Yes it is, Bob! I don't think I've ever seen a DuoPar so fully used!

There is risk and there is serious risk. The only serious risk I see is whether +2 is enough to let the chain ride over the teeth to shift. Which is another way of sayin' "Just what do you mean by 'sized to big/big'?" (Ya' gotta' love punctuation!)

One other possibility, which isn't catastrophic and may depend on the RD geometry, is that pulley cage winds the tension pulley backwards and upwards so far that more tension in the lower chain section can't pull it downward and forward. (See Pastor Bob's second pic.)

[Aside: I once did half of my morning commute with a seriously sagging chain when the RD's pulley cage broke. If I wasn't careful I could throw or bounce the chain off the rings. But it was doable without catastrophic consequences and I even managed a rear shift or two successfully before I wised up and stopped trying to be stupid.]

Now that you mention it, yeah.

Hmm @jimmuller, I think we're getting down to semantics. My understanding is that sizing a chain big/big + 2 should be enough chain for most systems. Too short a chain can pose a serious risk.


But say your chain is long enough but you're exceeding the rd capacity by "too much". (5 teeth, 10t, 20t, whatever.) As I see it the main risk here is that the chain will sag and/or rub on the derailleur in small/small -- not a good thing but you and the bike will be fine. But what about "overstretching" the rd in big/big? My thought is that as long as the chain is long enough this shouldn't be catastrophic, though I suppose an rd could break if overstretched too much -- say parallel to the chainstay.


Anyway, for most real world situations (i.e. exceeding rd capacity by -5t) I see no catastrophic risks **as long as the chain isn't too short**.

This is not intended to be harsh, just helpful.

Option 1 is not boring, it's almost mandatory when building up a bike for someone else. If you're riding it, at least you will be aware of the details of the final build and whatever limitations it will have.

Option 2 It won't be creative, it will be risky. Sure it may work on the stand in the shop but the real world has other plans.

I agree that 1 is not boring. I went with a MTB long cage derailleur and I could not be happier with my ridiculous range of gearing.

Option #3

Put a 46t chainring on the outer position of the crankset. That will drop the the chain wrap value to 29 units. Any Shimano rear derailleur can handle that. She will have plenty of range and will never have to worry about cross chain issues. A 46t chainring linked to an 11t cassette cog provides 30 mph at a 90 rpm cadence.

well put.