How Accurate IsYour Car’s Speedo?

Thursday, 16. May 2019

Auto Express investigated how accurate the speedometers were on 10 cars were. They did this by comparing how fast the speedos said they were going with the actual speed, revealed by a VBox meter.

Car speedometers are not allowed to ‘under-read’ – they can’t tell you that you’re going more slowly than you really are – but they are allowed to over-read by up to 10 per cent plus 6.25mph. So they could read 50.25mph at 40mph.

All the cars that were assessed were well within legal limits, although some read with near-perfect accuracy, while others over-read by 3mph. This, with the different approaches police have to enforcing limits, means some variance will always remain around speeding.

Commenting on the investigation, AA president Edmund King said it is “sensible to have some flexibility” with speed-limit enforcement, “as the last thing we need is drivers concentrating solely on the speedo and not the road”.

King added that, with speedometers becoming increasingly accurate, “Auto Express’s testing is a valid reminder to drivers not to gamble on their speedo perhaps providing some leeway”.

The speedo accuracy test explained:

The VBox is a clever piece of kit that uses a GPS signal to measure a car’s speed. It’s very accurate, gauging velocity to within 0.1km/h, so is perfect for assessing speedos.

They set their test cars to 30, 50, 60 and 70mph using the built-in speed limiter or cruise control to ensure a steady speed, then used the VBox to measure how fast they were going. This gave them a fair idea of the discrepancy between actual and indicated speed.

“Not many drivers have access to a VBox, but a separate smartphone app or sat-nav can give you an idea of how accurate your speedo is. Here are the results of the tests:

Model	True speed at indicated 30mph	True speed at indicated 50mph	True speed at indicated 60mph	True speed at indicated 70mph
Kia e-Niro First Edition	27mph	47mph	57mph	67mph
BMW i3s	28mph	48mph	58mph	68mph
SEAT Arona 1.0 TSI 115	29mph	49mph	60mph	69mph
SEAT Tarraco 2.0 TDI 150 manual	29mph	49mph	59mph	68mph
Skoda Kodiaq 2.0 TDI 150 manual	28mph	48mph	57mph	67mph
Peugeot 5008 BlueHDi 130 manual	28mph	48mph	57mph	68mph
Volvo XC40 D4 auto R-Design	30mph	49mph	59mph	69mph
Mazda MX-5 2.0	27mph	48mph	58mph	68mph
Dacia Duster dCi 115	28mph	48mph	58mph	68mph
BMW 330i M Sport	28mph	48mph	57mph	67mph