cal trac top hole vs bottom

I have always had the bar in the top hole and haven't changed it since I put the bars in, best 60' has been 1.44 foot braking just
wondering what it would do in the bottom hole?
anyone got any data?

The top hole moves the instant center closer, and made my car more prone to wheelie.

When I first put them on, Calvert told me that you want to put the bars in whichever hole makes them more parallel with the ground.

For me, that was the bottom hole. Started out that way and had good success.

Tried putting them in the top hole for a while, but with the short 20" front segment in the Duster it always wanted to pull the wheels.

How does going from top hole to bottom hole on the bar change instant center..

It doesn't BUT it does change the hit towards the harder side and I`m in the bottom hole w/just a tick of preload but not even a flat......

currently the car just pops the wheels real quick and sets them down, just think it could 60' a bit better
https://www.youtube.com/watch?v=rfFMW8JROMc

As mentioned the top/bottom hole does NOT change the instant center. On a leaf spring or ladder bar car, The Instant Center (IC) is defined by the single point in which the suspension is attached to the car (so in this case it’s the front spring eyelet).

What the top and bottom hole does in a caltrac is determine how quickly the front spring segment goes stiff. If you think of the front spring segment without a caltrac, the axle tries to rotate pinion up. There are two ways this motion can happen. Either the spring segment is completely and 100% stiff (like a ladder bar) and the pinion angle changes from body rise. Or in the case of a leaf spring, the body can stay still temporarily and the spring can flex.

The sole purpose of the caltrac is to keep the spring from flexing, and essentially create a short stiff ladder bar.

If you look at how the caltrac works, the front hanger rotates around the spring bolt. This is caused from the axle rotating, pushing the bar forward, which rotates the hanger down until it contacts the top of the spring. At this point the system is “solid” (except for some high force flexing that can occur).

When the bar is in the upper hole, it take less forward motion from the bar to make contact with the top of the spring. The lower hole requires a longer “push” of the bar before this can happen. The amount of gap/preload in the setup, and the upper/lower hole, all have to do with the “timing” of how quickly the system gets to full stiff, and how abruptly it happens.

The reason the bar in the upper hole (and more preload), hits the tire harder then a low bar hole/less preload, is because the system goes stiffer/sooner. Anything other then the upper hole and preload, is wasted motion of the suspension which will slow 60ft times down. The exception to that is if you don’t have a good enough tire/shock to hold that immediate tire hit, the lower hole/gapping can sometimes be a “Bandaid” and help with traction by launching the car softer.

If you look at any of the fast leaf spring cars, they almost ALWAYS have the bar in the upper hole. If your car isn’t spinning, it’s unlikely that the lower hole will help anything.

Also, being that it’s a foot brake car, you’re already preloading the pinion up anyway, so you’re likely getting close to full “Stiff” on the front spring segment anyway while you’re on the converter (depending how hard you’re on it).

If anything it looks like you could tighten up the front shocks a LOT if that’s an option for you. Comes up way to easy. Keeping the front down is the best way to improve the 60ft if you’re not spinning.

Hope that helps…

I have always run the upper hole on my Cuda, and it hits like a ladder bar car with a 1.38 60ft. No wind up like a typical SS sprung car, and then launch, it just hits....Never tried the lower hole, but as stated, all the fast leaf sprung cars are in the upper....I run just a slight amount of preload with my weight in the seat. Street driven and raced, with no changes and I like them.

Don't have my papers that came with bars in front of me now, but I'm almost sure that the design showed the instant center forward of the spring eye, and changeable by moving to different holes, the reason behind the design. A stock suspension four link, not a ladder bar.
here is the diagram, changing from top hole to bottom hole moves the instant center, "the system emulates the four link system"

I run mine in the bottom hole, the 408 ran a bunch of 1.38s. I expect the 434 to run low mid 1.3s when the shocks and converter are tuned. The top hole hits harder for sure. If there is pre load regardless of the hole they will hit at the same time.

Thanks for the info guys, gonna keep them in the same spot
and maybe work on some better shocks in the future

I wouldn't, I'd try the lower hole and play w/that a bit since you want more and that COULD help ya instead of hitting it too hard. This is how we learn right............

Never hurts to try... It is a free change, and could be a cheaper way to better ET then new shocks for sure!

If there is one thing I've learned, it's just how fast things happen on hit/launch. Way more then you can see with the naked eye.

I remember looking before, and my driveshaft speed goes from 0 to 10mph in something crazy like 0.03 seconds, and then drops back to near zero before the accelerometer starts to move. That is ALL just suspension travel/hit happening before the car starts to move forward.

My Dakota HATES, HATES the upper hole, I tried it out for the 1st time Saturday, even with new slicks, spin city.

Some need/like the harder hit and some don't.............mine doesn`t.........

Our car likes the top hole. Try it both ways for weeks each way

Back when my car ran in the mid 10s, it was doing a lot of bouncing through the 60' when using the top hole. Dropped it down to the bottom and it smoothed right out.
Been in the bottom ever since.

That's the same exact thing that my Dart did when the 340 was in it. Mine have been in the bottom hole ever since.

Wonder if it has to do w/the short 20" ft. segment...........I run the 25" myself and love it so far along w/more straight up n down shocks...........

I have always been in the bottom hole.Has anyome tried to increase the preload?? What happemed?? I was gunna try it,,,,,,

that jumping around sounds like the shocks r to short

Sounds like the harder hit in top hole topping out shocks and causing it to bounce.

So maybe the top hole (harder hit) w/ a stiffer rebound shock setting may be faster?

Chip it could be, only one way to know for sure.

I may give that a try soon...I'm still not sure exactly what this car of mine likes on these slicks.

I know mine stopped doing it when I switched away from rancho shocks.

Does this look right, or should I be on bottom hole?

I would stay there.

Do you have shims-spacers between spring and housing-perch? Perch sitting on the spring I mean?

Does this look right, or should I be on bottom hole?

Do you have shims-spacers between spring and housing-perch? Perch sitting on the spring I mean?

No, I don't have any spacers or shims. Not sure what difference that would make?

You have to try both.. lots of variables to
play with here.. how much torque, weight distribution,
gear ratio and the front end set up.. the only way to
make sure is testing it... and that includes adjusting
the shocks... and if the shocks are good enough to control
it.. its never as easy to say.. this way or that.. do
you have a low ratio first gear is just another thing

Raising or lowering that bottom plate in relation to the housing changes the instant center just like the first or second hole in the front pivot. Pretty much the same way moving the bottom bar in a four link at the housing. One way of getting the bar level to ground and the farther away the hole is from the center of housing, more leverage, closer, less

I raced my car again this weekend and it was hooking really well, but doesn't 60 ft. like it did with SS springs.

The car leaves smoother and more level and felt really good, though.

It had done a best of 1.54 60 ft. with SS springs but not consistently. It did 1.67 all day long with the Cal-Trac setup last Saturday. I have 3.54 gears ET Street Pro's and leave off idle. The engine is like a low rpm diesel and makes massive torque.

I use the Calvert (Rancho) 9 position shocks set on 7. We did change the upper mount on the shocks to get them more vertical.

The car drives excellent but I would really like to shave a tenth off consistantly.

Should I move the bar to the upper hole? I thought about rear sliders, too, but use the car a lot on the street and have heard they are noisy.

Will double adjustable shocks help?

The only way to find out what your combination and car likes the best is to test, test, and then test some more
Have you tested leaving at different RPM yet? If not try that also

Not yet, but planned on that too! Not gonna experiment until next spring. Have some paying races coming up and always do well at both so don't want to change much..

x2 on Cab's comments.

I ran a best of 1.54 on SS springs, then switched to CalTracs with standard leaf springs and the same Rancho 5-way dampers I was using with the SS springs and dropped to a best of 1.51 and more consistency. Better engine and changing to split mono-leaf springs saw a best of 1.45, and still with the same old-style Ranchos. But there were preload & damping adjustments, launch RPM changes, tire pressure changes, etc., along the way.

Hole location has zero to do with IC as that is fixed however it changes the "hit" lower softer, upper harder.........

To be 1000lbs lighter.....

Would love to try bottom hole on mine but they had been cut off already when I purchased the car.

You can buy replacement side plates , just call Calverts

Tex

Read dizus’ reply. I think I can add to it though...
The forward hole changes the angle of the link bar. If the link bar is angled upwards in the front, the rotation of the housing (or the force trying to do so) forces the axle downward, effectively causing chassis separation. More traction. More shock needed to control separation.
If you could get the front of the bar low enough, you could theoretically cause the chassis to squat, even with the same instant center location. (Spring eye)

A simple way to visualize this...
Try pushing a car with a 20” long pry bar. If it is parallel to the force you are applying, the pry bar will move the car without pushing your arms up or down. Now try pushing the car with the pry bar at an upward angle. The more force you apply, the more your arms will be pushed toward the ground. That same effect causes separation with the Caltrac bar.

Unless something is severely under powered, I personally don't ever see the need to use the lower hole. I think it's better to get the bar as stiff as possible, as quickly as possible... and use the shock to control the hit.

GY3... when you say shock settings are at 7, do you mean 7 clicks from full tight? What front shocks do you have on it? In the 60ft range you're in, I would definitely move to the upper hole.

I suggest moving to the upper hole and continue to click the shocks tighter 2 clicks at a time. The car will pick up 60ft as you do it until it gets to a point where it spins. Then back them off 1 click. That will get you close...

From there it's a balance of rear shock setting and front shock setting to optimize further.

Two things came to mind that I wanted to bring up:

1. I've never tried the upper hole since switching to CalTracs.

2. However, until this rebuild, I've always had the shorter 20" SS/A-body front segments on my E-body, rather than the standard 22" front segment. With the switch to the Strange S-60, I also put 22" fronts on the car.

How would increasing the front section & bar length by 2" likely change the settings?

I race a low 11 second Dodge Dakota on a [censored] track, traction has always been an issue. I have relocated DA viking shocks, Monoleafs, catracs, spring sliders...And instant spin.
A local 8.5 my got my truck from blowing the tires off to lifting the fronts an inch in four passes...I was bottom hole, no preload he moved me to upper hole with 1.5 TURNS preload with shock changes front and rear.
I'm still going to 14" tires and a 4 link...I'll be making more power next year with a looser converter and launching off a brake.
In summary...video tape your launch and play it back in slow motion, only way to see what is happening.

I never thought about adding a spacer to lower the rear hole position relative to the axle. I know the Assassin bars have a lot of adjustment holes up front and in back but think so many options could lead to more confusion on how to set it up.

A few racers I know swear by the Assasin bars but agree, the Calvert stuff is on some fast stuff and to add to this, Calvert has recommended the bar parallel to the ground also as a starting point.......I think you guys may be on to something and I will try the upper hole on the street, then install Shilo's ft. Vikings and do a few 60's to see how it acts then one full boogie............

I am at two clicks from Full tight. I did 9 for a while which is the fully tight setting and it spun a little. My main problem is the track prep goes away quickly at a Friday night Grudge night because of all the super hard street tires pulling up the prep and the rubber. Going to get some hits in on a decent track in the next few months and we'll see what happens. Definitely going to try the top hole but probably won't get to it until next season.

You seem to have a ton of knowledge on this subject. My car I just put together with no real adjustments. Ran 1.12 1.13 last year. I added maybe another half a thousand horsepower this year and I can't get it off the line. Same shock settings, they spray fresh glue for me and drag the track, I leave with only 2 degrees of total timing, bringing it up to 3 degrees in .6 seconds. I have been told the hit is just way to hard, caltrac bar is about parallel with the ground. I have been thinking today maybe lowering it to the bottom hole to slow down that first motion. It will probably point downward. I seen you say all the fastest cars use top.....I have Santuff' on the rear, but have been told "The shock adjustment won't affect the initial" Please help if you can

Any thoughts about how lowering the rear pivot point by adding a spacer between the spring and the mount would act differently than going to the top front hole from the bottom? Both ways would make the Caltracs hit quicker.

I can vouch that adding a 1" spacer 'tween axles and spring will hit the tyre harder and increase axle rotation. Top hole on front bracket always hits harder so much that it will likely "wad up" a std bias ply. Front travel is also important on how it hits, less front travel will cause porpoising (load and unload of the rear) but this is also dependant upon Hp/Torque and weight. Tubes and Stiff sidewalls will help but my Caltrac setup works great on Radial tyres. This is what has happened on my car, in a nutshell as I've been running Caltracs since 2001. Though your results may vary

Tig - I see that you run a spacer under the spring, but what hole do you use up front?

Bottom Hole, hit is hard to control otherwise. The big gun Afco's ran out of extension damping even on the bottom hole. They couldn't control the rise and would wad up the bias ply's bad. I got them re-valved... for Radials. I'm quickly finding out that's a different ball game but so far the cars 60ft is way better, once we go forward instead of up, I think we could go hi 1.20's

This is a slow motion video of a 1.19.
Short time menscer rear shocks Calvert mono leaf.. Cal track bar in lower hole.. with the preload set to make the car go straight..
https://youtu.be/ddVLS0nreuM.

Bias ply slicks I'm guessing??