Monster Pete

I'm looking at changing the drivetrain on one of my bikes, since it's got very worn and ideally needs new chainrings, freewheel and chain. Currently it's got a 14-28 5-speed freewheel, and a 38-48 double crankset. I'm looking to switch to a 6-speed 'megarange' freewheel, with a 28-45-48 crankset. This would give a half-step setup in sprockets 2-6, with the small chainring providing an extra six low gears, including the 28/34 bailout gear. Alternatively I could use a 14-24 5-speed freewheel, and not bother with the bailout gear.

Obviously, I'd have to put this kind of crankset together myself, which is new territory for me. It also doesn't help that the middle and outer chainrings are close together in size, and a 45t middle chainring is difficult to find. On the plus side, I actually already have spare 28t and 48t chainrings from when I converted an existing triple to a single. If I could use these, I'd only have to find a suitable crank and middle chainring.

Any advice on putting this oddball crank together?

Cheers

Pete

JohnDThompson 

I've put together many cranks like this, but all vintage models e.g. TA "Cyclotouriste," Stronglight 99, Sugino AT, etc. What cranks are you considering?

HillRider

I expect any 110/74 mm BCD or 130/74 mm BCD crank could be built up using this chainring configuration. There are dozens of choices from ancient to relatively modern.

Where you may have problems is finding a front derailleur with the inner plate shallow enough to allow half-step gearing without having to place it excessively high over the outer ring. Newer fds are typically designed for a 10 tooth minimum between the chainrings so you might have to find an older one. My '85 Bridgestone 400 came with a Sun Tour ARX fd that let me use a 46/42 half step chainring pair with proper positioning over the 46t ring. Something like it or Shimano's 600 fd from the same era should work. Of course, friction shifting is assumed.

Bill Kapaun

How easily available is a 45T ring?
I would expect that might have a "premium" price for a bike originally equipped with a 5 speed???

Have you explored the option of having the dropouts respaced and going to a 7 speed freewheel, or maybe even more speeds with a cassette/new wheel?

tcarl

I just googled "45 tooth chainring" and found that Salsa has one in 110 bolt circle. It's 8-9-10 speed compatible, no ramps, etc., but I'd guess it would work or could be made to work, especially with friction shifting. Any of those cranks listed above would work.

Monster Pete

I have a 7-speed freewheel with very little wear on it, which is an option I've considered. The wheel is actually spaced for 6-speed anyway, with a spacer to centralise the 5-speed freewheel. There is some interference however with my rear rack mounting bolt with the 7-speed installed, which I'd have to find a solution to.

Another option that could work is to use a 'standard' 5-speed (14-17-20-24-28) with a 28-44-48 half-step, which would still give a relatively close spacing of gears, and have a more commonly available set of chainrings. Would it be feasible to buy a 'single speed' 44t crankset (if I can find one with a 3/32" chainring) and bolt on the extra chainrings?

The reason I'm looking at half-step though is for the logical shifting pattern it gives, rather than the current '1.5-step' setup with 38-48 chainrings.

shelbyfv

You need to tentatively decide on a triple crank you like, then see what rings are available in that bcd. Probably a 110/74 like a Sugino XD or something from Velo-Orange. That would give you a 48 and a 28 and you would only need to source the middle ring.

HillRider

Surly sells 44T stainless steel "flat" (i.e. no ramps or pins shifting enhancements) chainrings in both 110 and 130 bcd. Look here: https://surlybikes.com/parts/stainless_steel_chainrings

Bill Kapaun

As Hillrider mentioned in his 1st post is that you may have FDER issues.
I took a couple 22-32-44 cranks and made them 22-32-36 & 22-32-38.
I had to place the FDER about 1/2" higher than the big ring to get it to clear the middle ring. Once past that, it's basically doing a "normal" shift to the small ring.
With your combination, you'll have both shifts "mismatched" in either direction.

Monster Pete

I've just bought a Suntour crankset with a 44t chainring. This has a regular multispeed chainring in the inner position and a bashguard on the outer. I'm just going to replace the bashguard with a compatible 104bcd 48t chainring.

fietsbob

Surly, of Stainless steel and the Salsa of 7075 Al are both good choices from QBP
ramp-less chainrings are now sold as single speed , but are functionally identical
to all derailleur CR before the engineers took away the feel of involvement in shifting the gears
by de skilling friction shifting.

rccardr 

Monster, if that doesn't work shoot me a PM. I have an SR Apex triple that's a 48/44/28 (or 30) and matching Suntour Cyclone triple FD that works well with that particular crankset. All in very decent condition, too.