How we tested them

WE tested two types of system: external sensors that replace the valve caps, and those that are fitted inside the tyre. The former are easier to set up with tools provided, but the increased weight affects both valve stems and balance.

Internal sensors cost more and require professional fitting. We used Kwik Fit to install ours; it charges around £10 per tyre.

The test compared readings at 22, 36 and 44psi against a calibrated gauge (above), plus reaction times and warnings. Consistency of readings was also rated over a 50-mile drive, as were online prices, correct at the time of testing.