From Conventional to Bump Setup
From Conventional to Bump Setup

How We Helped a Local Team Convert.

Bob Bolles

After a local Pro Late Model team posted an in-car video of their last race on their Facebook page early during the season, I knew immediately they had some serious problems. The car was very tight-loose and the driver was really struggling with the car, but doing an amazing job of holding on. I couldn’t help myself, and I commented, “I can fix that.”

Blaise Hetznecker, the driver, said he would love for me to help, and so began a journey that taught me a little more about what I already know something about. This may be of great interest for those who have already converted from conventional to bump setups and are struggling, or anyone who contemplates making the change.

The car in the video had been involved in a crash, and basically, destroyed. Blaise’s father,Rainey, was able to pick up a seldom used, but older design, Late Model that hadn’t worked very well for the previous owners. We’ll tell you why that was so.

In this story, I will provide as much detail as I can so you can understand the problems you might encounter when trying to convert a car that may not have been designed to run bumps into one that is. Between five to 10 years ago, the chassis manufacturers were in the process of converting to the new-style front ends, but some were sold that still had the conventional design. This car was one of those.

About the Car

This is a Port City chassis circa 2005. The car came with everything the team needed except the motor and tranny. Those were salvaged out of the old car and were perfectly fine. A very good set of adjustable shocks came with the car also and that helped us when it came time to do the setup.

First, we needed to look at the previous setup to see what went wrong. That front-end design was very similar to the new car, so any problems I could identify would carry over to the new one. And we did find significant problems.

First off, the front top and bottom shock mounts were not spaced far enough apart to allow room to mount the shocks so that there was enough shock shaft showing at ride height to allow bumpstops or bump springs. On the old car, they had been trying to run bumpstops, and they set the static cambers like everyone else does. Without the required shock travel, the dynamic cambers were all wrong.

When I realized what the cambers were Blaise was trying to use to steer the car with through the turns, I was more amazed he was able to hold on and not wreck the car. The actual wreck that totaled the car was due to getting caught up in someone else’s mess.

Shock Mount Changes

So, the first thing I suggested was to modify the upper shock mounts to do two things. One was to raise the upper shock mount to allow room for bumps so the car would travel enough to get down low in the turns while also allowing the tire cambers to be correct. The second was we needed to be able to quickly adjust the upper shock mount height so that we could adjust the spacing between the shock body and the bumps.

Being do-it-yourself kind of guys, they proceeded to fabricate upper mounts that were a bit large, but very effective for our use. By using screw jack upper coilover mounts, they didn’t need to run packers, or spacers, to tune the point where the shock lays on the bumps.

That done, the next thing I suggested was for them to run on bump springs, instead of the bumpstops. I donated a pair of 1,500ppi bump springs I had left over from my foray into the bumpspring market a few years ago, and we installed a pair of 175ppi ride springs.

The car also had a nice NASCARstyle, three-piece sway bar that was 1 1/4-inch diameter, which seems small in today’s bump world, but it had 0.375-inch walls. That made it a stiff bar, which when installed in this car amounted to a 600lb/in rate.

Bumpsprings don’t like high sway bar rates, and this one was too much. So we installed a 3/4-inch diameter solid sway bar that rated around 120lb/ in. This would free up the bump springs to do their job, plus we could pre-load the bar without jacking the ride heights around like happens with a stiff bar.

We also measured the front end for moment center location and found this car was very close to what I wanted. With a little tweaking, we were able to get the dynamic location to 0.2 inch high and 14 inch left of centerline. For all of you “jacking force” people out there, this is a good location for you, too.


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April 2017