Mixed surface riding - GRX di2 or Ultegra Di2?

I'm building up a Moots Routt RSL for mixed surface riding and trying to decide between Ultegra di2 or GRX di2 component group.Will use the bike for about 50% asphalt riding and 50% gravel - not hardcore single track gravel, but jeep trail type gravel with hills. The terrain where I live is hilly, but not mountainous.

I'm leaning toward's Ultegra with 50/34 crank paired with 11-34 cassette, but would like to hear others recommendations. I know GRX offers 48/31 crank, but I'm concerned about losing the higher end of 50/34 for road rides and thinking the low end of Ultegra may be enough for my hilly gravel rides. Also, I think the aesthetics of Ultegra are superior to GRX. That GRX crank is just plain ugly. 

What am I missing?  

Well one other benefit of the GRX crankset might be the tire clearance it offers, since it is set further outboard.

As far as the gearing, only you can know for sure, but you do realize that 48 is only 4% lower than 50 right?
So if you were spinning at 96 rpm with the 50t, you’d be spinning at 100rpm on the same descent...
or, if you were at your max cadence, you’d spin out at 48mph instead of 50mph...
Hardly likely to break your day, unless you are racing at a high level.

Rather the opposite, the 48 would allow you to stay in the big ring longer, so, a bit more efficient maybe.

GRX RD has a clutch, which is less of a big deal with 2x, but pretty much mandatory with a 1x...

FWIW, the RX805 provides an Ultegra Di2 option with a clutch. However, the GRX 817 can handle a larger max rear cassette tooth count (40 or 42 vs 34 for the ultegra).

I haven't worked w/Di2 components, but seems like you 'should' be able to use ultegra on the front, and grx on the rear to get the best of both worlds (this is possible with mechanical). A brief search seems to indicate this is supported with Di2. Maybe someone else here can provide a more authoritative indication.

On the gearing: how often do you use your 50-11 top gear?
For me(not a wattmonster)and the riding I do, the answer was “rarely”, and I was happy to swap my 50/34 for a 46/30 for mixed-surface riding.  I wouldn’t go back.
If you do the numbers, a 46-11 is almost identical to a 50-12, so you’re not losing much on the top end.  With the 48/31 you gain proportionally more on the low end than you lose on top.

My bike(pre-GRX) came with Ultegra 8000 mechanical with the clutch rear derailleur.  My setup is 46/30, 11-34, and I've had no issues with the drivetrain or brakes.  
If I were buying now, I'd probably go with GRX for the gearing options and the ergonomics of the levers.

One thing is that Shimano USA has great customer service so if you call them you can ask about potential component combinations and they will tell you if they will work together. Also, consider making your own chainring combinations; I have 52-34 on an Ultegra crank on my gravel bike with Di2 and it works great. I have been running 53-36 on a road bike for about 5 years and that also works perfectly. Di2 front shifting is very capable..

Yes, I ride in my 52-11 quite a bit on gravel. I am a low cadence rider so pretty much any longer/steeper downhill I'm in it.

Angstrom wrote:"Yes, I ride in my 52-11 quite a bit on gravel. I am a low cadence rider so pretty much any longer/steeper downhill I'm in it."

If we were all the same it'd be a boring world.. ;-)

That's a great example of why all advice should be taken in context.  My riding style and riding conditions may be completely different from yours, and drive a different set of equipment choices.  

With age(and hopefully, wisdom) I try to be less concerned about what is "The best....", and try to be smarter about what is the best for me.

Exactly. And don't be afraid to create what you think will be best for you. Frankly, I am amazed at the very limited number of chainring combinations that are offered. 

tallen67 wrote:I'm building up a Moots Routt RSL for mixed surface riding and trying to decide between Ultegra di2 or GRX di2 component group.Will use the bike for about 50% asphalt riding and 50% gravel - not hardcore single track gravel, but jeep trail type gravel with hills. The terrain where I live is hilly, but not mountainous.

I'm leaning toward's Ultegra with 50/34 crank paired with 11-34 cassette, but would like to hear others recommendations. I know GRX offers 48/31 crank, but I'm concerned about losing the higher end of 50/34 for road rides and thinking the low end of Ultegra may be enough for my hilly gravel rides. Also, I think the aesthetics of Ultegra are superior to GRX. That GRX crank is just plain ugly. 

What am I missing?  

So i've just been through the exact same thing. I have an R8000 Ultegra crank with 4iiii double sided PM. I don't believe there are GRX cranks with dual PMs yet so that was a big factor for me. I think that in terms of top end a few friends have said that 48 would be fine on road - how many times have I spun out my 50 on the flat - prob never at my level of fitness and i'm not concerned about being unable to push down hills steep enough to spin out because i want to rest some on long rides. Agree re how ugly the GRX cranks are too.

I use my gravel bike mainly on road but in the UK our 'gravel' is farm tracks, some actual gravel, flint tracks, single track, mud, etc, not lovely long fire roads, so i'm about 80% road and in the winter prob 90%. i did a 600k gravel ride in South Africa last year and only on a couple of climbs was I wishing I'd had lower gearing, the rest were manageable on 50/34 11-34. 

I *think* you can pair an 11-36 with a road Ultegra RD and I imagine it might be slightly easier with a GRX RD but I'm not technical.

All said and done last week i ordered:
GRX Di2 shifters (regardless if you go all road Di2 apparently these shifters are the best in terms of ergonomics and braking with a number of reviewers saying they'd spec them on future road bikes because they are that good).
GRX callipers
GRX Di2 RD
R8000 Di2 FD

HTH

Like a few other posters have already said you have to find out what works for you. At my end I came from a completely different end. I had Sram Rival 1 on my Raleigh Roker gravel race bike and hated it. Ok when riding alone but when riding with a group I was shifting all over the place to ride their speed. I went with the GRX mechanical Ultegra 800 series I believe and have 48/31 and 11-40 on the rear. It has plenty of top end spend and with the 40 on the rear 31 x 40 I can climb almost anything. I call it my bail out gear. Not sure your age but I am 69 and not afraid to admit I am out of shape. I love my GRX and that is all about I can say. I have the bucket list goal of riding a 50 mile gravel bike ride/race in all 50 States so I never know what I am going to come up against.

Good luck on your build. Maybe see if you can find a GRX Di2 on a bike somewhere and see if they will let you take it for a test ride.

Zman

My $0.02.  I'm running the Ultegra 805 Di2 with clutch.  I have the luxury of swapping from 1x or 2x because of an Easton crank.  Shimano plays things conservatively in terms of what they claim the derailleur will manage.  I'm currently running 11-42 with a 42 tooth ring and the derailleur handles it with aplomb, across the range and no issues.  I know that the OP is planning to run 2x.  I haven't mated the 50/34 2x with the 11-40 cassette. 

Just a mention about the 1x.... I only miss the top end speed on prolonged downhills.  I have plenty of gear for flats and gentle downhill grades.  I tend to pedal out at about 32-34 mph.  I'm not racing with this setup.

Terry_BetterShifting wrote:

• All derailleurs must be from the same category.
  (GRX/Road is one category, MTB is the other)

This saved me a lot of headache, I was hoping to go xt derailleur in the rear to do 1x w/ a 46T cassette. I guess 2x GRX DI2 it is.. THANKS!

Only the front and rear derailleurs need to be from the same grouping, meaning GRX/Road FD will only work with a GRX/Road RD.  You can't use an XT/XTR RD with GRX FD.

If you want to run 1x, I believe you can use any combination of Road shifters and MTB RD you want.  I run an XTR Di2 RD with Road SWR-9150 road climbing switches mounted on my drop bars....

JWB475 wrote:
If you want to run 1x, I believe you can use any combination of Road shifters and MTB RD you want.  I run an XTR Di2 RD with Road SWR-9150 road climbing switches mounted on my drop bars....

Wow, so I can run GRX DI2 1x with a Mountain DI2 rear der? Hmm.. What kind of gearing do you run? I ran 1x on my mountain bike with 9-42 and felt like i was missing some range (or i was in denial it was a mountain bike.. so maybe it wasn't meant to have road oriented gearing?)

I was considering running the 9-46 XCX cassette with maybe a 40-42T front ring.. but i tend to do a lot of climbs so i might be underestimating how small of a ring i should go in front.

JWB475 wrote:Only the front and rear derailleurs need to be from the same grouping, meaning GRX/Road FD will only work with a GRX/Road RD.  You can't use an XT/XTR RD with GRX FD.

If you want to run 1x, I believe you can use any combination of Road shifters and MTB RD you want.  I run an XTR Di2 RD with Road SWR-9150 road climbing switches mounted on my drop bars....

Yep, definitely correct. My comment on mixing derailleurs only applies to.... derailleurs. 
If you only have one derailleur then you can use whatever you like.

You could also use two MTB derailleurs with GRX shifters if you wanted to, or e-bike shift buttons / brakes, or any other crazy combination you can think of.

The compatibility charts will always tell you whether or not things will work together: https://e-tubeproject.shimano.com/guide/#guide_list

arctic84 wrote:

Wow, so I can run GRX DI2 1x with a Mountain DI2 rear der? Hmm.. What kind of gearing do you run? I ran 1x on my mountain bike with 9-42 and felt like i was missing some range (or i was in denial it was a mountain bike.. so maybe it wasn't meant to have road oriented gearing?)

I was considering running the 9-46 XCX cassette with maybe a 40-42T front ring.. but i tend to do a lot of climbs so i might be underestimating how small of a ring i should go in front.

I live in Minnesota, so a major climb for me is ~300' of elevation in a half mile or so.  I use a 10-42 cassette and a 42 tooth chainring and it is plenty of gearing for me around here.  I have an XCX 9-46, but have only used it on my fatbike.  If I were to do some bikepacking, or ride in real mountains, I would definitely use it on my gravel bike.

I ride in NH/VT where 1000’ vertical for every 10 miles is normal.  I knew I wanted better than 1:1 for my lowest gear.  Currently using a 2x setup with 46/30 front and 11-34 cassette.

There are a number of gear ratio calculators you can play with to help determine if 1x is going to work for you and provide enough range.  

https://www.berkshiresports.org/bicycle-gear-ratio-comparison-calculator/

Obviously the bigger the cassette the bigger the jumpsbetween gears.  I have plenty of range with my setup, but the jumps between gears are not ideal, there can be a 10+rpm difference with a single downshift.  It never used to bother me, but I notice it more lately....