Originally Posted by 79pmooney

Easy way? Don't take the chain off. Get the 17. Screw it on. Try the wheel. Does it fit in the dropout? Do you like where it sits? Does the dropout allow you to move the chain in say 1/4" in both directions? If yes to all, simply "cut" your new chain to the same length. Don't even bother to read the rest of my post.

If the wheel sits too far forward in the dropout, see if there is room to slide the wheel back 3/8". (Two links of chain will allow the wheel to go back 1/2". One link on the upper chain run, one on the lower. The added cog tooth takes up 1/2" but that is split between the front and back, then again on the upper and lower runs so 1/8" per tooth.)

Or just look. Is the wheel 1/8" further forward OK? Go the same length. Add two links and it goes back 3/8" Or if you are using 1/8" chain (old fashioned single speed chain) you can go to a hardware store and buy a "half link" - one that is male at one end and female at the other. Single speed/fix gear shops will also have them but most other shops won't. A half link will alter the wheel position 1/4"

Edit: your stretch is almost certainly no more than 1/8" in 12 inches. Fix gear/single speed - roughly 100 links = roughly 4 feet so 1/2" total stretch. Divided by two for top and bottom runs = 1/4". You can measure the stretch easily with a regular steel tape measure. measure pin front to front of the pin 12 pairs of links away, Brand new chain - that is 12" exactly. Everything over that 12" is your "stretch". So the wheel will need to come forward roughly twice your "stretch" when you put on the new chain before you look at the cog size change. Again, do you like where the wheel (and axle nut) will be sitting after you move it forward?