what happens at launch?

[Mike Peters]

If the car was up on jackstands and you whack the motor in gear, the only resistance to the rotation is the friction in the rear end gears, bearings, flywheel effect of tires rotating up to speed, it all equals minimum amounts of force. The tire has to be on the pavement in order to start actually generating any significant forces where the suspension can start doing anything.

Yes. That pesky Newton's law of physics. There has to be resistance for the force to take place. If there's no resistance, it doesn't mean the force doesn't take place. The separation is a result of the force acting upon the ring gear due to the resistance. The power goes through the pinion and ring gear first and the fact of the miniscule lash being taken up pushes the ring gear carrier/housing in the opposite direction of the ring gear rotation. Might be an immesurable amount of difference but, the power doesn't go through the tires before it goes through the ring gear. We're talking what happens during launch. Car on the ground and suspension free to move. If you were to dump the clutch while the rpm is in the stratosphere and the car is on ice, the rear end would still separate.

[John_Heard]

Point being the TIRE is what connects the mass of the car to the axle, ring gear, pinon, driveshaft. No traction = absolutely minimal suspension movement. I know this is really not a real useful discussion, but I'm just trying to make a point. The suspension will not extend, front end won't come up, force isn't transmitted through the links on the rear end if the tire doesn't hook.

[Mike Peters]

No traction = absolutely minimal suspension movement.

GOTCHA!!! You did say "minimal suspension movement". The first force (pinion on ring gear) has to act before the second force (tire rotation) takes place. Slow-mo vid shows this happens almost simultaneously but, the sidewall is first compressed due to the pinion acting on the ring gear before the tire rotates. You're right, all these actions of front end lift, etc.... you describe won't take place without the resistance caused by traction. The initial compression of the sidewall leads some to believe their car "squats" on the hit when, in fact, there is no lessening of the distance between the car's body line and the axle C/L. Just a fun discussion. Oh, if only Billy Shope were here..........

[Craig W.]

What I have that shows it the best is some rapid fire still shots. From one frame to another I can see the rear tire move straight down. It also shows a little movement of the front but if that shot had been just a tad earlier, I think you'd only see the rear tire move straight down.

Here's a link to a sequence of four shots.

https://picasaweb.google.com/1130568295 ... ugust32011

I say neither of you are right. The front end can't lift before some motion takes place at the rear. The movement of the front is a reaction to the forces applied through the rear suspension and tires.

The first thing I see on video of my car is some extension of the rear suspension quickly followed by rotation of the tires.

Craig have you got some slow motion video you could post!

[John_Heard]

Link no worky, I think you have to set those as public access?

[Craig W.]

Oops. Thanks John.

Try this link:
https://picasaweb.google.com/8seccraig/ ... a-U8b_tpgE