Whizzer Speedo inaccurate?

Discussion in 'Whizzer Motorized Bicycles' started by jbcruisin, Aug 3, 2008.

  1. jbcruisin

    jbcruisin Member

    Are Whizzer speedometers accurate?? My wife happened to get behind me today & when I got home I asked her "how fast was I going, 35?". She says "35, you were going 45. You better be careful you don't get a ticket!!"
    I've been thinking since I installed Quenton's NE upgrade that I'm going faster than my speedo says.
    Ain't it great,

  2. Quenton Guenther

    Quenton Guenther Motored Bikes Sponsor

    Hi Jay, I am not sure if the following comments are true, but here are my results. I live in a small fishing village on the east coast and the local law enforcement places a radar unit near one of the bridges about a mile from my shop several times a year. I have checked Whizzer's speedometers against the radar unit at least 50 times in the last few years [I have to pass it on the way to my special test road], and here are the results, the speedometer with the black face [50 MPH version] is approx 1 mile off at 50 MPH [radar reads 51], and 4 MPH off with the later white face speedometer [at 50 MPH the radar shows 54 MPH]. The black face version is almost 100% at 35 MPH, whereas the white face version is indicating 35 MPH when the radar shows 37 MPH. I thought both speedometers are the same, but for some reason they always check differently from the earlier version. On the Whizzer I was testing for the "Dirt Drags" at Dawson Springs, KY had one electronic tachometer, one electronic speedometer, and a Whizzer [black face] speedometer, and the elctronic speedometer and the Whizzer speedometer always checked the same. Hope this answers your questions, but don't forget it is possible for some cable driven speedometers to vary depending mainly on the condition of the cable, speedometer drive gear, and the amount of lube inside the cable.
    Have fun, but don't get a speeding ticket!

    Whizzer OuterBanks LTD
    A North Carolina Corporation
    Last edited: Aug 3, 2008
  3. JemmaUK

    JemmaUK Guest

    If there is that much of a difference in the standard whizzer instrument it might be worth getting a secondary digital one...

    If thats set up as exactly as possible by physically measuring and inputting the wheel radius manually - then it will tell you what your actual speed is.

    Jemma xx
  4. JE

    JE Guest

    On my 08 Whizzer when I pass the local radar trailer doing 28mph my speedo is reading 30mph.
  5. Quenton Guenther

    Quenton Guenther Motored Bikes Sponsor

    Duh! I just realized some of the bikes I compaired to the radar were 24" and some were 26". I often ride with a friend and he has a 24" and most of the time I ride my 1999 26", he has a white face speedometer and I have a black face. I guess that would explain the different numbers.

    Whizzer OuterBanks LTD
    A North Carolina Corporation
  6. del

    del Guest

    OK, now you've got me curious. As soon as there's a break in the wicked weather around here I'm gonna do a temporary mount of a GPS...

  7. Zev0

    Zev0 Member

    I have a white faced whizzer speedo and a digital speedo. They are within 1 mph of each other. Haven't been able to find a radar setup yet. Don't think they have them within the Phoenix City Limits.
  8. del

    del Guest

    The GPS is temporarily mounted. Tomorrow I'll do a test run to see if I can come up with an indicated v.s. calibrated ground speed chart.

  9. del

    del Guest

    First speedometer test results.

    Today I took the bike out and tried to compare the speedometer with the GPS reported speed. There were some problems which I'll type about further down this article. But the initial results are:

    Speedometer GPS Difference.

    20 16.7 3.3 Mph

    30 26.7 3.3 Mph

    35 32 3 Mph

    The two major problems were holding the bike at a constant indicated speed. (Slight hills would slow down or speed up the bike.) And the lag time in the GPS. (It takes a second or two to get the measured speed to settle down.)

    Another problem came when I tried the 35 Mph run. Around here, speeds like that or faster are hard to hold for very long. Folks in SUV's, talking on cell phones, are likely to back out in front of you at any moment. So I'm not that sure about the accuracy of the 35 Mph measurement.

    However I do find the first test interesting. The error seems to be fairly constant. Now I have to try to get some accurate measurements at slower speeds.

    And, FYI, I'm riding a 2007 NE5 with 24" wheels and a white faced spedo..

    As with all things mechanical, your results might be different....

  10. KilroyCD

    KilroyCD Active Member

    Del, I would guess that the 3mph difference is likely to be due to the fact it's a 24" bike. The speedos are likely calibrated for 26" bikes. Looking on Whizzer's website, I don't see any speedometers listed as being for 24" bikes. As a 24" tire is smaller in circumference than the 26" tire, you will be covering less ground for every rotation of the tire. As a result, you're traveling a bit slower than one would on a 26". This is probably why your actual speed is less than the indicated speed.
  11. del

    del Guest

    Well, Jim, you did it again...

    I I had to haul out my calculator to find out how much of a difference 24" and 26" wheels would make. If anyone wants me to "show my work" I will. But the results were....

    At 20 Mph a 24" wheel would be traveling 1.5 Mph slower than indicated, and at 30 Mph it would be going 2.3 Mph slower.

    However at both 20 and 30 Mph I was getting a constant 3.3 Mph difference. So, while the difference in wheel diameter might be a part of the reason for the difference, I don't believe it's the whole story. There seem to be other confounding factors involved.

    Maybe it's the yellow paint....

  12. WZ507

    WZ507 Member


    Just a couple thoughts. What kind of confidence do we have in the GPS, i.e., what might the error be on its reported speed at 30-40 mph if you try the test 5 times? Do your car speedometers agree with it down to the fractional mph at 30 or 40 mph? Also, since you've narrowed the error down to ~ 1.8 mph we're getting to the point where small measurement differences anywhere would get us very close to an agreeable answer.

    Although this is not necessarily germane to the 24"/26" tire comparison mentioned above, when anyone inputs a tire circumference into a formula for their specific bike or speedometer, the tire circumference that the bike is running on is not that of the free standing tire. Rather, the circumference you are interested in, and actually riding on, is calculated from the tire radius, measured from the ground to the center of the axle with the rider seated on the bicycle. This approach takes into account both tire inflation pressure and rider weight which in turn account for the tire deformation (flat spot where the tire contacts the pavement) that occurs when us little 250 lb pixies settle on to our Whizzers.

    I'm not by any means trying to be nit-picky, just noting that any small perturbation could get us to agreement within 1 mph, which might be as good as it's going to get here.

    Keep us posted on your findings, as this is interesting.
    Last edited by a moderator: Dec 15, 2015
  13. del

    del Guest


    You pose many questions. All of them good.

    First, when we're talking about a difference between indicated v.s. actual ground speed, a difference of even 3-4 Mph is a bit nit-picky. So we're all talking small variances here. But it's fun...

    Your statements about the working circumference of a tire/wheel v.s. measured circumference is dead right on. And I did not take that into account. I do have some personal limits to nit-pickyness...;-)

    As for confidence in the GPS. Well... Once the government turned off the dithering of the satellite signals a few years ago, I've found it to be pretty danged accurate. For example, I've spent a bunch of time driving my old Toyota pickup comparing the difference between the indicated speed and the GPS reported speed. The difference in speeds is quite consistent, down to at least 1 Mph. So, I'm fairly confident in the numbers I reported for 20 and 30 Mph on the WHizzer. I tried to hold the indicated speeds constant for a long enough time to give the GPS time to catch-up. And did that more than once.

    In addition, once I get up to speed in the pickup, the difference between indicated and measured speed seems to be fairly constant; whether I'm going 30 or 70 Mph. (About 5 Mph.)

    Of course, when you're going 0 Mph, that's gonna be your speed no matter how you measure it. But if the speed differences were simply due to a difference in wheel diameter, the difference would become greater as you went faster. The faster you went, if the speedometer was calibrated for a larger wheel than you were using, the more the indicated speed would show a slower speed. (I could do the calculations for Mach 1, but 40 Mph around here is scary enough..)

    However, in the case of the Whizzer, just like in the pickup, I find that once I get up above some critical speed the difference between indicated and measured speed is fairly constant at varying speeds above critical-slow. I'm not sure what that's about. But I'm getting convinced that it could be in the design of mechanical speedometers. If I remember correctly it's a magnet spinning inside a metal drum counter-balanced by a spring..??

    But, in spite of the fact that I'm not gonna get an NSF or NASA grant to fund further research, I'll keep on studying it for a while. I want some better data, especially for slower speeds. And it's another excuse to ride the Whizzer... (As if I needed one...)

  14. smitty

    smitty Guest

    I think the best way to figure your wheel circumference is to set the valve at the bottom of the wheel, get on the bike and ride it (or maybe some Fred Flintstone action) for maybe ten revolutions of the wheel, (nice and straight of course) then measure the distance traveled, and divide by ten. That should reduce any mis-measurement by 90%.
  15. smitty

    smitty Guest

    Oh yeah, I did the GPS thing on my Whizzer and found the speedometer read about 2 !/2 mph faster than the GPS at 40mph on the speedo.
  16. kerf

    kerf Guest

    The Whizzer speedo is calibrated for a 26 x 2.125 tire. My tires have a diameter of 26.34" using the circumference in the calculation.
  17. jbcruisin

    jbcruisin Member

    she clocked me

    I rode my Whizzer to church yesterday & told my wife to clock me on the way home. I had to go before her we do usually go places together:smile:.
    My speedo goes to 40 mph & was pegged. She said for sure I was going a good 45 mph. Love Quenton's NE upgrade.
  18. John-Forrest

    John-Forrest Member

    Speaking of speedometers - where can you get the old style anlogue NON-DIGITAL kind? I tried to put a pyramid pro speedometer on front wheel of WildFire that has disk brake, large tires. The piece of metal on the drive wouldn't reach the spoke, and it broke on disk brake. On my searches, this is the ONLY one on the market! Computerized speedometer doesn't fit my extra large frame; computer magnets are no good. Is there a drive that fits OVER hex nut (15 mm wide) and reaches over a disk brake?
  19. Whizzer speedo's

    Hi John, all of us Whizzer dealers sell the speedos I would think.

    I know I usually have them