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Thread: 88 R100RT odometer off

  1. #1
    Registered User
    Join Date
    Jul 2006

    88 R100RT odometer off

    Hi Guys
    My summer house is 150 miles away, have rode there many times. My new to me 88rt reads only 130 miles for this trip. So the odometer is off. Is the speedo off too?
    What do you guys think, what is the math adjustment, and what is the repair.

  2. #2
    Registered User toooldtocare's Avatar
    Join Date
    Mar 2008
    Lake Saint Louis, MO
    I have never owned an airhead that did not read at least 8 miles off at 60mph. I repaired the odometer on my 78RS, it was slipping. There is a link someplace here on how to do that. While inside the unit I pulled off the needle and repositioned it so it would read correctly at 60. There is also a thread someplace here on how to do that.


  3. #3
    Registered User kgadley01's Avatar
    Join Date
    Dec 2006
    South Carolina
    check it against a GPS. I just use a Garmin Zumo as my speed guide.
    Lifes too short to ride an ugly Motorcycle

  4. #4
    Administrator 20774's Avatar
    Join Date
    Sep 2005
    San Antonio, TX
    Are the speedometer and final drive original to the bike? Are the speedo and final drive ratio properly matched? This seems quite a bit off if you ask me. It's been discussed before and there's even a BMW service bulletin that defines how much the speedometer can be off, generally reading higher than real speed...kind of a CYA and/or safety thing. IIRC the 85mph speedos were some of the most accurate.

    Beyond using a GPS, find a nice piece of interstate and ride a specific distance at a constant speed. Note the odometer reading and the time to cover the distance. Then do the math to see where you are.
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  5. #5
    MonoRT MonoRT's Avatar
    Join Date
    Jun 2011
    Huntington Beach, CA
    The quickest way to trouble shoot your speedo/odo would be to use a GPS or Smartphone with a speedo app. Go for a ride and watch the GPS/Smartphone speedo vs. the bike's speedo. At the end of the ride, compare the bike's odo to the GPS/Smartphone odo.

    If the bike's speedo and odo are both reading low compared to the GPS/Smartphone, then you probably have a ratio issue - either the PO got tired of the too-short final drive and put in R100 gears or they replaced the speedo with a unit that does not match the final drive. I believe that speedo shops like Palo Alto or Overseas can change the speedo ratio and re-calibrate the unit for some $.

    If the bike's speedo agrees with the GPS/Smartphone, but the odo comes out low, you have one of two possibilities: either the speedo ratio is off, but someone recalibrated the speedo needle spring tension so that the needle reads OKish while the odo reads low or the ratio is fine but the odo drive gear is slipping on its shaft. If you think you have a slipping odo drive gear, take a couple more test rides with the GPS/Smartphone and check to see if the odo error varies with each trip - the slip factor tends to vary from ride to ride.

    If the odo drive gear is slipping, you can glue it to the shaft - Kurt's resources page has a link to a nice tutorial on that repair. In my case, I had a couple of shaft/glue failures over the years so I gave up and sent my unit to Palo Alto. They installed jam nuts on the odo drive gear so that it looks as if it should not ever slip again. They also cleaned, lubed and re-calibrated the speedo. A couple hundred bucks. Not cheap, but the speedo/odo works about as well as I could hope for now.

  6. #6
    Registered User lkchris's Avatar
    Join Date
    Mar 2003
    Albuquerque, NM
    BMW calls it "speedometer advance," their term for EU mandated reading high. At the same time they claim the odometer is correct. If your odometer is off as you think, something's mismatched in the ratios or gearing.
    Kent Christensen
    '12 R1200RT, '02 R1100S, '84 R80G/S

  7. #7
    Registered User
    Join Date
    Feb 2012
    I compared logs for each of the three 150-200 mile segments of a recent camping weekend (to/around/back) I took riding my ?93 R100R. GPS to odometer was ?mile perfect.?

    Each time I have checked over the past five years or so the speedometer on both my ?93 R100R and my ?94 R100RT read between 5% and 7% high across their scales vs. GPS.

    Current - 1974 TR5T : 1993 R100R : 1994 R100RT ~ Past - 11# 1970s BSA/Triumph Singles & Twins : 2# 1970s CZ 125s : 1# 1985 BMW R65 : 1# 1976 Moby X7

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