Team owner and driver Troy...
Team owner and driver Troy Loomis recommends always returning your race car back to your baseline setup at the shop each week. This can help you see how any handling changes you made at the track have affected measurements in other areas.
Based on the IMCA-style Mods, Dirt Modified racing is one of the more inexpensive ways to get into full-scale circle track racing. The class seems like it has been around forever, and it's still going strong all across the country because the general recipe keeps the cars simple, easy to work on and fix, and (relatively speaking) inexpensive. We call it the IMCA-style Dirt Mod because that's the sanctioning body that is most widely known for these cars, and probably sanctions more races at this level than anyone else, but numerous racing organizations and tracks host this style of racing, so we're definitely not talking specifically about IMCA alone.
One of the key features of what we'll call the IMCA-style Dirt Modified is the stock front clip. Although the rest of the car can be constructed from scratch from steel tubing, the front clip, including the front suspension mounting locations, must come from an OEM vehicle. By far the vast majority of race car builders go with a Chevrolet Chevelle front clip, but there are others out there.
Theoretically, the stock front clip rule is designed to slow the advancement of technology, thereby making working with the cars simpler and cheaper. If it's kept stock, the conventional wisdom says that there will be fewer tuning options and that essentially translates into fewer choices for the racer to make.
The signature feature of IMCA-style...
The signature feature of IMCA-style Dirt Modifieds is a stock front clip, which also requires stock suspension mounting points. This means most handling changes will take place at the rear of the car with the exception of spring and shock changes.
However, over the past years we have stressed maintaining a correct front end geometry layout, including the bumpsteer, Ackermann, and roll center characteristics regardless of whether or not you have a stock front clip or a tube frame car. Make sure your car is correct for front geometry issues. You can refer to the numerous Circle Track articles already written on these subjects.
If you do your homework, you will benefit by having a car that turns much better allowing more turn speed and better bite off the corners.
With that said, we will make an assumption that your front end geometry is good to go. As a result, you will notice that a lot of the handling adjustments recommended here will be located at the rear of the car where making adjustments with the precision necessary for racing is much easier.
To find out more, we travelled to the race shop of Troy Loomis, a Dirt Modified racer located in Sherrils Ford, North Carolina. Interestingly, Loomis' day job is the shop manager for Michael Waltrip Racing's Nationwide Series race shop. Loomis began his racing career in the Northeast before moving to the South to work in NASCAR. He took several years off while concentrating on MWR's racing programs, but a few years ago he decided to get back behind the wheel himself and chose Dirt Mod racing as a good way to break back into racing. In 2009, he won the track championship at Wytheville (Va.) Raceway.
At the rear end, a four-bar...
At the rear end, a four-bar suspension like you see here is by far the most popular option on cars these days. Adjusting the four bars (two on each side) gives you a lot of options but how each change affects the car can be confusing to drivers who are new to this particular design.
We chose to work with Loomis because he offered to share everything he knew with us to help other racers go faster and be more consistent. You might think with his resources and contacts with a top-level NASCAR Sprint Cup and Nationwide Series organization, Loomis' car would be a piece of engineering art constructed in the MWR shops with Cup tricks that the average racer could not hope to have the engineering or financial resources to match.
Actually, nothing could be farther from the truth. Loomis races a BMS chassis (www.bmsmods.com) which he purchased from Close Racing Supply (www.closeracingsupply), which sells chassis to racers all across the country. Loomis' chassis is also not the freshest off the jig. It is, in fact, a few years old. Loomis says he plans to replace it eventually but it is still working so well for him that he hates to get rid of it.
"I started from ground zero when I got back into racing," Loomis says. "People think I had all the answers when it comes to setups because of my job, but this chassis and the racing is so different, it really doesn't translate. And it had been so long since I had last raced, all that knowledge was dated too.
"So I don't think I was that different than most racers when they are getting into this class. And the thing I did that helped me progress the fastest so that I was able to win the track championship-and a lot of people aren't going to want to believe this-is I purchased a chassis that is basically mass produced. Not because the chassis is anything magic, although it is a good chassis, but because of the knowledge that goes with it."
Raising the rear ballast (which...
Raising the rear ballast (which also includes the battery, which is also visible in this photo) can tighten a car that is too loose because it helps the car roll over on the right rear tire, helping it bite into the track more.
For starters, the Belleville Motorsports chassis, has had all of the previously mentioned front end geometry work completed by the manufacturer. On BMS' website it even states that, "We complete the 'homework' for our customers with a geometrically correct front suspension." What this means is that BMS has already worked out the geometry issues in the front so you can hit the ground running.
Beyond the front end, Loomis said that the customer service made a real impression on him. "A gentleman by the name of Joel Smith is the BMS representative at Close Racing Supply, and it has been his knowledge and willingness to work with me that has been invaluable.
"Joel has so many cars out there that are racing on so many tracks, he's able to gather more information in a single weekend than a team can in several years' worth of racing. So even if you are the first one racing one of those chassis at a track, he probably has somebody racing on a similar track somewhere and can give a baseline setup that will get you going in the right direction right away. I'm not saying everybody has to go and call my guy, but when you are getting into a class and buying a car, the level of customer service he offers after the purchase is definitely something that you should consider."
In this shot you can see where...
In this shot you can see where the J-bar mounts just to the left of the pinion on the rearend. Raising the mounting point here can help loosen up your race car on turn entry.
Loomis races a class that requires sealed crate motors for competition. The motor is the popular Chevy 602, which is the iron-headed 350hp V-8. It means he may be a little bit down on power compared to those racing with a built motor, but the setup adjustments still work the same way.
"The thing that racing a lower horsepower motor forces on us is we're always working to free the car up," he adds. "If the chassis gets bound up in the turns, it tends to bog the engine down and that just kills your momentum. There's not enough horsepower where if you get tight you can use the throttle to help loosen the car up by spinning the tires. So even though we may be different in that regard, I think lots of racers in these cars are keeping their cars free so they can drive them through the corners nice and smooth."
You probably are like Loomis and unable to use fancy adjustable shocks, but they can still be a valuable tuning tool-even if you have to spend the loot for two sets. Loomis says he's found that if the track goes dry/slick, one good way to help this without compromising a lot of other things is a swap of the shocks. On the right front try a shock with more rebound and on the left rear, switch to one with more compression.
Where the upper bar on a four-link...
Where the upper bar on a four-link suspension connects to the chassis can affect forward bite. Raising the bar at the chassis should help the car dig in and accelerate in most situations.
The idea here is to use the added compression on the left rear to hold that corner up and the rebound on the right front to force that right-front tire down and help increase traction on the front of the car. This, in most situations, should help steering.
Watch Your Tires
If your track doesn't require a specific brand of tire or you travel to tracks that force you to use a specific brand you may find yourself switching back and forth between Hoosiers and Goodyears-the two most popular brands among Mod racers. But even though they may be rated as the same size, when pumped up they can have quite different characteristics. If you have baselined your setup with a specific tire and bolt on a different brand, you probably will find things are a bit different. Loomis recommends going back and rechecking at least your stagger and chassis heights. The changes won't be big, but they can definitely be enough to change the way your car handles.
Adjustments For Turn Entry
If you are working to perfect your setup, a good rule of thumb is to always start at the beginning of the turn and work your way through. Even if the handling problem on turn exit feels worse than any problem you have on turn entry, never work backwards. This is important because handling problems compound themselves. You often will find that fixing your handling problem on turn entry will reduce the severity of the problems you are experiencing on turn exit.
The following are just a few of the handling adjustments Loomis recommends for specific situations and has noticed other racers using the most. There are definitely others, and some may work better for you. Still, these tuning changes are great to keep in your mental toolbox. Also, we're talking about fixing tight situations, but doing the opposite will help if your car is too loose.
Crew chief Randall Bradford...
Crew chief Randall Bradford helps Loomis scale the car. If you are looking for more forward bite, increasing your rear percentage can help this but it can also make you too tight on turn entry.
If your car is tight on turn entry you have several good options. First, you can raise the J-bar (essentially a Panhard bar that's curved to clear the driveshaft) at the pinion. Don't try to make a change bigger than a 1/2 inch at a time, and be aware that moving the J-bar without adjusting the length can move the rear end laterally. You can also lengthen the right-side wheelbase in increments of 1/4-inch.
Adjustments For Middle Of Turn
The middle of the turn is the area where the driver isn't hard on the throttle and is trying to get the car to rotate. These changes usually also help the entire turn.
A simple change that will affect handling in the center of the turn without compromising a lot of other setups is the height of the rear ballast. Moving the rear ballast up if the car is tight anywhere in the turn and down if it is loose. Loomis recommends avoiding the temptation to move the ballast weight back behind the rear axle as this can create an unpredictable pendulum effect. Also, even though you may have much more fuel tank capacity than you need for a heat or main event, don't add or subtract fuel as a way to adjust rear ballast. The problem with doing this is that your rear weight percentage will change as the fuel burns off. Instead, try to get a handle on how the car changes as the fuel burns off and compensate for that.
Watch out if you switch brands...
Watch out if you switch brands of tires. Although they may be marked with identical sizes, once aired up you may find that your stagger and frame heights have changed.
Another change if the car is tight all the way through the turn is to raise the right-side rear bar up one hole at the rear (next to the rearend). This, obviously, only works on four-bar rearends, but that is also currently one of the most popular rear suspensions.
Finally, the simplest-and probably most popular-adjustment when tight is simply to change the air pressure in the right-rear tire. Increasing tire pressure will help a tight condition all the way through the turn while decreasing the pressure by a half pound or so will help a loose condition.
Adjustment For Turn Exit
If you have your car working properly from turn entry through the center, you often will have few problems on turn exit that a gentle right foot can't handle. One adjustment that helps turn exit without affecting the rest of the turn too badly is the right-front spring (although it will affect turn entry some). Softening the right-front spring can help loosen up a car on turn exit, and stiffening the spring will do the opposite.
Adjustments For Forward Bite
Forward bite is the ability of your race car to accelerate without spinning the rear tires. This becomes a factor once you finally have the front wheels pointed straight ahead after you get out of the turn and you want to get down the straight.
Jack screws are an easy way...
Jack screws are an easy way to change both your frame heights and your weight percentages.
To increase forward bite you can raise the upper bars on both sides of the car next to the frame. Another option is to drop the front of the pull bar. The pull bar is what keeps the rear end from rotating counter-clockwise too much under acceleration. This works because lowering the front of the pull bar (without adjusting the length) will move the pinion angle on the front end down, which can increase traction.
Finally, you can also increase forward bite by increasing your rear weight percentage. This is simple to understand because the more weight you put on a tire the more traction you will have. But be careful with this adjustment because it can also make you too tight getting into the turn.
Don't Stack Adjustments
Finally, one last word of advice. We've just given you a lot of options when it comes to tuning your car. It can be tempting to throw a lot at your car at once. One word of caution here: Don't.
Loomis' advice is to always return to your baseline setup each week. When you get to the track and find you need to make adjustments to dial in the handling, make them one at a time and test them on the track before adding another. At the shop the next week, return your car to your baseline setup and check how much the settings have changed. If you find you are consistently making the same chassis change week after week, you can adjust your baseline to include it. Just be careful to always make one handling change at a time because as a rule, every change has secondary effects beyond the problem you are trying to address. It can be easy to make a couple of changes and have the secondary effects make the car mysteriously worse than before.
Loomis' Baseline Setup
During our visit, Loomis kept no secrets from us. He laid out his setup book and allowed us free access. So we thought we'd share his baseline setup. While we make it a policy to never give out specific chassis setups we are providing Troy's to give you an idea of what has worked for this track champion. Your specific needs will be different based on your chassis, engine, track, and driving style.
2,400 lbs after race (with driver)
Left/Rear Cross (Bite): 0-50 lbs
Front: 0-1/2 inch
Rear: 1/2-1 inch
Springs (Chevelle Front Clip)
LF: 2-4 degrees positive
RF: 4-6 degrees positive
LF: 3 degrees positive
RF: 4 degrees negative
Camber Gain: Less than 1 degree change
1/4 inch out (tracks 1/2-mile or bigger)
3/8 inch out (tracks 3/8-mile or smaller)