BSB Mfg. Performance Driven
Selecting tire sizes and predicting changes in stagger is somewhat a black art. Top teams always have a designated person who selects, sizes, and manages tires. It is a very important job. Get it right, and the stagger works along with the rest of the setup; get it wrong, and the stagger works against everything else.
If you talk to a dozen tire gurus, you’ll hear different opinions on the correct procedures. But, you will also see critical similarities in each one’s process. These are important facts to know when working with race tires.
Stagger is measured with the tires inflated to operating pressures. Safety Note: Some teams stretch the tires by inflating them to very high pressures. Do not ever do this. It is unnecessary and potentially dangerous. Team members have been seriously injured doing this.
Match Stagger to the Racetrack
One of the most important bits of knowledge gleaned from the tire gurus is to match rear stagger to the racetrack. Using more or less stagger than the racetrack requires ruins your handling.
Only one stagger amount is needed for a particular track, and it is dependent on the track width, the turn radius, and the car’s tire size. Adding more stagger is a crutch and less stagger is a mistake. You can find a more valid solution to your handling problems.
A racetrack with a given turn radius (average radius of both turns) requires a distinct, pre-calculated rear stagger amount. That stagger number represents the difference in circumference of the two tires on the same axle, with the left the smaller one (for left turns), which results in both tires turning the same number of revolutions through the middle of the turns. This is truer in asphalt racing than dirt but the same applies, also it is hard to get stagger in a dirt tire, but do the best you can.
There is only one stagger amount you will need for a particular track. It is dependent on the track width, the turn radius, and the tire size. More stagger is a crutch and less stagger is a mistake.
Dirt Cars Stagger
One thing you need to understand is on dirt someone is not making our tires for each track like Nascar has, and the run out is not as great as it is for asphalt cars, but you can still achieve some stager. The other consideration is that dirt driver can over drive the tire were asphalt guys can't. I guess what I am trying to say is do the best you can because it will help but don't feel like you are at a disadvantage because you can't find the correct stager. Remember that stager in the rear of a dirt car is more important than in the front because it is hook to a solid axle, small amounts of stage, like 3/4 inch work well in a dirt car.
Stagger is the difference in circumference of two tires on the same end of the car. Take a measurement around each tire near the middle of the tread. Subtract the two measurements to find stagger, or roll out as it is sometimes called. Always inflate the tires to race pressures before measuring.
Here’s how to calculate the correct stagger for the inside and outside tires to rotate at the same RPM and follow the arc of the turn. This is for a flat track, although, the track banking angle does affect how much stagger is needed. Banking reduces the stagger amount. For instance, for a track banked 90 degrees, you need zero stagger.
Correct stagger is a must. To determine the best tire sizes, consider the correct stagger amount for the track, how much and how quickly each tire might enlarge, and how to quickly solve a stagger problem using your car’s four tires.
The correct amount of stagger produces equal revolutions of the rear wheels when driving around the turns. This factor is not as big a concern at the front because the tires are not connected by an axle like the rear tires.
One critical concern about front stagger is its effect on stability under braking. Braking causes a lot of load transfer to the front, and the front tires and brakes work harder than the rears. When both wheels are turning the same number of revolutions, the car brakes mostly in line with the direction the car is traveling.
In cases when the left front wheel is turning faster—with a smaller tire circumference, and therefore, more stagger—than required, the car may pull to the left on entry under hard braking. In cases when the front stagger is too little, the car may not pivot as needed and develop a push on entry.
As a general rule, you want to maintain a front stagger amount that is close to the stagger needed to create equal revolutions of the wheels in the radius the wheels are running in. The wheel radius on entry is much more than at mid-turn, so you need less stagger than at the rear of the car. This is more true on dirt, front stager is nice but not the most important thing we got going on, also remember that in some class or series of dirt racing you can’t get the right amount of stager you need because the tire will not allow it. Also in dirt unlike asphalt racing we over use our tires and we can because the track is not so hard on them, allows tire to slide without large amounts of damage. Over driving your tires on in the corners is not a good ideal even on dirt because it builds unwanted heat and wear on the tire.
As a ongoing thing it would be best to make one person in charge of tire perp and maintenance for your team, this will consist of several things and will be one of the hardest jobs you will do each week. It is best to make this a responsibility of one or two guys depending on how many tires you, because it will make him accountable for what is done each week. Things he will need to do each week.
Check tire pressure, before scaling and at the track.
Check tire stagger both cold and hot, add this to setup notes.
Check tire temperatures after heats and features.
Grove and sipe tires, keep them cleaned and sanded each night.
Check tire hardness and track heat cycle.
The hardest thing to do is to document all this to a good note system so you can determine that you are headed in the right direction with your tire program, please don’t do this in your head it will be lost information at some point.
Here are some grooving and siping technique to help improve your grip and tire wear.
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Special thanks to Bob Bolles for help in writing this page