Steve,
I would encourage you to find a race team and offer to lend a hand. All teams need thinkers to help sort out the chassis setup and solve problems with the design of the suspensions, including moment center location and migration. That way, when you acquire knowledge, it can go to good use.

The moment center is located by using the angles of the upper and lower control arms. If you extend the alignment of the centers of rotation of the ball joints and inner mounts for the upper and lower control arms, they will (should) intersect at some point we call the Instant Center (IC). Each side of a double A-arm suspension has its own IC.

Once we determine where the ICs are located, we draw a line from the IC for a particular side of the suspension to the center of the contact patch for that same side. We do this for both sides and where the two lines from the IC intersect is the Moment Center (MC).

When the chassis dives and rolls as it negotiates a turn, the arm angles necessarily change and therefore the ICs change their locations. This in turn changes the location of the MC. We are most interested in the location of the MC as the car goes through the turns because this is where the influence is felt affecting the moment arm length and that influences the magnitude of the rolling moment.

Dirt To Asphalt Questions
Hello,
I read the article in your past issue about the Dirt Late Models' special race on asphalt (Ed Note: Jan. '09). I was wondering what tire they switched to and what they had to all change over setup wise to run the asphalt? I'm thinking about trying to put on some kind of special on a local asphalt track here in Wisconsin next season and wanted to try some testing with a few other guys first.
Thanks,
Justin

Justin,
Check out the article titled "Dirt Late Model Asphalt Test" in the Dec. '08 issue of Circle Track (page 48). It does a good job explaining what we did and how we did it. The tires were left over Goodyear asphalt racing tires from a former series. They were put on 12-inch-wide Aero steel rims for this race. Please read over that article and follow our path as we prepared this car.

What I really liked about this whole concept was how much the racers enjoyed it. They were all dirt racers at heart and weren't going to change that, but this was a welcome diversion and it taught a lot of them the finesse that is needed on dirt. Contrary to throwing the car sideways entering the turns, they had to learn to focus on a definitive line and keep the car straight. Believe it or not, there are many dirt tracks where driving asphalt-style is faster.

If you put on such an event, please drop us a note here and tell us about it. We are very interested in any of these events and how they turn out across the country. We can mention it in CT and let the readers know how it goes. Who knows, it might catch on in more sections of the country.

Street Stock Crash Changes
Bob,
This may be a little off the beaten path. I have a Street Stock that was hit fairly hard on the right front and subsequently expertly repaired. But now when I weight-balance the chassis on four-wheel scales, it takes a significant amount of wedge on the right front just to achieve good balance.

I can't seem to get a handle on which way to go in my A-arm mounts to reduce this wedge: raise the lower right mounts or lower the upper right mounts. There's no obvious damage visible. Can you point me in the right direction here? And since I'm supposed to know what I'm doing with this stuff, please withhold my name if you print this.
Thanks,
JD

JD,
If you need to add wedge to the car now, I assume more so than before the crash, then the components that were repaired are not in the same place as before. That corner of the car may be higher than it was previously.

One other thing is that the control arms might be different if they were replaced. Longer or shorter control arms have different motion ratios and that can affect the wheel rate. A lower wheel rate, from a longer control arm, would result in less load on that wheel and a lower ride height.

If a different spindle was installed, then the spindle pin might be higher on the car now than before and cause a lower ride height on that corner. Most spindles run in 1 inch increments in measurement from the lower ball joint to the spindle pin. One inch is a lot when we're talking about ride height and load changes. Ask the expert what components needed to be replaced and if maybe they were different than the old ones. Chances are something changed in the process.