Speedometer is WAY Off!

Discussion in 'Mechanics Garage' started by Galo, Jul 26, 2008.

  1. Galo

    Galo New Member

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    So, I'll be going 85mph on Interstate on the bike and everybody else going the same speed also.
    So I took my GPS with me and sure enough, the speedometer shows anywhere between 6 and 13 mph off what the GPS displays.
    I can understand 1,2 or even 3 mph off, but when I'm going 70mph on the GPS, the bike speedo shows 84, WTF???

    Is there an easy fix on that, or will I have to take it to the dealeship?
     
  2. derstuka

    derstuka Lord of the Wankers Staff Member

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    Has the bike been re-geared (count front and rear teeth, and compare to stock numbers)? If so, you will need a speedohealer. Does it still have the stock tire profile?

    Bike speedo's are notorious for being off. My FZR1000 was 8-9MPH off at 80MPH.
     
  3. Galo

    Galo New Member

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    The only modification the bike has is the PowerCommander II, I put new tires but the same size as factory. Everything else is Factory.
     
  4. Al the old biker

    Al the old biker New Member

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    Typical...

    My 2004 was off by about 5% and my bike is bone stock. I checked it like you did, with my GPS and promptly bought a "speedo Healer" so I wouldn't be racking up mileage on the odometer without actually doing it. The speedo healer was super easy to install, they have instructions for a VFR with photos on the web site and even a calculator to give you the correction factor. Took about an hour including removing the left side fairing. $120 later, it's perfect.

    Cheers,
    Al
     
  5. mello dude

    mello dude Administrator

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    I went though the Speedhealer debate myself. The thing is if you correct the speedo, you induce errror into the odometer. Cant have both correct - bleah.

    MD
     
  6. Al the old biker

    Al the old biker New Member

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    I don't understand what you mean about error in the odometer. Does the odometer not read mileage based on input from the speedometer? My odometer seemed to change the some 5% that my speedo did after the healer was connected. It also seems to read perfectly now according to my trip log on my gps.
    Better than putting artificial mile on the bike which will (in theory) decrease the resale value more quickly...
     
  7. GWWalks

    GWWalks New Member

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    I could be wrong but I'm pretty sure that the error on the speedo is deliberately added by Honda as do most auto manufactures. I don't think I've ever heard of a speedo on a new vehicle under reading the speed (so you're going faster than you think). Its always the other way around. So if it is deliberate, then changing it would have an effect on the accuracy of the odometer because if Honda have setup the speedo to over read the speed but accurately measure the distance travelled, then changing the way the speed is read will change the way the odometer calculates the distance travelled.
     
  8. SCraig

    SCraig New Member

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    I keep posting this on forums and people never see it.

    Taking your bike to the dealer will accomplish nothing. Motorcycle speedometers HAVE to read high. They ALL do.

    Many states / provinces / jurisdictions have laws that motor vehicle speedometers can read up to 10% high but they can NOT read low by any amount. When a motorcycle goes into a corner it leans over onto the sides of the tires. This effectively lessens the radius of the tire meaning that the circumference, the length of one revolution, is less. To compensate builders force the speedos to read high on straights so that when they are in curves they do not. It doesn't matter whether the speedometer is driven from the wheel or the gearbox they are all based on the assumption that one revolution of the tire is "x" inches (or feet or meters or whatever).
     
  9. DANIMAL

    DANIMAL New Member

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    Yeah, I wouldn't think that mileage and speed calculations would interfere with each other.
    Mileage would be base on wheel revolutions times tire diameter and speed would be based on nuunber of wheel revolutions per unit of time.
    My 86 VFR had a speedo cable on front wheel, my 2006 must get the reading from somewhere else for the digital speedo gear box ECU maybe
    Does anyone know how the new speed or mileage is accomplished
    Inquiring minds
     
  10. Lgn001

    Lgn001 Member

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    My SV and the VFR are exactly 5MPH fast above about 40MPH, according to the California Highway Patrol-installed boxes that they put in construction areas and miscellaneous places.

    I looked through the 6th Gen shop manual, and I have concluded that it kind of sucks. There is a sensor called a "VS Sensor" located in the area of the countershaft sprocket, so I am assuming that it is counting either gear teeth or something internal on the transmission output shaft. Like I said, the manual is not really clear on many details about a lot of things.
     
  11. mello dude

    mello dude Administrator

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    The speedo and odo use the same sensor and acuracy is biased to the odo. So if you tweek the sensor for the speedo to be correct, you screw up the accuracy of the odo.

    http://vfrworld.com/forums/general-...metor-innacuracy.html?highlight=Speedo+healer

    If this heresay proves out wrong - I gots to know. I didnt buy a heeler because a correct odo is more important to me.

    MD
     
  12. eleman

    eleman New Member

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    Odometer off?

    Went for a couple hours ride yesterday with some friends who have Harleys. When we filled up, we were comparing mileage and my odometer was consistenetly about 5 miles more than his for each 120 or so miles. I read 112 while he had 107 on one fill up. He said his is right according to his GPS. I knew that speedometers are often wrong (showing faster than actual) but never heard anyone get into this discussion until now. Would a speedo healer bring my odometer back to correct?
     
  13. Galo

    Galo New Member

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    according to Mello Dude, "NO".

    When I took the GPS with me, I did not keep track of the miles, I will tomorrow. Gives me another excuse to ride!!:biggrin:
     
  14. mello dude

    mello dude Administrator

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    Let me know how it goes..

    Thanks,
    MD
     
  15. VT Viffer

    VT Viffer New Member

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    My '96 is not quite so bad - it reads about 4-5 mph fast.

    If you know your gear ratios (found in the service manual), and can calculate or measure the circumference of the rear tire, you can use this handy calculator:

    Ryan's gearing formula javascript page

    Very cool to use. I am going to measure (as opposed to calculate) the circumference of my somewhat worn rear tire ane re-do this...
     
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