The rear axle is located fore...
The rear axle is located fore and aft by both a forward link and also a connection to the torsion bar arm at the birdcage. This Z-link arrangement, if properly designed, can help keep the rear from rear-steering during bump and roll. Larrie Ervin
In reality, there are small differences in the spring mounting points as well as the heights of the panhard bars or other lateral location devices. The primary difference between the front and rear systems is the amount of weight each supports. This is important in planning out how we should spring our cars.
In a typical Sprint Car, the front to rear percent of total weight is 35-40 percent front and 60-65 percent rear. With more weight supported by the rear suspension, we would imagine the spring stiffness would be greater at the rear. Traditionally, all Sprint Car teams install either similar rate or stiffer springs at the front than the rear. Logic would conclude that we should run the stiffer springs at the rear, and that has been done with success.
This reverse "theory," as such, has been evaluated and some Sprint Cars have been setup whereas the rear springs were stiffer than the front springs. The cars setup this way had very good results.
Here, we can see the connection...
Here, we can see the connection of the end of the torsion bar arm to the bottom of the birdcage at the end of the axle tube. The torsion bar provides both spring rate and fore/aft location control of the axle. Bob Bolles
Remember early on that we stated these cars were typically tight and hard to turn. If the rear is sprung too lightly for the load it carries, then excess load transfer will occur at the front and the left front tire will have much less loading on it at mid-turn. In a worse case scenario, the car will carry the LF off the track surface. A three wheel car will not turn as well as a four wheel car.
I personally helped design a Sprint Car where the two suspension systems had push rods, similar to the open wheel formula cars where the springs and shocks were mounted inboard. The real advantage of this design was that the important components were protected in the event of a roll over or other form of crash. The push rods were simple and easy to make and could be replaced in minutes if need be.
This car was sprung stiffer in the rear. It won its very first and only race it ran. It was banned from competition from then on. The point here is that different designs can work. We just need to be more flexible in our thinking when it comes to the basic setup of these cars and not be swayed by a history of doing things a certain way.
The front straight axle is...
The front straight axle is located fore and aft by parallel radius rods. This helps to maintain caster in the axle while the car is rolling and moving vertically. Note that the torsion bar arm is resting on top of the axle tube. The shocks limit the amount the axle can rebound. Bob Bolles
Most Sprint Car teams don't scale their cars. Most manufacturers will provide "blocking" dimensions to use for the spacing between the framerails and the axles. These are set distances to be used with suggested spring rates so that the wheel weights will be "right" for the intended use. But this setup system leaves a lot to be desired.
Some teams will scale the car to use as a baseline, especially when the car runs well. Then they will try to repeat those wheel weights in the future. No matter which way you set up the weighing of your car, certain processes must be used to ensure consistency and accuracy.
The car should be blocked back at the shop on a flat concrete surface. Ideally, you would find four spots that are the same elevation to roll the four tires onto. As per the manufacturer's instructions, set the car on jackstands and block under the axles with predetermined height blocks. Set the adjusting bolts so that the torsion arms are neutral. This is a baseline you can use at the track to re-establish your weights, but that's not all you need to do.
This Mini Sprint Car uses...
This Mini Sprint Car uses a coilover front suspension. This system is not as popular with the full-sized Sprint Cars. Space may be a factor in the choice. Bob Bolles
Now that the torsion arms are set with the ride blocks, remove the blocks and set the car onto the leveled scales and record the wheel weights with the driver and fuel in the car. Record the tire sizes that result in those weights. If different tires are used later on, the wheel weights will change.
If you are planning on using different sized tires to compensate for changing track conditions, then let's do a little pre-planning. Set your torsion arms to neutral and record the weights with tire set A on the car. Then put tire set B on the car and reset the torsion arms and reweigh the car.
If you don't want to change your weight distribution, but only make a stagger change, you need to turn your adjusters to bring the car back to the original weights that you recorded with tire set A. Also, record the number of turns you made to the adjusters so you can recreate the adjustments at the track when you change tire sizes.