I truly believe that artists are mostly born and improve with age. That idea conflicts with my other belief that setting up a race car is a form of art, too. The whole process of setup comes easy for some and more difficult for most. Can this art form be learned? I've often wondered if it can. My daughter, Christa, is an artist. I knew it from the time she was only five. She would sketch scenes with depth and imagination at that early age. It comes easy for her.
The truly gifted race car setup artists also seem to have a natural knack for putting all of the pieces together in the proper order and where all of the parts fit. When that happens, the car has a look to it, while negotiating the turns, that, to me, resembles art. A well set up race car is a thing of beauty. You know exactly what I mean. You've seen it countless times, be it your team's car or someone else's.
The driver can tell from inside the cockpit. The car just feels like it wants and needs to go through those turns. The effortless way it settles in on entry, the neutral feel in the steering wheel and as it rockets off the corners all tell us something that just feels right. The driver exits the car after 100 hard fought laps with a lot less sweat and energy loss than with other cars they've had to drive.
I've seen it done by some who are masters. They can take a completely different car than what they're used to and transform it into a piece of art. Others struggle to apply the first stroke and waiver through the process, not really being able to see the picture in their minds like the artists do when painting the landscape. Can these types learn the art or are they doomed to struggle year after year?
There's a truth to the ideology and it falls somewhere between and includes the artist and the engineer. And I'm not talking about education being the determining factor in labeling a person either. We are what we are by deed. Most artists never had any instruction, Christa didn't. They can learn something from the masters though. And, most engineers never took a course in school, but they can acquire the skills they need through association with other more experienced engineers. They just do the art and are the artist.
There is hope for the aspiring setup artist. It comes with developing, or being born with, the desire to "paint" and the willingness to work hard at it. Associate yourself with other "artists," watch what the masters do and listen when they talk. Ask questions without fear. No one ever learned anything by being quiet. And seek only to please yourself. The true masters care not what others think of their art, if it's appealing to your eyes, then it will most likely appeal to others.
If you have comments or questions about this or anything racing related, send them to my email address: Bob.Bolles@sorc.com, or mail can be sent to Circle Track, Tech Editor, 9036 Brittany Way, Tampa, FL 33619.
I'm an engineer by day and a weekend warrior running in Hobby Stock at Heartland Park Topeka. I have a hard time wrapping my head around your moment center calculations and would like to follow your algebra someday. I've taken a different approach using equivalent horizontal and vertical loads to move my center of gravity around for cornering, braking, and acceleration. Forcing the front roll to equal the rear roll and solving four equations and four unknowns gives you wheel loading and allows you to figure out how the car needs to weigh on the level to get balance in mid corner.
This is all entirely too geeky ... I have a spreadsheet that seems to give good results. My question for you is if you've already discounted this method and have moved to moment center as a better solution? Lately, I've been wanting to hook up an accelerometer and tachometer to take some actual track measurements. Have you tried anything like that? I could probably just buy software but it's way more fun to reinvent wheels.
I love Circle Track and am sorry to hear Stock Car Racing is retiring. Keep up the great writing and thanks for encouraging me to think every once in a while.
Jeff Grimm, Field Engineer
We have discounted nothing. The roll angle balance is still as valid as ever. The location of the moment center is a large variable in the front end dynamics, as my sketches illustrate.
Notice how when the MC moves to the right, the moment arm gets shorter, quickly. The various locations can result in either a softer (left placement) or harder (right placement) front suspension, regardless of the springs installed. Once we figured that out, tuning the front suspension and balancing both suspensions was easier to attain. This process and methodology has been proven time and time again by lots of car builders and teams. It represents the true dynamics of race vehicles.
As far as software is concerned, I try to keep a separation from my articles and that business. Too many CT writers in the past have had a more personal agenda in the content of the articles. I found a method that's beneficial and I can't help but promote it. That being said, there are routines and methodology in the program that are not spoken of and/or known by the industry that make it work. If you discover those and can make your calculations work, that's great. In doing that, try to imagine all of the influences that act on the chassis in the turns. Leaving just one out will negate all of your hard work, just like in any math equation.
Rear Metric Roll Center
I'm a longtime and happy subscriber of Circle Track magazine, and look to it for much technical info for my racing. However, I can't find out how to figure out and diagram the rear geometry for a stock GM four-link metric chassis. Can you point me in the right direction or tell me how to do it?
There seems to be unlimited information for the front suspension, but nothing for the stock GM rear. I hear that the roll center in the rear is way wrong in relation to the CG and the height of the front MC. To me, that means when the front is in a roll situation, the rear can't correctly follow suit and it results in the weight in the rear "skidding" the tires sideways. Please clarify this for me.
The Moment Center height for a metric four-link design is very high compared to other rear suspension systems. A typical Panhard bar is set at a height of from 9 inches up to around 12 inches, give or take an inch. The metric four-link MC height is upwards of 14 inches or more, depending on the ride height.
The metric MC height is the average height of the two instant centers created by extending the upper and lower arms out until each set intersects. The height of those intersections are added together and divided by two.
To compensate for that high MC, most racers need to run a softer right rear spring than the left rear spring. This promotes rear roll that compensates for the short moment arm the high MC creates and helps the rear match the front in roll angle desire.
Finding Front Roll Center
I've enjoyed reading Circle Track for many years. I was a mechanic for 46 years-ASE Certified Master Tech in cars and trucks for 31 of those years. I owned my own business for 24 years and was forced to retire after a serious injury. I did all phases of auto and truck repair and specialized in repair and rebuilding automatic transmissions, aligned many front ends, and four-wheel alignments.
I'm not connected with any race team-just an avid race fan who is very interested in race car technology. One would think that with this background I could understand how a roll center is determined. But I just can't seem to figure it out. I would deeply appreciate it if you could explain how this is done.
Thanks for your help, and keep up the good work.Steve Currier
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
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.
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
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.
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.