Speedo inaccurate

[billywingnut]

My speedo reads  35mph when doing 30mph, I say this because I pass a camera in my car each day which I'm using for comparison. Can anybody suggest a company that can  calibrate it for me.

[Nurse Julie]

Contact Kent400 on the forum here, Peter Horton, he will sort it for you.
 peterhortongauges@gmail.com

[THUNDERDOWNUNDER]

I have a similar problem . My 400/4 has a speedo from 350/4 in mph . But down here in Oz we are kms . So I go past the friendly check your speed camera at 40 mph thinking I am doing 65 kms but the camera says 56 very confused!

[Trigger]

Never had a accurate 40 year old clock yet. Even on a modern bike I past a speed indicator spot on 30mph on the clock and the roadside indicator showed 28mph 

[Moorey]

They are made to read high otherwise the manufacturer could be held libel in some accident or speeding cases . It's the manufacturers safety margin.  Tyre size and wear also effects speedo accuracy. GPS ones are more accurate but then can be out when it come to taking bends and hills into account and need a clear view of satellites .

[Bryanj]

Other problem with gps(satnav) is they usualy give you an average reading from 10 seconds ago

[Erny]

They are made to read high otherwise the manufacturer could be held libel in some accident or speeding cases . It's the manufacturers safety margin.  Tyre size and wear also effects speedo accuracy. GPS ones are more accurate but then can be out when it come to taking bends and hills into account and need a clear view of satellites .

+1

this is standard rule, all bikes, cars etc have to show higher speed than real one due to above reasons, provided bike is fully up to stock specs incl. tyres (that is hardly possible today due to different tyres profiles).
I'm doing calibration by GPS and then stick small piece of highly visible red sticker on the clock to mark important limits - here in Slovakia 50, 90 and 130 kmh. As I have 550 and 750 with mph clock, it is even more important for me 
The rest I don't care much 

[kent400]

All good replies here, usually around 10% fast so the speedo mentioned is just a little over that. Unlike the old Smiths speedometers there is no external calibration adjustment, Japanese ones were calibrated when manufactured and are not to easy to re-calibrate. As the calibration is controlled by an internal hairspring it's likely that the spring weakens with age so all that can be done is to bend the bracket that secures the spring to place it under a little more tension. I re-calibrated mine by fitting it on the bike minus the body and com- pairing with a sat nav and managed to get it 'spot on'. Many stops and adjustments required! I could then use that one to check by comparison other speedometers.     

[Erny]

Normally, calibration is done on the bench - usually it should be 1000revs of cable = 60kmh. At least this is for bikes and cars I've been working on in the past.
But this assumes tyre is according to original spec. If you know original and new circumference, you can get difference and calibrate on the bench accordingly. But still the biggest difficulty is opening and then proper closing of gauge body

[Spitfire]

I was very surprised when I got my CB750F1 back on the road to find that the speedo is 7mph fast throughout the speed range. I was following my wife who was driving the car and was shocked at the speed that she was going through Liverpool with all the speed cameras there, later we drove along at 30, 40, and 60 mph me on the bike and her in the car and discovered the problem.
I thought it might be due to the 410x19 front tyre but the post from Mooray reminded me of hearing the same thing several years ago.

Cheers

Dennis