Some of you might wonder why we get so darn technical. I realize that some of the tech we put in CT might go way over some of our reader's heads, but in every article, there is something that might spark a thought in your head to where you go, “Wow, that makes perfect sense,” or “Hey, I never thought of it that way.”
We have Jim McFarland's Enginology column that goes very deeply into the functions and mystics of racing engines and a lot of the information and discussion is complicated. But when I read it, I try to understand the flow of the progression and I get in touch with the overall theme.
Then, as I read along, things start making sense. I was not always a chassis guy, I actually worked with engine builders when I was in my early and mid-teens. I cleaned the carbon out of piston grooves, measured crankshaft and rod bearing clearances with plastigage (yes, it was on the market way back then), and assembled the valvetrain, adjusted valve lash, and bolted down heads on rebuilt motors.
Most of you have a cursory knowledge of the simple things that go into engine building and chassis setup. In my current field of knowledge, the one I profess to know the most about, but not all about, I try to pass on the information I have been blessed to have attained.
I know I fail to make things as simple as they need to be at times. It's hard to translate sometimes. It's much easier to tell how to measure caster and camber, or tire circumferences and toe than to explain moment centers and the dynamics of a race car.
But what I wished our readers would do is what I do with Jim's Enginology articles, read along and follow the gist of the story. Try to understand what your car really needs and wants. Because that is what all of this engine and chassis tech is all about anyhow. It is finding exactly what the car, be it engine or chassis, wants in order to perform at its best.
Once we get that theme firmly in our minds, we can then open up our thought processes and apply the tech. For example, moment center location is not so hard to understand. Generally speaking, the farther left and lower the MC is located, the softer the front end is going to feel to the car.
The more right of centerline and higher the MC, the stiffer the front suspension is going to feel to the car. It will also feel those ways to the driver. Race car dynamic balance is also easier to understand if we think in terms of what the car feels and wants. The more the rear suspension wants to roll verses the front suspension, the tighter the car will feel. And the more the front suspension wants to roll verses the rear suspension, the looser the car will feel.
What the car wants is for both ends to want to roll to the same degree and then all is right in the chassis department. I used to compare that to two circus clowns in a horse outfit. If they move together and the back one follows the front one, all is well. But when one goes right and the other goes left, they look like, well, clowns.
It is the same for chassis and engines. When we give our motors what they want and need, then they run efficiently and produce the most power that the displacement and fuel mixture flow will allow. For the chassis, when we make it happy with a nicely balanced combination of moment centers, spring rates, and more, it will respond with the fastest and most consistent lap times and much better tire wear.
I'm personally going to try to keep making my writing more understandable and easier to follow as I get into the more technical areas of chassis setups. I'm also going to cover some of the more basic principles of chassis preparation and setup that are not too hard to understand, but at the same time are critically important.
All I ask of you, the reader, is to try to get a feel for why the particular article is written in the first place, where we might be going, and why, and then get out of it what you can to improve your car's performance. And then, if you have questions about the parts you don't fully understand, my email and snail-mail addresses are listed on the following page.
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, Senior Tech Editor, 9036 Brittany Way, Tampa, FL 33619.
Bumpstop Setups for a Rough and Bumpy Track
First, I would like to say I'm a big fan, and it was a pleasure to meet you at I-25 Speedway in Colorado. We were the group with the 45 car that won the feature that night.
I'm getting ready to run a new Lefthander chassis at Colorado National Speedway in Denver and was wondering if you could give me some advice on running a bumpstop setup for the track, or would you recommend staying away from that setup since it is a little rough?
I've always been pretty good at balancing a car with the SSBB setup, but haven't worked a lot on the bump stuff, but would love to start working with that style of setup. Any advice would be appreciative. I'm a shock guy, so what style of bumps should I use?
Thanks for all the hard work,
Good to hear from you. You ran a great race that night. As for running any type of bumpstop setup at CNS, you should know that track and how bumpy it is. It's not so much the roughness of the track as it is the extreme dips.
It would be marginally helpful to run bumps there, especially the rubber or plastic types. Various companies are experimenting with spring type of bumps and we did a test on a carbon-fiber disc type of spring that we used as a bump spring.
These provide more travel and are more forgiving when running over rough surfaces and tracks that have large bumps. I don't think I heard anyone say they ran bump setups at CNS when I was there. But that doesn't mean it can't be done. Just don't be too disappointed if it makes the car unstable due to the surface of that track. After all, CNS is a unique track in that respect.
As for the shocks, you need to run the rebound on the left front shock at around the same rate as the bump at 3 inches per second speed, which in most cases runs around 1,000 to 1,200 pounds per inch. And you need to have a “nose,” which is like a pre-load in a shock to where at very low speeds of less than 1 inch per second the rate is 200 to 300 pounds. On the right front, you can just use high rebound, but not as high as the LF and no nose.
Metric Four Link Rear Steer Tricks
I must say you do a great job in CT magazine and I think it's great what you do with the AMSOIL Great American Circle Track Tour.
I'd like to ask you a tech question. I saw your last article where you noticed at the Dells and Grundy there is a new trend about rear steer. You mentioned the RR wheel goes back on braking then goes to a neutral state in the center of the corner, then RR goes forward when accelerating out of the corner.
I too have noticed this on some competitor's cars and race a Sportsman asphalt car with a Metric four-link. How exactly would you get the rear end to do this?
I have never worked with this type of setup stuff, but I have heard rumors. Some teams will drill holes in the rubber bushings (one or more) in the right side of the Metric four-link rear suspension to make those bushings softer and compress more so than the left-side bushings.
If you can find different hardness (or softness) rear bushings for the car, or use neoprene bushings (usually stiffer) on the left side and leave the rubber bushings on the right side, you will also achieve the same results.
Here's how it works. When we brake, the rearend wants to move rearward, and if the right-side bushings are softer, then that side will move farther than the left side causing rear steer to the right and loosening the car on entry. This rotates the car in the direction of the turn.
At mid-turn, there are no fore or aft forces working to move the rearend and so it stays in its neutral position the same as it was at ride height, or hopefully square in the car. This part of the corner is usually of a very short duration.
Under acceleration, the rear end wants to move forward and if the right side bushings are softer, then the RR will move farther forward than the left side causing rear steer to the left which tightens the car coming off the corner.
What a team must do to exact the proper amount of rear steer (you can over do that), is to experiment with different softnesses for the bushings in the right side links to regulate the amount of rear steer. I have seen it work and it works quite well when tuned properly.
Metric Four Car On High-Bank Tracks
So I think I've read everything you've ever written on moment centers—at least twice. I race a Metric Monte Carlo in a Sportsman class at the Rockford Speedway in northern Illinois. It's a quarter-mile 20'ish degree banked track.
My main question is what are the tradeoffs related to rear spring split—roll angles—and forward bite coming out of the corner? The 50-pound spring split gets quoted often in regards to overcoming the high rear MC of the Metric four-link. When I model it in my setup program I get some high roll angles, around 5 degrees, with the 50-pound split.
It seems that the split is needed more to tighten the car on acceleration off the corner. Do you see a trade off here? For a 20-degree bank track the program advises to keep the roll under 1.5 degrees. To do this I pretty much have to even up the springs, say 175s in both the LR and RR. I haven't actually tried it yet but I think I'm gonna lose what precious little bite I have now.
My second question is, is it worth it to try the low crossweight setup when I'm trying to solve a chronic loose off (no bite) condition with my 55-percent cross setup? I feel guilty not following your advice there. I've read it probably a thousand times. It seems counter intuitive to shift weight from the LR to the RR when that happens all by itself.
The recommendation for a spring split, with a softer RR spring, is mostly useful for running on flatter tracks. With the high banking of Rockford, and I have been there a couple of times, you do not need to do that.
With the high banking there comes a high amount of mechanical downforce. This causes more roll due to spring split and the softer RR spring will definitely tighten the car too much.
What you now have is probably a tight/loose condition due to the unbalanced setup. Once you stiffen that RR spring and make it equal to or even stiffer than the LR, then the loose will probably go away. So, trust that when you balance the setup, you'll have plenty of bite off the corner.
Usually, we don't need to run the high crossweight for high banked tracks. You have a greater than 50 percent rear weight percent since you need to run the 55 percent low range. I would try to move the car close to a 50/50 front to rear percent. Yes, your crossweight percent will need to be lower that way, but trust that it will work.
Micro Sprint Moment Centers
I've been having some trouble setting up my dirt Micro Sprint. I'm following the chassis manufacturer's setup guide. My car is always very tight, and when I make changes, they have little effect. I would like to find the moment centers of my car, and really know what is going on rather than following an instruction sheet.
I have read and applied the theories in your Stock Car Setup Secrets book for a dirt Street Stock. Have you written a book on Sprints? I haven't been able to find much info on solid axle torsion suspension, and the ideal locations for their MCs in a Sprint. Is there a possibility of a future article in CT?
Thanks in advance,
In a solid axle suspension, the average height of the ends of the Panhard bar, or locating devise, is the roll center. In your case, the adjustment for heights might be limited.
If you are tight, you can adjust the spring rates of the torsion bars. To free the car up, soften the front bars or stiffen the rear bars, or only the Right Rear bar.
I find that in most Sprint Cars, they run stiffer front spring rates (either coil springs or torsion) than in the rear. There is usually more rear weight in those cars, so it makes more sense to run stiffer springs in the rear. The two suspension systems are the same, unlike in a stock car where the front is a double A-arm.
So, rather than trying to adjust the MC heights, try installing different rate torsion bar springs. If you go to www.circletrack.com and click on the MultiMedia tab, you will find a sway/torsion bar calculator that will get you close to the rates you are running. It uses an average steel coefficient number and yours may vary slightly, but it's the difference in bar rates you are looking for, so it will be OK for your use.
Run all of your torsion bars through the calculator and record their rates. Experiment like I said to soften the front and stiffen the rear, especially the RR, to achieve a more balanced setup. If you find a great combination that makes you fast, don't share that information, or it might end up in the manufacturer's setup sheet.
Cambered Tires for Stock Cars
Hello, my question is go kart racers and Legend racers all swear by cambered and cut tires, how come you don't hear more about this technology for dirt racing or asphalt racing? Is it out there and does it work?
Who would be the leaders in this industry? Any information in this area would be helpful since we have learned we are racing against someone who supposedly has cut tires.
Love the track tech! Thank you,
In stock car racing, we can adjust the cambers in the front wheels more easily than with karts or Legends cars. So, the cambered tires make up for not being able to get the correct tire camber.
Since you can adjust your front cambers, and with stagger you will have some rear camber, you don't need cambered tires. They would be way too expensive to build for the larger and heavier cars anyway.
Cutting the tread for a stock tire does help add grip because the grooved tires will roll over on the surface of the tire. So cutting them down adds grip. Dirt Late Model racers often groove and sipe (cut) their tires to add grip, but that is legal in that division. Most asphalt divisions that we know of, outlaw any kind of tire prep.
There is another factor to consider. The karts and Legends cars develop much more lateral force on asphalt and therefore the tires need more camber than a street stock or even a late model car due to tire roll-over.
When I ran a special race in my Sprint laydown kart at New Smyrna Speedway back in the mid-1980s, which I won, I never lifted and went more than 90 mph through the turns. I don't think a Super Late Model can do that.
By the way, racing karts on asphalt tracks with concrete walls is a stupid idea. Never try that at home. If your track does this, ask it to stop. I got lucky.