Effect on Chain Geometry: Calculate number of chain links needed to compensate for lack of wheel adjustment
When there is no more room for adjusting the rear wheel in the right direction, the only option left is to alter the chain length, i.e. the number of chain links.
Suppose you want to switch your sprockets form Current (14-36) to Custom
(15-38). This means the following sprocket distance change:
Using the current chain, you would have to move your rear wheel 12.24 mm closer to the front. Now lets assume the rear wheel is already at the maximum front position. This means the only option is a longer chain. To find out how long you will have to experiment by changing the number of links. First try a chain with 95 links:
This still means moving the rear
wheel 4.26 mm to the front which is not possible.
So now try a chain with 96 links:
This means moving the rear wheel 3.73 mm backwards which IS possible ! So a chain with 96 links would be long enough for this sprocket combination.
By the way, normally the minimum increase or decrease of chain links is 2 as you do not want to remove 1 link and replace the ends with a special connecting link. (Keep the number of chain links even.)
Next: Decide on whether to go smaller in front sprocket or bigger in the rear sprocket