Tyres: compound, wear and traction compound

Tyres are worth more than every other part of your setup put together. A mid-range car on the right tyre beats a beautifully set up car on the wrong one, and it is not close.

Compound and tread are two separate choices

Tread is the pattern, and it is chosen for the surface: pins for loose dirt and astroturf, blocks or ribs for hard-packed clay, slicks for asphalt and carpet.

Compound is how soft the rubber is. Softer grips better and wears out faster. The naming is entirely per-manufacturer — one brand's "soft" is another brand's "medium" — so a compound name only means something next to the brand.

The rule of thumb: softer for cold, smooth and low grip; harder for hot, abrasive and high grip. A soft tyre on a hot abrasive track goes off in five minutes and then feels worse than the harder one you did not fit.

Just ask

This is the one setup question where local knowledge beats reasoning from principles. The people at your club have run every tyre on that surface in every temperature. Ask what is working today. Most will tell you happily, and the answer will save you an entry fee's worth of rubber.

Carcass and inserts

Under the rubber, the carcass stiffness and the foam insert control how the tyre deforms. A softer insert gives more grip and more squirm; a firmer one gives better response and less roll. This is a real tuning tool on dirt, and one of the first places to look if the car has grip but feels vague.

Gluing

Do it properly, once.

1. Clean both the bead and the wheel with motor spray or isopropyl alcohol and let it dry. Mould release on new tyres stops glue sticking.
2. Fit the insert and seat the tyre evenly on the wheel.
3. Work around in short sections, pulling the bead back just enough to get thin CA glue in. Thin glue wicks along the bead; a big blob does not.
4. Let it cure fully before running.

A tyre that lets go mid-race usually takes the bodyshell with it. Check the beads when you clean the car.

Truing and wear

A tyre truer takes a new tyre perfectly round and lets you match all four diameters. Round matters more than the exact diameter: an out-of-round tyre makes the car hop under braking.

Wear does two things. Grip drops, which you expect. Less obviously, the diameter shrinks, which gears the car up — the same pinion and spur give you more rollout as the day goes on. Worth knowing when the car feels sluggish out of corners late in a meeting, and worth checking with the rollout calculator if you swap between new and part-worn sets.

Traction compound

Additive, sauce, whatever your club calls it: a solvent that softens the tyre surface to increase grip for a while.

Check the rules before anything else. Plenty of clubs and classes ban it, some allow only specific types, and some ban it outdoors and allow it on carpet. Using banned additive is cheating, whether or not you meant it.

Where it is allowed:

• Apply evenly and to the whole tread. Patchy application makes an inconsistent tyre, which is worse than a dry one.
• Timing matters. Most compounds want a few minutes to soak in and are then at their best for a limited window. Learn your product's timing and apply the same number of minutes before every run.
• Do not soak it. More is not more. Excess softens the carcass and takes the edge off response, and it shortens the tyre's life sharply.
• Be consistent front to rear unless you are deliberately using it to shift the balance — which works, and is a legitimate tuning tool where allowed.
• Keep it off everything else. It attacks paint, bodyshells and some plastics, and it will pick up dirt from the pit table.

Tyre warmers, where permitted, do a similar job more consistently and without chemistry — they bring the tyre to temperature so lap one is not a lottery.

Storage

Keep glued sets out of sunlight in a bag or box; rubber hardens with age and UV. Label sets with what they are and roughly how many runs they have done. A drawer of unlabelled tyres is a drawer of unknown tyres, and on race morning that is the same as having none.