Originally Posted By Evil Spirit
Originally Posted By Monte_Smith
Last observation on the subject..........seems the guys who BUILD or RACE cars and who have been doing it a long time, McAllister, Bob George, Darren Tedder, Al Alguire, myself.......seem to do it one way and the keyboard warriors and parts vendors do it another.........hmmm.....Oh yeah, lets not leave out David Wolfe, builds car for a living........he apparently is all wrong as well.

Evil, your wrong and Darren Tedder is right. Suspension angle changes aside, more pinion angle CAN make a leaf car hit the tire harder. You can crunch all the numbers you want and SHOW any amount of proof it can't help........but it does at the track and that is what matters. That's an "old school" trick that was used long ago when tracks and tires were junk, but it DID work.........wouldn't be needed today. Now, you want "engineering" logic as to why, sorry can't help you, even though I have mechanical engineering background myself, just know it works. But it is nothing new for the "numbers" not to make sense. How many millions of new things you think have been engineered that SHOULD have been better, but were not. Race cars in particular are full of things that SHOULD or should NOT work better or worse.........but what SHOULD happen at times don't always work out like that

Oh, and Jerry, YOU are wrong, how about YOU get over it


Monte


Unless you cut the perches off and re-weld them every time you make a pinion adjustment, you are making other changes that affect traction. Anything that you do that effects ride height changes static/instant centers and CHANGES TRACTION. Using a shim changes rear ride height, which CHANGES TRACTION. Moving the front mount point up or down to adjust pinion angle changes ride height and CHANGES TRACTION. Simply clamping the front segment together, Cal Trac bars, slapper bars, etc. shanges the spring rate which CHANGES TRACTION. Pretty much anything that you do, other that re-welding the perches back in the same location/different angle CHANGES OTHER THINGS WHICH IS WHAT ACTUALLY CHANGES THE TRACTION.

You guys aren't the only ones that ever raced or built cars, chassis, etc. I've welded a few bars and made a few passes myself, starting in the mid 70's at Detroit Dragway, among other places. The fact that I never tried to make a living at racing doesn't mean that I never raced successfully or built cars CORRECTLY.

And as to the guys that have been doing things forever, so it must be right. Over 20 years ago I was having a driveshaft made for a car, and to make a long story short, they hand me a shaft with the u-joint grease zerks lined up. I told them that I didn't want that style joint, and they had them installed wrong, anyways. He very arrogantly informed me that was the correct way and he had been doing it that way for over 20 years. I explained to him that for 20 years he was doing it wrong - under power the joint is stronger when you are compressing the zerk hole, not opening it. I then showed him in the Spicer powertrain book where it explained the same thing. Yeah, it will work that way; most won't know the difference - but in my case I had ordered a performance shaft and it wasn't what I needed. Fast forward 20+ years - a friend manages that shop now. I had them build me a shaft for my Dakota. He hands me a shaft with the u-joints installed with the grease zerks lined up. When I mentioned it to him, his boss comes out of the office and informs me that they have been doing it that way over 40 years. I laughed and left the shaft there and ordered one from AutoZone. It came with the grease fittings correctly staggered LOL.

Morel of the story is you can show some people why they are doing something "wrong" and show them why it is "wrong" but they refuse to accept common sense logic or "textbook explanations". I may be hardheaded, but I try to learn something new every day, and I'm not so blatantly arrogant that I can't accept help from others. I take things at face value, not implied worth - I evaluate the material, instead of simply accepting opinions. I am not a sheep that can be blindly led down a blind path without reason. If that offends people or causes differences in opinion, so be it.

Monty, you are obviously an intelligent person, and believe it or not, I respect your opinion. We simply dis-agree. You may be right - I may be right, or it may be somewhere in the middle. But one area that you are dead wrong is assuming that I have no experience at racing or building cars - far from it. I've spent far more time in the shop or at the track than I have at the keyboard.

It's been FUN up

On a leaf car, when you shim the pinion down.......have you changed the spring, have you changed the pickup point, have you changed the leverage point on the chassis, or have you changed the instant center........the answer to all is NO. The amount of ride height change with a 2* shim MIGHT be a 1/4".

On a 4-bar car, you shorten the top, lengthen the bottom and you have put more pinion angle in the car, with the SAME instant center, the SAME ride height, the SAME everything, but it WILL hit the tire harder. Every action or force, has an opposite and equal reaction. Angles DO change that. So the angle that the force hits the pinion can change how the housing initially reacts as the pinion trying to climb the ring gear is what rotates a housing in the first place. All about leverage. Now MORE angle at the pinion WILL eat some power, but it will initially hit the tire harder. So maybe THATS why it will help it hook, who knows, but it will. Like I said though, would never do this today with better tires and tracks.............but we used to. Now days you adjust the suspension to hit the tire and set the joint to eat as little power as possible.

My theory and it is ONLY a theory as to why this works, is that with excessive pinion angle and the way it speeds the joint, is that on initial "hit" with lots of pinion angle, is that the joint tries to "throw" the pinion up, which rotates the housing faster, which will hit the tire harder. Don't know if that is what it does, but is only legitimate reason I can come up with.

On a modern car with a data logger, shock sensors, pressure transducers and other things, it would actually be very EASY to test. But whats the point, I really don't care enough to find out..........Although I will point out something that happened recently that I just thought about. A customer with a new 4-link car that I set up. I set the front/rear percentages, set the 4-link, shocks and everything else. It SHOULD have worked just fine. When it was carried to the track, it was just "crushing" the tire and should not have been. Finally got him to bring it here and sure enough, it was trying to put the rims through the track. So I am jacking the car up to move the 4-link, when I notice it has about 6* of pinion angle. Asked him who changed it. He said the body shop took the rear apart to powder coat the bars(guess he didn't like my rattle can job)........this I did NOT know. Anyway, set the pinion angle back to 1.5* and car acted like it SHOULD have. This is a 2600 car with a 4-link, 738 nitrous motor and a 10.5x 29.5 M/T slick. Last pass that day had a 1.03 sixty foot. Earlier was in the teens, just "crushing" the tire. So, form your own conclusions. I form mine by what happens to me at the track, not by what a formula tells me "should" happen

Last edited by Monte_Smith; 05/09/15 04:24 PM.