Long to Short cage mech?

[Wold Ranger]

Big Big

Never done that in 40 years! but OK respecting that this is retro bike, but if you omit the big ring then you won't run into problems. I run an 11-26 Dura ace cassette on a Zaskar with a 36/24 front set up, can get up anything(the bikes sub 22 tho) short cage rear mech and even on full cross over, there's no problem.

 

[hamster]

Pal of mine tore his rear mech off, but not before it had ended up at the top of the wheel, ripped off several spokes and dumped him face first onto the kerb...

But I do agree that gear ranges are just hilariously large nowadays and I run a short cage mech with a 42/29 front and 11-28 cassette. It wouldn't be ideal if I lived in the Peaks, but I don't.

 

[jimihendrix]

I tried a short cage mech and road cassette combination on my Clockwork, (after i read someones suggestion of a road cassette on a super light Pace on here a while ago)

Running 34 + 44 on the front, a 12-23 block on the rear with an XTm739 short cage mech, found i hardly ever used a granny ring when i had one.

I love it, look's very neat, the gearing could be a bit taller (maybe 25 or 28 on the rear) but i've not found a hill i've had to get off and push yet .

 

[Anthony]

So look, I've got a short-cage M735 that I haven't fitted yet and it has a capacity of 28t. All my other XTs are long-cage and don't say the capacity, but as modern RMs seem to have a difference of 12t between GS and SGS, maybe a long-cage M739 might have a capacity of around 40t?

With a 22/32/42 11-28, you need a capacity of 37t, and with an 11-30 you need 39t. So my long-cage mechs are fine, but my M735 is 9 bricks short of a load for an 11-28 cassette.

And Shimano and Scant say stick to the chain length = big plus big plus two links formula, but the chain will be slack in the granny ring on all the sprockets smaller than 19 (28 less 9) - i.e., from gears 4 to 8, right?

And this isn't too important because in the granny you probably wouldn't use fourth anyway and even if you did the chain wouldn't be all that slack? And it only gets way slack when you get into quite small sprockets that you really really wouldn't use in the granny ring?

If so, that doesn't seem too big an issue to me, so I don't see any point in taking even a small risk in shortening the chain.

 

[Wold Ranger]

Short gears

I tend to find I run out of traction, well before I run out of heft. If your running a heavy FR rig then you may need a 22 to 32 or 34 but on most retro steds, which will be below 25 pounds this just isn't necessary, a 12/28 rear on a 40/29 or 38/28 if its hilly would do fine.
On a point of getting up big hills, when I used to race, I also used to compete in fell running at a high level and was pretty fit, I just used to shoulder the bike and run, its far quicker than grinding the cranks! BITD this was regular practice in XC races.

 

[Wold Ranger]

Mechs

Just a thought but why not run a Medium cage MTB or Long cage road? The Dura ace/Ultegra triples are equivalent to a medium cage mtb and U'll save about 100 grammes over a long cage mtb! thats a quarter of a pound!

 

[Iwasgoodonce]

Just try and stick to the ratios we used to use BiTD and you should be fine. If Shimano used to spec it back then it should still work now right? My top spec (back then) Saracen ran XTII M735 groupset with the short cage mech. It had 12-28 at the back and 24-36-46 at the front. It always worked fine although I always avoided the extremes big/big or small/small.
I am going to recreate the set up when I build the Potts.