Shimano GRX 48-31T, 46-30T - RX810, RX600, RX400

Especially for light weight issues concerning cyclocross / touring bikes & parts.

Moderator: Moderator Team

Post Reply
User avatar
TonyM
Posts: 3263
Joined: Thu Jan 22, 2015 4:11 pm

by TonyM

bm0p700f wrote: Xtr FD will not work with a road chainset.
I was thinking of a Dura Ace 2x crankset with a XTR Di2 rear derailleur in order to have 42+ cassettes.

Which Di2 front derailleur can I then use? I read that mixing Road FD and MTB RD doesn’t work in etube.

User avatar
pdlpsher1
Posts: 2424
Joined: Thu Jul 19, 2012 6:09 pm
Location: CO

by pdlpsher1

You don't need the XTR RD to run a 42 cassette. You can use the 8050 GS or RX805. I have the 8050 GS with a 40 cassette. I don't see why it wouldn't work with a 42. Shifting is fast and accurate even on the smaller cogs.

by Weenie


ooo
Posts: 814
Joined: Sat May 21, 2016 12:59 pm

by ooo

ST-R9150 vs ST-RX815

Image

ST-R9150 vs ST-R785

Image
'

bm0p700f
in the industry
Posts: 4932
Joined: Sat May 12, 2012 7:25 pm
Location: Glermsford, Suffolk U.K
Contact:

by bm0p700f

The Rx rd for 2x is rated to 34t only. You'll run out of capacity with a wide range cassette.

For 42t you'll need the xt di2 rd as the xtr only has capacity for an 11-40t with 12t chains gap up front.

Bcoxa
Posts: 30
Joined: Fri May 26, 2017 8:44 pm

by Bcoxa

bm0p700f wrote:
Thu May 09, 2019 1:19 pm
The Rx rd for 2x is rated to 34t only. You'll run out of capacity with a wide range cassette.

For 42t you'll need the xt di2 rd as the xtr only has capacity for an 11-40t with 12t chains gap up front.
Based on documentation you are correct. But in practice it's happy running a wider mtb cassette.

Am running a standard gs r8000 rd with a 46t up front and an 11-40 at the back. And an rx800 with a 40t (also had 38 and 44) and 11-42. With a goat link there is plenty of capacity for 46-11 I'd bet. Obviously this is also dependent on frame... Etc

User avatar
pdlpsher1
Posts: 2424
Joined: Thu Jul 19, 2012 6:09 pm
Location: CO

by pdlpsher1

bm0p700f wrote:The Rx rd for 2x is rated to 34t only. You'll run out of capacity with a wide range cassette.

For 42t you'll need the xt di2 rd as the xtr only has capacity for an 11-40t with 12t chains gap up front.
There’s plenty of chain wrap capacity with the 11-40. I can run big-big 50-40 or small-small 34-11 without the chain being too tight or loose. It’s out of the spec but it runs perfectly fine in practice. The Shimano Shadow RD is very flexible.


Sent from my iPhone using Tapatalk

MichaelB
Posts: 626
Joined: Tue Apr 22, 2008 4:31 am

by MichaelB

bm0p700f wrote:
Thu May 09, 2019 1:19 pm
The Rx rd for 2x is rated to 34t only. You'll run out of capacity with a wide range cassette.

For 42t you'll need the xt di2 rd as the xtr only has capacity for an 11-40t with 12t chains gap up front.
Know it's not Di2, but currently running 10-42 & 36/46 combo with RX800 RD and no issues

Frisco
Posts: 92
Joined: Sat May 09, 2009 6:23 pm
Location: Bay Area, CA

by Frisco

I also run the RX805 with a 46/30 and 11-42

User avatar
nickf
Posts: 828
Joined: Sat Mar 06, 2010 10:34 pm

by nickf

What kind of terrain you guys riding that you need 46/30 with a 42 out back? Honest question though. I'm a flat lander and run regular road gearing on gravel.

bm0p700f
in the industry
Posts: 4932
Joined: Sat May 12, 2012 7:25 pm
Location: Glermsford, Suffolk U.K
Contact:

by bm0p700f

its not 50-40T thats the problem, it is chain tension in the little ring. your outside the published specs shimano make so recommending that combo is not something anyone should do.

Some may think if there is no chain tension in little ring and the smaller gogs then that no problem. for a mechanic like me if there is not chain tension in all gears then then the drivetrain is not working properly.

from shimano's site
Chain Stabilizer mechanism adopted from MTB design
ON/OFF switch
Compatible with current road DUAL CONTROL LEVER
Max. front difference: 16T
Total capacity: 39T
Low sprocket: Max. 34T/Min. 28T
Top sprocket: Max. 12T/Min. 11T

Capasity is 39T
A 11-40T cassette use 29T of that capasity so while you can get it to work in the big ring you cant have all gears in the small ring. i.e the drivetrain does not work in all gears = it does not work in my book. Essentially the 11and 13T cogs will have marginal to no tension in the chain. 15, 17T and 19T will have marginal tension and you start to see proper tension in the 19T or 21T cog depending.

So when people say I have this combo work with no problem I simply dont believe it because I have tried these combos and there is a lack of chain tension in some gears, maybe not gears you use but as I have defined that not how I define no problem. I am not being pedantic either. I am just tried of people saying this works without defining what they mean by it works i.e context.

User avatar
pdlpsher1
Posts: 2424
Joined: Thu Jul 19, 2012 6:09 pm
Location: CO

by pdlpsher1

I would never ride a bike that has improper chain tension in ALL of the gear combos. Because doing so can rip the RD off the hanger and cause irreparable damage to a frame.

I've seen far too many YouTube videos where people adjust the B screw or add a WolfTooth RoadLink to accommodate a larger cog, and claim 'it works'. Most if not all of these setups have improper chain tensions. They claim that's not a problem because they never use those extreme cross-chain combos.....until one day they accidently shift into those combos.

Now let me repeat this one more time. As I have said many times previously, on my setup I have proper chain tension on the big-big and small-small gear combos. And I'm not using a WolfTooth RoadLink, a modified derailler cage, or any after-market add-ons. I'm using a GS Shadow-based RD. I simply adjust the B-screw and adjust the chain length to get this to work. bm0p700f- I don't know why you can't get it to work. Did you use the GS RD and not the non-GS RD? GS is the long cage version.

I'm using the 11-40 because it's a tandem, and tandems need extra low-range gearing for going uphill. I also need a minium of a 50T front because tandems also go downhills very fast, and I spin out easily in the 50x11. To my knowledge hacking the B screw on the GS RD is the only way to have a 50/34 and 11-40 combo. I've read that the Shimano MTB RD cannot be mated to a road shifter. Even with the new GRX I'm still not able to run 50/34 and 11-40 according to Shimano's offical specs. So what other choices do I have besides running a triple to get the wide gear range that I need?

User avatar
TonyM
Posts: 3263
Joined: Thu Jan 22, 2015 4:11 pm

by TonyM

pdlpsher1 wrote:
Fri May 10, 2019 5:30 pm
I would never ride a bike that has improper chain tension in ALL of the gear combos. Because doing so can rip the RD off the hanger and cause irreparable damage to a frame.

I've seen far too many YouTube videos where people adjust the B screw or add a WolfTooth RoadLink to accommodate a larger cog, and claim 'it works'. Most if not all of these setups have improper chain tensions. They claim that's not a problem because they never use those extreme cross-chain combos.....until one day they accidently shift into those combos.

Now let me repeat this one more time. As I have said many times previously, on my setup I have proper chain tension on the big-big and small-small gear combos. And I'm not using a WolfTooth RoadLink, a modified derailler cage, or any after-market add-ons. I'm using a GS Shadow-based RD. I simply adjust the B-screw and adjust the chain length to get this to work. bm0p700f- I don't know why you can't get it to work. Did you use the GS RD and not the non-GS RD? GS is the long cage version.

I'm using the 11-40 because it's a tandem, and tandems need extra low-range gearing for going uphill. I also need a minium of a 50T front because tandems also go downhills very fast, and I spin out easily in the 50x11. To my knowledge hacking the B screw on the GS RD is the only way to have a 50/34 and 11-40 combo. I've read that the Shimano MTB RD cannot be mated to a road shifter. Even with the new GRX I'm still not able to run 50/34 and 11-40 according to Shimano's offical specs. So what other choices do I have besides running a triple to get the wide gear range that I need?

What is the method that you use to determine the length of the chain so that you have a prope chain tension in big-big and small-small?

mattr
Posts: 4673
Joined: Fri May 25, 2007 6:43 pm
Location: The Grim North.

by mattr

pdlpsher1 wrote:
Fri May 10, 2019 5:30 pm
As I have said many times previously, on my setup I have proper chain tension on the big-big and small-small gear combos.
I find you can get 5-6 teeth outside of spec capacity on most "normal" bikes. And still achieve proper tension, and full coverage of all gears with shimano mechs. I'm running out of spec on several of my bikes, MTB and road (all shimano), and don't have any issues with all the gears, except the one with massively ovalised rings. Thats more to do with the rings than the range!

A few oddballs you have to be more careful with regards the position and angle of the hanger in relationship to the axle. Recently been playing with a rear facing dropout on a low profile and a *very* short hanger plus very short stays and even a stock set up is pretty marginal. I doubt even one tooth out would still work.

spdntrxi
Posts: 3145
Joined: Sat Jul 20, 2013 6:11 pm

by spdntrxi

I'm lazy... but if the GRX FD works with the XTR Di2 RD... I'm might be going back to 2x.

by Weenie


User avatar
TonyM
Posts: 3263
Joined: Thu Jan 22, 2015 4:11 pm

by TonyM

spdntrxi wrote:I'm lazy... but if the GRX FD works with the XTR Di2 RD... I'm might be going back to 2x.
Why back to 2X?
(I still have to decide between 1X and 2X for my gravel bike...)

Post Reply
  • Similar Topics
    Replies
    Views
    Last post