I'll say it now. tires are the MOST import part of any suspension. and should be the FIRST modification... then setting the suspension to make those tires work should follow. buy the best tires your racing class or budget will allow. and if you tune your car to take advantage of those tires you will ALLWAYS be faster then someone that is chasing the math.

My tires are a spring?

Yes the only TRUE unsprung weight on any car is the tire itself, not only is that weight truly unsprung, but it also has the most rotational inertia in the entire drive train system, This is why you'll see "True" racing tires as light as possible. one lb of tire weight is equal to 8 lbs off a flywheel. so that fancy flywheel does not seem so important now. even some R-compound tires continue to use old fashion cloth radial bands to keep the weight down. while this practice was okay with flobbery bias ply tires, when applying it to radial tires it tends to make them less then streetable. since the radial bands actually support the weight of the car and do not just hold the tire together. but we are not here to talk about tire technology details. that could take a whole other FAQ.

What you need to know is the stiffness of the tire directly effects the dynamic spring rate. A stiffer carcass will deform less under cornering and transfer more of that weight to the contact patch as will stiffer springs. in retrospect a softer or taller sidewall will transfer less road vibration into the suspension and offer a softer ride.

what is best. well for performance as light as possible and as rigid as possible while these things might seem not to go hand in hand a true racing tire can achieve both of course it does not have to worry about sustaining it's rigidity over 30,000 miles or handling potholes, neither of which racing tires are known for.

A new terminology has cropped up since I first started tuning cars. it's called "tire spring rate" and it took the invention of the run-flat tire and it's effect on ride quality to raise the eyebrows of tire engineers.

Keep in mind a tire IS a spring, and that spring rate is variable with pressure. however also keep in mind a tire is almost a living breathing part of the suspension, it has an internal damping, which can be overcome essentially with too much air pressure, in addition the tread surface has a tendency to bow out (reduce contact patch) with too much air pressure. so while stiffer tire spring rate can help handling... like EVERYTHING else we discuss here there are limitations. and that all depends on the construction of the tire, rim width, and what you are asking it to do. This is why racing tires cost up to $600 each and you can buy a pep-boys special for $25. there is as much technology in a set of tires as in the rest of the suspension of your car. and this can be proven by taking a standard road car and fitting racing tires on it. it will lap a track 5-7 seconds faster then the standard car, where a full suspension kit might only provide 3-4 seconds on the same car and track.


So what is the "Gription" thing you keep mentioning. well it's a combination of traction and grip. neither word perfectly explains what is going on when a tire is being used in a racing environment. when a tire reaches it's optimum temperature, there is actually a physical bond between the road surface and the tread surface. many times this exceeds the friction provided between rim and the tire so in some racing they actually use glue or screws to fasten the tire to the rim. this is also why you will see black marks left from a car when not visibly sliding left from the tires. the friction between the surface of the tread and the road has exceeded the friction between the rubber molecule and it's neighbor molecule. so that small part of rubber stays bonded to the road surface instead of staying with the tire. as you can imagine that's A LOT of grip and really only common with true racing tires and only in a small temperature range.

this also explains racing tires terrible reputation of being unforgiving at the limit. as the tire reaches it's optimum tempature it grips more and more (a street tire is almost never designed to reach this temp) and when you exceed that temp it begins to slide, well. then it gets hotter and slides more. this is commonly referred to as a tire getting "greasy" so when it lets go it usually does so in a speticualar display of smoke and in RWD a spinning car , or fwd a car that cannot stop occasionally into a hard object. so we don't want that.

This is why you'll see racing tires available in several compounds, with engineering data so you can tailor the tire to the track and driving style as to approach the limit of grip but not exceed it. This is also why you'll see a Drag car do a smokey burnout, to bring the temp beyond the designed maximum so when they line up it will have cooled close to the optimum. providing a much cleaner getaway and in turn a lower ET. and yes a burnout can help a street car launch, but without the technology and perfect temp known, it's very hard to predict how much heat and when to line up. done right it can shave a lot of time from a drag racing time, done wrong... well a powerful car will spin the entire quarter mile.