epfatboy

I have a Trek Domane with DI2 Ultegra 12 speed. I plan to ride the Mt Washington hill climb. Not racing anyone just want to get up it so I need to gear appropriately. The rear cassette is a 11-34 which should work assuming I swap out the front which I hope I can do.

My thought is buy a 48/32 crank and appropriate BB. That should give me the gearing I need plus some bail out.

2 questions:
Will the Di2 front derail be setup to work with a new front crank? I really probably only need the inner ring for the climb but if I could get the big ring too I’d take it as I’ll do a few training rides near mt Washington before the race.

Any comments about the gearing? Again I just want to get up it, thinking 90ish minutes assuming no snow/wind/whatever else…

HillRider

Lower is better and too low is barely enough. Your proposed 32x34 gives a 25.4 gear-inch low gear which isn't all that low. At a minimum, I'd buy a 46/30 crank to get a 23.8 gear-inch low. I know of past Mt. Washington riders who would use a 24T or 26T granny ring on a triple crank with similar cassette gearing for that climb.

Iride01 

As long as you can move the front DR to the proper height above your big chain ring it should not care what you put on it. Though the settings in e-Tube may not have the ring combos to display to you so it can show you the proper ratios of the combos when you set up semi and fully synchronized shifting patterns, but that's not a issue for the shifting of the chain.

No comments I can make on your gearing since I don't know how strong you are or even if the change is from a 50-34, 52-36 or 54-40. If you currently push Shimano's 54-40 crank up a 5 - 6 percent grade, then I think you'll have no issues with the 48/32 on a 9% grade for 7¼ miles.

Between now and August 20, ride as many long steep hills as you can.... often.

pdlamb

What you call a low gear I'd call a road-bike-too-high gear.

But if you're substantially younger, lighter, and stronger than me, good luck!

xroadcharlie

It looks like your bike came with a 50/34T chainring. If that's the case, Switching to a 48/32T isn't worth the effort. To make it worth the effort and cost you would need to go as a minimum to a 46/30T chainring.

For serous Hill climbing, Which it looks like you'll be doing I'd go with a 44/28T chainring if that's feasible. The 46/30 might work, But it probably won't be fun, and I doubt very much you'll have a bailout gear. The 44T ring will still permit 41+ kph at about 80 rpm and you'll have lower gears for climbing.

freetors

I'd also throw in the option of getting a wide range cassette. I seem to recall many gravel riders stating that the di2 ultegra derailleur being able to shift some pretty big cassettes, like in the 40t+ range.

Iride01 

Which specific version of the Ultegra Di2? The road group 12 speed DuraAce or 12 speed Ultegra DR the OP must have is only spec'd to a large cog of 34 teeth.

Though I know the yada yada of the specs being conservative and the yada yada yada of the wolf tooth extended hanger. But to me any of those are an experiment and may or may not work depending on specifics of the bike they are being put on.

freetors

I don't know the specifics, only suggesting an alternative.

My personal bike has a grx 2x di2 derailleur that's only supposed to work up to a34 or 36t cassette, I don't really remember. But I'm using a wolftooth link and 42t cassette and it works just fine.

epfatboy

After more research I think I’ll just go with shimano’ 12 speed mtn double/bb. I’ll be able to keep my 11/34 rear and have plenty of room to tweak the gearing up front. Thinking a low side of 26 would be a good place to start.

This hill climb thing isn't something I want to make a habit of. I’ll cut back to the road cranks after the climb. I guess I should mention I’m not in a hurry to cut over to the mtn cranks either but I figure I should sort this out.

Once I’m set up I hear a weekend trip to Mt Ascutney will help me dial in the gearing, lovely 😎