raria

Hi,

I had a touring bike (Fuji Touring 2009). It has Deore MTB RD and a triple 52/42/30. I currently have a 11-32 cassette. The capacity of the RD is 39.

I want to keep the triple but wanted to increase the largest gear in the cassette to have a bail out gear when climbing. It's a SRAM cassette (https://www.sram.com/sram/mountain/p...ur8g12oirsm56k)

What's the largest rear cog I could go to *in practice*? I'm not concerned that there will be a jump b/w the largest and 2nd largest gear.

Steve B.

Personally I’d get a touring crank, 24-36-48

ThermionicScott 

You're already exceeding the capacity of your RD, so hopefully you're sizing your chain by the big-big+1" method...

Do you know what the model number of your RD (should be stamped somewhere on the back)? I'm finding a max cog of 34T and capacity of 45T for the M591 Deore RD: Shimano Deore RD-M591 Rear Derailleur | Jenson USA

I think this idea has a lot of merit. If you're not using that 52/11 top gear (!), you might be happy bringing down the whole range of gears with a more suitable crankset.

raria

I thought about this, but the bike is perfectly geared for my likings ... except ... sometimes when at the end of a really really long climb, I'd like to just spin at 5mph! This happens very rarely (on climbs more than 1 mile) and changing my crankset (which is fine the other 99% of the time) seems drastic. I'd rather just replace the 32t cog with a 40t or as big as possible as a bailout gear.

Cyclist0108

My medium-cage Ultegra rear derailleur can handle 11-36, with a 46/30 double crank. Your mtn bike derailleur should be able to cope with something significantly bigger. You can adjust the B-screw if needed. At worst, you have to avoid using the big chain-ring with the lowest cog.

HillRider

What model crank do you have? If it has a separate 74 mm bolt circle for the granny chainring, you could replace the 30T granny with as small as a 24T. That should provide a much lower low gear without altering the upper range of gears.

Andrew R Stewart 

+1. I have done this very swap on many bikes for me, friends and customers. My usual suggestion is going to a 26T granny. Andy

HillRider

Which is exactly what I have done on numerous triple cranks including SR, Sugino, Shimano and Campy. They have all worked very well.

raria

How did you get the 24t min?

Cass diff = 32-11 = 21
Crank dif = 52-24 = 28

Capacity = 49

But i won't do that. For the tours I ride the bike is oerfect. I just want a bail out cog. Changing the front ring would mean I wouldn't use many of those gears.

twodownzero

you'd probably be shocked at what 48-36-26 offers for range

cpach

You can probably run a 36t large cog with a longer chain and probably clear the cog. You may need a longer b tension screw or turn the existing screw backwards. Your chain will probably run slack in the small small.

I agree that a smaller small chainring or a touring crankset are better ideas. Also you seriously don't need a 52-11 high gear. Consider a cassette with a 12t small cog to keep your gear spacing more reasonable.

raria

Actually I do. With rolling hills and 30+pounds of cargo I charge down the hill to minimize climbing effort on the next.

CliffordK

I was looking at cassettes and gear ranges a couple of days ago. Assuming you're changing more parts than just the cassette.

The crankset I chose was a 53/39/30, although perhaps there would be an advantage of going with the 48x24 as above, but I like the vintage Dura Ace triplized crank... I think... I hope...

Some will depend on the shifters and derailleurs one chooses.

What I found for derailleurs is the GS is the typical "medium/long" cage. "SGS" is the longer cage.

So, I'm hoping to friction shift an M8000 SGS derailleur with my setup. I think it is rated for a 47T total capacity with a max rear sprocket of 46T.

Shimano has messed around with pull ratios and different derailleurs, so friction seems to be a good, cheap alternative.

If your front chainrings have a 22T difference, then that should leave you 25T + 11T = 37T for the rear... hopefully a little conservative.

But, if you're using the front 30T as an escape, then hopefully you will also avoid cross-chaining 30T x 11T.

Anyway, if not cross-chaining your small/small, one should be able to reach 40T on the rear, or even slightly more.

Perhaps there are other derailleurs with a larger capacity, but this seemed quite large.

I'll let you know how it goes together once the parts arrive.

cpach

To each their own. I would not feel the need in the same scenario, and would appreciate the closer spacing. I do spin a relatively fast cadence and focus on tucking into an aerodynamic position when speeds exceed 30mph, as it's generally faster than pedaling from a less aero position. The only time I've wanted more than 50-11 was pacelining smooth descents.

Also, CliffordK, I definitely haven't tried it out, but there's some chance you won't be able to friction shift through an M8000 derailleur. 11 speed dynasys requires a lot of cable to be pulled for each shift, and its possible the total cable pull of your shifter won't be enough. I'd be curious to see how it works.

fietsbob

I have a 16t drop from middles.. 42, 26 and 40, 24, My MTB crank has a 110-58 bolt circles , i have a 36, 22 on it