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Easy change compact / sub-compact??

Old 01-01-22, 09:17 PM
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tomgdaly
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Easy change compact / sub-compact??

I have a compact Ultegra R8000 (manual) groupset on a Trek Domaine but I also use the bike for light touring and ultra-racing a couple of times a year and then I like to use a sub-compact (or reduce the gearing somehow - Iím also 67 years old, so donít have much power).

In the past I have changed to a 32-small ring Sugino sub-compact chainset with a front derailleur extender (along with a regular 34-tooth rear).

But changing the chainset is a pain, especially setting up the front derailleur each time, and so Iím wondering if thereís any better options to reduce the gearing occasionally and easily??

For example, could the standard rear derailleur (GS?) handle an 11-40 cassette, or would some other rear derailleur do this without compromising the quality of the change on an 11-32 cassette (which I use as an everyday gear).
I have also posted this in the Long Distance thread

Thanks, in anticipation.
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Old 01-01-22, 09:46 PM
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Cyclist0108
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I replaced my Ultegra 50/34T crankset with a GRX 46/30T crankset, and that worked fine, despite claims to the contrary (the chainline is 3mm further out, so you need to adjust the limit on the front derailleur).

11-36 (SRAM) is the widest I could get on the back with an Ultegra mid-cage. Adjust the B-screw.
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Old 01-01-22, 10:19 PM
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If you can find a crankset that will accommodate both your "big" and "small" chainring pairs, there will be less work in the changeover than when changing the crankset. How about a 110/74mm triple, with just the middle and inner rings? I just installed a Campagnolo Centaur 135/74 mm set up that way, and apart from re-tuning the FD there was nothing else to do when going from a 48-34 to a 46-30. Even the chain length was good in my case. I could switch it all back in an hour.

My challenge was finding a selection of middle rings (with shift aids) in larger sizes for that 135/74mm campy crank, but I did. It will be easier to find 44, 46, or 48T middle rings if you go with a 110/74mm crank. If you do need to adjust chain length, avoid the over complex Campagnolo or Shimano chain joining schemes by using a chain with a master link. To avoid having two master links in the longer version of your chain (twice the risk of failure), just plan to swap chains when you swap rings. KMC chains are not expensive.

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Old 01-02-22, 02:52 AM
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Just ride a small crank all the time? Likely you do no not need very tall gears anyway, being 67 and all. Im 47 and seriously considering a 46/30 grx or a 31/48 grx, with the matching FD. That way a big cassette wont push your RD to (or beyond) its limit and it will retain proper function without it becoming finicky. The grx FD and crank is 100% compatible with your r8000 sti-shifter, even according to Shimano, so no hacking.
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Old 01-02-22, 08:45 AM
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I'll second the GRX crank recommendation. Assuming 700c wheels, a GRX 46/30 crank with an 11/34 or 11/36 cassette gives you a 113 gear-inch high and a 24 or 22.5 gear-inch low which is a pretty wide range and should be an adequate low gear for almost anything but loaded touring.
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Old 01-02-22, 10:43 AM
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The RD-R8000-GS that you say you have is spec'd to handle a max front difference of 16 teeth. That's the small ring up front subtracted from the large ring. So if you can find a crank with rings that meets that, then you should be good. You might can even go outside that, but why be experimental unless you absolutely have to.

A GRX crank might have your chain line further out which will be worse if you use the low ratio gears often. But I haven't looked at the specifications for it. Since you are getting stuff for a road bike, you should look at components stating they are for road groups. Otherwise you might find yourself well out of spec somewhere. Not necessarily, but might.

You also need to consider what the BB shell is on your bike. You can open up more crank selection if you are willing to replace the BB too. They aren't much money. However a threaded BB will be easier and less problem potential than a press fit. Not sure which type shell a Domain is. Some model lines vary depending on component tier.

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Old 01-02-22, 10:48 AM
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Or keep the ultegra crankset and just change the rings to absolute black oval sub-compact 48/32 or 46/30. They aren't cheap but then neither is changing out the whole crankset.
https://absoluteblack.cc/oval-road-c...-for-110-4bcd/
I run their 46/30 on my road/gravel bike.
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Old 01-02-22, 10:59 AM
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I needed a sub compact to ride the hills around Pittsburgh so I changed to a sub- compact by purchasing the 46/32 Chain rings from Absolute Black. They are an easy fit with the Shimano 8000 groupset and it takes a few minutes to make the switch. This switch has given me the lower gears needed to ride some of these steep hills and to get into a comfortable cadence on the long ones. The other alternative is to buy a rear cassette the size of a dinner plate.
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Old 01-02-22, 11:16 AM
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I'm with @oldschoolbike.

Perhaps look for a single crankset that can support the range you are wanting.

Say, 50/30? 48/32?

I think I have 53/34 on one bike which is a fairly wide range shift, and it generally works. Riding with a older Campagnolo setup. 11-speed Super Record shifters, and 11-speed Chorus front derailleur. 10 or 11 speed Chorus cranks. Stronglight rings.
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Old 01-05-22, 05:32 PM
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Whit51 
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I like 46-30 cranksets. I’ve converted some Ultegra triples to this configuration, using only the inner and middle ring positions. BikinGreen sells a 46-30 combo on EBay that bolts onto a 110bcd crank. I have one of those and may buy another.
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Old 01-10-22, 01:32 AM
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cpach
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You could try a grx fd and crankset with 48/31 rings and see if that gets you adequate range. Radically changing your cassette would require drivetrain hacks and be a pain to switch to and fro with.

I'd see if a 48/31 with an 11-36 (just outside shimano spec but probably fine) could meet most of your needs with one drivetrain.
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Old 01-10-22, 08:06 AM
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It's relatively easy to change the chainline on grx cranks. I found washers at McMaster-Carr, part number 98370A015. I've also modified 1/4 inch washers by enlarging the hole and grinding down the OD, but that's a lot of work and requires more tools than the average person has. Each washer should have the same thickness within 0.003 inch and often they don't since washers thickness is not usually critical. Grx chain rings mount behind the spider, so adding washers moves the rings inward.
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