now how much differance will a adjustable torque arm make on a car?

 

It'll make a 100% improvement if your torque arm is off. How much of a difference? To this question I would say, atleast +/- 7 degrees. My (very nice!) UMI torque arm looks like it has a lot of adjustment room.

Ben T.

 

ya the benefit of an adjustable T/A is being able to adjust your pinion angle

 

A adjustable torque arm will allow you to adjust pinion angle which can really help with traction issues. They are also built with a more solid construction then the factory arm, this eliminates flex found with the stocker which can lead to traction issues and brake hop.

If I can help anymore please ask. Thanks!
Ryan

 

Ryan, I've read that pinion angle can affect traction, but I've also read that pinion angle only keeps your u-joints in service longer.

I understand how moving the instantaneous center rearward will help traction improve, but I'm not sure how pinion angle helps traction. Can you set me straight? I thought it was a myth that pinion angle can affect traction;

http://www.eng-tips.com/viewthread.cfm?qid=49028

Ben T.

 

pinion angle helps traction by creating a machanical down force threw componets. the different angles create either a mechanical advantage threw the drive train thus spinnning the wheels, or recreate a slight restriction causing some of the force to be used to straiten the angle, thus no wheel spin. This was the best explanation some one gave me a the track. virdict, well I got a bmr adj for a cheap price a long time ago before I knew about umi, and I droped 60' times a good bit, but thier design and increased drive train noise has me saving for the umi set up that takes the mounting point of of the tranny and puts it on the tunnel brace, add to that umi's price and quality, plus thier intergrated drive shaft loop and you would have a sick set up that is near the best you can buy if not the best. Plus it would match my pan hard and lca's nicely. I relatively cheap mod that will yield at least a solid 10th at the track, getting the angle right takes some time and a good angle finder by thier are ton's of write ups here and you should get the answers you need direct from umi if you need to.

 

as by your post, here Mark, as Greg indicates, there is no traction advantage associated with pinion angle other than the losses when they end up not being 0 under dynamic conditions. As to your friends, I would suspect both are right, with different cars/suspensions come varying pinion angle requirements! I would bet your drag racing friend has a leaf sprung rear, complete with slapper bars? If so, he must dial in more pinion angle as the rear rotates far more than a comparable 4 link or ladder bar setup would.

basically what this is stating it that if your angle is zero and will stay at zero during acceleration, there in theory is not advantage to the adj arm, but this is taking about a four link, you at best have a 3 link,not as solid as the true 4 link so basically say the stock arm is at -1 degress(guessing) launching here will torque the rear to 0, and spin some tire. putting your arm at -2 more force is required to raise the angle to 0, so launch here, car takes off minimal spinning. after the car is rolling the power is moving the drive train and the angle no longer comes into play as much. add to this the new strengh of the arm and the poly bushing the rear stays centered more and offers straiter take off. true you can wear ujoints faster, if your at like -4 degress (not recommended -1 to -3 best for a 6 speed, -2.5 for auto) but at 60 bucks a set not a huge deal, plus it still takes a long time, I had over 20,000 on my stockers before they came out.

 

I did not follow your logic.

For the street having the pinion down ONE degree will allow the u-joint to operate smoother and will lengthen the life of the pinion bearings. You want more "nose down" or "pinion angle" when you are launching your car. It is at this time the rear of the car will "wrap". On a leaf-spring set-up the rear wraps more. So, to keep your pinion angle 0 degrees at the line you put the nose of the differential down further (with leaf springs) so it's aligned when you leave.

FWIW, consider your rear more like a 4-link than a leaf-spring set up. Your pinion angle needs to be closer to -1.5 to -3.0 instead of -4 or 5 degree for a leaf spring set up.

Daryl, you lost me when you started talking about loading the tires and pinion angle. What if the pinion came in from the TOP of the differential? Your theory would say what?

I'm not so sure that you really understood this;

"pinion angle helps traction by creating a machanical down force threw componets. the different angles create either a mechanical advantage threw the drive train thus spinnning the wheels, or recreate a slight restriction causing some of the force to be used to straiten the angle, thus no wheel spin"

It sounds like it may have originated from someone who half way knew what they were talking about, but it appears it was lost in the translation. lol

Oh, I'm not so sure that an adustable torque arm was responsible for you dropping your 60' times. Were you talking about a well-tuned [suspension] race car or about the car that went 11.99 with a 150 shot?

A traction advantage will be had by changing your IC not your pinion angle. You're not going to change your instant center location with an adjustable torque arm. Traction by pinion angle is a myth.

Ben T.

 

Let's continue this thread, shall we? My many searches have also led me to believe the arguement that pinion angle does not affect traction. On our cars, the lower control arms is what will change Instant Center. On one end of the spectrum is a hard bite that will not keep the tires planted for very long. On the other end of the spectrum is a softer bite that will hold traction for a longer period of time. Of course the result could be either shocking the tires too hard and losing traction or not planting the tires hard enough and spinning right away. Finding the perfect balance is what is so difficult.

Keep in mind, I'm talking about cars that are set up right for the drag strip and are looking to fine tune their suspension for near perfect launches. If you have a car that is running high 11's @ 120 plus, chances are you have a lot more work to do to the overall setup before you even want to worry about fine tuning the suspension.

I'm running high 10's @ 122 with 1.50 sixty foots. I can dead hook off a foot brake on ice. Slight exageration. But my record off the trans brake is not so good. 2 successes out of approx 15 attempts. I'm at the point where I need to experiment with instant center if I'm ever going to be able to launch off the trans brake like I do off the foot brake. However, no matter where my instant center is, I still need to set my pinion angle to be zero under acceleration...so for our cars -2.

Someone please set me straight if I have anything wrong. I would like to see this thread continued.

 

One thing I am not sure about is whether or not you can adjust the torque arm without elongating or shortening the lower control arms at the same time. In other words, do I use method A or method B below?

A:
1. Set lower control arms as desired (ie bottom hole, middle hole, top hole, tires moved forward slightly, tires moved rearward slightly) then tighten nuts until LCA's are locked in place.
2. Measure pinion angle
3. Adjust torqure arm to achieve -2 pinion angle

B:
1. Set lower control arms as desired (ie bottom hole, middle hole, top hole) but do not tighten, leave loose.
2. Measure pinion angle
3. Adjust TA AND adjust LCA's (forward or backward) to achieve -2 pinion angle. May have to go back and forth (adjust TA a bit, adjust LCA's a bit, adjust TA a little more, adjust LCA's a little more) until -2 is reached.

Anyone know which method is correct? I assume method A is right but I just want to be sure. I don't want to put any stress on my rear. I've been trying to picture it in my head but I keep doubting my self.