Advanced options
The trick the price tag hides: only tread above the 1.6mm legal minimum is usable. A new 8mm tyre sells 6.4mm of driving: a 4mm part-worn sells 2.4mm: so the "half-price" tyre often costs MORE per mm, plus a fitting fee per change, plus more frequent changes, plus buying someone else's unknown history (kerb impacts and repairs don't show). Trading Standards investigations have repeatedly found high proportions of part-worns on sale with defects. Budget NEW beats premium part-worn on the maths almost every time.
What The Part-Worn Tyre Calculator Works Out
- New tyre cost per mm: the price divided by the usable tread, which is the tread depth minus the 1.6mm legal minimum. A new 8mm tyre sells 6.4mm of driving, so a GBP 60 tyre is GBP 9.38 per usable millimetre.
- Part-worn cost per mm: the same sum for the used tyre. A 4mm part-worn sells only 2.4mm of legal driving, so the "half-price" GBP 30 tyre is GBP 12.50 per millimetre, and the per-mm division routinely shows part-worns costing 20-60% more than the new tyre beside them.
- Verdict: the percentage difference per millimetre. Even in the rare cases where the part-worn wins on paper, you are buying a tyre with an unknown history: kerb impacts, run-flat episodes and poor repairs do not show on inspection, and Trading Standards sampling has repeatedly found high proportions of part-worns on sale with defects.
- Fitting and balancing (advanced): the per-tyre fee paid on every change, typically GBP 10-20. Because the part-worn needs changing nearly three times as often at typical tread ratios, it pays this fee nearly three times as often too.
- Replace tyres at (advanced): the tread depth at which you actually change tyres. Safety organisations recommend 3mm because wet braking distances lengthen sharply below it; at 3mm a 4mm part-worn sells just 1mm of driving and the comparison collapses.
- Miles per mm of tread (advanced): how far a millimetre of rubber takes you, typically 2,000-3,000 miles depending on the car, the tyre and your driving. Used to turn tread into expected life.
- Cost per 1,000 miles (advanced): tyre price plus fitting divided by expected life. This is the honest way to price tyres and the number that makes budget-new beat premium part-worn almost every time.
- Expected life (advanced): usable tread multiplied by miles per mm for each tyre, with how many times more often the part-worn needs replacing.
- Cost over the comparison distance (advanced): how many sets of each you would buy to cover the distance, for the number of tyres you are replacing, including fitting each time. Twenty thousand miles is roughly two to three years of average UK driving.