This is a discussion on How off is your speedo? within the Monkey Talk forums, part of the Honda Monkey 125 Forums category; I was under the impression that with the stock gearing, the speedo was pretty darn accurate. I put on a 14t front sprocket and went ...
I was under the impression that with the stock gearing, the speedo was pretty darn accurate. I put on a 14t front sprocket and went for a ride with a GPS to test. As I expected, the speedo was off and read high, but by about 9% and not 7% like I expected. I never measured the stock speedo with GPS, but I'm guessing it reads about 2% high. That's still pretty accurate, but not dead on like I expected.
I never look at my speedo. I just WOT everywhere. Only time I know my speed is when I see those speed trap radars, but it tells me to slow down
Tire treadwear is a factor, too. The Koso DB03R allows you to punch in the current tire diameter to get a more accurate reading.
2018 Honda Grom (Matte Gray)
Engine: DHM 186 | 2x ECU: DHM 186 & Stock+PV3 Dank Tuned | Koso DB-03R w/ RaceDash | UEGO | MTake | DHM Header+Cheap Slip-on | Kitaco 60% Springs+Stock Plate | Superlite 16/32
Suspension: RacingBros Front (7.5N/mm) / Rear (100N/mm)
Chassis: Chimera Race Bolt | Speed Spacers | Womet-Tech Sliders | NDC Adjusters | TST Fender Eliminator | ProTaper SE Honda Mini | Neverlandback Mirrors | Corbin Saddle | Driven TT Rearsets
Believe it or not, I've never had a speeding ticket, but my goal is to get one on the Monkey.
I doubt I've done much to the tire diameter with just over 600 miles on the bike.
I have a 14t front sprocket. 55mph indicated is 50mph using Waze.
Stock sprockets on my Grom. Speedometer is right on the money by GPS and a LEO friend's radar gun too. My KTM is off nearly 10%, but that is due to a screwy EU regulation.
with my stock speed sensor, Takegawa 5 speed transmission, 16/32 sprocket setup, and 140/70-12 rear tire, every time I pass one of those electronic speed device near a school it shows 28-30mph when my gauge shows 25 and in residual area where the speed limit is 35mph and if they have a speed trap LED display if I go 35mph it shows 37-38mph.
Koso 4V GF Ported / Drowsports 181 piston / Takegawa Oil Pump, Cam Chain Tensioner, Crank Support Kit & Catch Can
Koso 34mm TB GF Ported / DynoJet PCV, WB2 & AFR / GF Manual Cam Chain Adjuster
Drow Sports CF Intake & Oil Cooler / Hindle Exhaust / OPMID 2 Temp Gauge
Kitaco Clutch Cover / SMR 6 Disc Clutch & 60% Springs / Chimera Clutch Plate
RacingBros Adj Fork Kit and Shicane HLR Shock / Vagabond Fender Eliminator