DragStuff

I have been having a debate with some co-workers as to what happens at the hit.
I say when the car leaves the line the first thing that happens is the front end rises and then the rear shock extends planting the rear tire and this creates separation between the the tire and the body.
Co-worker says that the front end rises and the rear squats down over the tire compressing the shock.
To me that would make it spin and not hook up!

Who's right?

I have tried finding some video of John's car (ol blue) leaving the line but I ain't having any luck.

Thats a pretty loaded question, isnt it.

There are alot of variables, and there is more than one way to get a car to leave.

what he said^^^^^^^^^^^^^6

ok, I'll ask this way.
Does your car squat at the hit?

I've watched some slow motion video of our car leaving and it seems to do both, it squats a bit right at the hit, "I'm guessing the shocks cant keep up with the axle", then the whole car raises up and leaves.

ok here is a few passes leaving different what looks like is happening to you
http://www.youtube.com/watch?v=D_c0-eay ... re=related
http://www.youtube.com/watch?v=dlp6Q7ZJCtk

What people often see as "squat" is actually the tires hitting and wadding up, not the rearend itself actually compressing the shocks, typically the rear end is going to separate at the hit.

First movement is going to be the tires rotating, once the resistance (traction) develops then everything else daisy chains starting at the rear end applying torque through it's links to the car.

Here's a real old video in slo mo of my car with oh so soft QA1 shocks. Watch what the rear end and tire does.

Hey John thanks for posting the video. I saw that on the blog, didn't know it was your car.
Looks to me the shock extends at the hit.

Carolina Kid wrote:Hey John thanks for posting the video. I saw that on the blog, didn't know it was your car.
Looks to me the shock extends at the hit.

Oh yeah, it got plenty of extension. That's when I switched to Afco's, then I updated later to Santhuff's. Needless to say it doesn't do that any more.

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.

Carolina Kid wrote:I have been having a debate with some co-workers as to what happens at the hit.
I say when the car leaves the line the first thing that happens is the front end rises and then the rear shock extends planting the rear tire and this creates separation between the the tire and the body.
Co-worker says that the front end rises and the rear squats down over the tire compressing the shock.
To me that would make it spin and not hook up!

Who's right?

I have tried finding some video of John's car (ol blue) leaving the line but I ain't having any luck.

I still would like to wager it's the tire that must rotate first. Consider what happens if the car was on ice. The suspension would never separate, but the tire would rotate.

John_Heard wrote:I still would like to wager it's the tire that must rotate first. Consider what happens if the car was on ice. The suspension would never separate, but the tire would rotate.

ok,I guess first the tire rotates, front rises and the rear shock extends.
Co-worker says the shock compresses.
I said it extends.....


Thanks for the feedback

[quote="Craig W."]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!

The suspension does separate first. Separation does not occur due to the act of tire rotation but, the force of the pinion acting on the ring gear. All cars separate (anti-squat) to some degree because of this force. This force is visually perceived as the sidewall compressing.

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.