2024 Shimano RX825 2x12 GRX Di2

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fizzaz
Posts: 303
Joined: Wed Nov 07, 2018 5:02 pm

by fizzaz

The longer I've set with this release, the more of a flub I've come to see it. Wtf Shimano, please don't make me use Sram. Please.

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pdlpsher1
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by pdlpsher1

Gavin929 wrote:
Wed May 29, 2024 1:45 pm
Just installed the new GRX 825 rear derailleur on a build that is otherwise ultegra 8100. E-tube will not allow me to turn off the gear position control feature with the grx rear derailleur. I had previously been able to navigate around this on 9200 and 8100 di2 12 speed. Looks like its a hard no with the grx. Please let me know if anyone has a workaround. I don't usually cross chain but hate not being able to shift all the way through my cassette range.
So the GRX locks out the two smallest cogs when in the small ring? I don't see any downsides to having this feature.

AFAIK the 9200's gear control cannot be defeated. The 9100 can be defeated at one time by selecting a different cassette size. But this is not possible with the newer versions of E-tube. AFAIK the 8100 and 7100 lack gear control to begin with. How did you manage to defeat it on the 9200?

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pdlpsher1
Posts: 4167
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by pdlpsher1

fizzaz wrote:
Wed May 29, 2024 7:29 pm
The longer I've set with this release, the more of a flub I've come to see it. Wtf Shimano, please don't make me use Sram. Please.
The expectations were quite low before the offical annoucement. We all knew there isn't any groundbreaking new features prior to the release. If you're looking for 1x13 you'll have to wait until next year. Sram's 1x13 is rumored for later this year.

OtterSpace
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Joined: Sun Mar 08, 2020 6:28 am
Location: California Silicon Valley

by OtterSpace

Gavin929 wrote:
Wed May 29, 2024 1:45 pm
E-tube will not allow me to turn off the gear position control feature with the grx rear derailleur.
Is this just locking you out of small-small or also big-big?

small-small would just be a rare inconvenience and reminder that you are in the wrong gear while big-big being locked out would be a hard pass for me. big-big is useful for short sharp climbs that are not worth shifting the front for.

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pdlpsher1
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by pdlpsher1

On the 9200 it locks out the two smallest cogs while on the small ring. This is a fantastic feature because it essentially increases the chain wrap capacity by two teeth while not needing a longer cage, saving weight and being more aero. The big-big can't be locked out even if the user wanted it. On the 8100 and 7100 no gear control is present to my knowledge, presumably because Shimano doesn't want a flood of warranty requests from people claiming that their RDs are broken. Plus weight and aero aren't priorities for 8100 and 7100 users.

OtterSpace
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by OtterSpace

pdlpsher1 wrote:
Thu May 30, 2024 2:45 am
On the 9200 it locks out the two smallest cogs while on the small ring. This is a fantastic feature because it essentially increases the chain wrap capacity by two teeth while not needing a longer cage, saving weight and being more aero. The big-big can't be locked out even if the user wanted it. On the 8100 and 7100 no gear control is present to my knowledge, presumably because Shimano doesn't want a flood of warranty requests from people claiming that their RDs are broken. Plus weight and aero aren't priorities for 8100 and 7100 users.
I understand what you are saying at a user level. However, for 12s road I think this comes from RD-R9250 only offically supporting a total teeth drop of 37T and a front drop of 16T which leaves 21T drop for the rear (11 (smallest cog)+ 21 (rear tooth support)= 32T which isnt enough for the officially supported 11-34 cassette. Meanwhile Ultegra supports a 38T total drop and 16T front. Therefore for safety Shimano locks out 11T and 12T when in the small ring on RD-R9250 like you say. We are basically saying the same thing but in different ways but I am trying to work out why this applies to GRX and to what degree.

Following this RD-RX825 offically support a total teeth drop of 40T and a front drop of 17T leaving 23T drop for the rear (11 (smallest cog + 23 (rear tooth support) = 34T which isnt enough for the officially supported 11-36 cassette. Interestingly 105 supports 41T total drop and 16T front which natively supports a 11-36 so no lockout.

I dont have RD-R9250 so I dont know if they only lock you out if you select a rear 11-34 or if they also do if you select an 11-30 to guarantee extra margin and have the same function for all cassettes.

Basically I think the same RD-R9250 logic applies for RD-RX825 given their officially supported drops which would mean that big-big should be supported.
Last edited by OtterSpace on Thu May 30, 2024 3:23 am, edited 1 time in total.

Gavin929
Posts: 79
Joined: Sun Nov 27, 2011 4:50 am

by Gavin929

pdlpsher1 wrote:
Thu May 30, 2024 12:42 am
Gavin929 wrote:
Wed May 29, 2024 1:45 pm
Just installed the new GRX 825 rear derailleur on a build that is otherwise ultegra 8100. E-tube will not allow me to turn off the gear position control feature with the grx rear derailleur. I had previously been able to navigate around this on 9200 and 8100 di2 12 speed. Looks like its a hard no with the grx. Please let me know if anyone has a workaround. I don't usually cross chain but hate not being able to shift all the way through my cassette range.
So the GRX locks out the two smallest cogs when in the small ring? I don't see any downsides to having this feature.

AFAIK the 9200's gear control cannot be defeated. The 9100 can be defeated at one time by selecting a different cassette size. But this is not possible with the newer versions of E-tube. AFAIK the 8100 and 7100 lack gear control to begin with. How did you manage to defeat it on the 9200?

Yes. Only the small ring locks out the 11 and 12 tooth cogs. Big ring allows for full use of the cassette. I know it's a safety feature. I just always liked having access to the full cassette in both rings. Sometimes it's just better to drop a gear and cross chain for a bit then go through the hassle of shifting both front and rear derailleurs. Especially in nasty conditions. YMMV.

To defeat 9200 you just choose the 54/40 chainrings and it enables you to turn it off.

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pdlpsher1
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by pdlpsher1

OtterSpace wrote:
Thu May 30, 2024 3:18 am
Following this RD-RX825 offically support a total teeth drop of 40T and a front drop of 17T leaving 23T drop for the rear (11 (smallest cog + 23 (rear tooth support) = 34T which isnt enough for the officially supported 11-36 cassette. Interestingly 105 supports 41T total drop and 16T front which natively supports a 11-36 so no lockout.
I think the 40T takes the lockout into account. With the lockout the 11-36 essentially becomes a 13-36.

Here's an interesting thing about the lockout. If you have a cassette that starts with 11-13-15-xx you basically get some free chain wrap capacity. On my gravel bike I'm running the RD-RX815 which has the lockout. And with my 11-40 cassette the lockout essentially turns it into a 15-40 cassette. So 40 - 15 + 17 = 42 tooth gap. The official capacity of the RD-RX815 is 38T but the 38T doesn't make sense if you do the math. In any case the 11-40 is working great with the RD-RX815, but only with the lockout enabled. Without the lockout I imagine the chain might be too short or too long on the cross-chain combos.

Gavin929
Posts: 79
Joined: Sun Nov 27, 2011 4:50 am

by Gavin929

I figured it out. Ultegra FD has a max capacity of 52T (according to shimano). DA has a max of 54T. So it won’t let me choose 54T on E-TUBE because I’m using an ultegra FD this time. Normally not a problem as ultegra and 105 don’t have a gear position control feature. BUT the new grx does use GPC and limits my chainring choices because it knows I have an ultegra FD. So my old plan of choosing 54/40 and turning off GPC for dura ace no longer works.

Going to test this out later with a DA front derailleur.

Blindspot
Posts: 1
Joined: Wed May 22, 2024 12:00 am

by Blindspot

fizzaz wrote:
Wed May 29, 2024 7:29 pm
The longer I've set with this release, the more of a flub I've come to see it. Wtf Shimano, please don't make me use Sram. Please.
Same over here, Shimano just doesn't care much about Gravel. The lack of Options is annoying. 165mm cranks only come from GRX 610 Crank which is heavy AF. Them shifters are just damn heavy while you can use SRAM Red Shifters.

The Cassette for 11-36 only comes with a 105 Level Design. You can use light weight cranks with other manufacturers but you'd be forced with Road Gearing. No Power Meter too, SRAM is making a killing.
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satanas
Posts: 368
Joined: Sat Jul 04, 2020 5:45 pm

by satanas

In one of the (many) manuals Shimano says you cannot lock out GPC with 52x36, 50x34 or 48x31, and to make sure the correct chainring combo is selected. What this is not saying is that GPC may presumably be overridden in other combos i.e., 54x40, 46x36, 46x30. If it was me, I'd just lie to the system about the chainring sizes if I wanted to defeat GPC, but don't care if those gears can't be selected, so wouldn't bother.

Gavin929
Posts: 79
Joined: Sun Nov 27, 2011 4:50 am

by Gavin929

I have read the manuals. The problem is that it will not let me select 54/40 or 46/30 due to having an ultegra front derailleur. The 46/36 has also been moved to the no category as it won't let me choose to disable GPC with that chainring combo. This is the most recent updated e-tube software. I had to update my e-tube because it wouldn't sync up to the GRX 825 di2 rear via bluetooth until I did the update.

satanas
Posts: 368
Joined: Sat Jul 04, 2020 5:45 pm

by satanas

@ Gavin929: Are you saying you can only select one of the standard Shimano combos, and then only those from the same groupset? WTF?!? 46x36 is the combo that has the least use for GPC too, and is available in Ultegra; sigh.

Maybe I should just stick with mechanical GRX. :-(

Gavin929
Posts: 79
Joined: Sun Nov 27, 2011 4:50 am

by Gavin929

I can choose 46/36, 50/34, and 52/36 with the ultegra front derailleur installed. It does not show 54/40 as an option. That being said. I am not at home right now to check and see about 46/36 GPC. I want to say that it was grayed out as well, but come to think of it, it might have been missing altogether with that combo. If that's the case then maybe it will be like the rest of ultegra and let me run it without asking. I'll check when I get home.

LainOTN
Posts: 85
Joined: Sat Feb 15, 2020 3:01 pm

by LainOTN

LainOTN wrote:
Fri May 24, 2024 10:07 am
I'm a bit puzzle about the levers, they claim it have 1 SD300 satallite port and another SD300 e-tube port, like the ultegra levers

https://bike.shimano.com/en-US/product/ ... 825-L.html
https://si.shimano.com/en/ev/ST-RX825-5053

But the manual says that only wireless.?? and the e-tube port is only for pc linkage...
https://si.shimano.com/en/dm/GADBR10/in ... trol_lever
The ST-RX825 is for wireless gear shifting only. It does not support wired gear shifting.

What?!?!? Is not that a bit stupid?

I was hopping to run this totally wired due the ammount of advantages it gives to me. Consider running ultegra levers...
I answer myself, I just hooked a wire from a ST-RX825 to a free port on my R8150 system and it just works as expected. No pairing even needed. That is all I needed to know. Wired FTW. :p groupset incomming.

Wondering why it states that the lever doesn't support shifting via wire...

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