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