Selecting tire sizes and predicting changes in stagger is somewhat a "black art." The top teams always have a designated person who selects, sizes, and manages the tires. It is a very important job.
If you talk to a dozen of these tire gurus, you will probably get different opinions on the procedure. But, you will also find critical similarities in each one's process. The following are important points to consider when working with your race tires.
* Over-inflation Warning-Stagger is measured with the tires inflated to operating pressures. Safety Note: Some teams will stretch the tires by inflating them to very high pressures. DO NOT do this, ever. It is unnecessary and potentially dangerous. Team members have been seriously injured doing this.
* Match Stagger to the Racetrack-One of the most important considerations to know is that rear stagger should match the racetrack. Using more or less stagger than the track requires will ruin your handling. If it does help at all, it is usually a "crutch" and a more correct solution to your handling problems should be found.
A racetrack with a certain turn radius (average radius of both turns) will require a certain rear stagger amount. That number represents the difference in circumference of the two tires, the left being the smaller one, that would result in both tires turning the same number of revolutions through the middle of turns. This number should not change. The chart at the top of page 40 shows typical stagger amounts for different types of racetracks.
* Type of Rear Differential-Stagger influences a car using a spool (both axles locked together all of the time) rear differential on entry to the turns as well as through the middle and off the corners. With a "Detroit Locker" type of rear differential, the rear wheels are unlocked when entering the turns. The Detroit Locker will lock both rear wheels under acceleration and mostly affects handling off the corners.
* Less Stagger-Too little rear stagger will try to turn the car toward the outside wall and cause a push on corner-exit. That is because the front wants to go that way (toward the wall) anyhow due to centripetal forces, and a little help in that direction will quickly develop into a serious push.
* More Stagger-Excess stagger will usually show up as a loose condition because the rear tires are not able to turn the car to the inside of the track, and so one or both rear tires will slip, causing loss of traction.
* Important Considerations-Correct stagger is a must. To arrive at the best tire sizes, we need to consider: 1) The correct stagger amount for the track we are running, 2) How much each tire might grow and how soon, and 3) How to quickly solve a stagger problem using the four tires on the car.
* Correct Stagger-This is the amount of stagger that will produce equal revolutions of the rear wheels when driving around the turns. This factor is not a consideration at the front because the tires are not connected by an axle like the rear tires are.
* Front Stagger-A definite consideration for front stagger is stability under braking. Because there is a lot of weight transfer to the front under braking, the front tires and brakes work harder than the rears. If both wheels are turning the same number of revolutions, then the car will brake mostly in line with the direction the car is traveling.
If the left-front wheel is turning faster (i.e. a smaller tire circumference and therefore more stagger) than required, the car may pull to the left on entry under hard braking. If the front stagger is too little, the car may not pivot as needed and develop a push on entry.
The general rule is to maintain a front stagger amount that is close to the correct stagger needed for equal revolutions of the wheels.