15/37 gearing. How far up or down accurate speedometer?
Close
Login to Your Account
Honda Grom Forum

15/37 gearing. How far up or down accurate speedometer?

This is a discussion on 15/37 gearing. How far up or down accurate speedometer? within the Grom Performance forums, part of the Honda Grom Garage category; Hit 67 mph on stock speedo, wondering if accurate or true speed is off by how far.thanks in advance for any info....

Results 1 to 8 of 8

Thread: 15/37 gearing. How far up or down accurate speedometer?

  1. #1
    jsk
    jsk is offline
    Member
    This user has no status.
     

    Member #
    301
    Join Date
    Jun 2013
    Posts
    37

    15/37 gearing. How far up or down accurate speedometer?

    Hit 67 mph on stock speedo, wondering if accurate or true speed is off by how far.thanks in advance for any info.

  2. #2
    Senior Member
    is dialing in the bike for my
    wife !
     

    Member #
    32050
    Join Date
    Jul 2019
    Location
    Ottawa, ON, Canada
    Odometer
    3400 km
    Posts
    124
    Try entering your setup here:. https://www.gearingcommander.com/
    2015 OG Grom in Yellow - AODRacing loop exhaust, ContiScoot tires, EBC HH front pads, RideItMoto levers, Renthal kevlar grips, Road low bars, CJR ECU, TB cam, MNNTHBX Mtake, Outerwears, Koso temp gauge, short shift linkage, TST sliders, Aliexpress tail tidy, Aliexpress axle sliders

    Pending - oil cooler, CoreMoto braided lines, high mount exhaust, rearsets and GP shift conversion

  3. #3
    Senior Member
    This user has no status.
     
    tooter's Avatar
    Member #
    30592
    Join Date
    Jan 2019
    Location
    unincorporated rural Los Angeles County
    Odometer
    2000
    Posts
    721
    Quote Originally Posted by jsk View Post
    Hit 67 mph on stock speedo, wondering if accurate or true speed is off by how far.thanks in advance for any info.
    Stock gearing is 15/34 and 15/37 gearing is 9% lower, so your speedometer reads 9% faster. This makes an indicated 60 mph on your speedometer actually 55 mph. This is in addition to the stock speedometer's already high reading which makes your actual speed about 53-54 mph.
    2018 GROM: Modified for reliability longevity gas mileage... and fun.

  4. Remove Advertisements
    HondaGrom.net
    Advertisements
     

  5. #4
    jsk
    jsk is offline
    Member
    This user has no status.
     

    Member #
    301
    Join Date
    Jun 2013
    Posts
    37
    Quote Originally Posted by tooter View Post
    Stock gearing is 15/34 and 15/37 gearing is 9% lower, so your speedometer reads 9% faster. This makes an indicated 60 mph on your speedometer actually 55 mph. This is in addition to the stock speedometer's already high reading which makes your actual speed about 53-54 mph.
    Thank you for the detailed explanation.That was exactly the information I was looking for.

  6. #5
    Junior Member
    This user has no status.
     

    Member #
    7328
    Join Date
    Apr 2016
    Location
    Coastal NC
    Posts
    2
    I have one method to recommend. There are numerous speedometer apps that you can download for free.
    1. Download an app.
    2. Turn it on and run the Grom on a level space at 60mph (based on the phone app speed). Identify the speed you Grom indicates.
    3. Upon returning from your ride, you can calculate the variation of Grom indicator/Actual speed.
    There are several electronic correction devices which can be wired (Plug and Play) into your wiring harness to adjust the corrected speed error with whatever gear choices you make.
    Good luck!
    REinNC

  7. #6
    Junior Member
    This user has no status.
     

    Member #
    32386
    Join Date
    Aug 2019
    Posts
    3
    Download a speedo app for your phone and check your speed with that.

  8. #7
    jsk
    jsk is offline
    Member
    This user has no status.
     

    Member #
    301
    Join Date
    Jun 2013
    Posts
    37
    Thanks for the other suggestions to figure out actual top speed vs speedometer. Much appreciated.

  9. #8
    Member
    is Member
     

    Member #
    29978
    Join Date
    Sep 2018
    Location
    USA
    Odometer
    5200
    Posts
    38
    Quote Originally Posted by tooter View Post
    This is in addition to the stock speedometer's already high reading
    I checked my speedometer on stock gearing with GPS and radar and it was dead on, no more than 0.5mph difference at 55mph. Also checked the odometer over a ~15 mile distance and found it to be near-perfect.

    I have ridden a Grom with lowered gearing and found the stock setup to be much better, I think most of what people 'feel' when they mess with the gearing is a placebo based partly on their expectations, and partly on their now-inaccurate speedometer readings.

    If you do change your gearing though, you should consider a speedometer recalibration tool. In addition to avoiding the nuisance of constant mental adjustments to guess your speed, you will also preserve the accuracy of your odometer for maintenance intervals, resale value, and in some cases insurance purposes.

    https://www.amazon.com/OclockLabs-Sp...dp/B01JLL4V3A/

Sponsored Links

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •