Pinion angle with truck arm suspension?

[Operatorfailure]

I have a 68 c10 short step with a 5.3/4l60e, bone stock with 3.73s. I can't seem to find exactly how to set up the pinion angle to hook up the best. I have read some places to set it exactly in line with your engine/trans, some say to just have it nose down a couple degrees and no mention of engine trans. I know I am not making very much power in all reality and don't see why I couldn't hook up with street tires if I am only running 15.6 in the quarter. I know part of my bad times are from spinning, I have like a 2.3 60'. Any ideas? I plan on getting a 1" drop block for the rear and I work at a machine shop so I will mill it to whatever angle is needed.

Thanks!

[Super73]

Treat the truck arms like a ladder bar and put a couple degrees of negative pinion angle in it. As you apply power, the pinion will naturally want to go up distorting the arms slightly and bringing the pinion in phase (zero degrees).

Your biggest problem right now sounds like tires. You can do all the suspension tricks to achieve what should be great results, but with out a good or at least decent tire you will see minimal gains.

Two biggest bang for buck mods regards to 60' equating in much better ET's are tire and converter. Get those right and you could drop anywhere from .5 - 1.5 off your ET'S.

[Operatorfailure]

My dad has a 66 with m&h 28" drag radials and still spins a tiny bit out of the hole, I'm pretty sure his is pinion angle causing that along with needing some adjustable shocks up front for a little weight transfer. I'll provably steal his drag radials this spring and make a stab at getting some non embarrassing times. I've been faster than him for years with past vehicles and he just loves to rub it in that he beats me now.

[Keith Seymore]

Originally Posted by Super73

Treat the truck arms like a ladder bar and put a couple degrees of negative pinion angle in it. As you apply power, the pinion will naturally want to go up distorting the arms slightly and bringing the pinion in phase (zero degrees).

Your biggest problem right now sounds like tires. You can do all the suspension tricks to achieve what should be great results, but with out a good or at least decent tire you will see minimal gains.

Two biggest bang for buck mods regards to 60' equating in much better ET's are tire and converter. Get those right and you could drop anywhere from .5 - 1.5 off your ET'S.

Agree on all counts.

Ideally, from a torque loss standpoint, you would want the drive shaft/pinion nose perfectly straight. But that's never going to happen, so you favor the pinion nose slightly down (compared to the shaft; the ground is never a reference in this case) so that it comes up straight(er) under acceleration.

Additionally you wouldn't want the u joint perfectly straight because then the roller bearings would not rotate causing brinnelling in the bearing cups.

So: set it a couple degrees down from the engine/trans angle and be done with it.

K

[Keith Seymore]

Originally Posted by Operatorfailure

My dad has a 66 with m&h 28" drag radials and still spins a tiny bit out of the hole, I'm pretty sure his is pinion angle causing that along with needing some adjustable shocks up front for a little weight transfer. I'll provably steal his drag radials this spring and make a stab at getting some non embarrassing times. I've been faster than him for years with past vehicles and he just loves to rub it in that he beats me now.

By the way, pinion angle has nothing to do with traction. It can't.

The suspension reacts through the attaching points creating the resultant instant center. The relationship between this instant center and the center of gravity of the vehicle is what affects the launch.

All the pinion angle does is affect the rear u joint working angle and the transmission of torque from the engine to the ground.

K

[Operatorfailure]

I don't know much about this topic, but I had always heard so often about pinion angle and traction.

[Keith Seymore]

Originally Posted by Operatorfailure

I don't know much about this topic, but I had always heard so often about pinion angle and traction.

It's a fairly common misconception, even among some pretty advanced racers (mostly leaf spring guys).

I am waiting to get blasted as we speak.

K

[68racer]

I'm with you Keith on this one. Pinion angle does not affect traction, especially on an arm suspension. I believe this all started with the Mopar guys adjusting pinion angle and seeing a traction change. But what was really happening was that they were adjusting the height to the pinion snubber. Only my opinion or my angle on it!

[Operatorfailure]

Alrighty. What you guys are saying makes total sense to me, I never understood how pinion angle changed traction, but that is what I have always heard.

[dwcsr]

Originally Posted by Operatorfailure

Alrighty. What you guys are saying makes total sense to me, I never understood how pinion angle changed traction, but that is what I have always heard.

They may be confusing spring wrap up with the angle change being the problem. when the spring wraps up it does change the angle and it can lose traction but wrap up is the issue not angle change. Truck arms and ladder bars usually don't suffer this problem

[Super73]

What will impact traction with a truck arm is how high off the ground the front mounting point is. That adjusts instant center of gravity. Also, if the are was shortened or lengthened. Height (off ground) and distance (from axle center) will dictate wher you icg is.

[Keith Seymore]

Originally Posted by Super73

What will impact traction with a truck arm is how high off the ground the front mounting point is. That adjusts instant center of gravity. Also, if the are was shortened or lengthened. Height (off ground) and distance (from axle center) will dictate wher you icg is.

Agree - although one correction in semantics: that adjusts the instant center of the suspension (not "instant center of gravity". No such thing).

The "instant center of the suspension" reacts upon the "center of gravity" of the vehicle.

K

(Four link vehicle shown)

[tinydb84]

Can we talk more about the squat/antisquat concepts? This post is really helpful: http://www.pirate4x4.com/forum/2366355-post9.html

I understand that 100% anti-squat is neutral and "best" as well as more than 100% anti-squat will lift the rear. What are the actual effects on the tire though? Say I was setting up a 4 link and was going to shoot for 100% anti-squat. If I was not able to get 100% what would be better for traction? Would 75% anti-squat produce more force on the rear tires (and potentially more traction) or would 125% anti-squat (rear lifting up) produce more traction?

I understand I am leaving a ton out and over simplifying it but I am trying to understand the forces on the tire/traction in each situation.

[Super73]

There are tons of concepts on Anti-squat %.. Just a couple things to consider.

Antisquat for the rear can also reduce rate of rise in the front.

Too high of an antisquat can cause the rear tire to want to bounce back the other direction. If you don't have enough shock control for a given %, you will unload the tire.

[Super73]

Duplicate..