what happens at launch?

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Carolina Kid
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what happens at launch?

#1 Post by Carolina Kid » Thu Jul 28, 2011 5:19 pm

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.

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Moparious Maximus
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Re: what happens at launch?

#2 Post by Moparious Maximus » Thu Jul 28, 2011 9:31 pm

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.
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chpcamaro
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Re: what happens at launch?

#3 Post by chpcamaro » Thu Jul 28, 2011 9:39 pm

what he said^^^^^^^^^^^^^6
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Carolina Kid
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Re: what happens at launch?

#4 Post by Carolina Kid » Thu Jul 28, 2011 9:51 pm

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

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Moparious Maximus
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Re: what happens at launch?

#5 Post by Moparious Maximus » Thu Jul 28, 2011 10:06 pm

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.
'63 Plymouth, Straight axle, Leaf springs, Drum brakes, 31x10.5wx15 Rears 3215lbs
Best time to date 7.99 @ 170 mph
572" Wedge 8-71 @ 28% OD, ALKY, Glide, Dana

http://www.youtube.com/watch?v=vq-xzFWHtFk
http://www.youtube.com/watch?v=JfyZSw59R_o

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chpcamaro
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Re: what happens at launch?

#6 Post by chpcamaro » Thu Jul 28, 2011 11:58 pm

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
best to date N/A 8.91@153
psca westcoast heads up racing open comp
67 Camaro RS/SS
BBC Powerglide 4800 stall 4.11 29.5x10.5W
http://www.chpdragracing.com

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John_Heard
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Re: what happens at launch?

#7 Post by John_Heard » Fri Jul 29, 2011 7:05 am

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.

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Carolina Kid
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Re: what happens at launch?

#8 Post by Carolina Kid » Sun Jul 31, 2011 6:56 pm

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. :mrgreen:

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Re: what happens at launch?

#9 Post by John_Heard » Sun Jul 31, 2011 10:15 pm

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. :mrgreen:
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.

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Craig W.
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Re: what happens at launch?

#10 Post by Craig W. » Tue Aug 02, 2011 4:28 pm

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.
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Re: what happens at launch?

#11 Post by John_Heard » Tue Aug 02, 2011 4:51 pm

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.

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Carolina Kid
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Re: what happens at launch?

#12 Post by Carolina Kid » Tue Aug 02, 2011 8:59 pm

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 :thumb:

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Carolina Kid
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Re: what happens at launch?

#13 Post by Carolina Kid » Tue Aug 02, 2011 9:03 pm

[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!

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Mike Peters
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Re: what happens at launch?

#14 Post by Mike Peters » Wed Aug 03, 2011 9:05 am

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.
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Re: what happens at launch?

#15 Post by John_Heard » Wed Aug 03, 2011 9:17 am

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.

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