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Speedometer drive

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JezzaPeach:
My speedo reads 4-5mph or say 10% too high. Does anyone know if there is a drive gear that would fit that would get this more accurate? Thanks in advance.

Johnwebley:
This is not going to be very helpful,

But all my bikes are similar

Maybe 12% higher than the correct speed

And I fit the correct tyres

Just think of being a money saving device

No nasty speeding fines



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badger_eng:
If that’s 4-5mph at 30mph, that’s bad.

If it’s 4-5mph at 100mph, that’s not far off being normal. Most speedos read fast. My 2026 Suzuki digital speedo reads about 3mph fast at 75mph. My 2023 Kawasaki was very close at 1mph fast at 70mph. These were measured Vs GOOGLE maps. The only standard in all of the tests was GOOGLE maps.

Have you changed the tyre profile / size to make this suddenly worse or has it been like this all the time?
If the unit is mechanically sound, the magnitude of error should be constant at a constant speed (always 4mph fast at 30mph for example and a larger error at say 70mph), if the error varies at the same constant speed then the speedo drive, cable or speedo itself will likely be the cause.

I haven’t started my Honda resto yet but the two Suzukis (1974 & 1976) I have previously done used the same wheel mounted speedo drive using the same ratio. There was no option to fit another type or a slightly tweaked ratio.

Bryanj:
There is no option for drives or head, all speedos read high, at one time the legal tolerance was +or- 10% but i believe the - has been removed so you cant argue in court

McCabe-Thiele (Ted):

--- Quote from: JezzaPeach on September 11, 2026, 10:07:00 AM ---My speedo reads 4-5mph or say 10% too high. Does anyone know if there is a drive gear that would fit that would get this more accurate? Thanks in advance.

--- End quote ---

How are you measuring the actual speed against the indicated speed?
If its a Satnav - thats pretty standard.
Construction & Use Regulations  at the time allowed for 10% inaccuracy.
How far out is your oddometer, might be worth checking it against fixed road markers for accuracy.

Lastly the damper oil in the speedometer might need fixing, pretty sure there are fixes that clock restorers like KENT400 (Peter Horton) could advise you on.

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