2022 speedometer accuracy

448 Views 8 Replies 5 Participants Last post by Magilla, 9 d ago

Magilla

Discussion Starter · 15 d ago

Has anyone checked the late model Monkey or Grom with GPS? The ratio from crank to tire should be about the same. Or is the speedometer reading front wheel speed?

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Speed sensor is reading off the output shaft, I believe, based on it's location on the engine. Mine was 5 or 6% off from factory, I forget the exact number. Swapped sprockets and was closer to 11 or 12% off so I fixed with a 12oclocklabs speedoDRD healer.

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invadeChu

· #3 · 13 d ago

I've been using the speed limit warning signs on some of the roads here, my 2023 Grom is off by about + 11%
for me; 77 km/hr is actually 70 km/hr

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Magilla

Discussion Starter · #4 · 13 d ago

Maybe the Monkey speedometer is more accurate. Mine doesn't seem that far off according to radar used in school zones

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Zeep

· #5 · 12 d ago

I verified my'19, with GPS, after first getting it. Checked within 1 MPH.

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Magilla

Discussion Starter · #6 · 10 d ago (Edited)

I measured the diameter of my stock 130/80 with about 1000 miles on it at 20". Calculated, it comes to 20.189" so using the more realistic 20" and the stock 37/14 final reduction, I calculated the mph/rpm for 4th and 5th gears. Now I just need to attach a temporary tacho.

4th (130/80-12 and 37/14) rpm :
15 mph = 2179.5
20 mph = 2906.5
25 mph = 3633
30 mph = 4359.5
35 mph = 5086
* 38 mph
40 mph = 5813
45 mph = 6539
** 46.5 mph
50 mph = 7266
55 mph = 7992.5
60 mph = 8719.5
65 mph = 9446

5th (130/80-12 and 37/14) rpm :
20 mph = 2295
25 mph = 2869
30 mph = 3443
35 mph = 4017
40 mph = 4590.5
45 mph = 5164
* 48 mph
50 mph = 5738.5
55 mph = 6311.5
** 59 mph
60 mph = 6885.5
65 mph = 7459.5
70 mph = 8033.5
75 mph = 8607
80 mph = 9181

Max output :
* 8.1 ft/lb TQ @ 5500 RPM
** 9.3 HP @ 6750 RPM

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galen

· #7 · 10 d ago

If the roadside radar signs that read your speed are to be assumed accurate, then my 2022 Grom is very close, within 1 MPH. Now these are speeds of 20 MPH - 30 MPH, so I’m not sure if it would be as close at higher speeds.

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Magilla

Discussion Starter · #8 · 9 d ago

I temporarily rigged up my old, trusty Stihl tacho with a few strips of velcro. The engine rpm and mph match my calculations so the speedo seems to be spot on once the tire gets a bit of wear. I also noticed my idle speed was 1500-1600. Idle screw was over 2 turns out. Set to 1 7/8 turns put it well within spec.

Here's my 5 minute installation. Sorry I couldn't get a snapshot of the speedo and tacho for verification at speed.

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Magilla

Discussion Starter · #9 · 9 d ago

galen said:
If the roadside radar signs that read your speed are to be assumed accurate, then my 2022 Grom is very close, within 1 MPH. Now these are speeds of 20 MPH - 30 MPH, so I’m not sure if it would be as close at higher speeds.

I went past a school today at a steady 41 mph according to both my speedo and the radar.

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2022 speedometer accuracy

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Magilla

Zeep

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galen

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