Can i change grx 2x 12 speed to mountain bike 2x 12 speed

vitellan
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Can i change grx 2x 12 speed to mountain bike 2x 12 speed

Postby vitellan » Thu Dec 21, 2023 9:25 am

Looking at getting a gravel bike (Canyon Grizl 7) with Shimano GRX RX61 crank 2x12-speed - 46-30 Teeth
But i am after lower gearing
Can i replace this with a Shimano FC-MT610-2 Crankset 2x12-speed - 36-26 Teeth?
(still an easy 35kph at a cadence of 80rpm in top gear)
(20 inch low 91 inch high)

rkelsen
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Re: Can i change grx 2x 12 speed to mountain bike 2x 12 speed

Postby rkelsen » Thu Dec 21, 2023 9:32 am

I don't see why not. Might have to take a couple of links out of the chain, but should work fine otherwise.

Andy01
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Re: Can i change grx 2x 12 speed to mountain bike 2x 12 speed

Postby Andy01 » Thu Dec 21, 2023 9:55 am

You must be doing some serious hill climbing if 30T up front and around 51T at the back isn't enough - ±6.5km/h @80rpm :shock:

A change from 30T to 26T only buys you an "extra" ±0.8km/h (5.7 instead of 6.5) at the low end, but you will lose ±12km/h at the top end (36T vs 46T).

warthog1
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Re: Can i change grx 2x 12 speed to mountain bike 2x 12 speed

Postby warthog1 » Thu Dec 21, 2023 10:01 am

I dont think 2x12 will run the 51t cassette.
https://bikerumor.com/shimano-grx-12-speed-mechanical/
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vitellan
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Re: Can i change grx 2x 12 speed to mountain bike 2x 12 speed

Postby vitellan » Thu Dec 21, 2023 10:55 am

Bike comes with 46/30 up front with 11/36 at the back
I am almost 60 and like the hills so can always use a lower gear but the top gears are unused
Coasting down the hills now.
When i am now on my go fast bike i rarely hit 40kph on my own on the flat

jasonc
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Re: Can i change grx 2x 12 speed to mountain bike 2x 12 speed

Postby jasonc » Thu Dec 21, 2023 11:06 am

warthog1 wrote:
Thu Dec 21, 2023 10:01 am
I dont think 2x12 will run the 51t cassette.
https://bikerumor.com/shimano-grx-12-speed-mechanical/
you could swap the cage on the rear derailleur to a longer cage. i've read it done for grx 11 speed

warthog1
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Re: Can i change grx 2x 12 speed to mountain bike 2x 12 speed

Postby warthog1 » Thu Dec 21, 2023 11:16 am

jasonc wrote:
Thu Dec 21, 2023 11:06 am
warthog1 wrote:
Thu Dec 21, 2023 10:01 am
I dont think 2x12 will run the 51t cassette.
https://bikerumor.com/shimano-grx-12-speed-mechanical/
you could swap the cage on the rear derailleur to a longer cage. i've read it done for grx 11 speed
Interesting. What cage?
I have grx 2×11. 48/32 and 36-11. My understanding is you can get away with 40 on the std cage.
Interested in what is needed for more range though?
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jasonc
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Re: Can i change grx 2x 12 speed to mountain bike 2x 12 speed

Postby jasonc » Thu Dec 21, 2023 11:45 am

warthog1 wrote:
Thu Dec 21, 2023 11:16 am
jasonc wrote:
Thu Dec 21, 2023 11:06 am
warthog1 wrote:
Thu Dec 21, 2023 10:01 am
I dont think 2x12 will run the 51t cassette.
https://bikerumor.com/shimano-grx-12-speed-mechanical/
you could swap the cage on the rear derailleur to a longer cage. i've read it done for grx 11 speed
Interesting. What cage?
I have grx 2×11. 48/32 and 36-11. My understanding is you can get away with 40 on the std cage.
Interested in what is needed for more range though?
https://www.mtbr.com/threads/711-range- ... e.1209452/
deore cage

edit: that may be the wrong link

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MichaelB
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Re: Can i change grx 2x 12 speed to mountain bike 2x 12 speed

Postby MichaelB » Thu Dec 21, 2023 12:29 pm

vitellan wrote:
Thu Dec 21, 2023 9:25 am
Looking at getting a gravel bike (Canyon Grizl 7) with Shimano GRX RX61 crank 2x12-speed - 46-30 Teeth
But i am after lower gearing
Can i replace this with a Shimano FC-MT610-2 Crankset 2x12-speed - 36-26 Teeth?
(still an easy 35kph at a cadence of 80rpm in top gear)
(20 inch low 91 inch high)

The bike comes standard with a 11-34 cassette, so your low gear is a 30/34 ratio which is better than 1:1.

What sort of gearing are you after ? and what % grade are you looking at climbing ?

If you put on the MTB crank, need to remember that they are typically for a different Bottom bracket width (73mm vs 68mm), and then unless the FD mounting is not a band clamp, there may also be issues.

A simpler solution may be an 11:36 cassette (not sure what is actually available as 12 sp)

Don't know why a 51 tooth cassette has been mentioned by others :?: :?:

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Re: Can i change grx 2x 12 speed to mountain bike 2x 12 speed

Postby jasonc » Thu Dec 21, 2023 12:32 pm

https://handsonbike.blogspot.com/2020/1 ... -rear.html

google-fu says the standard cage (on the 2x rear derailleur) will handle an 11-40 cassette without mods
this guy modified his 1x rear derailleur
https://handsonbike.blogspot.com/2020/1 ... -rear.html

i still can't find the 2x
then again 31/40 is a damn low gear

jasonc
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Re: Can i change grx 2x 12 speed to mountain bike 2x 12 speed

Postby jasonc » Thu Dec 21, 2023 12:45 pm


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MichaelB
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Re: Can i change grx 2x 12 speed to mountain bike 2x 12 speed

Postby MichaelB » Thu Dec 21, 2023 3:49 pm

jasonc wrote:
Thu Dec 21, 2023 12:32 pm
https://handsonbike.blogspot.com/2020/1 ... -rear.html

google-fu says the standard cage (on the 2x rear derailleur) will handle an 11-40 cassette without mods
this guy modified his 1x rear derailleur
https://handsonbike.blogspot.com/2020/1 ... -rear.html

i still can't find the 2x
then again 31/40 is a damn low gear
OP is talking 12sp, so not sure if 11sp compatability is the same.

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Re: Can i change grx 2x 12 speed to mountain bike 2x 12 speed

Postby warthog1 » Thu Dec 21, 2023 3:55 pm

jasonc wrote:
Thu Dec 21, 2023 11:45 am


https://www.mtbr.com/threads/711-range- ... e.1209452/
deore cage

edit: that may be the wrong link

Cheers. :)
Yeah my praxis alba chainset has a 32 inner ring. 32/36 is low enough for me but good to know it will go even lower.
Last edited by warthog1 on Thu Dec 21, 2023 3:59 pm, edited 1 time in total.
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jasonc
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Re: Can i change grx 2x 12 speed to mountain bike 2x 12 speed

Postby jasonc » Thu Dec 21, 2023 3:59 pm

MichaelB wrote:
Thu Dec 21, 2023 3:49 pm
jasonc wrote:
Thu Dec 21, 2023 12:32 pm
https://handsonbike.blogspot.com/2020/1 ... -rear.html

google-fu says the standard cage (on the 2x rear derailleur) will handle an 11-40 cassette without mods
this guy modified his 1x rear derailleur
https://handsonbike.blogspot.com/2020/1 ... -rear.html

i still can't find the 2x
then again 31/40 is a damn low gear
OP is talking 12sp, so not sure if 11sp compatability is the same.
yes. but warthog asked when i mentioned 11 speed

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Re: Can i change grx 2x 12 speed to mountain bike 2x 12 speed

Postby warthog1 » Thu Dec 21, 2023 4:02 pm

Yeah I had heard the std 2x derailleur would go 40t cassette in 11s. Hadn't heard about any hacks to go larger though.
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MichaelB
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Re: Can i change grx 2x 12 speed to mountain bike 2x 12 speed

Postby MichaelB » Thu Dec 21, 2023 4:19 pm

warthog1 wrote:
Thu Dec 21, 2023 4:02 pm
Yeah I had heard the std 2x derailleur would go 40t cassette in 11s. Hadn't heard about any hacks to go larger though.
NP. Can confirm 42 worked for me with the RX805 RD, but it was a bit graunchy shifting down from it.

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Re: Can i change grx 2x 12 speed to mountain bike 2x 12 speed

Postby warthog1 » Thu Dec 21, 2023 4:25 pm

MichaelB wrote:
Thu Dec 21, 2023 4:19 pm


NP. Can confirm 42 worked for me with the RX805 RD, but it was a bit graunchy shifting down from it.
Thanks, I have grx 810 rd.
11-40 I have read on multiple sites.
https://forum.ridinggravel.com/post/shi ... %20problem.
Haven't read of larger for that deraillleur though. Doesn't matter as that is already lower than I need to go.


Edit; just read further down on my link. Somebody has run 11-42 cassette on that derailleur too.
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Re: Can i change grx 2x 12 speed to mountain bike 2x 12 speed

Postby nickobec » Thu Dec 21, 2023 6:33 pm

Running Shimano GRX RD-RX810 in 2x setup with 50/34 chainring (with spider power meter) and 11-42 cassette with 126 link 12 speed chain.

No issues in regular use, needed 34 42 combo for a couple of 20%+ climbs yesterday.

Gets grumpy in the 50 42 combo and lets you know, very noisy, does not feel right.

Replacing chainrings, the GRX FD requires the chain rings to sit 2.5mm further out than a regular FD/chain ring combination. Unsure about Shimano MTB spacing, but you probably will need to add 2.5mm spacers either side of the BB to get the Shimano MTB crank combination to work.

If you switch to a regular road FD, you can get a road direct mount crankset and direct mount 36/26 or 38/28 chain ring.

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Re: Can i change grx 2x 12 speed to mountain bike 2x 12 speed

Postby warthog1 » Thu Dec 21, 2023 7:13 pm

nickobec wrote:
Thu Dec 21, 2023 6:33 pm
Running Shimano GRX RD-RX810 in 2x setup with 50/34 chainring (with spider power meter) and 11-42 cassette with 126 link 12 speed chain.

No issues in regular use, needed 34 42 combo for a couple of 20%+ climbs yesterday.

Gets grumpy in the 50 42 combo and lets you know, very noisy, does not feel right.

Good stuff, thanks :)
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Andy01
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Re: Can i change grx 2x 12 speed to mountain bike 2x 12 speed

Postby Andy01 » Thu Dec 21, 2023 7:52 pm

MichaelB wrote:
Thu Dec 21, 2023 12:29 pm
vitellan wrote:
Thu Dec 21, 2023 9:25 am
Looking at getting a gravel bike (Canyon Grizl 7) with Shimano GRX RX61 crank 2x12-speed - 46-30 Teeth
But i am after lower gearing
Can i replace this with a Shimano FC-MT610-2 Crankset 2x12-speed - 36-26 Teeth?
(still an easy 35kph at a cadence of 80rpm in top gear)
(20 inch low 91 inch high)

The bike comes standard with a 11-34 cassette, so your low gear is a 30/34 ratio which is better than 1:1.

What sort of gearing are you after ? and what % grade are you looking at climbing ?

If you put on the MTB crank, need to remember that they are typically for a different Bottom bracket width (73mm vs 68mm), and then unless the FD mounting is not a band clamp, there may also be issues.

A simpler solution may be an 11:36 cassette (not sure what is actually available as 12 sp)

Don't know why a 51 tooth cassette has been mentioned by others :?: :?:
This is one of the 51T cassettes I was referring to;

https://www.pushys.com.au/shimano-deore ... ilver.html - there are a few other 51T cassettes as well (up to $570)

I assumed that it would be an easier / cheaper change than a crankset, but perhaps not if the RD doesn't work with it.

There is also a couple of 45T cassettes that may work with the RD ? I have no experience with GRX bikes.

https://www.pushys.com.au/shimano-xt-cs ... sette.html
https://www.pushys.com.au/shimano-slx-c ... sette.html

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Duck!
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Re: Can i change grx 2x 12 speed to mountain bike 2x 12 speed

Postby Duck! » Fri Dec 22, 2023 12:05 am

STOP!!!

The OP specifically asked about changing the crankset. Only two replies out of about 20 have remotely brushed on answering the question; the remainder discussing derailleurs & cassettes, and all being 11-sp. are totally irrelevant to the question posed!

First, as one relevant comment noted, Shimano's MTB cranks are designed for a 73mm threaded BB shell + outboard bearings or 92mm shell + press-fit bearings, giving an assembled bottom bracket width of 96mm. Road and its GRX derivative is built for a 68mm threaded or 86mm press-fit BB shell; therefore the MTB crank has a 6mm longer spindle to fit through properly. To fit a MTB crank to a road/grovel frame, an additional 3mm spacer is required on each side to take up the slack.

The second point is the front derailleur. The GRX model designed for a quite large 17T jump between chainrings is not going to play ncely with the closer 10T jump of the MTB crank, if it can even be lowered enough on the frame to work on the crank properly....
I had a thought, but it got run over as it crossed my mind.

warthog1
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Re: Can i change grx 2x 12 speed to mountain bike 2x 12 speed

Postby warthog1 » Fri Dec 22, 2023 8:40 am

Fair enough I guess with respect to the OP's question.
Sorry about that. :oops:

I enjoyed the discussion nonetheless and learnt what the GRX derailleurs can handle..:)
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nezumi
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Re: Can i change grx 2x 12 speed to mountain bike 2x 12 speed

Postby nezumi » Fri Dec 22, 2023 2:23 pm

Duck! wrote:
Fri Dec 22, 2023 12:05 am
STOP!!!

The OP specifically asked about changing the crankset. Only two replies out of about 20 have remotely brushed on answering the question; the remainder discussing derailleurs & cassettes, and all being 11-sp. are totally irrelevant to the question posed!
With respect, I'd say that there's a difference between what the OP asked, and what they are trying to achieve. The desired outcome is clear: have lower gearing than the default that the bike ships with. The means by which this can be achieved may be smaller chainrings, but that's not the only solution, and definitely not the automatic option.
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baabaa
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Re: Can i change grx 2x 12 speed to mountain bike 2x 12 speed

Postby baabaa » Fri Dec 22, 2023 5:25 pm

Buy a frame and fork
Build your own bike up with the parts that you think you need first up - preferably for simplicity and future compatibility avoid Shimano bits
Whispering - have a good look at all things micro shift, the gravel group sword may not be what peoples want but looks and should work way better than most people will ever need
Also do you really need x12? Seems to really narrow down low gearing options.

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Re: Can i change grx 2x 12 speed to mountain bike 2x 12 speed

Postby WyvernRH » Sat Dec 23, 2023 5:53 pm

Slightly off-topic... to in one way back up what Duck! said but also to show what can be done with a bit of fiddling, here is a current project done solely to achieve these targets:
1) Seeing I don't peddle above 35kph much these days build a bike for the hilly/rolling terrain around here with gears I will actually use - say a 100" top and a circa 1-1 ratio bottom.
2) Use a triple chainring setup with a standard short arm Shimano 600 derailleur
3) Use up parts on shelf only preferably
What we have here is a BB30 FSA MTB 42/32/24 triple mounted using a BB30 to standard converter set to a 65mm bottom bracket with the chain being moved around by a Claris 11spd (I think) front changer driven by a set of Shimano 9spd triple Brifters.

As Duck! says outer chainring is too far out for the standard fitting with the MTB chainset so I made an extension. The Claris front was meant for a 50/38/30 I believe but it drives the MTB triple file OK from the extension. Overdid it a bit actually, would work better maybe 2mm further in but works fine as it is. The changer's curve and indents appear to work with the smaller chainset very well tho it does stick out the back a bit. So, running to a 11-25 9 speed rear I hit my high and low gear targets.

Possibly not a setup for those whose gear sensitivity can feel the pea through 20 mattresses but works fine for me. :P Surprisingly the tread is not excessive nor is the chainline too acute if you don't do silly things. However, it will run the 42/25 combination happily tho I will admit that you cannot/shouldn't use the outer 3 sprockets with the 24t chainring.

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