iain.dalton

I just went on a tour, and was unsatisfied with the 26-36-46 x 11-34 gearing, so I'm considering going to 24-48-52 x 14-32 (7-speed). Unfortunately, this calls for a rear derailer capacity of 46, and my RD-M760 is only rated to 45. OTOH, Sheldon Brown says derailer capacities are rated conservatively, and as long as I don't go into a crazy cross gear, I should be fine. Can I go ahead? If not, are there derailers with 46-tooth capacities?

Also, my front derailer is an FD-4503, which is a triple, and I hear half-step + granny works best with a double FD. How much trouble will I have if I don't switch? If I need to switch, do I need to spend a bunch of money or can I get something cheap?

Jeff Wills

The problem with that derailleur on a half-step-plus-granny setup is that the inner cage plate will hit the middle chainring before it completes the shift onto the top chainring. That's why double front derailleurs are recommended: the inner cage plate is shallow enough to make the shift to all the rings. Any cheap Shimano double front derailleur will work.

FWIW: Back when Deore and Deore XT derailleurs were the latest cool stuff (in the late '80's), Shimano offered "alpine" and "half-step" versions of each. The half-step derailleur's inner cage was much smaller to clear the large middle chainring.

zzyzx_xyzzy

RD will probably work; if it doesn't you can leave the chain a bit long and let it drag on the small/small (which you really shouldn't use anyway.) I half step with an RD-M560 rated for less chain wrap than yours probably.

FD will be a bit more problematic, it will have to sit high on the seat tube to clear the inner part of the cage over your middle chainring, so it might not have capacity to clear the chain on the granny gear, and it'll require a lot of trimming if it does.

A 24 tooth jump is pretty extreme even for a half step plus granny. My tandem has a 24-42-46 * 12-34 7sp (get the 13-34 K cassette and substitute a 12 and 14 onto the first two positions) which has both a higher top end and a lower low before reaching for the granny.

fietsbob

80's SBI expedition came with 48,44,28 crank FD was shallow back plate, but the rear gear was a 6 speed .. bigger gaps between the ratios needed, in order to make half step work , like a 13,15,17,20,24,30,[26.32] .. a shimano K cluster for cassettes

it adds a low gear , last 3 24,29,34 7 SPEED, 8 and 9 gain little but near-redundant ratios.

iain.dalton

You're right, the jump is pretty big. zzyzx_xyzzy, I like your setup, but where do you find replacement cogs? Or do you buy two cassettes to build your ideal gearing? It seems I could get a similar effect by keeping the cassette stock and increasing the chainring sizes by 2 teeth.

HillRider

Will a current double fd work with half-step gearing? Most road doubles are 53/39 or the current compact craze of 50/34 so the tooth difference is 14T to 16T and I believe the inner cage plate is sized to handle this kind of difference.

I used a half-step plus granny crank in the late 80's (46/42/26) with a Sun Tour ARX and later a Shimano 600 fd but both of these had rather shallow inner cage plates. I don't know if a modern double fd will still work.

fietsbob

depth of the pusher plate on the inside of the FD cage is the impediment, if it's too deep it will hit the middle chainring, while pushing up to the outside one , the 53 etc, is describing the radius of the outer plate, not really the inner one but that is what is mass produced so thats what we have to work with..

davidad

I'm set up on the tourer with half-step. I found the front der at The Third Hand, but I don't think it is made anymore.
I run a Richie mountain front crank with a 44-40-20. The rear is a 7sp with 11-13-16-19-23-28-34 cogs. I think that you will need to order a couple of cassettes to get the cogs you will need. shimano doesn't make individual availble anymore.
The 44-11 gives a gear of 106 inches which is higher than you really need for a tourer.

zzyzx_xyzzy

I bought a K cassette and found a 12 and 14 off a used cassette. There are a few shops around with bins of used parts and plenty of 7 speed mountainbike cassettes in the bins.

fuzz2050

My touring bike has a 50-46-28, and it shifts just fine with an old Deore triple derailer. I am using friction shifting, and even so, shifting out of the granny can be a bit of a chore.

Gonzo Bob

Many of the Shimano derailer specs are conservative (max cog, max capacity, max difference) but the min difference between middle and large ring for recent triple front derailers seems to be one that is not conservative. I have a MTB FD rated for 12T min difference. I wanted to run 44x34 so I bought the new 44 outer ring. But what I found is that I need to have a gap between the FD outer cage and the big ring to get the inner cage to clear the middle ring. Since I'm under spec by only 2T, the gap is not too big and shifting performance is not degraded. But a 4T or 6T difference with a min spec of 11T (the FD-4503 spec) will not work.

Garthr

1. I'm curious why you want to use a 14-32 24/48/52 ? Are you limited by the choice of cogs or what? I assume this is a Shimano CS?

2. Your RD will be fine.

3. FD's for HS+G don't need to be too specialized, other than being a double(with a few exceptions). Looking at the design of the Tiagra Triple FD, I don't think it will work. Good news is, there's many FD's that will. Recent 9 speed Shimano FD's work well, 105, Ultegra, and Dura Ace. 10 speed FD do not without modification, this according to a builder who uses HS+G on many of his custom bikes. Most vintage road doubles will work too(before being labeled as any speed), older Shimano, SunTour, Etc. The good news is these are inexpensive.

4. I use a 26/44/48 with a 13/17/17/20/24/28/32 FW. This particular combo is very smooth. Since I think you're using a Shimano CS, I would suggest a 13-34 CS would work well with a 26/44/48. You get the same high gear, and same low. You can keep your 26. Get a double 9sp or lower FD and you're good to go. https://home.earthlink.net/~mike.sherman/shift.html

5. A 48t 110 BCD ring is less prone to deflection that a 52. I've found the bigger the ring on a smaller BCD, the more is exaggerates any deformities in the spider or rings. This means more trimming of the FD.

iain.dalton

Garthr, a 26/44/48 × 13-34 does indeed sound better, and I think I will probably change to that. This will be somewhat expensive, so I think I will not change my drivetrain until something wears out or my next tour, whichever comes first. Not sure which is likely to die first, a cassette or a chainring.

Edit: Garthr, does your cassette really have two 17s?

Garthr

Oops .... just a typo. It would be a 15 in there.