SOHC.co.uk Forums > CB350/400
Speedometer speed vs GPS speed
taysidedragon:
--- Quote from: Bryanj on August 06, 2025, 11:20:03 PM ---Follow an english hgv on the motorway, speed limited to 90kph(56mph)
--- End quote ---
😁 Not the ones I got stuck behind a few times today on M5 and M6!
Athame57:
--- Quote from: TrickyMicky on August 06, 2025, 10:43:35 PM --- If you feel brave or cheeky enough, you could ask your local friendly ;police traffic pfficer or motorcyclist to follow you for short periods at set speeds.
--- End quote ---
Nah....you'll end up getting nicked! ;D
TrickyMicky:
--- Quote from: taysidedragon on August 06, 2025, 11:33:25 PM ---
--- Quote from: Bryanj on August 06, 2025, 11:20:03 PM ---Follow an english hgv on the motorway, speed limited to 90kph(56mph)
--- End quote ---
😁 Not the ones I got stuck behind a few times today on M5 and M6!
--- End quote ---
Just to help with a common misunderstanding, I think we all agree that virtually all car and motorcycle speedos are not 100% accurate, so it is a regular occurrence when following a vehicle fitted with a tachograph, to accuse them of speeding. Also, when we are driving our car/motorcycle, we may hold a steady speed to the best of our ability, then , when the road starts to climb gently, we look at our speedo to see we have dropped maybe 3 or 4 MPH and open the throttle to regain our previous speed. The truck or coach behind you is running on cruise control or speed limiter, and as soon as the speedo starts to drop, even minutely, it allows more power to the engine, leaving us declaring "that cheeky git has just accelerated past me". When I first drove a coach with a limiter, it was a peculiar feeling at first when you felt more power being applied at the very beginning of an up-slope, this would happen far earlier than if you had been driving "manually", and the speedo did not move at all.
Bryanj:
Plus all trucks for the past 3-4 years have to have the auto braking if you get too close, lane nagging and most have a gps type cruise control which eases the throttle at top of an incline and puts more n climbing one
Mikep328:
Went out yesterday and, during the ride, checked the speedo vs the Tach using road test data from 1975 showing 11 MPH per 1000 RPM in top gear. At an indicated 60MPH, the tach showed 5000 RPM. SO the actual speed, assuming the gears/sprockets are OEM spec (yes) and the tires are OEM size (yes) was 55 MPH.
Of course, whether the tach is accurate is another question! ;)
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