Shimano GRX 12-speed question

[Xrslug]

Because I love tinkering with my bikes, I’ve been kicking around the idea of converting my hardtail into a drop bar configuration. Currently running XT 12-speed.

I’ve read in various places that the new GRX 12-speed STI lever is not compatible with Shimano 12-speed MTB derailleurs, supposedly because of “different pull ratio.”

Given that the the new GRX lever unit shifts the GRX long-cage 12-speed derailleur, which is expressly compatible with Shimano 12-speed MTB cassettes, how can the GRX lever unit not be compatible with a Shimano 12-speed MTB derailleur? It’s shifting on the same cassette, both in cog spacing and cog size, but somehow the “pull ratio” is different and incompatible?

I like to understand how things work (and would prefer not to replace my XT derailleur), so curious for the explanation here.

[EB]

Originally Posted by Xrslug

Because I love tinkering with my bikes, I’ve been kicking around the idea of converting my hardtail into a drop bar configuration. Currently running XT 12-speed.

I’ve read in various places that the new GRX 12-speed STI lever is not compatible with Shimano 12-speed MTB derailleurs, supposedly because of “different pull ratio.”

Given that the the new GRX lever unit shifts the GRX long-cage 12-speed derailleur, which is expressly compatible with Shimano 12-speed MTB cassettes, how can the GRX lever unit not be compatible with a Shimano 12-speed MTB derailleur? It’s shifting on the same cassette, both in cog spacing and cog size, but somehow the “pull ratio” is different and incompatible?

I like to understand how things work (and would prefer not to replace my XT derailleur), so curious for the explanation here.

The cable pull ratio is different, thus the indexed GRX shifter won't put the derailleur in the right place, as the amount the cable is pulled when you push the trigger differs between these two systems. You need to replace your XT derailleur, or look into weird solutions like a travel agent (if such a thing even exists for this particular ratio change).

Or you could use a friction shifter, but I wouldn't recommend it on 12 speed.

Or or... you could use an indexed bar-end shifter. Microshift makes a 12-speed Shimano MTB compatible barcon (https://www.microshift.com/models/bs-m12-r/)

[Xrslug]

Originally Posted by EB

The cable pull ratio is different, thus the indexed GRX shifter won't put the derailleur in the right place. You need to replace your XT derailleur, or look into weird solutions like a travel agent (if such a thing even exists for this particular ratio change).

OK, so put another way — the GRX 12-speed derailleur requires a different amount of cable pull to move the same distance as compared to the XT 12-speed derailleur when shifting on the same 12-speed cassette? And if so, holy hell is that stupid.

Thanks for the heads up on the Microshift. That’s what I was considering before I went down the GRX 12-speed rabbit hole. The “budget” option would be the Microshift barend, Wolftooth drop bar dropper lever, and TRP Hylex RS brakes. I’ve done a lot of off-road riding with barend shifters so that doesn’t put me off.

The Gucci build would be GRX 12-speed levers, calipers, and rear derailleur, with the left lever actuating the dropper.

[EB]

Originally Posted by Xrslug

OK, so put another way — the GRX 12-speed derailleur requires a different amount of cable pull to move the same distance as compared to the XT 12-speed derailleur when shifting on the same 12-speed cassette? And if so, holy hell is that stupid.

Yes.

Look at it this way - Shimano decided (because reasons) a really long time ago that their road and MTB shifters would have different cable pull ratios.

My only possible guess here is that they wanted people to be able to use 12 speed road brifters with their 12 speed GRX derailleurs, and that putting the 12 speed GRX brifters on the MTB pull ratio "standard" would have meant those GRX derailleurs would be in a weird isolated place relative to the other 12 speed road components.

Of course I'm assuming 12 speed GRX and 12 speed Shimano road use the same pull ratio - if that's also not true then I got nothing here.

[yinzerniner]

Originally Posted by Xrslug

OK, so put another way — the GRX 12-speed derailleur requires a different amount of cable pull to move the same distance as compared to the XT 12-speed derailleur when shifting on the same 12-speed cassette? And if so, holy hell is that stupid.

Thanks for the heads up on the Microshift. That’s what I was considering before I went down the GRX 12-speed rabbit hole. The “budget” option would be the Microshift barend, Wolftooth drop bar dropper lever, and TRP Hylex RS brakes. I’ve done a lot of off-road riding with barend shifters so that doesn’t put me off.

The Gucci build would be GRX 12-speed levers, calipers, and rear derailleur, with the left lever actuating the dropper.

Different cable pull ratio for different rear derailleurs has been present forever. You can call it "stupid" but unless you've been under a rock for the last 40 years nothing has changed in that regards.

Now, there have been a few doohickeys that try to compensate for the different ratios, such as the wolftooth tanpan, but as cassette cog spacing has gotten tighter due to more speeds there's only so much precision a thin steel cable can muster.

But if you're trying to keep stuff at a sensible budget while staying 12s there's deals to be had. A complete GRX 1x12 group is street pricing for about $700 now, same for SRAM Apex or Rival XPLR AXS, and once you factor in selling off the other components that's roughly a $4-500 upcharge, give or take.

Or if you really don't mind tinkering then something like SRAM mechanical shifters and a Ratio Technology kit will be roughly $300 or so, and should work with the XT 12s cassette.

Originally Posted by EB

Of course I'm assuming 12 speed GRX and 12 speed Shimano road use the same pull ratio - if that's also not true then I got nothing here.

What is this mythical beast you speak of, cable actuated "12 speed Shimano Road"

[Xrslug]

Originally Posted by EB

Look at it this way - Shimano decided (because reasons) a really long time ago that their road and MTB shifters would have different are cable pull ratios.

Yes…. Different pull ratios between road and MTB made some sense to me when the cassettes had either wildly different ranges or a different number of cogs, or both. What throws me off about 12-speed GRX is they’ve designed it to work with the MTB cassettes. But as you point out they had to choose between road or MTB pull ratios for the STI levers and perhaps it was just too out of the box for them to change an STI system to the MTB ratio. Or maybe it’s something as simple as adopting the MTB pull ratio would require the STI lever to swing too far (either subjectively from a user experience or objectively it made the design of the lever more difficult). Anyway, appreciate the responses!

[Xrslug]

Originally Posted by yinzerniner

What is this mythical beast you speak of, cable actuated "12 speed Shimano Road"

105 12-speed mechanical

[EB]

Originally Posted by yinzerniner

What is this mythical beast you speak of, cable actuated "12 speed Shimano Road"

I swear I didn't hallucinate this:

https://bike.shimano.com/en-EU/produ...anical_lp.html

[yinzerniner]

Originally Posted by EB

I swear I didn't hallucinate this:

https://bike.shimano.com/en-EU/produ...anical_lp.html

Wow, I definitely missed this. Still pretty pricey and rare considering the other options, but at least there’s some hope for the analog set

[wyatt_]

Originally Posted by Xrslug

OK, so put another way — the GRX 12-speed derailleur requires a different amount of cable pull to move the same distance as compared to the XT 12-speed derailleur when shifting on the same 12-speed cassette? And if so, holy hell is that stupid.

Thanks for the heads up on the Microshift. That’s what I was considering before I went down the GRX 12-speed rabbit hole. The “budget” option would be the Microshift barend, Wolftooth drop bar dropper lever, and TRP Hylex RS brakes. I’ve done a lot of off-road riding with barend shifters so that doesn’t put me off.

The Gucci build would be GRX 12-speed levers, calipers, and rear derailleur, with the left lever actuating the dropper.

Just chiming in to agree, even if it has been going on forever, the pull ratio incompatibility is stupid. The only reason for it is to force people into a few extra purchases in upgrade/conversion situations like this. So dumb.

Also, want to say I was in the same situation a couple of years ago and went with the Microshift barend and TRP Hylex levers solution on a drop bar 29er build. I assumed I'd keep them around for a minute and then upgrade to GRX or AXS when I had the money, but now I can't imagine why. The Hylex levers are probably my favorite brakes I've ever had (though I think I'm in a minority where the hoods seem to be a perfect fit for my hands) and the friction barend does stuff that indexed shifting just can't do. It's a great solution.

[Xrslug]

Originally Posted by wyatt_

Just chiming in to agree, even if it has been going on forever, the pull ratio incompatibility is stupid. The only reason for it is to force people into a few extra purchases in upgrade/conversion situations like this. So dumb.

Also, want to say I was in the same situation a couple of years ago and went with the Microshift barend and TRP Hylex levers solution on a drop bar 29er build. I assumed I'd keep them around for a minute and then upgrade to GRX or AXS when I had the money, but now I can't imagine why. The Hylex levers are probably my favorite brakes I've ever had (though I think I'm in a minority where the hoods seem to be a perfect fit for my hands) and the friction barend does stuff that indexed shifting just can't do. It's a great solution.

Appreciate the feedback — that’s good to hear about the Hylex. The draw for GRX for me is the slickness of the left lever actuating the dropper. And, of course, it would give me the option of being the only person in the known universe running interrupter levers with hydraulic brakes.

[Mark McM]

Originally Posted by yinzerniner

Different cable pull ratio for different rear derailleurs has been present forever. You can call it "stupid" but unless you've been under a rock for the last 40 years nothing has changed in that regards.

There was a time when Shimano's derailleur cable pull was uniform. Originally, Dura-Ace had a different cable pull than the other indexed groups, but the cable pull was unified starting with 9spd (1996). MTB derailleurs at that time also had the same cable travel. It was only later than MTB derailleurs diverged from road derailleurs.

[2metalhips]

I use an Ultegra 10s shifter with a 10s XT rd and cassette utilizing a Wolftooth Tanpan and it works quite well.

[zzy]

Originally Posted by 2metalhips

I use an Ultegra 10s shifter with a 10s XT rd and cassette utilizing a Wolftooth Tanpan and it works quite well.

10sp MTB (dynasys) doesn't play with road shifters. 9sp works perfectly. Trigger shifters and STIs have very different designs and functions, so it makes sense that they're different. Esp in the 12sp era.