How to manage tire temperatures for improved on-tr...

Tires: Scorching or Chilly?

First, let’s dispense with the notion that tires work higher once they’re “scorching” or “chilly.” The true reply is that each tire has an optimum temperature, one the place it’s at its grippiest on a given floor.

Talking in very common phrases, the explanation tires get grippier when scorching is as a result of warmth excites the molecules of the polymer that makes up their “rubber.” This pleasure softens the rubber, making it extra pliable and thus higher capable of squirm into the tiny imperfections within the observe floor, creating extra mechanical interface between the rubber and the street. Extra interface means extra friction, which implies extra grip.

Mainly, that’s why concrete surfaces have a tendency to supply higher grip than asphalt. Concrete has extra texture, that means extra nooks and crannies for the rubber to squirm into.

However you might have to run on older concrete, the place the floor has grow to be so textured that the tiny peaks and valleys can now not provide resistance in opposition to the tires shifting over them. These peaks subsequently break off, producing mud or gravel. That’s truly considerably analogous to what occurs when a tire will get too scorching: The polymer chain breaks, and as an alternative of remaining pliable, the tire begins to shed tiny (or not so tiny) items of overheated rubber.

Extra generalizations: Most devoted race rubber or R-compound DOT tires are designed for optimum efficiency when their carcass is hotter than ambient temperature. Why not design them to provide some wonderful grip proper off the pit lane? As a result of the inevitable stress and friction throughout use would rapidly overheat the tires to the purpose that they’d aggressively break down. Take-home message: Race tires are usually designed to provide their optimum grip at typical observe temperatures.

So-called road tires, however, have a tendency to provide their greatest grip at a lot decrease temperatures, and rapidly fall off when overheated. That is very true of the present crop of 200-treadwear tires which might be widespread in observe and autocross courses requiring road tires. However the best ranges for even these tires might be extremely variable. It’s common to stroll by means of a national-level autocross grid and see some opponents cooling their tires with water whereas others are utilizing blankets to maintain their tires heat. Every tire–and even every chassis setup–can have its personal candy spot.

The takeaway right here is to pay attention to the traits of your tires at totally different temperatures. Know what’s too scorching, what’s too chilly, what’s excellent, and measure in a constant manner. Skidpad testing and a pyrometer will assist decide best working temperatures.

Underneath Stress

The opposite huge variable with tire temperature is air stress. A tire is basically a spring, and roughly air stress modifications the speed of that spring, the form of the contact patch, and the tire’s interplay with the street floor. Plus, heating the tire heats the air inside it, and warmer air will increase in stress.

How a lot? Effectively, David Podolsky from Hen Hawk Racing confirmed us a helpful chart that he constructed utilizing information from a take a look at of his energetic tire heaters: Stress elevated slowly at first because the tire warmed past ambient temperatures, however the curve rapidly ramped as much as reveal a reasonably linear relationship between temperature rise and stress rise. His testing confirmed a 6 psi achieve in stress with a 75-degree bump in tread temperature alone.

Chart Courtesy Chick Hawk Racing

Even at decrease responsibility cycles, a modest improve in temperature–from round 100 to 140 levels, which might be pretty typical for a scorching day of autocrossing–confirmed a 3 psi achieve. That’s a couple of 10% distinction in tire stress as temps improve, so this variable is very price monitoring.

Getting Them Scorching

So, we’ve established that most often, some warmth past ambient temperatures is sweet for tires. How, then, can we construct that warmth?

Typically, with friction: the friction of the tire tread on the street floor and the friction of the brake pads in opposition to the rotors. All this friction contributes to warmth throughout the wheel-and-tire meeting.

The frequent trick of slaloming the automobile backwards and forwards throughout a tempo lap or an out lap can contribute some tire temperature. Total, although, it’s not one of the best ways to construct tire warmth, as there’s no sustained cornering to provide extended friction intervals. This method does, nonetheless, forestall the tires from accumulating gravel, preserve the driving force alert, and look tremendous cool.

A greater technique for producing tire warmth throughout tempo laps includes extended brake purposes, or brief intervals of exhausting braking. The longitudinal tread that friction imparts places extra warmth into the tread floor than lateral friction, and extra radiant warmth is produced by the braking system. Simply be sure that to test your mirrors first.

There’s additionally the choice of preheating your tires, and that’s the place Hen Hawk Racing and its tire heaters are available. Having up-to-temperature rubber on the out lap is usually a enormous profit, particularly when ambient circumstances don’t lend themselves to quick tire heating.

Pictures Credit score: JG Pasterjak

The Hen Hawk tire heaters begin at round $1650 for a set of 4 and may get a set of tires as much as working temperature in lower than half-hour. In our testing, we noticed durometer reductions of 15 to twenty% between ambient and working temperature, and the flexibility to exactly monitor tire pressures because the tires warmth in your pits is a big benefit.

The draw back to tire heaters is that many competitors venues particularly disallow them throughout racing. Even so, as a testing and improvement instrument, they will improve the effectivity and accuracy of your testing exponentially. They’ll additionally protect tire life by decreasing the variety of warmth cycles your tires endure.

Whereas we’re at it, let’s speak a bit about warmth biking and what it truly does. We talked about earlier that tires are fabricated from an elastic polymer. Correct warmth biking includes not simply heating–which weakens these bonds and makes them much less resilient–however bending and stretching of the tread, which helps extra constantly align the granular construction of the elastic tread.

When the tire is heated, the weakest molecular bonds are damaged after which realigned by the dynamic forces of the tread on the pavement. Because the tire cools to ambient temperature, these bonds relink in a stronger, extra constantly aligned trend. Tire heaters, however, preheat the tire to working temperature earlier than it’s despatched out on observe for a therapeutic massage; then they can be utilized to slowly cool the tire over 24 and even 48 hours.

Sure, you possibly can precondition tires a bit by merely heating them and cooling them with out the extra dynamic train. That’s higher than nothing, and strengthens a number of the weaker molecular bonds, however it’s not as thorough a course of as dynamic warmth biking.

Preserving Monitor

All this speak of tire temperatures and no dialogue of easy methods to take these measurements? Okay, right here it’s: Get a pyrometer. As for probe versus infrared, an infrared pyrometer that reads floor temps solely is not going to be as constant as a contact pyrometer that pierces the floor of the tire barely. The tread floor will shed warmth faster and extra variably than the portion of the tire slightly below the pores and skin, so readings with a non-contact pyrometer might be much less correct and extra variable.

Pictures Credit score: JG Pasterjak

That stated, a $30 infrared warmth gun–whereas inferior to a correct insertion pyrometer–is worlds higher than not taking tire temps. So don’t speak your self out of it simply because you possibly can’t get the final word instrument. No matter you utilize, simply use it constantly so your information might be simply in contrast from session to session.