean to say parallel? Because perpendicular means two lines that cross each other at or near 90 degrees. I would imagine that would be difficult to do. Especially in the dynamic state as pull bars usually lose a little angle with axle wrap.

[Anonymous24]

Perpendicular? Did you mean to say parallel? Because perpendicular means two lines that cross each other at or near 90 degrees. I would imagine that would be difficult to do. Especially in the dynamic state as pull bars usually lose a little angle with axle wrap.

Yes thank you for correcting my mistake. I posted at 430 this morning from phon with my 1,yr old daughter going crazy. I will edit my post. Thanks again for catching my mistake. Much embarrassed.

[Dirtrunner35]

How does the length make a difference, example 2 foot or 4 foot length

[clbaker25x]

Our experience was the longer pull bar created more forward drive and had more of a tendency to lift the left front. I think this is due to the mounting point being more forward and having more effect on the center of the car. With the shorter pull bar we didn't have as much of a problem with the left front coming off the ground, but did lose a little forward drive.

[kraftkar7x]

Shorter pullbar reacts faster and longer takes longer to come in

[Anonymous24]

To determine length is rather complicated. Properly, the center of gravity location needs to be located. The front pull bar mount should be located directly underneath that point. The rear mount should be located over the rear differential center line. That determines over all length of pull bar. Now it gets technical. The pull bar transfers weight from the front of the car to the rear suspension to maximize traction. The weight of the car must be properly balanced. If it is not, you are not achieving maximum effect of the pull bar. Example... If you are pulling the LF off the ground, you are transferring too much weight from the front. If you are lacking forward bite, not enough weight is being transfered. Many racers with 4 link rear suspensions chain the rear end to the chassis limiting rear end travel thinking it is the excessive travel causing LF hike. That is not the case. The problem is improper weight distribution... Not balanced. A balanced set up allows the pull bar to transfer weight to the rear suspension while maintaining drivability. All the bite in the world is useless if you can't steer the car! The key is consistent weight transfer while maintaining drivability. Make sense?

[Anonymous24]

Shorter pullbar reacts faster and longer takes longer to come in

You are incorrect.

[clbaker25x]

Anonymous, That is actually a pretty easy formula to solve:center of gravity height front to rear will equal your rear percentage times wheel base. For example say you were running a modified 108 wheel base car and ran 57% rear weight then your center of gravity will be about 46.5 inches ahead of your rear wheels. If you use some basic math you can figure out that your pull bar with that logic will be between 65 inches - 45 degree pull bar angle; to 56 inches long if the angle was only 23 degrees.

[Anonymous24]

Anonymous, That is actually a pretty easy formula to solve:center of gravity height front to rear will equal your rear percentage times wheel base. For example say you were running a modified 108 wheel base car and ran 57% rear weight then your center of gravity will be about 46.5 inches ahead of your rear wheels. If you use some basic math you can figure out that your pull bar with that logic will be between 65 inches - 45 degree pull bar angle; to 56 inches long if the angle was only 23 degrees.

Now we are cooking! I can't tell all the info. Since we went there let's go phase two. There is another angle that is critical that needs determined. lateral angle...looking at the car from over head view, the pull bar does not go in a straight line. In static the pull bar should have angle also. When car is in dynamic the rear tires do not truly track straight with the chassis. Especially during corner exit. You want the front to rear weight transfer to the rear wheels equally. If it is not, you can have either a loose or tight off condition that many people believe is a shock issue. Opening another can of worms.

[7uptruckracer]

I don't run lateral angle I will however offset the bar in the brackets I found running a LR to RF for example as an angle you don't get enough misalignment in the heims and bad things can happen lol To each their own. I will say I run Long in high Horsepower applications and go shorter for less HP.

[JHobbs26]

So what makes pulling from the driveshaft loop better? Shaw cars don't and they are one of the fastest chassis out there.

this is how I see it, correct me if im wrong. 40" pullbar mounted to the driveshaft loop at a 23* angle. As torque is applied the bar is trying to pull the front end up.

Same 40" pullbar @ 23* angle but the mount is hung between the dash bar and rear hoop cross bar. Wouldn't the torque being applied try to drive the front end down?

[Lizardracing]

There are only absolutes in theory's. Theory's don't have a place in practice.

I don't agree with much about the anti-squat opinions of Anonymous24 but he/she has seem to put some thought it to it and I got respect that. The only comment I wanted to make was about the Pull Bar lenght location. Longer bars tend to change angle less between ride height and full droop with axle wrap rotation than shorter bars. Mounting the rear axle ahead, behind, or in front of the axle vertical center line has an effect as well on the angle change and can be used to increase or decrease the effects of the bar lenght.
There is no right or wrong answer here. Much of this depends on over all chassis design and what the driver wants to feel the car doing.

[MM90]

So at what length is a bar considered Long or Short?