Atlas Shrugged

I would like to use an 11-40 Cassette on my new 2X GRX build and wondering if anyone here is using this configuration. 48-31 Crankset and GRX 810 rear derailleur, does it have enough capacity to go from big-big to small-small without breaking anything in a real-world application. There are one or two videos on YouTube saying yes, but they are still a little vague as they avoid extremes. Understanding real-world situations, eventually, I would attempt to shift into a gear not to be used due to fatigue or general inattention.

jonathanf2

You could probably do it with a Wolftooth Goatlink, but honestly shifting will be so-so. I was running an 11-40 cassette for awhile on my GRX 400 setup, but I went down to an 11-36t cassette and focused on cutting weight as opposed to lower gearing.

Atlas Shrugged

Were you able to go big-big and small-small and not break anything? I was planning on going Wolftooth on my set-up.

jonathanf2

Yes I was able to shift big-big/small-small, just make sure to size your chain correctly. The main issue will probably be when you're in high gear shifting your small cassette cogs, it might not engage as smoothly versus using an in-spec cassette. Also depending on your frame chain stay, your RD cage might be closer to the ground at your lowest gear making it susceptible to damage from rocks or uneven terrain. You'll also have to be mindful of chain slap if your clutch isn't engaged.

These are all worst case scenarios, as long as you're aware of the limitations you should be able to run a proper setup. Though for me it was more hassle than necessary and I went back to an 11-36t cassette for smoother shifting. Also l found cutting loaded and rotational weight to be just as beneficial as lower gearing. I also increased crank arm length to give me additional torque when climbing. So there are other available options to consider.

Atlas Shrugged

Thanks for the heads up. The plan is to build up a multi-day long-distance, endurance set-up. Will give it a try and if I run into wrap issues I will install an SGS long cage from an XT M-8000 derailleur.

HTupolev

I don't use it personally*, but I have several friends who use a 16-tooth or 17-tooth front difference with an RX400 or RX810 rear derailleur and an 11-40 or 11-42 cassette. It's a common approach in PNW gravel.

People usually still size the chain for big-big-plus-1-inch (to prevent things from exploding when you desperately grab the big cog while in the big ring), accepting that things will be sloppy and slack if you try to use the small cogs while in the small chainring. Some bicycles may require a hanger extender for it to work reasonably (a Roadlink DM is usually the appropriate choice if so), and the required b-pivot adjustment means that shifting may be less perfectly-consistently snappy than an in-spec Shimano drivetrain, especially toward the small cogs and when things are grungy.
It can work very reasonably, if you understand what you're dealing with. If you need the gears and range, it's an entirely serviceable approach.

*My gravel bike has a triple crankset with a 24T small ring, and an 11-32 cassette gives me a 19" low gear. Which is mostly adequate, at least when I'm in shape.

996

I am using a Shimano 105 R7000 medium cage RD with a 50/34 front chainring setup and an 11-40 Deore XT cassette. No wolf tooth involved. Everything works fine and I have taken the bike on some harsh gravel and banged it up quite a bit.

The only gear ratio that does not work (causes the chain to rub against itself without much clearance) is the 34 up front and 11 in the rear... which I never will use.

Have some pics... will try and find them.

MikeIndy

On my ‘21 Diverge with GRX 2x, I run a 11-36. I don’t think a 40 would fit without hitting the pulley wheel. On my new Seven, it is hitting on the pulley wheel. I may be able to work around with an adjustment or change to the hanger, but I literally just added the bike this week and have not yet started trying to solve that one.

sean.hwy

For the last two years I have been running 48/32T with a 11-40T on Rear Derailleur Shimano GRX RX-810. Just have to adjust the B screw.

Atlas Shrugged

Great real world example! How does big-big and small-small react. Obviously not going there on purpose but you know it happens.

sean.hwy

The only time I do BIG and BIG if it's a rollings hills and I am only going to using it for a minute or two.

The small and small is not any different than my MTB except maybe a tad chain rub on the front derailleur. The derailleur is working over time trying to keep some tension on the chain small and small on both the 2x gravel bike and the 1x MTB bike. I 99% of the time don't cross chain though. I never use small and small on the gravel bike if I am on bumpy gravel/MTB trail. Just too much chain slop.

I think it shifts 95% as good as when it was stock 48/32T and 11-34T GRX. With my injured knees from motorcycle accident a few years back I love the 40T vs the 34T.
It probably shifts about 80% as good as my friends Durace road bike. That's probably to be expected of a 11-28T cassette and the top end shimano stuff. That was just snick, snick.

sean.hwy

Just adjust your B screw