Cal Tracs and Instant Center????
 

I have a set of slide-a-links on my 67 camaro, that I have modified to have a solid rod at the bottom to be like cal tracs. I have measured and roughly calculated using the main leaf as the upper link, that the IC is at about 78" in front of the rear axle, and about 5.5" off the ground. I beleive the neutral line on my car to be at about 9.5" off the ground at the same 78" in front of the axle.
1/2 the people say the cal-tracs dont effect IC, that the front spring eye IS the IC, and the other half say that YES the cal-tracks do effect how the rear suspension reacts to the "hit" just like altering a car's IC, and pivot point adjustments DO effect change.
What do you guys think????
If the cal-tracs do effect it, then where should I try to get the Instant Center. I know that I should have some anti-squat in the IC setting, but unsure where to attempt to position it, I have to modify the pivot points to acheive this so I am looking for advice.
Please dont tell me to spend $350 bucks and buy the CAL-TRACS, I would like too, but I have already wasted $350 on the slides inks, and I dont have alot of spare cash. I know I can modify the pivot points on the bars I have, to get them to work, I just need the technical advice about IC location.
If anyone has any other leaf spring setup advice, please share it
This on a stick shift 67 camaro, 6.0l LS, stock suspension, 28x 12.5 ET street bias. Car weighs 3425 roughly with me in it and has run a best of 11.39 @ 120 w/ a crappy 1.60 60 ft. I really need to improve traction to get it to 60ft better. Slow speed video of the launch shows the rear tires turning about 8-10 revolutions before the car even moves, and the rear does not separate untill after the tires start to bite.
Barrett

Re: Cal Tracs and Instant Center????
 

Whatcha using for a clutch?

Re: Cal Tracs and Instant Center????
 

11" Ram Single iron. it is at about 550lbs static right now, has no counterweight added to the CW levers.
I have tryed the static down so low to where the car wont even move when you let out the clutch, only when revs come up to about 1800, and it still BLOWS the tires away, even with launch rpms as low as 5000rpm. In fact the 60ft improved when I forgot to turn on the 2step, and left of the 7200 high side limiter lol, that was the 1.60, all others were 1.64 - and up, sometimes way up.
I am convinced the problem is in the rear suspension??????

Re: Cal Tracs and Instant Center????
 

Have you tried another set of slicks? I have set that just wont hook for some reason. Switched them out and picked up big time.

Re: Cal Tracs and Instant Center????
 

this is the second set of M/T et street bias 28x12.5's. 1rst set was an older pair, this set is NEW. EXACT results with both

Re: Cal Tracs and Instant Center????
 

Put slicks on it et streets just won't cut it. You need a stiff sidewall slick.

Re: Cal Tracs and Instant Center????
 

Ding, Ding, Ding, We have a winner!

Stiff sidewall slicks will be much better.

Re: Cal Tracs and Instant Center????
 

OK , I plan to try that type tire next
Do you have any input on the original question - does the cal tracs change the effective Instant Center of a leaf spring suspension?

Re: Cal Tracs and Instant Center????
 

I think your putting the cart in front of the horse.
It will be pretty hard to make your car work consistently with what you have. The traction bars will help but are not the answer.

Re: Cal Tracs and Instant Center????
 

I think you're overthinking the suspension. As stated, you need real slicks. Maybe take some clutch out and lower your launch RPM. Myself, and others I know struggled with Cal Tracs and adjusted them all over the place with no improvement until the rest of the setup was right. The lower pivot hole theoretically moves the I/C farther out and softens the hit. The top hole hits the tire harder. Do you have adjustable rear shocks?

Re: Cal Tracs and Instant Center????
 

Maybee your right about over thinking it all?
Shocks are DA's on rear. they are mounted in the oem location in front of the axle.
I cant beleive 28x12.5 ET street bias is not enough tire to hook this thing?, but I'll take you guys word for it, my next tire will be a stiff sidewall slick.
Thanks for your input about the top/bottom adjustment hole's effects. I keep thinking that because slow speed video is showing the tires turning before the suspension seperates, that I need the suspension to hit the tire quicker. I guess I have the rest of the season to mess with that, because new tires are not happening untill spring time.
Thanks
Barrett

Re: Cal Tracs and Instant Center????
 

[QUOTE=
Do you have any input on the original question - does the cal tracs change the effective Instant Center of a leaf spring suspension?[/QUOTE]

CalTracs most definitely change the instant center. The rear attachment point (the one directly under the axle tube), is much lower so that the angle is more acute through the the front attachment point (the one below the spring-eye), in other words, pointing upward.

I have to agree with what Dinsdale said. In back to back testing on two different cars, we found the lower hole on the front mount resulted in less separation between body and wheels, as you would expect from a lower Instant Center. The resulting hit was softer, and that enabled the cars to hook on hot tracks. In better conditions, the upper front hole sometimes resulted in better 60 foot times, but it was not nearly as consistent. These were both automatics.

But what really made it work was finding the right shock setting. Controlling the rate of separation, as you already mentioned, is key, and ADJUSTABLE SHOCKS CAN POINT YOU IN THE RIGHT DIRECTION WITHOUT SPENDING MONEY. Don't assume that it's a harder hit that you need. Try going both directions with the shocks. If a stiffer shock (when extended) improves your 60 foot, then you'll know the IC needs to be lower. If a looser extending shock helps, a higher IC. It's also possible that the shock adjustments alone will be enough.

Re: Cal Tracs and Instant Center????
 

Hey Barrett,
If my wheel offset will work on your car you can try my slicks for a couple passes...... not 12 ! I know how you like to make laps!! Ha ha
I know Ed doesn't buy it but I still think track prep is better on Saturday as well. Gary

Re: Cal Tracs and Instant Center????
 

I would love to take you up on that Gary, I am using 8.5" wheel w/ 3.5" backspacing
Yeah sat is probably the way to go

Tony - thanks for the advice, it makes sense. I will definately mess with the shocks to see if they can lead me in the right direction.

Re: Cal Tracs and Instant Center????
 

And I saw elsewhere that you had a pair of very old and probably worn out leaf springs. We all understand budgets but there is no "miracle band-aide cure on the cheap" when it comes to a drag race rear suspension.
I would put a pair of M/T 9x29.5 stiff sidewall slicks on it at the same time I put a pair of Calvert Racing rear springs. I'm guessing that would help a ton. Then you can save for a good clutch as offered by either McLeod or Advanced because the clutch and rear suspension are all inter-related. But I would definitely suggest the rear part of the car gets the first rehab.

Re: Cal Tracs and Instant Center????
 

My leafs are new, '68 style multileafs with an extra main leaf added in front of the axle.

I am not looking for miracles Jeff, I am just trying to learn how to build me a working stick car rear suspension.
Do I want antisquat, or no antisquat? what does a stick car want on the "hit" My car does not seperate the suspension at all on the hit, but after the tires spin a few(8-10) revolutions , then it seperates about 1.5" and the front comes up, and the car moves out - kinda makes me think i need to add some antisquat to the initial hit to try to get the tire to bite?
****, this car 60'd 1.60 with frickin drag radials that everyone said DONT work with the stick, now I switch to the Bias, and I'm havin trouble getting theese 28 x 12.5 bias to even run the same 60's.

Re: Cal Tracs and Instant Center????
 

Well, I'm far far from being any kind of suspension expert but it seems like your rear springs may be part of the problem. As soon as you have a spring that is trying to control windup and a traction device such as a Cal Trac then you end up with a conflict of interest. I've seen low 10 second cars with just a slapper bar and there are the old Mopar S/S springs that worked well without any help.

All the spring needs to do in a race car is set the ride height. Then the traction device (I.E. Ladder Bar, Cal Trac etc.) along with shock adjustment is tuneable. That's why a coil over setup works as well as it does. My suggestion for the little it's worth is go to a Calvert Mono spring for your car or keep the current ones and ditch your slide a links and clamp the front half of the springs or try a cheap set of slapper bars if you get wheel hop.

The other thing mentioned is a stiff sidewall tire but they don't come in many sizes so you have to do some research on that deal. I run a Goodyear 29x11 and they quit working long before they are worn out because they are a regular sidewall.

Re: Cal Tracs and Instant Center????
 

I think you are excepting the suspension to separate without traction and that's not how it works. The tires have to hook to some degree for the rearend to want to rotate which is what makes the suspension separate. Think if your car was on ice and you dump the clutch. You are not going to get any separation because you have no traction. Put a set of 3056 M/T's which are the 9 x 29.5 stiff sidewall on 10" wheels and you will see a completely different car.

Also, even tho you have 12.5 tires you have them mounted on 8.5" wheels which is not helping you.

Don't forget about the front suspension. The front and rear have to work together.

Re: Cal Tracs and Instant Center????
 

Good advice. Make a list and start testing. I am not sure how much you spend to go the track, but I bet it is at least $100.00. (not counting racecar expense) You can waste money going and still have less than desirable results. Skip a few trips to the track until you can get a few of the items mentioned.

Leaf springs are not expensive. If you get the calvert split monos or landrum monos. Sounds like you have a really stiff set up. Sometimes you can find thiis stuff on craigslist, or swap meets too.

Check to make sure you have enough rear shock travel too.

Slicks- make sure that you get a stickshift slick. If you are borrowing a set, more people have automatic cars. I have known many who think it doesn't matter that much.The auto slicks are also a different compound and a softer sidewall. It might be better than what you have, but not enough to learn anything.

The 60 ft improvement could be telling on your stiff suspension. Maybe it took that much to even atytempt to plant the tire. Probably wouldn't do it with those tires and your set up, but it was trying.

I think some of the guys that run those tires also use digital timing control to help. Either a digi 7 or an add on box. If you don't need to run them for any kind of rules, I would bolt a set of MT 3056sts on it as a tire choice on top of the other necessary changes.

Good luck!

Re: Cal Tracs and Instant Center????
 

The Ice analogy made sense to me, thanks Kris
Thanks for the advice everyone.

Re: Cal Tracs and Instant Center????
 

All advice here is proven. FYI - I ran SS style leaf springs from Tri-City Competition (Launcher springs) for a long time with Cal-Track bars. The car was reasonably fast but never 60' like I thought it should. In hindsight, I should have used the springs with no bars. And to make it worse, I used the front spring clamps that I was advised to run. That suspension was one bound-up SOB! But it was my doing, not Tri-Cities.
When I finally saw the light, I installed Calvert springs. Suddenly I had a whole new race car. Big improvements followed immediately.

Re: Cal Tracs and Instant Center????
 

You need to soften the rear suspension. When it is stiff the tire has to do all the
work, once it begins to spin , it cant recover. If you can not afford new springs,
remove some leaves from your existing springs. 2-3 leaves is all you need when
using a traction bar. I would suggest using 1 clamp on the front segment only.
Also as stated the shocks are very important, get a good set of adjustable rear
shocks. Make sure the front end is not binding, you want it as loose as you can
get it and use the front shocks to control it. This may not provide a complete
cure for your problem, but are steps in the right direction.

Re: Cal Tracs and Instant Center????
 

Barrett , You're in luck. My Welds are 15 X 8's with 3-1/2" backspacing to the flange (approx 3-1/8" to the bead). The slicks are ET Drag 28X10.5 which are actually a little narrower at the bulge than the ET street 28X12.50's.

The slicks have never been run... you mount and balance them and you can make some runs. You'll need long studs for these rims (I think you have those already?) I should have lugs in 1/2" or 7/16"

Gary

Re: Cal Tracs and Instant Center????
 

Awesome! I will phone you soon