Changing primary ratio or any sprockets has no effect on transmission ratios.
I'm not sure of how the internal parts work on japanese boxes, but quoting in part from my own article on british:
"Ratio Calculations
Triumph 4 speed transmission’s intermediate gears (1st through 3rd) are the result of power transmission through two pairs of mating gears, one of which is the mainshaft high gear being turned by the layshaft (countershaft) high gear. The gear ratio is the product of multiplying the two pairs’ tooth count ratios together: the high-gear ratio times the ratio of the individual gear pair selected (1st, 2nd or 3rd).
In 4th gear the mainshaft high gear, which turns the transmission sprocket, is locked to the mainshaft, so the ratio is 1-1. No power is transmitted through the intermediate gears. Although they still turn, they’re only idling.
The high-gear ratio is the ratio of the tooth counts of the high-gear pair for the transmission type selected (see “high-gear pair” in the header of the Table below). For example, the std. transmission (the most common model) has 26 teeth on the mainshaft high gear and 20 teeth on the layshaft high gear, so the high-gear multiplier will be 1.30000 for this transmission.
The 2nd number is the ratio of the tooth counts of the pair of gears (mainshaft & layshaft) for that ratio: 1st, 2nd or 3rd. In general all 1st and 2nd gear pair ratios will be above 1.000. Some 3rd gear pair ratios will be above and some below 1.000.
The std. transmission has 26 teeth on the mainshaft 1st gear and 20 teeth on the layshaft 1st gear, so the gear ratio for the 1st gear pair is 1.6875 for 1st gear in the std. transmission. To get the actual effective ratio of 1st gear, multiply those two numbers together:
High-Gear Multiplier × 1st Pair Ratio = 1st Gear Ratio
1.30000 × 1.68750 = 2.43750-1
The overall governing component for all ratio selection is the high-gear pair, which determines the “range” of ratio spread between 1st gear and 4th gear. The selection of which high-gear pair to use must be made first, since this limits the number of choices to a specific range."
Read the article here:
http://victorylibrary.com/tech/trans-ratio-tri.htm
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http://victorylibrary.com/MIK-BT.htm
Need help with your Mikuni VM? Click here:
http://victorylibrary.com/MIK-BT.htm