torque arm setting

[ajb59]

i noticed when it's tacky out my torque arm travels about 3" to 3-1/4" . But the last race it started out dry and ended up black slick. When i checked my torque arm the travel was only 2-1/4".

When the track gets slick is it a good adjustment to move the shock and spring out on the torque arm or soften the spring or both? The torque arm has the shock and spring on the first hole closes to the pinion with a 300 spring
thanks

[MasterSbilt_Racer]

Some people move out and soften. Some do nothing. It seems there are very fast guys in each camp.

[ajb59]

is that normal for the torque arm travel to be less in the slick? or is that a sign of something else going on ?

[billetbirdcage]

That is normal to have less travel as the track gets slicker. That just shows how much power is being aplied thru the rear tires. If the track can hold 800HP then it will move alot and if the track slicks off and can only hold 400HP then it won't move as much unless you change something to get more traction to the rear tires so they can put more power/same mount of power as before to the ground.

[ajb59]

If your using the same shock and spring combo, does moving the shock and spring out on the torque arm increase the amount of pressure to the rear wheels ?

[billetbirdcage]

In a sense, yes.

The farther forward you arm the less leverage the torque arm has to compress the spring and lift on the chassis. However the father forward it is the more it picks up on the front of the chassis and transfers that to the rear tires. This will add forward traction to the rear tires but at a cost of turning ability of the front tires.

Back: quicker intial traction, but less overall traction but better traction with the front end of the car to turn.

Forward: slightly slower intial traction, more overall tration but less front traction to turn or keep turning the car after throttle up.

I use the spring to control the quickness of the traction: softer to slow it down and stiffer to speed it up. Then the length for overall forward traction, but keeping in mind the car still has to turn. So it is a balancing act, although some will never move it and other do often. Same thing with rate, some never others often.

[ajb59]

thanks for the help

[wheel spinner]

Here is my take on the torque arm:
The changing the torque arm length effects the rear of the car more than the front. The amount of weight tranfered from the front through the torque arm to the rear is dependent on power applied and wheelbase and not length.

If you are applying 3000 ft/lbs (500 engine ft/lbs x 6:1 gear) through the rear axle then at 36" (3ft) you would have 1000 lbs of force. (A 300 lbs spring would compress 3.33") On a 100" wheelbase car 36% of this 1000 lbs would come off the front and 64% would come off the rear. 360lbs off the front springs, 640 lbs off the rear springs.

If you run a 38" arm then the force is 950 lbs (3000 x 12 / 38) with 38% or 360 lbs coming off the front (950 x .38 = 360) and 62% or 590 lbs (950 x .62) coming off the rear.

A 34" arm is 1060 lbs of force. 360 off the front. 700 off the rear.

If you apply 2400 ft/lbs (400 x 6) at 36" equals 666 lbs of force which is about 2.25" of compression on a 300 lbs spring and 288 lbs (2400 x 12 / 100) off the front on a 100" wheelbase car.

The shorter the arm the more (or sooner) the rear will rise under power and greater the dymanic wedge depending on springs (wheel rates) LR x RF vs RR x LF.

The effect on rear steer is more varied. Rear steer is increased until the left side extension is maxxed. Then as the right side rises the rear steer diminishes. The way you limit your max extension would effect the car.

Bar angles have a greater effect on dymanic wedge and rear steer than the torque arm so most leave the arm alone.

I will try to clear up any confusion I may have created.