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BJ’s Blog: K9 gets put on the scales.

The K9 Sport Mod is getting ready for it’s date on the track. Changing the suspension over to a full on three link with a urethane bushing pull bar was going to make some huge differences in the way the car reacts on the track. When a race car goes through a major change like this, or experiences race damage repair, it’s always smart to put it on the scales and get a new baseline.

I made a quick call to our guy at Intercomp, Aaron Van Heel, and explained that I was lazy and wanted a set of scales that would do everything for me. I didn’t want to do much work and lord knows that I didn’t want to think or do math. I just wanted a set of scales that would figure it all out for me. Aaron hooked me up with Intercomp SW500 E-Z Weigh Scale System. E-Z? Sounds like that was exactly what I was looking for.

When the scales arrived, I had all the tools I needed to do the work. Since there was no more excuses, I pulled the K9 mod onto the four post lift and started getting the chassis setup. Using a four post lift makes the job much easier. All four tires are resting on the lift so the car is just like it was on the concrete floor, but you can raise the lift and get under it to make the changes you need to make.

The first step is to square the rear end in the chassis which requires marking the center of each axle on the surface of the lift. In the old days we would break out the jack stands and run a string across all four corners of the car. I’ve found that marking the floor with tape and a Sharpee works just as well.

Intercomp's E-Z Weigh Scale System.

By adjusting the lower control arms, the left side wheelbase measurement and right side measurement should be made the same. This locates the rear end correctly fore and aft in the chassis. The rear end still needs to be located laterally in the chassis for it to be completely square. To perform the lateral measurement, it is common to measure from the brake rotor to the frame.

With the K9 Sport Mod, the frame does not have a frame rail under the rear end. The “underslung” frames are much easier to measure in this aspect. In the event that you have a frame like the K9 Mod, without a frame rail below the axle tubes, then you will have to drop a plumb bob line down from the upper frame rail and measure from the brake rotor to the line. Measure both sides and use the pan hard bar to make the measurements identical.

Using tape, a black sharpee and a measuring tape, you can measure the left side and right side wheelbase.

The next step was to adjust the rear suspension angles trying to keep the lower arms at about a 5 degree uphill angle on both sides and the pull bar somewhere near a 20 degrees downhill angle. K9’s lower arms were 6.6 on the left side and 7.3 on the right side. Close enough for a first measurement before the ride height measurements. The pull bar angle was around 14 degrees though, and that needed to be adjusted.

Measuring from the brake rotor to the plumb line.

So we adjusted the pull bar angle closer to 20 degrees then moved on to setting air pressures and ride heights. I made a guess at ride heights based on the track conditions that I had seen this year. The track has been pretty heavy so I chose to set the LF at 5.5, the RF at 6.0, the LR at 6.0 and the RR at 6.5 inches.

14.9 degrees downhill angle on the pullbar. No Bueno.

I had set the front end with a typical dirt track caster and camber setting with the LF at +2.5 degrees caster and +1 degree camber and the RF was set to +5.0 degrees caster and -3 degrees camber. I had set the toe to 1/4 inch out for extra stability for the car’s first time on the track. Now it was finally time to get the car on the scales.

Here comes E-Z

Intercomp’s E-Z Weigh System is every bit as simple as the name implies. E-Z. The wires and each scale pad is color coded so you really have to work hard at messing the wiring up. The controller box is all menu driven and simple enough that you don’t have to read the instructions. Just hook it up and go. The first screen that you come to is a list of choices on what you are balancing the car for. You can select between Oval track, drag, road racing or even dirt track scaling. God bless Intercomp for thinking about us dirt trackers when they did the software for this system.

Ride height measurement on the left rear.

When you select the type of race car scaling that you want to get measurements on, the next screen comes up with specific data to each desired measurement. For the dirt track scaling you can get instant read out on weight and percentage for Left side, rear and cross weight, with an added bonus of rear bits. In the olden days you had to take the left rear weight and subtract the right rear weight to get the rear bite. The E-Z Weigh does it all at a glance. Our numbers for the K9 car were a little out of wack so we got busy with some adjustments.

Intercomp's E-Z Weigh Scale opening screen.

After a couple of spring changes and some tweaking of the weight jackers, we were back in the ballpark. We made sure that the car was weighed with the driver in the seat and the fuel tank at maximum minus 5 gallons. This should give us a pretty realistic race weight and a great starting point for our basic setup. From here we will make changes at the track and keep a good record of any adjustments that are made.

Initial weight on the K9 Mod.

Things to keep in mind when scaling your car:

  • Weigh the chassis with the driver in the car and all fluids at race level.
  • Take at least 5 gallons out of the fuel cell to represent the weight of the car at the end of the race.
  • Weigh your car in the same location every time. Consistency is critical to chassis set up.
  • Level the scales to each other.
  • Make sure the tires are located in the center of the scale pad.
  • Make sure the scales are zeroed before putting weight on them. You will get faulty readings if you do not.
  • After any adjustments, bounce the chassis to settle the car to it’s normal ride state.

After our first set of adjustments.

Sources

Intercomp Racing
Phone: 1-800-328-3336

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  • January 1, 2017 at 1:05 pm

    you forgot to tell people to make sure that the tires have the proper air pressures

    Reply

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