GRX - advice on how to make gearing lower (easier)

[Sparky56]

I’ve got the GRX 812 rear derailleur, which is the mechanical long cage version designed for the 1x11

[Sparky56]

If your RD currently goes to 42T cassette then it will not require any changes to it. (no lowering needed)

I believe the GRX 1x RD is max 42t cassette, with total capacity of 31t. OP has it on a 11-46t which is already out of it's designed range. The GRX 2x is max 34t with 42t total capacity. The OP doesn't actually say which one he has (there is no GRX 600series RD). But he's 11 speed which implies he had the 800 series RD and probably the 1x.

I assume the limits can be stretched, as the OP has seen in other threads. but never tested it.

With a 2 ring set up the chain has to be long enough to wrap around big ring to big sprocket plus a link. This may require an extra long chain ?

Which is then possibly be too long a chain for small-small.... I believe that is why there is a total capacity for the RD.

OK I’d not appreciated that - so are you saying there’s more of a potential issue with small-small than large-large?

Anyway I will test it and report back in the new year- I’m reasonably confident that I’ll get something to work satisfactorily even if I have to go down to a 42 max cassette (which I have in a box having swapped to the 46). So it won’t be money wasted (which was my initial worry).

[Jupestar]

I’ve got the GRX 812 rear derailleur, which is the mechanical long cage version designed for the 1x11

It's not clear to me why the total capacity for this RD is stated as only 31t. Seems very low. Perhaps someone else knows .

so are you saying there’s more of a potential issue with small-small than large-large?

Not 100% sure what your asking. If the chain is too long for small-small the RD will not hold it away from the cassette. If the chain is too short for long-long then something is likely to break if you try and get it onto long-long.

Lowering the RD, with either hanger extender, or larger Jockey wheel. Will probably increase the length of chain it can take.

[Sparky56]

I’ve got the GRX 812 rear derailleur, which is the mechanical long cage version designed for the 1x11

It's not clear to me why the total capacity for this RD is stated as only 31t. Seems very low. Perhaps someone else knows .

so are you saying there’s more of a potential issue with small-small than large-large?

Not 100% sure what your asking. If the chain is too long for small-small the RD will not hold it away from the cassette. If the chain is too short for long-long then something is likely to break if you try and get it onto long-long.

Lowering the RD, with either hanger extender, or larger Jockey wheel. Will probably increase the length of chain it can take.

OK thanks and sorry for my ignorance. The guy who got the 2x working with 11-46 used a road link (Wolftooth components) to hold the short cage derailleur away from the cassette, plus a 16t jockey wheel to extend the derailleur a bit more.. the only difference with my set up would be that I have the 1x derailleur…. Anyway others have succeeded with the 1x derailleur and the 11-42 cage so that would also be acceptable if my ideal didnt work.!

[Sparky56]

Another video with same result - used a longer cage rather than a bigger jockey wheel.

https://www.youtube.com/watch?v=7kUxmkuJWNg

[gxaustin]

"I thought GRX bottom brackets had already been widenened to the MTB standard width ? Heres a quote from Shimano "Shimano GRX cranksets feature a +2.5mm outboard chainline, which improves rear tire clearance, making room for wide gravel tires. This also means that the GRX crank’s Q-Factor is +2.5mm wider on each side compared to Shimano road cranks"

GRX do fit a 68mm Hollowtech 2 BB. I fitted GRX in place of the 105 crank fitted to the bike because I wanted a wider chainline and lower gears. Nevertheless the Q factor is still the same as a Shimano road groupo. I checked against a spare Ultegra left crank.

[Sparky56]

Update -- I've just had the bike converted to 2x -- with the following arrangement that seems to work

Front chainring 28/36.
28t is a GRX inner chainring from Spécialités TA,
36t is an Ultegra inner chain ring with spacers added to the bolts to get the chainline correct.

Cassette is 11-46 Shimano XTM8000 (this is what I had on my 1x set up).

The rear derailleur is the long cage 1x GRX one (RD-RX812) and as others have reported it seems to work fine for 2x

Main reasoning for choosing this arrangement over a larger gap in the front chain rings was that the mechanic felt that using a 44 large front chainring would give little room for error etc & might fail more quickly. Also I don't need a larger chainring as I am slow.

I'll post a more detailed review after the bike packing trip I[m about to go on. So far I've just cycled it home.

[ed.lazda]

Bit late now, but a more radical (and very expensive) approach would be to add a Powershift hub to a 1x GRX setup.

40 front, 11-42 rear would give you a gear range of 18-98 inches, without needing to change the front setup and (allegedly) providing instant smooth changing into the smaller range.

[Sum]

Update -- I've just had the bike converted to 2x -- with the following arrangement that seems to work
(snip)

Interesting. Useful update that may benefit folk in similar situations.

Apologies if you've already covered this, but was your original Shimano GRX 600 crankset (that you was previously using with the 1x set up) the 2x version of the GRX 600 crankset? Or did you originally have a 1x specific crankset and the bike shop has swapped it out for a 2x version?

The cranks in the photo look well worn so I initially thought you was using your original 1x crankset, which made me ponder for a bit.

[Sparky56]

Update -- I've just had the bike converted to 2x -- with the following arrangement that seems to work
(snip)

Interesting. Useful update that may benefit folk in similar situations.

Apologies if you've already covered this, but was your original Shimano GRX 600 crankset (that you was previously using with the 1x set up) the 2x version of the GRX 600 crankset? Or did you originally have a 1x specific crankset and the bike shop has swapped it out for a 2x version?

The cranks in the photo look well worn so I initially thought you was using your original 1x crankset, which made me ponder for a bit.

Update -- I've just had the bike converted to 2x -- with the following arrangement that seems to work
(snip)

Interesting. Useful update that may benefit folk in similar situations.

Apologies if you've already covered this, but was your original Shimano GRX 600 crankset (that you was previously using with the 1x set up) the 2x version of the GRX 600 crankset? Or did you originally have a 1x specific crankset and the bike shop has swapped it out for a 2x version?

The cranks in the photo look well worn so I initially thought you was using your original 1x crankset, which made me ponder for a bit.

It was the same 1x crankset I originally had. I asked the mechanic and he told me that the 2x works with it - which it clearly does.

[Sum]

There's no denying it does work, judging from the photos.

Looking at the Shimano tech docs for the FC-RX600-1 and FC-RX600-11 cranksets, the GRX 1x11 and 2x11 drivetrains both use the same RH crankarm i.e. the 1x11 crankset isn't strictly speaking 1x specific:-
https://si.shimano.com/en/pdfs/ev/FC-RX ... -4579B.pdf

This is useful to know. As an aside, I think this also answers Jupestar's question on page 1.

[Flat Mt. Everest]

Yes, the 1x crankarm FC-RX600-1 seems to have both the 80 BCD and 110 BCD threads. So the inner chainring would just bolt on 1x crank.

The 30T chainrings are identical for 10 and 11 speed cranksets (Y0K630000). The 10/11 speed difference lies in 46T chainrings (11s Y0K698010 & 10s Y0K798010).

In other words, I assume 1x and 2x cranksets as well as 10s and 11s GRX RX600 cranksets use identical right hand crankarms.

There are two different gear fixing screw sets but not clear if truly different bolts (both sets are M8 x 8.5 / 1 Unit = 4 pcs):
Gear Fixing Screw set Y1WD98050: 10s inner, 11s inner & outer
Inner Gear Fixing Screw set Y1LV98060: 10s inner

[Sum]

Just for clarity; the Y1WD98050 chainring bolt is for the 10s outer chainring (i.e. not inner), as well as the 11s inner & outers.

Searching online, the online difference I can see between the Y1WD98050 and Y1LV98060 chainring bolts is the colour - black vs silver finish. Both seem to be made from stainless steel, take a 5mm Allen key and have the same number of threads.

[rivers]

If you do go the 2x with 11-42 route, is there any possibility that you could post a ‘blow by blow’ account of how you do it?

I read some of the very summarised accounts of people doing it, and I’m afraid that some of what they say goes straight over my head.

I've gone 2x (46/30) with an 11-42 in the back.
My gravel bike originally came with full 105. I swapped out the shimano 105 chainset for an FSA 46/30. I needed a new BB as well. I had the chainset kicking about.
For the rear, I swapped out the shirt cage 105 rear derailleur for a Deore long cage to accommodate the 11-42 cassette. To make my 105 shifters play nicely with the MTB rear mech, I needed to install a Jtek Shiftmate, which is a little widget that changes the pull ratio of the cable from road to MTB. The while thing (rear mech, shiftmate,cassette, and new cable and outer cost around £100).

[Sparky56]

As promised - more detailed review of this - I’ve now ridden about 1000 miles of the GB divide with this set up. For those not familiar with the route here is a link to it: https://bikepacking.com/routes/gb-divide/ Lots of steep hills up and down, with some pretty rough tracks. I was riding with full camping set up but bare minimum, so reasonably light weight compared to many cycle tourers

Anyway, the gearing was amazing — having 28 at front / 46 at back really made a massive difference to the previous set up and got me up stuff that I would have had to push the bike up. There was still a lot of hike-a-bike but that’s the route not the bike.

Minor frustrations with the gearing was that ‘cable stretch’ meant that after a few days the front derailleur didn’t shift up to the big cog, despite me tightening the tensioner to the max (I don’t have the skills to do anything more advanced). It would have been better to have more time between installing the new gears and heading off on the trip. Anyway it’s sorted now & I have an extra tensioner by the levers. At some point I might put a larger front chain ring on as I do spin out at about 30kph - that might help on unloaded club rides otherwise I’m happy coasting down hills.