Why don't we all post what we know (or think we know) think about getting a C4 to hook up at the drag strip? Andrew and I were talking about in another thread, and discussing it here (with a thread title that should come up in any search about traction or hooking up) with the whole forum pitching in what they know should make for a pretty valuable resource.

Here's some of what I know:

Obviously, tires are the most critical thing. On a prepped track, I seriously doubt there are many of us on here that need anything more than a set of bias ply ET streets or ET drags. I've never been able to get a set to spin. With about 18 PSI after the burnout, and anything resembling a drag strip, and they always dead hooked for me.

If you drive your car on the street, running an ET street or ET drag isn't really practical, so that's when all the other jazz can make a difference.

The rear ends in our cars are old. 14 years at least, 25 years or more at the worst. Parts are worn out.

"The car rides fine, handles great, and doesn't make any noise."

Guess what, parts are still worn out. I suppose it's possible that all your gear is working at 100% OE effectiveness, but it's pretty unlikely. The tie rod ends and bushings being worn will affect the alignment slightly as you drive. The rear alignment will change or shift slightly as the worn components allow slop / play in the various parts they hold together.

The rear alignment is important to how the car hooks up with a less than ultra-sticky tire. You'll notice that as the rear tire moves up and down through its arc of travel, that the angle at which the tire tread contacts the road changes. Not a real big deal, unless you are looking for every ounce of grip at the local stop light when the cocky neighbor kid is revving his Mustang at you from the other lane.

As the car squats down, the top of the rear tire will tilt inward. This causes the tread to ride up on it's inner edge, lifting the outer edge, and ultimately putting less rubber on the road. You can combat this a little with the rear alignment settings.

I have the best luck with about .5 degrees of positive camber. At full squat, I still get the outside of the tread to lift a little. So, at full squat I'm not getting optimal tire to road contact. The reason that works the best for me is that because my car doesn't instantly go to full squat when I launch. It has to get there over the course of the first few inches of movement. If you picture a car launching in slow motion, the car starts to squat before it starts to go forward. With .5 degrees of positive camber, and a full tank of gas, the point at which my car starts to move forward is when I have the tire flat on the road. Once the car has moved 6 inches or so, the tire is tilting in a bit, and I've lost optimal contact between tire and road. However, that's the price I pay for having optimal contact at the point that the car starts to move. This has given me the best results. Your results may vary.

Since I've spent so much time dialing in the rear alignment, a worn bushing or tie rod end throwing me out of whack .25 degrees is freaking slap in the face. I want my alignment to be what I set at it at. I want the neighbor kid's mustang to appreciate the difference between .25 and .5 degrees of positive camber.

I've put a few thousand miles on the car with the .5 degree of positive without any tire wear issues. I can't tell a difference in the way the car handles, but I don't push the car very hard in the corners, I don't Auto X, and I don't road race. I'm sure that someone who used the car like that would see a negative affect in grip because of the rear alignment being positive.

You can affect the rear camber with the mono-leaf bolts. What I did was to put the car on the alignment rack with the mono-leaf bolts set to give the car a level stance. Then, the alignment guy sets it up at .5 negative. Then, I put a paint mark on the mono-leaf bolts. Next, I tighten the mono-leaf bolts while watching the alignment machine. Once I get to .5 positive on both sides I make another paint mark.

I can then dink with it however I want. I'll leave it in the middle most of the time, loosen to my negative mark for a ride up the local canyon, tighten to the upper mark for drag racing or a night of cruising.

Josh, thanks for posting this. Great information.

I've noticed that my rear squats quite a bit. Before welding up my exhaust, it had C clamps that hung down about 3" off the ground. I've had folks tell me, from following, that when mashing the loud pedal, these C clamps were sparking or contacting the road. That is a lot of rear squat. I follow what you are saying and it makes sense. Would the .5 positive camber be enough for my application? I know things will vary from car to car, but I'm just trying to figure out how much of a difference .5 would make. I've thought about coil overs, but if this would do the same thing, this would be the way to go.

Thanks again Josh! Great thread...

C4 hook-ups is a good subject to discuss. I've done quite a bit of experimenting with this years back.... I'll share some of this later, do not have time right now....

But, I will say, my initial advise to new racers that are hunting for a strong 60 ft and et.... skip the test n tune and go race in a bracket points event. Track will be very well prepped and no street tire cars to tear into the groove.... thus typically the track will hold through the day. Radial tires tend to cut into the groove, hence, part of the reason for all of those bb sized rubber balls at the starting line..... not to mention the shards of rubber pieces that literally got ripped out.

A little negative camber, and a tiny bit of toe-out will help when it squats.

The tire cambers out and toes-in on squat.

I also like to burnout while rolling partway up to the beams, to reduce the amount of crap sticking to the tires. Plus it looks way cooler than a lame linelock burnout.

I think most of it is just mental preparation. I'd suggest getting staged early, even if your tires cool a bit, and get your composure and staging and RPMs set before the other guy does. Because if you can't concentrate and eliminate those other factors, you'll never be able to get any consistency on the launch, especially if you only get 4 runs in a night.

I used to waste my first few runs every time. Took awhile before I could get my head straight and pull off a respectable run on the first trip out.

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You could try disconnecting your rear sway bar for even more squat.

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Do I want more squat (that sounds kinda bad)? I think that weight transfer is good, but wouldn't too much require a very strange positive camber on an IRS rear end? I thought a 3" +- was too much. I'm not questioning your logic, I just don't know much about IRS rear end geometry.

Typically you want your rear to be a bit on the stiff side and you want your front to be soft.... this is the opposite of what a lot of people think. But, the front is where you are getting your weight transfer. You want those fronts to go wheels-up to a certain degree and you want the rear to capture it....

Having a soggy rear can cause a lot of problems, at one time with mine it would literally transfer back, squat so hard it would have a rebound a few feet out.... which is not good considering you're still in the box and the weight shifts back to the front.

If you look at the high power corvettes launching in the mid 80's, you see a lot of squat.... they hadn't figured it out yet. Nowadays, if you snap a picture of a well put together high power C4, you'll see the rear has minimal squat, but a lot of lift on the front.

I'm not an expert though.... I'm just a hobby racer.

Your car shouldn't be able to squat much more than any other C4. The bump stops should hit the knuckles and prevent the car from squatting any further.

I built some bump stop extenders that stop the rear end from squatting once the half shafts are parallel to the ground. On my car, the stops had to be extended by exactly one inch. If you put your car on jack stands, and then jack up the knuckle until the half shaft is parallel with the ground, then measure the distance between the rubber snubber and the knuckle. That's the distance you'll need to extend the snubber by.

By doing this, when you hit the snubber the half shafts are straight, which is the point where the whole assembly will take the most abuse before breaking. I don't know if this is best place to stop the rear squat as far as traction is concerned.

If your car is rebounding that quick then it sounds like your shocks are too weak.

My car rides the snubbers for awhile when I get the launch right. I'm not sure how far, but I would guess a good portion of first gear.

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I agree, even on street tires that don't hook well.

Getting longer snubbers is a great idea. Also, CentralCoaster is on to what I've been debating. Coilovers a good solution??

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Changing to coilovers won't may any difference unless you plan to change the spring rate to one that's different from the leafs.
Changing to double adjustable shocks (coil or leak) will give you control ove how the car squats.
CC's right about the weak shocks.
With doubles, you can control the rate of the squat. If it's too fast and hitting the snubbers too hard, you can increase the bump to lower the rear slower.
You can also play with the rebound to control how long the rear stays down.
At the front you can control the way the car settles back on to the front tires.

They make drag shocks with these characteristics built in but they don't work well for street driving.

I can't imagine nailing the bump stops is ever a good thing. Ideally the suspension should settle out and stick that during the launch without bottoming out... right?

Yeah, toe out and positive camber are bad on the street also! Basically take a good roadcourse car and crank every adjustment the opposite way, lol.

In theory, if you hit the bump stops hard, the body of the car bounces off the knuckles and it can sort of unload the rear. I don't think mine smacks the stops that hard, it's never started to spin if it hooked right off the line.

One of the reasons I went to double adjustable shocks is what people are describing

With my single adjustables I could make it launch pretty good, but it would bounce going down the track on the top end

My $.02 on launching a C4 is to stick with the dual mass flywheel as long as you can. In my opinion it actually helps launch the car rather than hurting it. After consistent 1.7s on the motor and 1.5s on the bottle and never so much as a squeak from the rear in my '96 (including some wheels up launches), I'm convinced that sprung flywheel is key. Traction was never really an issue since the tires were not getting whacked by the clutch hit, including 4,000rpm launches on the bottle making 550rwtq.

Of course, a dual mass will only really work with the stock motor.