gellybellyman

Hello! Does anyone have a similar build for either setup or if these setups are even possible? I’m trying to push beyond the limits of the recommended compatibilities of the components. Any foreseeable problems with both setups?
Thanks in advance!

Setup 1
2 x 10 GRX RX 400 (RD, FD)
11-42T Deore 10-speed cassette
52/36T Tiagra

Setup 2
1 x 11 GRX RX 600 (RD)
11-46T Deore 11-speed cassette
46T crank—if available

Badger6

Theres another thread on here where someone did a 2x build like you just described. He made it work with a derailleur hanger extension. He has claimed success, but be forewarned it is far outside the capacity spec of that derailleur. Shimano lists it as having a total capacity of 41 teeth. That chainring set is 16T (between big and small) and the cassette you list has 31 teeth, for a grand total of 47 teeth.The hanger extenders don't increase capacity, they just make it possible to use the RD with a bigger low cog than they are spec'd to use. And while it is widely accepted that manufacturers spec the equipment conservatively, none of us (that I am aware of) really know what the hard limit is for RD capacity, just that as we play with it, it is clear we can squeeze a few more teeth in without issues. The question is how many teeth, and I've never seen a straight answer. What I do know is there is a point where the chain just won't be fully tensioned in the high gears if it is sized for the low gears and a proper RD cage angle, and all these extra teeth in the drivetrain will be the cause. When you first set it up, size the chain using the big/big +2 method, then see what happens in small/small. If the chain becomes slack on the bottom run when shifting into the small cogs on the cassette, it won't work.

The 1x you describe is similar to mine. I use a 46t chainring and drive a 10-42 cassette shifted by a RX817 RD. It hasn't presented me any issues, but it is 1 tooth greater than the spec'd capacity of 41 teeth, so if there is a problem down the road, it'll be on me to resolve since Shimano will politely tell me I used it out of spec. Your proposed set up though is aiming to exceed spec by 4 teeth. Based on what I experienced when sizing my chain, you may not be able to size it to work on the small cogs while using that same length on the largest (low) cog because it'll be too short and will pull the cage too far forward. Meaning, if the chain is sized for wrapping the biggest cog, it will be too long for the derailleur to take all fo the slack out in the small cogs (11, and maybe 10).

The better question to be answered first, why are you contemplating such large front gears? It appears you are seeking advice for running cassettes that exceed the design specs of the RD to get low gear ratios to climb, so you can have really tall gears on the high end. Do you really need the tall gears? Perhaps you'd be better off using either a more gravel oriented 2x chainring set, or going to a smaller front gear in 1x, or just run a cassette in the design spec of the RD. Good luck.

dwmckee

Badger6 has it covered very well.

gellybellyman

Thanks very much for your response. The large front gear for the 2x makes sure I don’t spin out but I’m heavily considering the 50/34, would this put less strain on the system? Same thing with the 1x, a high ratio for the flats and an even ratio for the steep climbs. I guess I’ll really have to work on fitness for the climbs then. Are there any issues with your 1x setup? Smooth shifting across all gears?

Badger6

Happy to oblige. I'll first say that like you I used to worry about the spin out, and on pavement, sometimes I would. But that was 3-4 years ago. Today, nearly all current gravel bikes have geometries that don't necessarily make them unsafe at high speed, but would certainly make them sketchy in a high speed curve, they just aren't designed to be ridden like a road bike. Spinning out is not something I'd be concerned with if you are concerned about climbing. So...

A 50/34 doesn't solve your problem, it just changes the gear ratios while still leaving you with the same capacity issue that will lead to the potential problems I described above. I really think your best bet is spec'ing a "gravel" crankset with chainrings that are sufficiently low enough that you can run a cassettes that gives you the low end you're trying to achieve with the big chainrings, and forgo the really tall (for gravel) gears you are trying to preserve from the road that won't see much, if any, use in practice. The 10-speed GRX RDs for 2x are spec'd up to 11-36 cassettes. With a 46/30 crankset and an 11-36, you'd have a total tooth count of 41 in the drivetrain...which is the RD spec'd capacity. For a comparison of the actual ratios and functionally how they apply to over the ground speed at a given cadence click here. What you'll see right away is that the 46/30 with an 11-36 has a low end ratio that is slightly lower than the setup you first proposed, with a high end that is a bit lower, but not by very much in practice. If you go the 11-speed 2x route, there is a GRX crank at 48/31 that can be paired with a SRAM 11-36 cassette, while slightly beyond spec, anecdotally seems to be just fine based on what people are reporting, and it would give you much fo the range you are seeking without all of the potential issues your first proposed setup could introduce.

I have no issues with my 1x. Again, as I admitted, it is slightly beyond spec at the rear derailleur, but I've been doing this for a long time, and I went into it confident that I could get it adjusted properly. It took me about 3 minutes on the stand once I had RD and chain installed. I shifted to the biggest cog, and ensured that the b-screw was set right, then shifted to the smaller cog to ensure the chain was pulled taught on the lower run, and then I ran through a Di2 gear adjustment to ensure I had it indexed correctly.

HTupolev

The issue with the chainring combo for the rear derailleur isn't how big they are, it's the chain wrap. There's a 16-tooth difference between a 36T chainring and a 52T chainring. That 16-tooth difference is what tells you how much slack is added to the chain when you shift from the 52T ring to the 36T ring, which the rear derailleur's tensioner needs to "wrap up" in order to keep your drivetrain from going slack.
A 50-34 also has a 16-tooth difference, so it doesn't really change this situation much. Nor would a 46-30 crankset.

The way that a smaller crankset would solve the wrap issue is by allowing you to get similar low gears with a smaller cassette. Consider these two drivetrains:
-52-36 with an 11-42 cassette
-42-26 with an 11-30 cassette
The low-end ratios of 36-42 and 26-30 are almost identical, but the first drivetrain has (52-36)+(42-11)=47 teeth of wrap, while the second drivetrain has just (42-26)+(30-11)=35 teeth of wrap. It would also have a much tighter cassette, which could feel nicer on the road. The main potential drawback is that it would have a lower top-end.


Do you have a road bike? How is it geared? How often do you use its highest ratios, and in what sort of situations?

I'm not sure what you mean by an "RX 600" rear derailleur. The GRX600 groupset doesn't have its own "600"-level rear derailleur; bikes that spec it usually borrow a GRX800-series mechanical derailleur. This would be an RD-RX810 for multi-chainring setups, or an RD-RX812 for 1x.

The RD-RX812 is only spec'd for up to an 11-42 cassette, but a lot of people run it with an 11-46 without any particular trouble. Evil actually specs the 11-46 cassette with the RD-RX812 as a default option on their Chamois Hagar.

This is a bit sketchier, but can usually still be made to work. I have a number of friends running 11-42 cassettes with either the RX400 or RX810 derailleurs.
You may run into chain wrap limits: if you use Shimano's normal chain sizing method of big-big-plus-an-inch, this will cause your drivetrain to go slack if you try to use the smallest cogs while in the small chainring.
If you have trouble getting it to shift well or clear the large cog easily, a hanger extender like a Wolf Tooth Roadlink DM will usually help.

"Sketchy" how? My gravel bike is far more geometrically weird than most production gravel bikes*, but I've used it extensively in spirited road rides without issue. Including lots of situations like fast pedaling shallow descents where the 48-11 top-end gear gets extensive use. As far as high-speed curves are concerned, it can require a consciously-noticeable amount of countersteer to keep it leaned in, but the combination of high trail and narrow handlebars makes this bike a very extreme case and this isn't an unlearnable skill.
Every time I've ridden a production gravel bike, my impression was that it handled much, much more similar to a road bike than my gravel bike does.

*Because it's a drop-bar conversion of an early-80s MTB. Around 80mm of trail and 475mm chainstays on 2.1" tires with a road fit.

Badger6

I'll answer, but not trying to hijack. The position on a gravel bike combined with longer wheelbases, in general, creates a platform that is quite stable, especially on rough surface, but that is sub-optimal for turning while descending. In general, you cannot get as low on a gravel bike as you can on a road bike, yes, I know there are the exceptional cases, but in those cases those bikes are probably sub-optimal for road or gravel.

Back to the thread topic, though, day to day, for most of us, we are never near those kinds of limits on handling unless we've some bad choices in the preceding moments, but in general, we also aren't making use of our tallest gears either. In fact, I went out deliberately looking for gravel and single track, and my 1x drivetrain with a 46t chain ring and 10-42 cassette had me thinking, that with the swap from an 11-42, I should probably reduce the chainring to 42t. Why? Because it'll give me lower ratios at the bottom, and I used my 46/11 combo exactly twice for less than a minute both times. Big tall gears just aren't necessary on gravel bikes unless we are pros going to race in Unbound Gravel or some other epic race.

jonathanf2

I built out something similar to setup 1 using the 11-42t Deore 10 speed cassette, but with a sub compact crankset of 46/30t and using a Goatlink. It's not the smoothest shifting either, but for the hills I was climbing I really wanted that 42t at the back. I ended up picking up a 2nd wheelset using the max size 11-36t cassette for those times I'm not hillclimbing just because it rides better. Also Setup 2 should be possible with the GRX 600, but again most likely with a Goatlink and you'd have to test it out at 46t or maybe go smaller like a 42t or 44t.

Have you considered going 3x and/or a different 1x groupset that accepts larger cassettes in stock configuration like Microshift or Sensah derailleurs? Seems like a hassle to push the GRX groupset way beyond spec unless you already have these derailleurs laying around.

rosefarts

I don't know if you've already purchased shimano stuff but if not, consider SRAM.

Their long cage is spec's at 42 but I know lots of people who use it up to 46.

I ran Rival 44x11-46 when I first got my bike. Once I made the chain long enough, it shifted fine. I still had room left on the B screw.

For weight reasons mainly, I switched to XD and went with a 10-42 (then wolf tooth 44) with a 38t front ring. I've got excellent climbing gears and the 38x10 gets me down whatever I need. And if you're wondering, it did allow me to get my steel rig under 20 lbs, meaningless but a milestone I wanted.

If you really want high gears, you could do a setup like mine but use a 42 front. 42x10 on a 43mm tire is 117 gear inches. My road bike (which I have gotten to 55+mph a few times) is 50x12 at it's highest, that's 110 gear inches.

I used to ride 53/39 and 11-25 on the road. Even with that setup, I still found myself coasting and tucking in fast descents. It's faster than pedaling. I do real damage to my friends ego's uphill. It's nice to let them beat me down by 30 seconds.

On a gravel bike, I haven't seen need to pedal much more than the low 30's. Besides, dirt descents tend to have washboards, switch backs, cattle guards, and large white trucks. All of which will check your speed before you're out of gears.