Spins on the flats

[kustombrad]

I was in a conversation last night with a guy who's been running at El Mirage and Bonneville for the last 20 yrs. and I brought something to his attention. We were talking about spools and open diff's and getting HP to the ground. I asked him if he noticed that most cars making horsepower always (sometimes aero is weird) spin to the right. I told him my theory and he kinda chuckled because he never really thought about it. Before I ramble my thoughts I'm curious if anyone else has noticed this? Go to YouTube and check  'em out!

[Ron Gibson]

And your theory is? Inquiring minds need to know.
I have my own and want to see how your's compares.

Ron

[kustombrad]

OK here we go... Landspeed racing is no different than drag racing, it's just a lot longer track. The idea is still to accelerate as quickly as possible with the traction available. If anyone has watched any drag race door cars (stock to pro stock) has seen the technology change on how they launch. In the old days the cars would pick up the left front AND the right rear with the brutal twisting motion of the engine vs. the ring and pinion. It went from a way stiffer right rear spring to an adjustable rear sway bar. Now with just a little right side preload on the sway bar, both tires plant (watch them launch now) on the ground evenly. On the flats everyone adds weight but never compensates for the rear suspension twisting. Under power the right side picks up ever so slightly and PLANTS the left...instant hard right! Now this is assuming the rear tires roll out is identical to rule out that possibility and it's a standard ring and pinion design. This is just my theory, but after seeing it happen over and over and climbing under the backs of numerous cars, this is the conclusion I've come to.

[Stainless1]

Coriolis effect... they spin the other way in Australia... 
The lakester has spun left and right... the liner went left.  Jonny Hotnuts went left as well, maybe it is only roadsters that go right...
or not
 

[kustombrad]

Did it go left or was that where the correction took it? A quick change is going to do just the opposite because power is coming from the back. Same if the engine is behind the rear end. My theory is with a bunch of horsepower involved. Sometimes stuff happens.

[Peter Jack]

Brad, I would think that a quick change would go the same way. It isn't the direction the pinion rotates, but the direction the driveshaft rotates. That's assuming that your theory has some credibility and I think it may. The reason for the twist is external and not what happens within the rear end. 

Pete

[Sumner]

.. On the flats everyone adds weight but never compensates for the rear suspension twisting....

I think that might not be totally true since I'm aware of some that have tried to pre-load the right rear.  

You are never going to be able to get the hit on salt you can at the strip.  Still when the throttle stuck wide open with me it went to the right and and the times I got in it experimenting it went to the right so maybe we should try more weight on that side,

Sumner

[kustombrad]

The rear end is trying to get power to the ground from a 90 degree angle and since the engine turns clockwise from the front, it's also trying to pick up the right rear. A quick change is making a 180 degree power change so it would be the opposite. Same if the engine was mounted behind the rear.

[Ron Gibson]

Kustombrad
I agree completely. Years ago Mickey Thompson wrote an article on leaving the line. On launch, if the car fishtails right, add weight or preload to the right side, or visa versa, until it launches straight. On the drag strip, if you watch the down the track cameras, if they get out of the groove, they pull hard in the the direction of the tire that looses traction.
At Bonneville, cross winds may have something to do with which way it spins.
Back in the 60's when I had a service station, I could tell whether a car had a posi by which tire was worn the most (young hot rodders) If posi, left tire was worn more because of torque loading and more weight on left when both are spinning.
IIRC Smokey even turned one of his Hudson's engines backwards to try to balance out the traction issues. Until he was caught.

Ron

[kustombrad]

The mild preload is to compensate for the twisting motion. Look at some of the records that were set by solid mounted rear ends. On a smooth track they planted BOTH tires and were gone. My theory is with suspended cars. Instead of adding more weight Sumner, throw a sway bar back there to even (bring the left weight over to the right with an eighth to quarter turn) it out.

[kustombrad]

When I posted my theory up, I wasn't trying to sound like a know-it-all, cuz I'm definitely not and still learning stuff EVERYDAY! It was more of me commenting on what I've observed and how I thought it would be a relative and easy fix. The sway bars are (in racing terms) inexpensive, can be installed with a minor amount of fab work and are infinitely adjustable! Will the car "plant" like a drag car? Not at all, but it will keep both tires "evenly" stuck on the ground without adding a bunch of unnessesary weight to the car!

[Peter Jack]

Brad, if I had access to large amounts of surplus cash I'd already be out in the shop setting up a quick change with an open rear end. I know that the front of the housing would still want to rise in reaction to tire grip and I still think the reaction of the housing will still be the same as a conventional rear end. I don't think what happens within the housing affects the reaction on the outside as long as the drive shaft and the drive axles rotate in the same direction.  

Pete

[Glen]

After close to 30 years in the timing venue I have seen more spins then I can remember. But it many cases a spin is caused by over correction when the vehicle is drifting to the side of the courses and the driver tries to correct and doing so over corrects. This results in the spin.

[kustombrad]

Glen, I'm sure you've seen more spins than anyone out there!

[kustombrad]

Just out of curiosity Pete, why would you run an open diff?