I was thinking, if you drop 1 tooth down in the front, it would make the speedo (on gearbox droven speedo's) read faster than actual......would this be on top of the speedo already 8-10% off from the factory, as is common I hear on most bikes? So it would be 15% or more shown than actual MPH ?
whatever the % change in gearing... you will throw off you speedo by the same amount.
So if you go from a 16/46 (2.875) to a 16/47 (2.938) that's a 2.2% change so your speed will be off by that much. 150mph will display 153mph.
Aslo speedo's are off from the factory mainly ot correct for changes in tire circumfrence as it wears. The difference between a new tire and work out tire can be at least 3%. Addtionally, so tires have a taller profile. SO the manufactuires add a lot of paddding ot be sure it never reads slower than your going. It's kind of like how that 12 oz can of soda is really closer to 12.2 or 12.5 oz of actual fill, because there is no penalty for giving you too much, but big fines if you are shorted.
Cherry's explanation is what I have heard b4. I'd go with that. ANd if ya wanna correct it right get the Yello Box. If ya want the cheap ass method, get a Bicycle Speedo. It works great for about $20-30 but unless you disconnect your bikes reg speedo, you'll really wack out your odometer.