Understanding the launch ?

[Canadian1968]

One thing I want to work on is the hole shot at the track this year. I have watched a lot drag racing and noticed two different launches .
1. The car seems to just stand straight up and jump out of the hole.  Seems to be little weight transfer.
2. The car shifts all the weight to the back , the front  raises and the back squats . If there is enough power the car will lift the  front wheels .

I see both of these happen in a leaf spring car. I understand but don't at the same time . Is it simply a matter of power or is it all in the dynamics of the suspension? 

[c00nhunterjoe]

Both. Depends on how the car is set up.
Ideally i dont want movement in the chassis on launch. I want the car to go if that makes sense to you. Any time still sitting at the line letting the chassis flex and suspension transfer is time im losing on the reaction which can cost you the race.

   I dont know the details of your car to give you tips on the track.

[John_Kunkel]

If there is enough power the car will lift the  front wheels .

Some would argue that lifting the front wheels is due to a lack of power i.e. more power would produce wheel speed and wheel speed is preferable to dead hooking. The energy used to lift the front wheels would be better used to propel the car forward.

IOW, too much weight transfer can hurt your ET by causing excessive wheel stands and lost forward motion.

[c00nhunterjoe]

Yes, bumper dragging wheelies hurt et. You dont want big wheel stands. You do want it to hook. This is not top fuel. Tire spin is not wanted.

[Mike DC]

 
Going from tire spin to body movement is progress.

Going from more body movement to less of it (without the tire spin coming back) is more progress. 

[Canadian1968]

My car doesn't seem to shift the weight to much. It's more stand up and go. But as far as I am concerned the car does not launch that we'll with out breaking the tire loose.

The car has CE 3 way shocks all around. Factory pinion snubber sitting approx 11/4" from the floor.  Factory leaf springs with rubber bushing.  I have installed custom made frame ties. Designed to the contour of the entire floor ( US car tool type ) . 

Tires are bf g force 2 tires ( 255/50/16).

The best 60ft is 2.1 so far .

[John_Kunkel]

Tire spin is not wanted.

Scenario #1: Car dead hooks, lifts the front and travels 60 feet in 2 seconds.

Scenario #2: Car has a little wheel speed (spin) at the launch and travels 60 feet in 1.6 seconds.

Which is more desirable?

[c00nhunterjoe]

Tire spin is not wanted.

Scenario #1: Car dead hooks, lifts the front and travels 60 feet in 2 seconds.

Scenario #2: Car has a little wheel speed (spin) at the launch and travels 60 feet in 1.6 seconds.

Which is more desirable?

Scenario #3. The car dead hooks with no tire spin, lifts the front wheels and travels 60 feet in 1.3 seconds. I have not seen any of my fellow racers fall into scenario #1. Scenario # 2 is a lost race in my classes. If you have enough power and chassis to wheel stand, then put bars on it to keep the front end at the desired height along with a properly setup front end.

[Canadian1968]

That is not really the main purpose of the thread. But I agree I don't see how any car that " dead hooks " can be slower than a car that spins a bit ?

I guess the answer is, what ever works best for your car? .  As I said before the car doesn't seem to "squat " much at all, so I will just work with that.

As far as pinion angle, and the snubber . Would I want the snubber to be right against the floor, at the track? OR do you want a bit of axle wrap to allow the leaf springs to do their job?

[c00nhunterjoe]

Without knowing anything else about your car, the 2.1 60' with bfg street tires is the 1st problem. Those tires are not going to get you the best et the car is capable of. The most you can probably muster is a 1.9 with alot of practice. Nothing you do to the snubber is going to change the fact that those tires will not hold a 2 ton charger.  If you had a set of slicks on it with stock springs, i would tell you to clamp the leafs and put the rubber of the snubber just touching the pad.

[HPP]

Mopars springs in general, and super stock springs in particular, create traction by generating body separation, IE, they are lifting the weight of the body to drive the tires into the ground. This is due to the asymmetrical design with a shorter front spring segment and a high percentage of anti-squat designed into the spring eye locations. Also in this scenario, a snubber is nearly worthless as the body separation only pulls it further away from the floor pan.

Many GM and Ford leaf springs of symmetrical design tend to squat.

Cal-Trac springs were designed to create a dynamic length change to allow the symmetrical Ford springs to emulate the Mopar asymmetrical design under power without altering the original mounting points required in certain class racing.

Hole shot is learning exactly how your car and its combination of parts react so you better know when to hit the gas as the lights come down. This does not require any hardware updates and instead relies on software (driver) improvements.

Reducing 60 foot times is a hardware update to more rapidly accelerate the car off the line. This requires mechanical advantage such as high engine speed, steeper gears, and significantly improved traction. Until these pieces are in place, you likey will never push the leafs beyond their capability to need more precise tuning.

[Canadian1968]

Alright , so the tires are weak point currently in the setup.  (And any other daily street tire)

They are going to break loose before any of the other components are pushed even close to their limits .

So basically play with them and see what I can get.

Positive note , the local track is getting resurfaced this year !l

[c00nhunterjoe]

Alright , so the tires are weak point currently in the setup.  (And any other daily street tire)

They are going to break loose before any of the other components are pushed even close to their limits .

So basically play with them and see what I can get.

Positive note , the local track is getting resurfaced this year !l

Bottom line- when you have the stock suspension on street tires, dont worry about the suspension until you can cut consistent 1.9-2.0 60' times. On slicks and stock suspension- 1.7-1.8