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Discussion Starter · #1 ·
Wanting to know what difference my 15t front sprocket made on my speedometer, I re-searched Goggle and YouTube, and this seems to be the average errors for stock , and the most common gear ratio changes
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Z 125 factory speedometer error with "stock tire sizes"

With the stock 14t front and a 30t rear sprocket
the speedometer will read +3 mph faster than your really going.
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With a 13t front and a 30t rear sprocket (-1/nc)
the speedometer will read +6 mph faster than your really going.
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With a 13t front and a 32t rear (-1/+2) sprocket
the speedometer will read +12 mph faster than you are really going.
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With a 15t front and a 30t rear sprockets (+1/nc)
the speedometer will read "the actual speed your really going"
Due to the stock setting is purposely set high.
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The stock speedometer reading is purposely set to read higher than you are actually going because it helps prevents car and motorcycle manufacturers from lawsuits. this keeps you a little under the speed limit so you cant say the vehicles speedometer is off and that's why you got a ticket.
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"GPS isn't perfect, but it's a lot more accurate than a vehicle speedometer,
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So the best way to know your actual speed is to use a phone/gps against your actual speedometer reading and compensate according next time you ride, so you dont have to mount your expensive phone out where it is excess able to damage


just my .02 again / anyone with different actual results post'em up
 

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Super Moderator
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Discussion Starter · #4 · (Edited)
Thanks colticus , i also tried to find out what my 130/70 kendas are going to do to my speed-o when i put them on but noting with real actual's was available .
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So a 1" taller tire (120/80 ) makes a 3 mph difference / then my 1/2" taller 130/70 will only make a 1 1/2 mph difference . good news because i only have bare bones flip phone i was thinking it might have been a 5 to 10 mph difference ?
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and for those following that want there speedometer to be dead on regardless of gearing or tire size, there's a Speedometer Re-calibration Device available if you haven't seen it yet
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http://www.z125owners.com/forum/hardracing/5305-z125-speedometer-recalibration-device-srd.html
 
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