Chi_Z

only the di2 has the new pivot, grx mechanical is exactly the same as ultraga but with different hood, in fact you can install the grx hood on ultraga mechanical. the lever does have a grippier finish though

zen_

Just echoing what was already said; there is not a GRX cassette. The 2x GRX systems are most commonly built with a 105 or Ultegra 11-34 cassette, while the 1x system usually comes with an 11-42 Deore XT. I would think that a 50/34 Ultegra crank would be fine for 80/20 road / off-road, but it just depends on your needs and climbing ability. You could build it with an 11-30 or 11-32 cassette that has road cogs (e.g. 11-12-13-14-15-17-19-21-24-27-30), an 11-34 that is more off-road oriented (11-13-15-17-19-21-23-25-27-30-34), or even a big 11-40/42 mountain cassette.

Having said all that, if you want the GRX levers, crank, and derailleurs...maybe best to wait a few months to build it that way unless you were really on the fence between Ultegra or GRX for a road bike that goes off-road sometimes.

xseal

There also aren't GRX brake rotors, people use either Dura Ace, Ultegra or my favorite, XTR.

MichaelTapp

Thank you for your feedback! So a 50/34 crankset with a 11-40/42 mountain cassette in the rear will still get you to a place with a low gear for climbs with luggage?

mstateglfr 

If the drivetrain can handle this large of a tooth count, then great.

The GRX 810 is a 2x rear derailleur with 40t of total capacity and handles a large cog of 34 officially(and can handle a little larger unofficially, like 36t for sure).
The GEX 812 is a 1x rear derailleur with 31t of capacity and handles a large cog of 42t officially(and could handle a little larger unofficially).


A 50/34 cassette with an 11-40 cassette gives you a 45 tooth capacity which is well above either official RD capacities. Crazier things have worked though, so maybe this will too with the 810 RD. I've seen posts about making it work by using a longer b screw and/or a goatlink.

...or just buy a 46/30 crankset and an 11-36 cassette. Using a 40mm tire...
50/34 with 11-40 gives you 126 gear inches down to 23.50 gear inches.
46/30 with 11-36 gives you 115.5 gear inches down to 23 gear inches.

So 46/30 with 11-36 is lighter, has a slightly lower bailout gear, and still has plenty of top end speed since you are moving at 27.5mph at 80rpm.

zen_

I saw a couple bikes setup that way last year with the Ultegra RX805 Di2 derailleur (listed capacity 39t). The 50-40 gear may not work, or be extremely marginal, so I guess it depends if a person is comfortable with taking it from suggested not to use, to do not use.

I agree with you though that a 46/30 crank is going to be a much better option if he doesn't know for sure what gearing will be needed, and will be hauling luggage too.

Cyclist0108

Before I switched from a 50/34T crankset to a 46/30T, I did a quick calculation. Assuming your cassette's highest gear is 11T, you lose exactly 1 gear off the high end. Unless you spend a lot of time in the 50T/11T combo, you will never miss it (and if you are spending a lot of time in that combo, you should be gearing up, not down).

MichaelTapp

Thank you all! I was ideally going to get the GRX RX810 groupset. It comes with a 48/31 crankset, not 46/30. Is there a noticeable difference between the 48x/31 crankset and 46x30?

mstateglfr 

https://www.bikecalc.com/gear_inches

Mess around with this website. enter your tire size(or closest avail) and enter the gear ranges you are considering. You will see how much different 31t is from 30t and 48t is different from 46t.

On the left you can also see the speed difference in gearing based on your cadence. That is helpful to me as it helps confirm that going to smaller gearing really doesn't hurt me much for speed.

Steve B.

That's a weird calculator. I punched in a standard Shimano 11-34 and it gives me calculations for cogs that do not exist. I would recommend this site though.

Mike Sherman's Bicycle Gear Calculator (mike-sherman.github.io)

mstateglfr 

You choose which cogs to pay attention to. Seems simple to me.
Maybe I misunderstand the issue though.

msu2001la

Other threads on BF have suggested that this doesn't work and/or isn't recommended by Shimano as the hood designs are slightly different. YMMV

msu2001la

I'm not aware of a GRX cassette. All of the GRX bikes I've seen are specified with normal shimano road cassettes.

babylovege

In case u ride on gravel, you'll know that you need rd with clutch(like ultegra rx or grx).

Chi_Z

on the shimano grx product page they literally have a picture of grx shifter with ultegra hood

MichaelTapp

Thank you sir! Yeah, I forgot about that and I am planning on doing a 350 mile gravel ride! Allegheny passage/Seminole path

Cyclist0108

You don't need a clutch. On my one bike that has one, I took it out.

mstateglfr 

I rode thousands of gravel miles for multiple years on a 105 5800 rear derailleur. Never dropped a chain and a simple chainstay wrap of old tube eliminated chips.
I have a clutched RD now and I guess its good, but its hardly a need.

shoota 

Agreed. I feel like people spout off about a clutch rd like it's the magic bullet for not dropping a chain. My buddies and I have had more dropped chains with our 1X systems in the last year than dropped chains I've seen in my whole life combined. The problem I'm finding out is that the clutch doesn't do anything for the chain tension from the chainring to the top of the cassette, it only keeps the lower portion of the chain tight. So if your chain is just ever so slightly worn and you hit a bump just right, there's more than enough side to side play in the top portion of the chain wrap to knock it off the (narrow-wide) chainring. It's absolutely maddening.

mstateglfr 

Funny you mention where the slack and tension lies within the chain because over the last 18 or so months that Ive had the Ultegra clutch RD, I have looked down at the chain while riding and thought 'man thats a lot of chain bounce. its as if the clutch isnt on'.
I am just looking at the part of the chain that isnt tensioned though, so from that perspective the chain is quite loose.
Glad you mentioned this as its one of those things Ive observed many times, but never cared enough to look into, yet question what is happening the next time I see it happening. repeat cycle.

shoota 

You just described my last year of gravel riding. I finally said "enough" and bought a fd to install. Back to 2X I go.

msu2001la

It may not be a magic bullet for all situations, but i also have no idea why someone would build up a gravel bike and not use a clutched RD at this point.
I don't really see a downside.

dwmckee

For gravel, the GRX groupset is superior and worth the small bit of extra cash in the log run. It is versatile so in the futire you can gear up or down easily and can convert 2x to 1x, has great hood grips, wider chainline etc.

When you put the 9er side by side with the Renegade S2 or S1 it is hard to see why you should shell out so much extra cash for the 9er. Both are excellent bikes with a deep investment in gravel and great brands behind them, but cannot see why to pay so much more for a 9er.

mstateglfr 

For sure. The 5800rd I used 5 or so years ago was because a road clutch rd didn't exist at the time. Had one been around, I would have bought it.
As you said- no downside. Heck run it turned off even...that really shows there is no downside.

dwmckee

+3!