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Speedo.........not the right speed

Discussion in 'Bling and Appearance' started by CB250_Newby, Jun 28, 2007.

  1. Hi All

    I failed my P's test today due to speeding though my speedo told me I was going 90kms the examiner said I was doing over 100kms. Is this something that a mechanic can correct and what is the issue.
  2. Sorry to hear about the test. Better luck next time
    your front wheel may have been doing 90 but your back wheel must have been doing over 100
    You sure you had the front wheel down during the whole test
    Weren't doing any wheelies were we?

    With all fairness it was probably a faulty speedo needle or something.

    buggered if I know.
  3. sounds like perhaps its had different sprockets put on at some stage ?? that will put your speedo out
  4. Most bike speedos read fast. Yep, 200 is not 200.
    If yours reads off the front wheel your tyre/wheel may be bigger than standard. There are speciallist instrument repairers about who can fix it. Have a look in the yellow pages.
    Or do what I did and grab a GPS and check against it. My speedo says 107 and the gps reads 100 so I know I can be sitting on about 110 and be pretty right. Then I'll select 2nd gear :LOL:
  5. I agree, but Newb's is reading slow.

    Likely causes are a gearing change (if the speedo is driven off the gearbox), or smaller aspect ratio tyres have been fitted.

    Check what the standard sprocket sizes and tyre sizes should be before going to a specialist instrument place.
  6. OP. How was your speed checked by the examiner?
    I dont think there is anything over 40k here in VIC.
  7. unless you got the dodgiest speedo in history, no tyre or sproket set will cause that much variance.

    Have it run over a dyno and get them to mark the correct speeds on a plate for you, then get it fixed.
  8. Is it possible that your speedo is quite close to correct but the examiner's speedo is overreading significantly? My Kawasaki, for instance, shows 115 on the dial at a genuine 100kmh. If somebody with a similar speedo error was following you and your speed is spot on, that could be what's happening.

    I've never come across a bike speedo that under-read before but with those rusty, dodgy CBRs anything is possible I guess.
  9. European bikes/cars are usually have a more true display of speed.

    Kawa are notorious for up to 10% error. I can back this up as I put a digital speedo on my zzr and tuned it to the right speed, and 10% isn't an overstatement.
  10. He just read his speedo and told me his was right
  11. Thanks for all the help I will get it checked out.

    Two different riders have since told me that my speedo is reading lower than theirs.

    Oh well all good ~ will pass next time for sure.
  12. what year is your cb250 ( i assume thats what you have)?
  13. Yeah thats the one...it's a 2001 model
  14. oh, im only familiar with the older ones. i know they havent changed much in the years, but i was thinking, that if the speedo read the speed via the gearbox/front sprocket then different sprocket ratios or tyre size would make it under-read.
    if it reads from the front wheel, the only way it could under-read is if you put a big mutha of a front tyre on there :?

    you pretty much need to know how much error there is because speed cameras will get you :shock:
  15. I might have to ride through a few road work speed displays and figure it out

    thanks again everyone.
  16. If you can borrow someone's GPS, temporarily mount it on the handlebars then go for a ride. Compare its reading to the speedo. GPSes are pretty accurate. Then you'll know for sure. Don't just rely on other peoples' speedos as there is no guarantee that they are accurate.

    If you discover that your speedo is reading right, you might be able to mount a case to get your licence without having to re-do the test if the tester's speedo was reading high.

    Good luck.
  17. As someone else suggested borrow or even hire a GPS.
    I used a Garmin 12XL (its my work unit) which has an error factor (according to garmin) of less than 1.5kmh if on a level surface. realistically you would need to be climbing a very steep hill to throw it out by much but the flatter the road the better.

    Remember what your speedo is reading at 60 - 100 - 110 and ride accordingly. My RF is over by 4 at 60 and 7 at 100 but pretty close at *cough* 160.

    It is unusual for speedos to read slow but they can be fixed if you can be bothered.
  18. Alternatively he could fit a cycle computer, say one of the Sigma Sport types (www.sigmasport.com). Calibrate it initially using the supplied destructions, then use a GPS to fine tune it.

    I found a flat road about 4kays long, no traffic. I reset the trip meter on both GPS and cycle comp. Then rode for about 3kays. Checked readings on GPS and CC (speed and trip), then adjusted the CC accordingly.

    Not only do you get an accurate speedo, but depending on the model you also get a nifty trip computer as well as a clock. to the OP they cost around $30 for a basic CC.