I have thought, for awhile, that I would make a 14-41, 8 speed cassette to replace my 12-34, 8 speed cassette. I'd switch from a 15 tooth, on the motor, to an 18 tooth. The ratios would be the same, but the chain tension would be 20% less, and 20% more teeth would be engaged. This can only be good for chain life. I was hoping to make this work with my stock derailleur, by running a longer B tension screw. I'm pretty cheap, so I didn't want to buy one of those pricey after-market big cogs, if it was going to mean a new expensive Shadow derailleur as well.
I have a pretty good stash of new and slightly used old stock, so I figured I would see what I could come up with. I didn't have a 14 tooth end cog, but I did have some 13's. I had a 110 mm BCD, 42 tooth Shimano chainring. I found a 25 tooth cog, and by luck the holes in the chainring lined up pretty well with the spaces between the teeth on the 25 tooth cog. I used M6, button head bolts to put it together. Unfortunately the button heads were too thick for proper cog spacing, and the nuts on the backside hit the spokes. I replaced each bolt, one at a time, with 3/16" stainless steel pop rivets, with steel washers at each end. I installed it on a spare wheel I had. It is 13, 16, 18, 21, 24, 28, 34, 42, with 8 speed spacers, except for between the 34 tooth and 42 tooth. This required a thinner spacer, because the chain ring is set back behind the 25 tooth "spider." I used a bottom bracket spacer to get the appropriate spacing.
Instead of tearing my electric apart, I popped the rear wheel off one of my other bikes, installed the spare wheel, and set it up in a trainer. The chain length and derailleur cage angle is about right, in the middle ring. It shifts fine up to the 34 tooth, and pulling the derailleur back a bit, so the jockey pulley just clears the 42 tooth, it looks like it will work OK with a longer B screw. I'll keep you all posted.
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I have a pretty good stash of new and slightly used old stock, so I figured I would see what I could come up with. I didn't have a 14 tooth end cog, but I did have some 13's. I had a 110 mm BCD, 42 tooth Shimano chainring. I found a 25 tooth cog, and by luck the holes in the chainring lined up pretty well with the spaces between the teeth on the 25 tooth cog. I used M6, button head bolts to put it together. Unfortunately the button heads were too thick for proper cog spacing, and the nuts on the backside hit the spokes. I replaced each bolt, one at a time, with 3/16" stainless steel pop rivets, with steel washers at each end. I installed it on a spare wheel I had. It is 13, 16, 18, 21, 24, 28, 34, 42, with 8 speed spacers, except for between the 34 tooth and 42 tooth. This required a thinner spacer, because the chain ring is set back behind the 25 tooth "spider." I used a bottom bracket spacer to get the appropriate spacing.
Instead of tearing my electric apart, I popped the rear wheel off one of my other bikes, installed the spare wheel, and set it up in a trainer. The chain length and derailleur cage angle is about right, in the middle ring. It shifts fine up to the 34 tooth, and pulling the derailleur back a bit, so the jockey pulley just clears the 42 tooth, it looks like it will work OK with a longer B screw. I'll keep you all posted.
View attachment 2
