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Discussion Starter #1
Hit 67 mph on stock speedo, wondering if accurate or true speed is off by how far.thanks in advance for any info.
 

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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.
 

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Discussion Starter #4
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.
 

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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
 

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Discussion Starter #7
Thanks for the other suggestions to figure out actual top speed vs speedometer. Much appreciated.
 

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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-Speedometer-Re-Calibration-Device-Honda/dp/B01JLL4V3A/
 
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