Part One - Dirt Designs And Evolution
Rear steer in a circle-track car is an effect caused by suspension movement. Dirt racing generates more chassis movement than what we see on asphalt. Under the right conditions, RS can be beneficial and enhance performance. Under the wrong conditions, it can ruin your handling. Much of the difference depends on the track conditions, which we all know change quite a bit on dirt tracks. We don't necessarily need to know the exact amounts of rear steer our cars are subjected to, but we do need to have a solid understanding of what produces RS and what effect it has on the handling in our cars.
Here we see the extreme, lots...
Here we see the extreme, lots of rear steer and lifting the left front wheel off the track. A four-bar Dirt Late Model rear suspension is designed to have a large range of rear steer. The adjustability allows the racer the opportunity to make adjustments for the changing conditions that occur on dirt surfaces. The attitude of the car on dry slick tracks can be quite radical.
The first and foremost fact related to RS is that it's caused by rear suspension movement. As the rear corners of the car move, along with the controlling arms that locate the rearend fore and aft, each side can move the wheel on that side forward or to the rear. Obviously, if both of the wheels didn't move or moved in the same direction by the same amount, we'd have zero rear steer. It's when one wheel moves more than the other that we have rear steer.
Rear steer can either tighten a car or make it very loose. Not only does RS affect the entry and middle-handling balance, it affects the handling under acceleration due to the thrust angle of the rearend being either right or left of the centerline of the car. In dirt racing, it may be advantageous to incorporate a larger amount of rear steer under certain conditions.
A rearend that is steered to the left of centerline will cause the thrust angle to be left of centerline and make the car tighter on entry and tighter on exit under acceleration. A rearend that is steered to the right of centerline causes the thrust angle to be pointed to the right of centerline and makes the car looser on entry and looser on exit under acceleration. Knowing these basics, we need to look at each type of racing to see how RS affects each type of car and how we might improve our performance using RS.
What Do The Experts Say
Is rear steer an important tuning tool? Opinions have changed for some. Five years ago we asked Joe Garrison of GRT Race Cars and Mark Richards of Rocket Chassis if RS was important in dirt racing and both said that having RS capability in a dirt car was critical. "Rear steer helps the driver get the rearend around on dry slick tracks without having to break the rear tires loose," Joe said. Mark said that "if the driver has to counter steer the car a lot, you need more rear steer."
Keith Masters of MasterSbilt Race Car Chassis told us that "the reason chassis builders build four-bar cars is because of rear steer. The entry is more important to design for than the exit, as far as rear steer is concerned." That echoed what Joe Garrison said in that keeping the rear tires connected to the ground going in and through the middle helps to provide traction off the corners too. So a smooth entry provides a faster exit.
At that time, we also talked with Sanford Goddard of Warrior Race Cars and he told us that his group of racers work with rear steer less than some other dirt teams although he feels that using a degree of rear steer is very important at times. He said, "Rear steer definitely helps get into the corners on dry slick tracks, but you can put too much rear steer into the rear suspension. A lot of guys take that to extremes."
C.J. Rayburn, of Rayburn Race Cars, has been a driver as well as a car builder and echoed much of what the other builders had to say in an earlier interview. "We have always wanted rear steer," he said. "Rear steer is important in any design of dirt car." C.J. builds the swing arm-type of rear suspension that typically produces less rear steer than the four-bar cars.
Today, we see a different attitude among many dirt car teams and manufacturers. A trend that has taken hold is one where the car runs flatter, has less body roll, and where the rear bars are positioned for less rear steer. That's the evolution we alluded to in the title of this article.
With the rearend pointed to...
With the rearend pointed to the left of centerline, the steering will cause the rear of the car to want to run under the front end, causing a very tight condition, especially under acceleration. This never happens on dirt. Typically, dirt cars are hard to turn anyway and this would only make the situation worse.
With the rearend pointed to...
With the rearend pointed to the right of centerline, as typically happens with Dirt Late Model cars, the car will be freed up going in, through the middle, and possibly loose off the corners with the rearend wanting to run around to the right of the front. This is why you see dirt cars sideways. It's not that they are sliding the rear tires, it's the rear steer moving the rear to the right in relation to the front tires.
If you notice, the No. 0 car...
If you notice, the No. 0 car of Scott Bloomquist is driven and set up for a more straight ahead attitude as opposed to the No. 45 car. This has been the design for Scott for more than a few years. He discovered long ago the advantages of less rear steer and more balance in the setup.