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Tyres: choosing, pressures and temperature

The only point of contact with the road — the most important modification and often the cheapest in gain per euro.

The tyre is the only point of contact between the car and the road — four patches the size of your palm through which everything the car does must pass. That makes it the most important modification of all, and often the one that gives the most time per euro. This guide shows how to choose the right tyre for the use, and how to get pressures and temperature right.

Why the tyre rules everything

Before spending on power, brakes or suspension, sort the tyre. The best damper in the world won't make up for a wrong or cold tyre; a good tyre, correctly inflated, transforms a standard car. It's the top of the order of priorities for a physical reason.

Types of tyre — and what they're for

From the most "road" to the most "track":

• Sporty road tyre (UHP) — good for mixed use and first track days; copes with rain and daily driving.
• Semi-slick (low treadwear, ~200–100) — far more grip in the dry, the jump most people feel most; less life and worse in the wet.
• Slick — no tread, dry competition only; maximum grip, needs temperature and rules that allow it.
• Wet — a tread pattern to clear water; a must-change when the track gets wet.

The treadwear (TW) marked on the sidewall is a good indicator: the lower it is, the more "track" (and less durable) the tyre tends to be.

Pressures: cold and hot

The correct pressure is measured hot, after a few laps. Over-inflated, the tyre rides only on the centre, goes "greasy" and wears in the middle; under-inflated, it rolls onto the sidewall and wears on the shoulders. Start from a recommended hot target for the tyre, measure as soon as you come off track and adjust cold to reach it. Road, track and hillclimb call for different values — note yours.

Temperature: the window and how to read it

Every tyre has a temperature window where it grips best. Cold, it slides; overheated, it goes "greasy". With a pyrometer (temperature probe) read three points — outer, middle and inner — right after coming in. Much hotter on the inner edge usually means too much camber; hot shoulders and cold middle means too little pressure. It's the cheapest way to tune tyre, pressure and geometry together.

Common mistakes

• Slicks in the rain — dangerous and, in competition, forbidden; switch to wets.
• Mixing types across the four corners — unbalances the car (and in competition leads to exclusion).
• Old or "cooked" tyres — the rubber hardens with age and heat cycles; a cheaper new tyre beats an old top-end one.