Half-step plus granny conversion questions
 

I have a 10-speed (2x5) bike from the early '90s I've been tinkering with, and was thinking of doing a HS+G conversion. It currently has 38-48 chainrings and a 14-17-20-24-28 freewheel. I was thinking of switching to a half-step setup, using 44t middle and 48t outer chainrings, with a 24t granny gear on the inside.

Am I likely to run into any problems with this? I would set the chainline of the middle/outer chainrings as if they were a double, allowing me to use the 48/28 combo as part of the half-step setup. This would mean only really using using the 28-20 freewheel gears with the 24t chainring (24/17 would be borderline acceptable) but that places the granny gears in a neat sequence off the lower end of the half-step anyway. I'm thinking it's possible I'll run into problems getting the FD working correctly with such a big jump from small to middle chainring. Would it be better to ditch the granny gear and just go for a double?

Pete

I bought a Specialized Expedition touring bike in the 80's , it came with a 48/44 triple.
28. is a 16t drop, 30 is a 14T drop, either pretty reasonable ,
as if you have a smaller difference you gain only 1 0r 2 lower ratios
making the added chainring more questionable benefit ,
Vs a 14-32 5 0r 6 speed freewheel.

then a granny gear seems less a gain..

need a shallow back plate FD to clear the bigger middle ring.

big jump between chainrings, is handled well at the summit of hills ,
when the pull of force on the chain can be the least.

I'm a big fan of the half step + granny, or similar configurations. They work fine allowing you to chose rings and a freewheel best suited to 99% of riding conditions, with a bailout for those long or steep grades that you run into occasionally. To make this work, you'll need to use a mountain or road triple FD, and possibly a long cage FD (maybe not if you only use the granny with larger sprockets) but other than that you'll be fine.

I used to be a fan of half-step +granny back when 5 and 6-speed freewheels were the norm. Mine was a 46/42/26 triple crank and a 13x28 6-speed freewheel and the gear progression was very even with almost no duplicates. The OP is dealing with a very old type of gear arrangement and the hs+g is the only way to get even gearing steps plus an adequately low gear.

Modern 9 and 10-speed cassettes have made half-step moot since the cog spacing is one tooth intervals for a lot of the range.

Good point, with the steps so fine of 9s+, half step chainrings don't make as much sense. I've adjusted to step-and-a-half spacing, packing a nice assortment of very closed spaced ratios into the mid-upper range.

In theory you could make half-step gearing with 9+ speed cassettes but the chainring spacing would be so close as to be useless. From a 12 to a 13T or a 13 to a 14T cog is about an 8% change. You would have to use something like 50/48T chainrings to get the 4% difference needed to "split" these.

I run half-step on a 7sp. freehub. The back is 11,13,16,19,23,28, and 34. On the front I have a 44-40 with a 20t grandpa gear. Of the 21 speeds there are 18 different usable gears.

What front derailleur do you recommend for this? In my experience all contemporary triple derailleurs, road and MTB, have a minimum gap from middle to outer of 10-12 teeth.

I can see why this works since your cassette has such a wide range the steps between adjacent cogs are quite big. It's analogous to a 5 speed 14x28 or a 6-speed 13x28 freewheel.