I have just replaced my 11-32 10 speed cassette with a 11-34 to get an extra granny gear.
Playing around with the Sheldon Brown gear calculator and reading the specs on my rear derailleur (Shimano 105 RD-5701 GS), I have calculated that I am out of spec for the RD, and have been so with the 32 granny gear, although everything has worked and shifted just fine.

10 speed bar end shifters
Triple crankset: Deore 48-36-26

Shimano's specs and my set up in brackets:
Max low sprocket = 30T (34T)
Max capacity = 40T (45T) calculated: (48+34)-(26+11)=45

Should I have concerns, or are Shimano's specs conservative?

Shimano specs are conservative. If it works or if you can make it work, don’t worry about it. My Cannondale T1 has a 44/32/20 with an 11-36 cassette.



I’ve used all of the gears and were glad to have them along the Wisconsin/Iowa driftless area. I did have to resort to a Wolftooth Road Link to make it work but I’m way past the capacities listed for either the front or rear derailer.



My off-road touring bike has a 44/34/20 11-40 drivetrain (but not in that picture). The XO derialer I’m using can be pushed to that gear by screwing in the B-screw. It works very well.

Thanks cyccommute. That’s very reassuring, especially coming from you.

That’s some pretty awesome low gearing you have!

I dont have experience with 5700GS RDs, but I have used 5800 GS RDs and 6800 GS RDs and both handle an 11-36 cassette without issue. I adjusted the B screw to ensure the RD wheel is not touching any cogs and also not too far away from any cogs, but that is just normal derailleur setup.
They have all been with 2x cranksets though.

So no comment on overall chain wrap, but 5800 and 6800 GS RDs definitely handle cassettes larger than what they can officially handle.

Check to make sure that putting on a bigger rear big sprocket will still work with your chain, you might need to add a couple links.

Best to find that out at home when you are using your hand to turn the crank.

Thanks Tourist in MSN, I got home from a two month france/spain tour a couple of weeks ago. It was time to take my bike apart and clean, regrease everything, so new middle chain ring, the bigger cassette, jockey wheels, and of course a new chain. Even new cables, housing, brake pads, bar tape… and rear wheel! … almost like a new bike 😬

I’m done but haven’t taken it out yet as my foot is messed up (long story, but getting better). On the stand, shifting is perfect and I tested big rings cross-chained to be sure.

Sometimes it works, sometimes it doesn't. The hanger length is part of the equation.

I changed our LHT disc models from a 32 rear to a 36 rear cog. It won't work on the large front ring and the 3 largest rear sprockets but you shouldn't need to use this combination anyway so we just avoid this. Has worked fine for years. Can't increase chain length as rear hanger won't handle a longer chain.

You would be better off having a long enough chain for big/big and avoiding the small/small combinations where the chain goes slack. You can ride with the chain slack, you can't ride with the derailleur hanger torn off.

I've had multiple MTBs set up with triples and short cage derailleurs this way.

hi imi, to be sure of your chain length, follow the excellent and accurate steps in this Park Tools video
In the video, he shows two methods, I find the method NOT running the chain through the rear derailleur to be the fastest, less faffing around so a faster job.
You can trust Park tools vids, they are excellent. Well shot, well lit, and the moustached fellow is a great communicator.


as someone else mentioned, having a bit more chain than perfect isn't a big deal, it just means in the small-small combo, the chain may rub against a bit because the rd is slacked all the way backwards, but not biggee at all----too short a chain and if you shift into big-big by mistake and things can get really ugly and the rd or wheel can get pretty much knackered.....you dont want that.

Max low sprocket: Keep in mind that 4T bigger is in circumference, and 4T/Pi/2 = 0.64T radius and this is 1/2" pitch chain and cogs, so 0.64(0.5") = 0.32" in radius difference; That's not much, I think within range of B-screw adjustment. Certainly less than rear derailleur hanger extension gizmos, but you can add one of those if needed.

For several years I had gearing that my rear derailleur could not take up all the slack. But I did not want to risk accidently shifting to the big and big and damaging anything. So, I had enough links that I could not use the smallest chainring and two smallest sprockets.

In my case it was the standard 11/32 cassette, but I removed the 30T granny gear from my road triple crank and put a 24T chainring on it.

That explains why you commented on the Ezy Clic cannister on a different thread recently. You probably had some personal experience with that.

Hah! Yes, although it was actually last year in Portugal that I ran into problems as I had a Primus Duo that broke. I bought a new threaded stove from Decathlon, counting on them having threaded cannisters as they usually do… until they don’t! 😅

This year I bought a Easy Clic adapter, and even a ”puncture” adapter which is useful in Greece as on some islands the small ironmongers/boat supplies can have a weird array of dusty cannisters hidden away since the 70’s.

Thanks djb! The park tool guy is great. My chain is good. I did check big rings cross chained just to be on the safe side

Good. Just wanted to be sure.
And ya, your bike must look and feel like new. Nice feeling getting new parts.

I still have two puncture type canisters. If I use them some day, not sure which I should use. My original Bluet stove that used them, or the adapter?



An old Primus stove on the adapter on the left. Couple canisters on the right. I always put a small piece of tape on the canisters, so after I was done with them I could put the tape over the hole so they do not stink.

I have 11-40t cassettes on both of my bikes with old derailleurs only meant to go to 32t. I used a $10 hanger extender on each and have done many miles without issue

Yes shimano's specs are conservative. If you can live with coasting down hills I would get rid of the 48 chainring.
If your bar ends are 10spd road, not MTB or road tiagra 4700....
Shimano RD-3040
Shimano CS-M4100 11-42
Crankset 22/36 or 22/30/40