Options for better hillclimbing with the GRX 400 groupset
 

I'm looking at options to get better hillclimbing with my 2x10 GRX 400 groupset currently on my bike. One of the options I was looking at was getting a bigger cassette from my current 11-34t. From previous threads on this forum I've read it's possible to go up to 11-40/42t with the GRX 400, though shifting might not be smooth on certain gears. Besides cassette, I'm guessing I would have to get a new chain to accommodate the bigger gear range? Is it possible I can also size down my front chainring from a 30t to a 28t instead of swapping out the cassette, would that be possible with my current setup? I'd lose some speed with the small chainring, but I'm usually riding solo and I'm mostly on the big 46t chainring when road riding, so I could focus the small chainring solely on hillclimbing.

I'm also open to any other practical suggestions, besides just getting stronger (I regularly strength train with weights)!

Thanks!

You can definitely go to a 36 tooth cassette in the rear with no issues (your current chain likely will cover that extra small amount. of reach) and that will give you about the same lowest gear as going down 2 teeth on the front. You cannot just go to a smaller inner front ring without likely affecting shifting performance since GRX 400 front derailleurs are designed to shift a 16 tooth difference between large and small ring. You may be able to switch to a smaller 2x MTB crank and derailleur matched to that crank, but I am thinking that is more than you want to do.

On the streets 11-34t is a breeze, it's just for these steep mountain fire roads I'm climbing where I feel I could go one more gear lower. Do you think 11-36t would affect my big front gear though? Not that I ever ride the 46t front with the 34t rear, since it's better just to drop to the small chainring, I just want to keep the bike riding smooth while gaining slightly better climbing. Thanks for the help so far!

I have a SRAM 11-36T cassette with GRX 46/30T up front and Ultegra derailleurs on one wheelset. This works without issue. I just had to adjust the B-screw (my derailleur officially goes up to 32T). You should be fine. A smaller front (if you could even find it) will negatively impact shifting. I can cross-chain with no problem (but you shouldn't need to do that).

The link I have is to Amazon, but it is better to buy from a company that doesn't make its employees piss in a bottle.

Thanks, I'll swing by my LBS and see if they have something similar.

I forgot to mention I'm on a 10 speed setup. Is there a big performance difference between the SRAM 1050 and 1070 series cassettes? The corresponding cassettes for 11 speed would be the 1130 and 1170.

Sorry I missed that. I put the equivalent 10-speed version on my wife's bike. If there is a difference, I didn't notice. In general, I am a Shimano person, so I really don't know anything about SRAM.

Just do not cross-chain the big-big combination. You should not do that anyway. When you ave the cassette on and while bike is in a stand clowly and CAREFULLY hand crank the bike and work your way up too he big-big combination. watch the rear derailleur as the chain comes up and if it is starting to reach the limits of stretch STOP and get a longer chain... The longer chain will then work in the big-big combination if you go there by accident, but you still should avoid the combination.

No. There will be no big performance difference. Typical cassette differences are...
- overall weight
- surface finish
- number of largest cogs paired together which reduces freehub gouging
- use of aluminum or plastic resin cog spacers

For SRAM, the cassette lockring usually weighs a little less on higher end cassettes and they use resin cog spacers.

Quick question since I'm already on a Shimano GRX setup, should I just go with the Shimano HG-50 vs the SRAM 1070, both 10 speed, 11-36t cassettes? I found the Shimano one for almost half off compared to the SRAM version. I'd presume the Shimano cassette would play nicer with the Shimano derailleur. Is there anything I'm missing?

On a side note I also have a set of 26" MTB disc wheels I was thinking that I could throw the old cassette on and use for rockier terrain. I was thinking it might be a cost effective way to get a second wheel set. Any issues I might find running 26" wheels on a 700c bike?

A Shimano cassette wont 'play better' with a Shimano drivetrain. There is 0 difference. Both Shimano and SRAM cassettes are designed to shift quickly and easily. To decide which you want, consider cost, appearance(some are silver vs gray vs black), and shifting gaps based on cog selection. If you really want a 12t cog and the Shimano goes from 11t to 13t, then you are out of luck. Thats just a general example. Some people really care about where the shifting gaps are located on a cassette and other people couldnt care less.


As for the 26" wheels, no harm in tossing em on and trying it out. The different wheelsize will change the steering feel, lower the bottom bracket which reduces clearance, and may or may not fit based on chainstay and seatstay bends. It doesnt hurt to try, but it also doesnt seem like you will gain much from it. If I am riding gravel roads and a 40-45mm tire isnt enough, then I would probably look at using an entirely different bike for the job.

In terms of application when you're turning cranks and shifting gears, no...in terms of how much money comes out of your wallet, yes. xx70 weighs less than xx50, but not by enough to matter for mortals like us.

Are the hubs compatible with your current bike's dropouts? Meaning, same dimensions and mounting system. As for rockier terrain, are you looking for something that rolls easier over the rough stuff? I recommend you do some research into 650b vs 700c comapros.....my takeaways (as a guy who rolls on 700c rims) is that 700c spins up slower, and requires more effort to climb, BUT it handles the rough imperfections of a trail/road better than 650b (meaning less deflection) which means it handles the rough much better than 26". That said, if you can mount them, go ride them and see how they compare.

The only reason I was even considering the 26" wheels was due to already owning them, freeing up a spare cassette with the upgrade and experience toe rub on technical terrain. I guess it'll be one of those things I'll have to try out to see if it works out for me.

I suggest buying the cheapest cassette, that way when you realize +2 teeth doesn't make enough of a difference, you wont have wasted so much money when you buy the 11-42.

But there is fair chance the 42 tooth will not work with current derailleur and chain. With the 36 tooth you are probably 95% likely to have no problems with current setup. The 34 to 36 tooth is about 1/2 of a typical gear step lower, and maintains decent spacing between your other gears.

Better than fair. Max low sprocket size (as spec'd by Shimano) is 36T. You will see where folks might get an additional 2T out their RD, but let's be realistic, at that point you're running the RD beyond spec and performance MAY be affected, as in won't shift reliably onto the low (biggest) sprocket.

IMO, without scrapping the existing drivetrain and converting to 11 speed (or even 12 speed) and 1x up front, the best option for the OP is to get the 11-36 cassette. It does increase the total gear range a modest 28% from 474% to 502% and it will drop the ratio from 0.882 to 0.833, again modest providing an addition 1.3 gear inches, but it is something.

The way to get a derailleur to handle huge cogs is to get the jockey way to sit farther from the cogs (through b-screw and/or hanger extenders), so poor shifting is more likely to happen in the high gears.

I have one friend using a RX400 derailleur with an 11-42 cassette and a 48-32 crankset, and it seems to work mostly alright. I don't remember if he's got a hanger extender, but they're easy to add if needed.


I don't see what that solves.

A mountain 1x could certainly achieve super-low gears, but that's got little to do with it being 1x.

Thanks for all the suggestions so far. I went ahead and ordered a Shimano HG-50 11-36t 10 speed cassette. I may consider going 11-42t down the road, but that depends how I feel after riding 11-36t. Also from what I read, it might be necessary to upsize my small chainring to a 31/32t if I do go with the 11-42t to insure smoother shifting. I think for now I'll see how the 11-36t works out. I want to keep things as close to plug-n-play as possible before doing more upgrades.

I'd be really curious what mods were performed to make a 41T capacity RD handle "alright" a 47T total capacity (16T on the crankset and 31T on the cassette). If the b-screw is long enough, in theory you could get the RD to clear a 42T sprocket, but the RD was designed to handle a 36T maximum low sprocket, and while it is common (I've done it myself) to run a few teeth more than spec'd, 6 teeth sounds like a lot. Regardless, the capacity of the RD is still 41T. Several years ago I set about to widen up the gear range on a bike, and ignored the capacity on the RD, and it shifted terribly, and then I got smart on why, and now won't exceed it. Maybe Shimano builds more fudge in the spec'd design now, such that when they say 41T it can reliably handle much more. This is a lot of words to say that the manufacturer specified design of the GRX400 RD precludes an 11-42 (25T spread) cassette with a 16T spread on the crankset.

If this is something the OP is planing to do, unless they've got extensive experience doing their own wrenching, it would require some serious discussions with a knowledgable and trusted mechanic. I will modify my earlier comments to say, these things may be possible, but they aren't as simple as juts putting on whatever cassette one desires to run and turning the b-screw in.

Also, one doesn't have to go to a MTB group to get the components to run 1x...but the GRX400 level won't do it. It was designed to be run in a 2x drivetrain.

Your RD will be beyond its spec'd capacity with that 11-42 cassette and any tooth spread on the chainring that exceeds 10T. Going with a larger small chainring will help offset that, any little bit will help. I don't recommend exceeding the RD capacity though. Good luck.

I found this lengthy thread on another gravel bike forum using a big cassette with the GRX 400. From what I'm gathering, 11-36t will be easiest to swap out with little to no issue and after that more care will be needed going 11-40/42t, but it is doable.

Honestly I don't need that much extra help in low gear if I'm riding a trail fresh, usually I can go uphill no problem with the 34t rear, but if I'm doing a lengthy road ride before hitting an uphill trailhead, fatigue starts kicking in and 34t starts to feel heavy on my legs.

I am pretty sure Shimano's spec for the 400 rear derailleur is 34 teeth max capacity and a stretch to 36 is almost always no problem. Some get away with 40 or 42, maybe with a hanger extender, but that gets sketchy..

"Total capacity" in Shimano spec lingo just refers to chain wrap. The caveat to exceeding it depends on where you err on chain length: err long and the drivetrain will go slack in the smaller cogs when you're on the small ring, err short and the drivetrain will pull taught when you're in the big ring and bigger cogs. The latter can catastrophically damage some drivetrains, so a lot of people choose to err long.

I say "alright" because it's true that it's not perfect. I'm not familiar with its specific ins and outs because I haven't ridden it, but he does say that his road drivetrains shift better. It doesn't look like he's having any notable trouble with it when riding with him.

I haven't checked the wrap of a GRX derailleur carefully, but I'd be surprised if the wrap specs aren't somewhat conservative.

GRX rear derailleurs (and all multi-chainring Shadow rear derailleurs) use an unsprung b-pivot and a jockey wheel concentric with their cage pivot. Vintage SunTour long-cage derailleurs also had those properties, so here's a comparison with one of them:
A circa-1985 SunTour XC 3600 derailleur has a 10-tooth tension pulley, and is about 3 1/8" from the pivot to the tension pulley. An RD-RX810 uses a larger 13-tooth tension pulley, and is an absolutely enormous 4 1/4" from the cage pivot to the tension pulley. The XC claims a total capacity of 38 teeth; the RD-RX810 claims a total capacity of 40 teeth. This is a ridiculously small discrepancy considering how much larger the latter derailleur's tensioning system is.
(And while it's arguably a muddled comparison because of the differing derailleur topologies, here's a comparison with another modern Shimano derailleur: the Alivio RD-T4000 has a 10-tooth tension pulley and roughly the same cage length as the RX810, but its specified capacity is 45 teeth.)

There's definitely some slop when it comes to cog clearance. The 34/36-tooth claims are based on what's sold alongside the GRX derailleurs in official-spec packages, and perhaps also correlates to what their geometry is optimized for, but b-pivot adjustment produces a pretty large range of jockey wheel positioning.

The 48-32 with 11-42 cassette isn't anywhere close to the most extreme out-of-spec work I've seen done with a GRX drivetrain. I was using it as a relevant example as what I know for sure is feasible within the drivetrain that the OP is using.
The craziest 2x GRX setup that I know of is on another friends' bike: he's running a 48-32 crank and an 11-50 cassette with an RD-RX810, a hanger extender, and a very long chain. I can't speak to how great it works; I haven't witnessed any trouble with it, but I've only graveled with him a couple of times, and only on mountainous terrain where the potential problem cases wouldn't necessarily have been getting put through their paces.

I wasn't saying that you'd need to. My point was that 1x wouldn't necessarily solve anything because most 1x gravel drivetrains aren't really spec'd to tolerate lower gearing than the OP's setup.

I usually don't, but I tend to make exceptions when there aren't many "correctly"-spec'd options.

Although in this case, there is at least one rear derailleur on the market that is theoretically correctly-spec'd for the use case: the S-Ride RD-M520C. It's nominally "11-speed road", but Shimano's 10-speed road drivetrains since 2015 use the same actuation ratio.

Swapping to a bigger small ring would lessen the chain wrap burden, but you'd need to use a longer chain and a different b-screw adjustment for the 11-42 cassette regardless of how big the small ring is. So the big small ring would just reduce the degree to which the drivetrain slackens if you cross-chain small-small. That's a nice quality-of-life difference, but I'm not sure that it would help your shifting smoothness.

Actually, it might worsen your front shifting because you'd no longer have a matched chainring pair.

Perhaps my earlier reply was a little flippant and I was referencing more my own experiences of seeking lower gearing rather than addressing the OPs needs. At some point you have to pick your poison - for me the benefits of substantially increasing the lower gearing far outweighed the bigger jumps in the tall gears, which for me is only a very occasional and a very minor drawback.