Motorsport tyres

Circuit racing sizes are written differently from road sizes: 240/610R17 is 240 mm section width, 610 mm overall diameter, on a 17 inch rim. Overall diameter is given rather than an aspect ratio because in racing the rolling radius is a gearing decision and needs to be an absolute number.

Slicks are chosen by compound against expected track temperature and event length, not by grip in the abstract. A compound too hard for the conditions never reaches its working range and feels lifeless; too soft and it overheats, goes greasy and blisters. The right answer changes between a morning qualifying session and an afternoon race on the same day.

Wets are a different construction as well as a different tread. They run a deeper, more open pattern and a softer compound, and the water they pump through the tread is part of how they stay cool. On a drying line a full wet overheats within a lap or two and is destroyed rather than worn.

Road-legal competition tyres are ordinary sizes with extraordinary compounds: a minimal tread pattern, an E marking so the car can be driven to the circuit, and a treadwear rating that many championships use as the class limit. Where a series specifies a treadwear figure, that number is the regulation and the tyre either carries it or it does not.

They behave like race tyres in the ways that matter. There is a warm-up period before they grip, an operating window they need to stay inside, and very little wet performance at low temperature. Check the manufacturer’s guidance on low-temperature and wet-road use.

These are the highest-volume lines in the sector and the ones most worth holding, because track day and club-level customers buy them repeatedly and in complete sets.

Gravel tyres are built around survival. A tall, flexible sidewall soaks up impacts, a heavily reinforced casing resists cuts and delamination, and a deep, open tread finds drive in loose surface material. Tread life is measured in stage kilometres and is short by any road standard.

Compound is chosen by surface hardness and by how much of the stage is on the racing line: soft for loose and abrasive-free surfaces, hard for rough, rocky stages that would tear a soft tyre apart. Many crews carry both and decide on the recce.

Support inserts are used in some gravel applications to keep the car mobile after a deflation. They change the fitting procedure and the wheel specification, so establish whether they are in use before quoting a tyre.

Tarmac rally tyres sit closer to circuit slicks than to gravel tyres: a stiffer construction, a shallower tread and compounds selected for surface temperature. Sizes follow the racing convention of width and overall diameter — 235/610R17 — because the rolling radius affects the gearing on stages that may run from a standstill to well over 100 mph.

The complication in the UK is weather. A tarmac event that starts dry and finishes wet is normal, so cut slicks and patterned tarmac tyres exist to bridge the gap, and hand-cutting is regulated by the event rules where it is allowed at all.

Check the regulations before the catalogue. Tarmac rallying is one of the areas where series regulations most often restrict what may be fitted, including compound choice and the number of tyres a crew may use.

Historic competition is governed by period-appropriate specification. Sizes, constructions and in some cases tread patterns must correspond to what the car would have run when it was current, and the event regulations and the vehicle’s historic documentation define what is acceptable.

In practice that means a narrower choice, longer lead times and a handful of manufacturers producing period-correct patterns in small runs. Cross-ply and early radial constructions remain in production for exactly this market.

Never specify a historic fitment from the size alone. Confirm eligibility with the entrant and scrutineer against the current regulations before ordering.

Kart sizes are given as overall diameter by width on rim diameter in inches: 10×4.50-5 is a 10 inch tyre, 4.5 inches wide, on a 5 inch rim — normally a front, with the wider 11×7.10-5 at the rear.

Karting is the most tightly controlled category in motorsport for tyres. Most championships nominate a single make and compound, often issued and marked at the circuit, and anything else is ineligible regardless of how well it works. The regulations are the specification.

Kart tyre life is counted in heat cycles rather than kilometres. A set that has been through a race weekend can be visibly fine and several tenths a lap slower than a fresh set, which is why teams date and log every set they own.

These are two different disciplines with one thing in common: the rear tyres are consumables measured in runs. Drag racing uses purpose-built slicks or radials at very low pressures, with a soft, flexible sidewall that winds up under launch torque, and the burnout is part of getting them to work.

Drift is largely a road-legal tyre discipline, with front tyres chosen for grip and steering angle and rears chosen for cost per run, because they are destroyed by the hundred. Many series set a specification for the rears precisely to stop the spending.

Both are wheel-and-fitment sensitive. Low pressures, high slip and heavy sidewall deformation put demands on the rim and on bead security, so confirm the wheel specification alongside the tyre.

Hillclimb and sprint compress a race into a single run of under a minute, from a standing start, on a cold tyre. That inverts the normal compound logic: the tyre has to work almost immediately, so a quick-warming soft compound beats a more durable one even though it will not last a season.

Where tyre warmers are permitted the choice widens; where they are not, warm-up strategy and starting pressures are most of the setup. Class regulations decide which, so read them before recommending.

Volumes here are small and the buying is seasonal. Most competitors plan a year’s tyres in the winter, which is the sensible time to have the conversation about lead times.