There's truth in what you say. In recognition that speedos are inherently inaccurate, the law (certainly UK law) states that a speedo must be within accurate within 10% at 30mph and at 70mph. However, there's also EU legislation that prohibits speedos from under reporting a vehicle's speed. To ensure compliance with both, speedos are calibrated to show a speed about 10% more than the measurement at the wheel.
www.autoexpress.co.uk
Speedos are unlikely to be getting more accurate unless they fundamentally change the way in which they calculate speed.Interesting article here
UK speed camera tolerances: Met police lowers speed limit enforcement threshold | Auto Express
The Met police has lowered its speeding enforcement threshold and speeding fines in London have gone up
Speedometers are getting more accurate and Police are reducing their speed camera thresholds.
My T6.1 Speedo is actually pretty accurate on stock 205/65R16’s
I think that you have to individually check your van with a GPS to be sure of how accurate your own speedo is and not go by others to a degree, as unless you’ve owned it from new, who is to say whether yours or theirs hasn’t been recoded at some time.
The article provides no evidence of increased speedo accuracy - it merely references a comment made by Edmund King (President of the AA): "King added that, with speedometers becoming increasingly accurate...”. Even if we accept that comment at face value, the accuracy of the speedo of an individual vehicle will vary as tyre pressure and tread depth vary across the lifetime of the tyres. Such inaccuracies are inherent in using the number of rotations to calculate distance travelled.
Well, it sort of does still apply. You're unlikely to get a speeding ticket if you're driving within 10% of the applicable limit - not because the authorities like to be lenient, but in recognition of the inherent inaccuracy of the speedo design (same reason the legal tolerance for speedos is 10% @ 30mph and 70mph). So, whilst you may be driving at 77 with your speedo accurately showing 77, someone else could be driving at 77 with their speedo showing 70 and the authorities have no idea if you're knowingly speeding or not (despite both speedos reading within required tolerance).
Tread depth isn't a red herring, it's merely one contributory factor to the inherent inaccuracy of speedos. Re tyre pressures, I was referring to reduced pressure due to lack of maintenance, rather than deliberately running tyres out of spec, (though there are also those who deliberately run their van at lower pressures in order to to gain comfort).
Hmm, I'm guessing the requirement not to under-report wouldn't have been applied retrospectively, so, theoretically at least. there'll still be cars on the road that that doesn't apply to. Re the discrepancy not representing a constant percentage, I can't offer an explanation based on how I believe speedos work.
In this case NAE is very apt...
I've considered this before. GPS has to be accurate otherwise it would drift off and you'd get lost! The only error I could see that would make speed inaccurate would be timing but that must have miniscule tolerances.
@PaulR83 Can you feed back when you’ve fitted them please
