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Gearing Change Effecting Speedo Reading - Solution?

Discussion in 'Technical Help' started by scotdoc, Oct 10, 2018.

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  1. scotdoc

    scotdoc New Member

    Jan 15, 2017
    2
    3
    Crewe
    I see a few threads about changing sprockets/gearing and comments about effect on speedo reading. Is this because the speedo now comes from engine revs/standard gearing calculation rather than the old fashioned front wheel spindle drive?

    If it is altered, is there a way of correcting it or do you just have to use mental arithmetic?

    I ask because I have seen about a 10% difference between speedo and tomtom mph since I swapped

    Russ
     
  2. Callumity

    Callumity Senior Member
    Subscriber

    Feb 25, 2017
    507
    250
    Nr Biggar
    It is only an issue if the speedo drive is from the gearbox output shaft and the ease of solution will depend on whether the drive is mechanical or electrical and availability of alternative cigs and dip switches. Sometimes GPS is the easiest option.
     
  3. Richard Neale

    Richard Neale Active Member

    Apr 20, 2018
    60
    28
    UK
    Will it also affect the TC and ABS on the latest bikes ?
     
  4. Red Thunder

    Red Thunder First Class Member
    Subscriber

    Dec 2, 2014
    999
    500
    High Wycombe
    IIRC bikes with ABS read the speed from the ABS sensor ring on the rear wheel so no adjustment would be necessary from changing the sprockets/gearing

    Bikes that electronically read from the output shaft should hopefully be able to be adjusted using TuneECU
    You can alter the ratio by + or - a few % I think up to 10% either way
     
    • Agree Agree x 1
  5. Richard Neale

    Richard Neale Active Member

    Apr 20, 2018
    60
    28
    UK
    That's interesting ! May explain why they don't offer the speed healer for some ABS bikes (including S3..) cheers for the info
     
  6. Glyn Phillips

    Glyn Phillips Member
    Subscriber

    Jun 21, 2018
    47
    18
    Essex
    If you find no way of altering the changes.
    Follow a friend at set speed limits take note and mark the speedometer at these points
     
  7. scotdoc

    scotdoc New Member

    Jan 15, 2017
    2
    3
    Crewe
    Using the satnav I worked out it is about 10% over reading ie; 30mph when indicated 33, 70 at 77
     
  8. BB3Lions

    BB3Lions If only your mum had swallowed
    Subscriber

    Jul 26, 2018
    142
    43
    Rochdale
    I just changed my front sprocket and I have no idea if my speed has changed or not as I don't look at it lol
     
    • Like Like x 2
  9. scotdoc

    scotdoc New Member

    Jan 15, 2017
    2
    3
    Crewe
    got caught by N Wales plod doing 33 in a 30 last year - 1 speed awareness course later I am keen to observe in town speed limits.
    Out of town is different - no point in trying to see the new drones;)
     
  10. BB3Lions

    BB3Lions If only your mum had swallowed
    Subscriber

    Jul 26, 2018
    142
    43
    Rochdale
    Keyword :)
     
  11. dilligaf

    dilligaf GRRRRRR
    Subscriber

    Mar 30, 2017
    3,347
    1,000
    Washington Tyne & Wear
    :confused: Dunno if it’s true but I thought you were allowed 10% speedometer error :confused:
    3mph=10% at indicated 30mph :)
    Think you could’ve argued against that one :confused:
     
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