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Converting to 1X Drivetrain ?

Old 04-28-21, 08:35 PM
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dkyser
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Converting to 1X Drivetrain ?

I want to try running a 1X drivetrain for my gravel bike and am a bigger rider with some paved hills I do on occasion so need climbing gears.
Currently Running the following.
SHIMANO Ultegra ST-R8020 STI Shifter - Set
SHIMANO Ultegra R8000 Mid-Cage Rear Derailleur
SHIMANO ULTEGRA FC-R8000 CRANKSET (GREY) (2 X 11 SPEED) (HOLLOWTECH II) (170MM) (50/34T)
11/32 Casette.

What all would you suggest changing over to do this correctly? I am hoping my Shifter set is fine and only need a derailer and front chainring.
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Old 04-29-21, 05:04 AM
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There are a bunch of ways to do this...I'm only going to offer the simplest (meaning fewest new required parts) to make this happen.

1. Crankset. You'll need a different crank and a 1x chainring. The chainring MUST be of a type that has a "narrow wide" or some other type of tooth profile that promotes chain retention. Shimano GRX crank with GRX chain ring is probably the easiest route, because it will work with your existing BB, so you won't need to change that also. There are other options, but all require changing the BB also. Number of teeth is up tot you, more below.

2. RD, you will need a new RD, period, with a clutch. Your current RD has plenty of capacity to "wrap" the chain (39t total) and could easily handle an 11-42 cassette (31t btw low/high) with an extender link, but, the RD you have is unclutched and you would likely experience a lot of chain drop on rougher surfaces. (a) Easiest (best?) option is the GRX RD-RX-812, it'll bolt right up, and is designed to work with 11-42 cassettes in 1x configuration. (b) Using an extender link, the RD-RX800-GS (essentially same RD you have now, with a clutch) should also work, but this is a two part solution where you are using the derailleur outside it's spec'd range, though there is a lot of experience doing it and it is known to work.

3. Cassette. Of course, easiest option for immediate out of the box functionality with little fuss using the GRX RD I mentioned above is an 11-42 cassette, CS-M8000 being the more economical choice, unless you want the trick and super light XTR. I am assuming you have a 11-speed Shimano Hyper Glide road hub, so you'll need a 1.85mm spacer if you don't have it, but it is cheap. It going on first, then the cassette.

This is the most straightforward way to do it, there are some other ways to get even lower gearing, but it'll require a bit more in depth study to get the right parts combos and get it tuned. Not impossible, just requires more effort initially. See this for a discussion on some options.

Lastly, gearing. I don't know how low you want to go, but if you choose to use an 11-42 cassette and pair it with a 40t chain ring, you'll gain a bailout gear below your current lowest ratio, but you'll lose your top end, topping out just past 50/14 in your current configuration. You could go a bit lower with a 38t ring (even lower than current), or slightly higher (though still lower than current) with a 42t. Try out this Gear Calculator to get a sense for how a 1x configuration would compare with your current setup.
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Old 04-29-21, 05:38 AM
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Originally Posted by Badger6 View Post
There are a bunch of ways to do this...I'm only going to offer the simplest (meaning fewest new required parts) to make this happen.

1. Crankset. You'll need a different crank and a 1x chainring. The chainring MUST be of a type that has a "narrow wide" or some other type of tooth profile that promotes chain retention. Shimano GRX crank with GRX chain ring is probably the easiest route, because it will work with your existing BB, so you won't need to change that also. There are other options, but all require changing the BB also. Number of teeth is up tot you, more below.

2. RD, you will need a new RD, period, with a clutch. Your current RD has plenty of capacity to "wrap" the chain (39t total) and could easily handle an 11-42 cassette (31t btw low/high) with an extender link, but, the RD you have is unclutched and you would likely experience a lot of chain drop on rougher surfaces. (a) Easiest (best?) option is the GRX RD-RX-812, it'll bolt right up, and is designed to work with 11-42 cassettes in 1x configuration. (b) Using an extender link, the RD-RX800-GS (essentially same RD you have now, with a clutch) should also work, but this is a two part solution where you are using the derailleur outside it's spec'd range, though there is a lot of experience doing it and it is known to work.

3. Cassette. Of course, easiest option for immediate out of the box functionality with little fuss using the GRX RD I mentioned above is an 11-42 cassette, CS-M8000 being the more economical choice, unless you want the trick and super light XTR. I am assuming you have a 11-speed Shimano Hyper Glide road hub, so you'll need a 1.85mm spacer if you don't have it, but it is cheap. It going on first, then the cassette.

This is the most straightforward way to do it, there are some other ways to get even lower gearing, but it'll require a bit more in depth study to get the right parts combos and get it tuned. Not impossible, just requires more effort initially. See this for a discussion on some options.

Lastly, gearing. I don't know how low you want to go, but if you choose to use an 11-42 cassette and pair it with a 40t chain ring, you'll gain a bailout gear below your current lowest ratio, but you'll lose your top end, topping out just past 50/14 in your current configuration. You could go a bit lower with a 38t ring (even lower than current), or slightly higher (though still lower than current) with a 42t. Try out this Gear Calculator to get a sense for how a 1x configuration would compare with your current setup.
Thanks for the detailed response, I really appreciate it.
I am not trying to go cheap, but do not want to buy shifters if they are not needed.
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Old 04-29-21, 06:50 AM
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i have 1x on my ultegra groupo. cassette is 11/34, rd medium cage gs... almost identical with what you have. only thing i needed was wolftooth 38 front chainring, and new bolts.
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Old 04-29-21, 07:51 AM
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That could work, but based on the OP's needs (climbing gear and gravel), it is not geared as low as the 2x drivetrain it would replace, and without a clutch there is real risk of dropping a chain, even if the chainring uses a retention profile.

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Old 04-29-21, 09:53 AM
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You need to think how well your current 34-32 setup works on hills. That is the key to this because if you want something a lot lower than what you have a 40-42, or 38-42 may not give you enough climbing. Maybe a 10-46 or 10-50.

Of course gapping gets worse the wider you go.

John
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Old 04-29-21, 10:44 AM
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The Wolftooth chainring made for Shimano Hollotech works great and will save you money, but the advice to go with the GRX-812 rear derailleur and M-8000 11-42 cassette is spot-on. Don't forget to include a new chain in the budget.
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Old 04-30-21, 12:11 AM
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Originally Posted by 70sSanO View Post
You need to think how well your current 34-32 setup works on hills. That is the key to this because if you want something a lot lower than what you have a 40-42, or 38-42 may not give you enough climbing. Maybe a 10-46 or 10-50.

Of course gapping gets worse the wider you go.

John
And using those bigger range cassettes exceeds the chain wrap capacity of the easiest to fit RD, and necessitates using an extender link with potential for a slack chain in the highest gears (smaller cogs)...or necessitates more complicated solutions to use a MTB RD with road levers (I linked a neat article that explains how to do it with examples). But, there comes a point where you just gotta ride, train, and condition yourself to pushing the cranks to make the bike go up grades...a far better solution IMO than using a RD way outside spec, for a lot of reasons, including personal health physically and mentally.
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Old 04-30-21, 07:40 AM
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I agree with everything you said.

I have a spreadsheet of all the gearing changes and potential changes over the decades. I can plug in any cadence and see any gains or losses a gear change will make. For me, nothing gets changed until I run the numbers.

I don’t know what the OP wants to accomplish, other than a 1x.

John

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Old 04-30-21, 05:32 PM
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Originally Posted by Badger6 View Post
That could work, but based on the OP's needs (climbing gear and gravel), it is not geared as low as the 2x drivetrain it would replace, and without a clutch there is real risk of dropping a chain, even if the chainring uses a retention profile.
I'm running 1x and with a 70s campy crankset and haven't dropped a chain yet for like 200mi so far (just finished the build this spring) riding mostly on road and gravel with 28mm tires. Using a deore4120 which is the new cheapest no clutch deore 11 speed. I looked into chain retainers but it hasn't seemed to be an issue.
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Old 05-01-21, 03:20 AM
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Chain drop is not something that just happens. If you're riding on smoother surfaces (even gravel can be "smooth") a non-clutched RD shouldn't have too many problems. On the other hand, hit the bumpy stuff- cobblestones, washboards, lots of potholes- and do it at speed, and I'm confident your experience will be different once that RD cage starts slapping around. In fact in those situations, having a clutched RD on a 2x system is helpful in my experience...but, then again I live in a place where they make roads with stones set closely together and they are B-U-M-P-Y!
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Old 05-01-21, 08:51 PM
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I'm gonna try it some more as is but I just ordered a narrow wide ring to fit my vintage crank in case it becomes an issue since I do like to ride on the rough stuff.
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Old 05-02-21, 06:36 AM
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With a NW ring you most likely donít need a clutch RD for most gravel riding.
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Old 05-02-21, 06:12 PM
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I've got a few 1x bikes.

My first build was 10 speed for gravel. It had a clutched SLX derailleur that I usually forgot to turn on. I dropped the chain at first but once I got the length right, it never happened again. I beat the crap out of it on washboards and ruts, it worked great.

A mountain bike with 10 speed XT, pre-clutch. I rode it for a year before doing a major 11 speed overhaul. I never dropped the chain. I ride it as seriously as my weak legs can.

My new gravel is pretty basic Sram stuff, so again, no chain drops.

The common denominator is a NW ring. I haven't noticed a difference between name brand and ebay generic. It's pretty basic.

Chain length should be about 1 link longer than you need for your lowest gear.

I love the clutch for the silent crash down the gnar. I can't believe I listened to that slap for so many years. I don't think it matters much for chain retention though.
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Old 05-04-21, 03:16 AM
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Take off the front derailleur and the cable. Buy a single chainring that fits your crankset, choose the tooth count you want. Shorten the chain to fit.
Ride it.

You might want to purchase shorter chainring bolts if needed. A 42 tooth chainring would be good.
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