Tire Stagger – How to check it. When to touch it. When to leave it.racingpartsales
What exactly is Tire Stagger?
Tire Stagger is the difference in tire circumference between the left and right side tires. Here in the United States we measure it in inches. On the front of the Chassis we measure the difference in size between the right front and left front tire. On the rear of the Chassis, we measure the size difference between the right rear tire and the left rear tire. When we are talking about tire stagger we are talking about the circumference of a tire. For the purposes of our tutorial, we are going to speak about stagger in circle track racing turning left. When turning left, Right side tires are larger. This is making assumptions about your racing circumstance. We are assuming that you are racing in a class that uses a locked rear wheel drive axle. If you are racing in a different type of class, that uses an open differential, then stagger is nothing more than weight on that corner of the car. The open differential does not care about size variation. Open rear axle racing will be the subject of another tutorial in the future. When we are only turning left, then we can concentrate on the following example. Think of our rear tires on our rear axle in the shape of a dixie cup, or in modern times a red solo cup. What would happen if we laid that cup flat on the table and then pushed it? It would spin in a circle! This is a quick way to always remember staggers effect on your car. The bigger the size difference, the quicker it spins. The reason why we need stagger is in a nutshell, to make the smaller tire turn the same number of rotations as the bigger tire as they rotate through the radius of a turn. This is in a perfect world where slip angles are at a minimum due to cornering forces. If we had the stagger just perfect, on a pair of tires fixed to an axle and gave it a shove in the beginning of a corner radius, it would rotate through just perfect without veering off one direction or the other. The tighter the radius of the corner – the more stagger needed. The larger the radius the less stagger needed. Short tracks that are 1/4 mile or so can end up in the mid 3″ to 4″ range depending on how tight the turns. The bigger the track, the bigger the banking, the more that need decreases. Superspeedways require fractions of an inch of stagger. Track width of the chassis and circumference of the track require differing amounts of stagger. If for example your left rear tire is 84″ and your right rear is 87″ – you are said to have 3″ of rear stagger.
When is the proper time to check it?
It is common practice in stock car racing to take a cold stagger reading and a hot stagger reading. Tires can “take a set” after an initial run in session. Taking a set means that they have went through a heat cycle. Lot’s of voodoo black arts mysticism gets thrown about as far as what happens in tires. What I can say for certain is this. Green fresh out of the mold tires do seem to behave differently than tires that are aged and have broken in. Another common mistake that happens is that people have the tire man just hand them the tire back without taking the tire up to proper air pressure just after the bead pops. This is a mistake. Always at the track, have the guy air it up to at minimum 30lbs of pressure. If you take a tire and mount it on the car without the bead being fully seated, 1.) You are going to have your bead seat at an inconsistent time. Your stagger will change when this occurs. It’s probably going to happen while you are on the race track, expecting predictability out of your set up. 2.) The bead can possibly roll off due to not being seated. If this happens at speed, the consequences could be catastrophic or at minimum, damaging the tire or your car. Take a few moments to fully air that tire, bounce it like a basketball and seat the bead. Your setup man will thank you. Your driver will thank you. Repeatability pays dividends in racing. The proper time to check the stagger is cold after bead seat and then let back to recommended air pressure. After the car returns from hot lapping check the stagger hot additionally. These are the proper times to check and record the stagger numbers on your car. Keep accurate notes with everything you do on your car. Especially tires. A minor stagger and or air pressure change can significantly alter the handling on your car.
what does the car feel like if the stagger is off or wrong?
Stagger can accomplish many different things for your handling, but this answer comes with a caveat. Stagger wont correct for long, effects that bad suspension geometry or an improper spring rate/bump stop/bump spring combo have on the car. Assuming the geometry is correct, too little rear stagger will make the car “push” or plow towards the wall in extreme cases. The technical turn for this condition is “understeer”. The old timer term is “When the front is gonna knock the fence down” Too much stagger will make the car “loose”, or free. The rear of the car wants to over rotate. The technical term for this is called “oversteer“. The old timers call this condition “When the ass is gonna knock the fence down” Stagger affects the car all the way through the turn. Most beginners feel the difference at the turn exit. As drivers gain experience, they can feel these effects at turn entry and mid turn. Even a novice can feel extreme handling woes due to the wrong stagger. There is only one proper stagger for the handling of a stock car on a given radius. If the car is experiencing tendencies other than a perfect feel and the stagger is correct, then another area of the chassis is inducing this problem. This part is where off season homework comes in. You have to have a balanced car to get through the corners. This next statement will offend many people, but if someone tells you your geometry and spring combo is right and you have to continually chase the chassis with major stagger changes to compensate, then you have other issues. (assuming your tires are fresh and not introducing handling problems themselves from being worn out)
What are the factors that change it?
If the car has a pushing condition, the right front tire is going to “grow” as any race goes on. It becomes a self fulfilling prophecy – if your chassis numbers were off for another reason, the characteristic in handling that this produced, is going to continue to get worse. A pushing car will continue to build heat on the right front tire – stressing and wearing out the tire and secondly that heat builds pressure. Pressure in a tire increases spring rate and reduces contact patch. Every one of those changes makes a pushing condition even worse. If the condition the car was experiencing was oversteer, then the right rear tire is the one building all the heat. The heat in turn makes the tire grow, and increasing the right rear tire makes a car more Loose or free. It also serves to increase the right rear spring rate of the tire, which adds to the problems the driver is feeling in the race car. A tight/midturn/snap loose off condition can make the right rear tire grow sometimes if you get excessive spin off the corner from that snap loose condition. This can be a tough problem for a novice to feel. A good solution is a go pro camera in the car and tape on the steering wheel. You need to see where your drivers hands are through the corners to ensure you understand what effects are making the stagger change. Normal racing is going to make for minor stagger changes. Chasing the chassis with very minor stagger adjustments is just a regular night of racing.
Do I use it to adjust the cars handling?
The quick answer to this is only as a very minor tuning aid. When you are at the track, it can be done, but it’s not the best time to be chasing chassis geometry. The adage is old, but true. Races are won during the week, in the shop in being adequately prepared. Doing the homework. Making sure nothing is bent or binding. Going through a complete chassis inspection and setup routine is how you win consistently. Yes there is the occasional lucky dog who lets his car sit in the trailer all week and comes out and pulls off a win. The safe money bet on consistency in handling is the team that does their homework. An 1/8″ change in stagger on the rear of the car is a chassis altering change if everything else is right. If you are having to make bigger jumps than this, It’s probably a deficiency from another area that you are chasing. If you have two right side tires that you are running, and one changes a great deal more than the other, The least finicky spot to place that changing tire is on the right front. The rear is far more sensitive to stagger changes. (remember our solo cup) Same thing for the left sides. If a tire you are stock working with, is put the larger changers on the front. Try and keep the consistency on the rear. We heard an adage from an old timer once that stuck with us. “If she’s pushin- close the front and open the rear. If she’s loose- open the front and close the rear”. If you can remember that and the red solo cup example, you can do you fine tune tweaking at the race track. Once we found our sweet spot with stagger, we went back to the same baseline each week and just made minor changes due to the weather conditions vs track conditions.
What is the difference in stagger use on a bias ply tire vs. radial tire?
Air pressure in bias ply tires changes the Stagger of the tire and the tire spring rate plus the cross weight of the car. Yes tires have a spring rate. In radial tires, air pressure only changes the spring rate and cross weight of the car. We have had success in heavy Street stock cars on radial tires, all the way down to light weight Bandolero race cars on bias ply tires. We were amazed at the amount of diagonal weight (wedge or bite) that changed in the car with simple air pressure changes. Same thing happens when you change air in your 2850lb Late Model Race Car. Spring rate and wedge changes. This will vary depending on the type of car you are racing, with the type of tire. You’ll have to do your own comparison testing. We bought a tire spring rate tester from a friend who had great success in the go kart world. We made adaptors for the intercomp tester to be able to accommodate the taller Bandolero tire and wheel. The results were amazing.
In conclusion: Can I not touch it? Do I have to chase it?
In our personal experience, if you’re running the same track each week, with a long tire life expectancy of a car like a Bandolero- You can sometimes not have to touch the stagger at all. Of course we checked it – and we changed the air pressure up or down to keep the stagger exactly the same as our “sweet spot”. On our big heavy car (street stock) after we got fast we worked very hard to get the exact same number for stagger each race night. Maybe an air pressure change on the left front up or down, and maybe a 1/4 turn on the sway bar if need be. We are going to work at finding a plug in to make an interactive program here for the blog that you can just punch your tire numbers in to, and it will spit out the recommendation. If that is something you are looking for please let us know in the comments below. If you’re good at math you can perform the calculations yourself. This will be an example only. You have to type in your own numbers.
Radius of Inside Tire = 200ft or 2400 inches (convert to inches multiplying the track radius in feet x 12″ for example 12″x 200′ = 2400″)
Radius of Outside Tire = 2465 (2400 inches + (Trackwidth center of tire to center of tire) 65″ = 2465″ for example purposes)
Outside of tire travels 2465″x2xPi(3.1416)/2=7744″ inches
Inside tire travels 2400″ x2xPi/2= 7540 inches
Outside tire = 85″ in circumference
Inside Tire =85″x(7540/7744)=82.75
Correct Stagger = 85-82.75 = 2.25″ of stagger for that particular radius/trackwidth combination.
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