Thoughts on this pinion angle statement?

[oldtrackchamp4x]

"Never mind how much angle.How much travel, is what really matters.Forward bite is the affect of th rear end/pinion never completely topped out or dropped out. Once your pinion quits rotating... you'll stop digging. The shock or abrupt snap of the rear end is what stops forward bite/ traction. It's also what gets you loose on entry.I start with as much down angle as possible. That way it can rotate up a looong ways without stopping rotating.Keep in mind it will rotate down even farther during deceleration. Short pull bar vs solid etc is just hocus pocus. Again, what really matters is that you don't snap the rear end and bust the tires loose. Either under acceleration or deceleration. Because you're already running the high clearance yoke, you can run a lot more than just 6 or 8 @ static. How much depends on the rest of your setup, driving style and corner radius etc. Tight corners generally need less pinion roll than say long sweepers where you're digging all the time." This is not my statement.

[Racer96m]

Forward bite is the affect of th rear end/pinion never completely topped out or dropped out. Once your pinion quits rotating... you'll stop digging. The shock or abrupt snap of the rear end is what stops forward bite/ traction.

This is what I have come to understand about pinion angle. Pinion angle does have an effect on forward bite but not exactly as this person explains it. The effect of engine torque is what aides forward bite. So as long as the pinion angle is negative to neutral, the engine torque provided by the spinning driveshaft, rearend rotation, and tire rotation create a downward force. This downward force is lost if the pinion angle goes positive. So this is why we start with neg angle and try to end up at neutral under full throttle. Neutral delivers the most power with the least drag while maintaining max traction. Your pullbar is a timing device, it should top out at the same time your pinion and driveshaft are neutral providing max traction.

Dave

[oldtrackchamp4x]

Dave, my thoughts are pretty much the same as yours. As I've said before, there are some really smart guys on here and wanted to get their thoughts on the statement.JMO.

[Matt49]

I disagree with all of this. The pinion angle isn't doing anything to load the rear tires. To say so implies that the driveshaft is somehow PUSHING into the rear end and that simply isn't true. We start with negative (downhill) pinion angle so that the pinion angle is more neutral when we are on the gas to decrease the strain and placed on the u-joints. This also maximized power to the rear end but that doesn't increase traction...in fact it decreases it.
Now if you want to talk about how pinion angle affects side bite, I can explain that. But that wasn't the question.

The idea that the rear end will rotate MORE if you start it pointing further down makes NO sense. What stops it from rotating? Nothing.

[LM14]

Matt49 has it.

Negative pinion angle is a necessity to combat the rotation of the rearend in birdcages or on leaf springs. What stops the rearends upward travel is resistance to the lift arm or pull rod, not the loss of torque. A common automotive u-joint has 20* of travel. All you are doing is making an educated guess on static negative angle so between acceleration wrap and braking wrap in the opposite direction we stay in that 20* range of motion.

Look at a big truck, some pinions point straight up and they still have traction. How do you explain the traction in a Corvette or any other car with IRS and a solidly mounted pinion section.

Yes, a pinion tries to climb the ring gear but that is not the forces the car is seeing. Take a rearend out from under the car and sit it on the floor with 2 tires/wheels attached. Spin the pinion and the housing will rotate upwards (the pinion climbing the ring gear and the housing is not restrained so it rotates) but it won't move from the spot it is sitting. Keep turning it and the rearend will rotate completely around itself and never leave it's resting place. Now rest your hand against the housing lightly (represents a lift arm or pull bar's resistance to movement) and it will stop the rotation of the housing but it will begin to move across the floor. You are turning the axles, rotating the tires, the tires have traction and the rearend is moving across the floor. The pinion never changes relationship with the ground in this example but the rearend moves from point A to point B. Pinion angle had nothing to do with it, resistance to rotation creating loading and traction did.

We use the pull bars and lift arms to control the rate this force is applied to the chassis and the trailing arms to control the angle it is applied. It is somewhat of a timing component if you want to look at it like that.

What you are seeing is traction at the tires trying to force the rearend under the chassis. Pinion angle is a durability issue, not a traction issue.

JMO,
SPark

[pig tracker]

Very interesting discussion. Gets a person to thinking.

[Lizardracing]

While there are multiple things going on here, the statement above seems to me to be confusing the loading effect of the LR from the DS torque acting on the axle in the Z axis. The DS torque probably feels like more forward drive because it tightened up the car on the gas. Many people on these forums confusing forward traction with a tighter race car.

On a side note, this loading of the LR is often counteracted in drag racing by the use of RR airbags so car will go straight.

[QQQQ]

Sounds like everyone posting is more or less saying the same thing in there own words, except the original thread post. That dude is out to lunch! lol

[drtrkr244]

I had a Spicer rep explain it to me this way. Never let the front and rear driveshaft angles become neutral. You always want a small difference. That is what keeps the needle bearings inside the ujoints to keep turning. Otherwise, they would suffer premature wear from the loads wearing on the same spot.

[Lizardracing]

That's true however race cars are concerned with performance with longevity second.

[drtrkr244]

I don't know about your car, but mine "performs" better, when the driveshaft is still hooked up and not layin on the track.

[Lizardracing]

I dunno. Last year I let someone borrow my DS and it worked for them better than me as they won.

[Matt49]

Check this out...
https://www.youtube.com/watch?v=gmV4qwLfOMY

[drtrkr244]

Check this out...
https://www.youtube.com/watch?v=gmV4qwLfOMY

That's definitely an eye opener. I wonder if their cv joints are applicable to dirt racin.

I could see a big use in low horsepower applications.

[let-r-eat]

There is a valuable point in the original post. The pinion angle must maximize the average speed of the output v/s input.

Anything less will compromise the use of the drive torque by varying it's output.

The loading of the contact patch is effected. We can look at the launching of a drag car as an example. We must offset the rotation of the drive torque to get the car to leave in a straight line.