alias5000

Hi everyone,
before I spend the money to try it out, maybe someone has tried this already and can tell me if/how well this works out:
Current gearing setup on our Cannondale:
53/39/30 front chainrings, 10-speed ultegra. Rear is 11-32T with medium-cage derailleur. For an upcoming trip it would be nice (though likely not absolutely required) to have some more lower end gearing. I already own a 9-speed deore rear derailleur (this guy) and some extra chain, so that a wider range cassette would theoretically be sufficient to get there. However: chain wrap capacity of this derailleur is only 43T. If I were to go to an 11-42T cassette, I'm at 54T difference. Would this be pushing the limits too far, or would this still be in the 'conservative design' buffer? Anyone tried this?
And: Did you have to (have to) use a roadlink?

Thanks!

sch

A road link would make the RD a lot more comfy with clearing the 42 though even then it might be better off at 40T. Chain wrap would be a problem
no doubt requiring rigorous attention to not going to far up the cassette when in the 53 or down the cassette when in the 30 chainring. Easy to lose
track of this however. $50-80 or so for a 50T big ring might help. That would drop you to 49T difference for relatively nominal costs. Do they make
a 10spd 11-42 cassettes? Seems like really big jumps there above 30T. I am building up a 10spd tandem with an 11-36 where the last 3 cogs are
4 tooth jumps.

A google shows the cassettes exist and are cheap: $35-45, whole bunches of them.

bakerjw

For our road tandem, I am using the same as you. 30-39-52 Chainrings and a 11-34 Cassette
For my rear derailleur, I have a Deore XT SGS derailleur. Although I've not tried going much higher than the 34, I believe that I could fit in a bit larger cassette if I wanted. When I get home I'll see how much leeway that I have and get back to you.

In the past I've pushed the envelope a bit on builds. My first bikepacking bike ran a 24/40 chainrings with an 11-36 cassette. Of course that is with an SGS cage.

alias5000

Thanks, that would be great

bakerjw

I went out and checked this morning. This is what I observed using the following gear combinations
Largest sprockets - Front 52 - Rear 32 - The chain is not completely straight through the guide and tension pulleys.
Smallest sprockets - Front 30 - Rear 11 - The chain coming around the tension pulley is parallel.
v v v Looks like this v v v
___*
*____________________

I might be able to squeak in an 11-34 but not anything greater.
To get the end result that you want, I'd look to drop the front 52 to a 48. That might give enough slack in the chain to be able to mount a 33-42 cassette.

I like playing with combinations like this to see what can be done. There are formulas and such but sometimes swapping out components and tinkering is more rewarding.

OneIsAllYouNeed

alias5000

Thank you everyone, your comments altogether make a very complete picture and should be enough to make a decision.
Tandem season has started as of today. So I'm hoping for a few opportunities to gauge our actual gearing needs on these teeny-tiny hills that we have.

Luckily I still have all the chain cut-offs, so that extending our fairly new chain won't be an issue. It seems to me that an 11-36 cassette would get me about half-way without much trouble. To get all the way, I would likely have to drop the smallest chainring from 30 to 26. Not sure yet if my front derailleur is going to take that (FD-6703 on 30/39/52). Dropping to a 50 chainring would be possible, though I'm not sure if I want to invest that much money into this particular project (cassette + 2 chainrings).

Good to know that the SRAM derailleur has a 47T capacity. This setup sounds amazing!

Carbonfiberboy 

We're running 53-39-26 and 11-34, using a Shimano 9-speed XTR rear. This XTR works fine with 10 speed. Chain is sized to big-big + 1 link. Chain wrap is never a problem.

alias5000

Thanks. Looked at the front derailleur and there seems to be tons of space for a 26T small ring without changing FD position. Also found an affordable 11-36T cassette. I'll pursue that route.

tyrion

I rode on a too-short chain for about a year with no mishaps (I managed to avoid shifting into big-big sprockets). It was on my mind though, when riding.

You can always make a chain long enough to handle whatever big-big sprockets you have, and if your derailleur can't handle that capacity you pay a price shifting into the small-small sprockets - but that price is a dangling chain and (usually) not catastrophic.

alias5000

Alright, a quick intermediate update: I found a cheap 24T chainring that is now on our triple. That makes for some very nice and easy gears and the job is almost done. Two things remain that I will deal with in the next few days:
(1) the chain drops quite a few times when shifting from the 39T to 24T chainring (haven't figured out the exact conditions yet, but I think they are pretty reproducible). Well add a chain catcher for that which will be ordered very soon.
(2) much more work for way less output: I have an 11-36 cassette that is supposed to replace the 11-32 cassette. Need to change cassette, swap out derailleur (road link to be used with current mid-size cage derailleur in the future on order) and extend chain length.
This should be a very workable setup in the end.