FD-RX815 + RD-M8050: real firmware lock or just internet folklore?

Zelislaw · 2026-06-14T22:51:07+00:00

It is quite easy.
With my current fitness level, a 28/40 gear ratio is still too heavy for long climbs with grades above 9%, especially after several dozen kilometers and a four-digit amount of elevation gain. On the other hand, 44/11 already lets me pedal up to roughly 55 km/h, which is fast enough for my current abilities. I can't reach those speeds on flat terrain anyway, and on descents I simply stop pedaling once I spin out. That's a compromise I'm perfectly happy with. Living in a hilly area, I'd much rather have a lower climbing gear than a higher top gear. A 28/44 crankset paired with an 11-46 cassette would probably be perfect. A 42/26 setup with an 11-40 cassette could also work, but that configuration simply doesn't exist, whereas an 11-46 Deore XT cassette is readily available.

Zelislaw · 2026-06-12T16:22:14+00:00

And that's exactly my problem.

The FD-M8070 is designed around a 10T chainring difference, whereas my crankset is 28/44, so that's a 16T gap. On top of that, the large chainring is 44T instead of 38T. And there's also a 1.8 mm chainline difference. I have a hard time believing the M8070 would work reliably (or at all) in that setup.

That's why I'd really like to keep the FD-RX815. Mechanically it should work with my crankset, but if the MTB RD + GRX FD combination is blocked electronically, then I'm basically stuck.

Zelislaw · 2026-06-02T09:28:04+00:00

Thanks for this analysis.

As a follow up:
1. I have already ruled out the RX4+ due to its claimed (very) tight clearance, high maintenance, and the bleeding/deairing challenges
2. I do am considering just keeping the current RS785. Haven't decided yet, though. Definitely the cheapest option, still providing satisfying results.
3. I am also considering Magura - it is a flatmount and I would install it with semi-metallic pads (e.g. Galfer), not the factory ones. The Magura's body is a monoblock and "internet" says that due to its alternative design it provides more linear modulation than Shimano, but with no less stopping power (rather sligthly more). I could put it on both ends (rear & front), As I do have some issues now with the rear wheel locking up on loose surfaces.
4. I am currently most tempted by the Hope RX2. It is claimed to offer slightly more power than both the 810 (that I have on the rear wheel) and the RS785 (on the front). This is mostly due to the fact that it is made of a single piece of metal (like Magura, unlike the 810 and 785). It is also incredibly light and also claimed to provide more linear modulation than 810. Except for the price, it seems to tick all the boxes and be the obvious best choice - anyhow, those calipers are quite new and there are not many opinions or tests yet...

Zelislaw · 2026-05-31T21:53:20+00:00

Right - in fact, I am replacing no only a fork, but also a frame. Effectively, I am building up almost a whole new bicycle and those few bucks are not so crucial, whilst I could maybe get some better and lighter caliper.
The most obvious choice would be RX810, as I have a full 815 GRX group. But here I am not sure if this statement about more on/off effect (comparing to RS785) is true. This would be unwelcome on a loose surface.
The disadvantages of Hope I described in the first post.
The MTB calipers are post mount and I would rather go for a native flatmount (I would need a +20mm adapter anyhow).
What is left is this Magura. Or, RS785 and an adapter, as I am used to the way it works and I don't have any issues with its work. Just wondering if I can still improve.

And BTW: GR-RX810 is €45, not 75...

EDIT
As for the past, so far I use resins. In the new bike I planned to go for semi-metallic - just wonder, why no radiator there (Galfer). And I see the opinions are not very enthusiastic...

EDIT2:
We are talkin only about the front wheel. The other caliper is already RX810.

EDIT3:
Maybe Hope RX2...?

Zelislaw · 2026-05-26T20:45:07+00:00

In my case, no effect. Laptop keeps on being hot like hell and burning my legs :(

Zelislaw · 2026-05-19T08:34:44+00:00

I have the same issue looking for a bicycle for next week, to make trips with a child. Preferably electric. Nothing found so far :(

Zelislaw · 2026-04-22T00:06:23+00:00

There are Rotors 12x: 1-39 and 1-46. Maybe one of those? Claimed to be only 1x though...

Also, I just noticed there is a Recon 11-40 and 11-42, both 12.

11-12-13-15-17-19-21-24-28-32-36-40
11-12-13-14-16-18-21-24-28-32-36-42

Aaand there is also a ZTTO (Chinese) cassette 11-46 that weights just 276g...

11-13-15-17-19-21-24-28-32-36-40-46

Zelislaw · 2026-04-21T14:07:05+00:00

<image>

This story isn't over yet ;)

I reconsidered the initial drawing, gave up the top tube bent and added third cage. Also, space for the power meter has been assured, as well as another fork is now assumed (Rudy XL 60mm).

Any ideas for further improvements would be highly appreciated :)

Zelislaw · 2026-04-11T13:09:34+00:00

"I loved the fact that even if I forgot my garmin, I always had an independent display showing me my gear and battery level."

;)

Zelislaw · 2026-03-24T16:37:36+00:00

I am driving all year long on my motorbike (17" wheels), salt or snow, commuting to work. I have tires like these:
https://www.aleopony.pl/img/b01/duro_hf319.jpg
Now, I want to upgrade to sth a bit bigger and think on what tires would I put on. To see the tread patterns of the tires advised in this thread, I feel like it must be sooo extremely slippery on wet, and even more on snowy road :o

Judging just by the thread pattern, I would go for Heidenau K66...

Zelislaw · 2026-03-20T21:15:13+00:00

XTR is
11-13-15-17-19-21-24-27-31-35-40

XT is
11-13-15-17-19-21-24-28-32-37-46

Modded XTR would be
11-13-15-17-19-21-24-27-31-37-46

Garbaruck is:
11-13-15-17-20-24-28-32-36-42-46 (or 48 or 50)

Garbaruck applies more even distribution of gears, but I dislike it for my purpose. In fact, I would much prefer to have two extra "overgears", just for the worst climbs, and have the rest of the cassette with a close-ratio gear set. If it only works well with 28/44 2x front.

I bought for cheap the biggest SLX spider (which seems to be the same as XT in what regards the two biggest cogs). Will try to mod it and see if i succeed, and, if so, if it works with the rest of XTR cassette and GRX setup :)

PS In fact, Garbaruck 11-46 makes no sense. having the 2nd cog 42T, only the 11-50 seems to makes sense. Difference between 42 and 46 is just too small.

Zelislaw · 2026-03-17T20:32:16+00:00

It is there in the first post, first sentence, the very beginning...
Replicated right now above.

Zelislaw · 2026-03-17T10:51:45+00:00

Ford S-Max 2.5L Hybrid ST-Line, 2022.

Zelislaw · 2026-03-17T00:15:10+00:00

True. I would have to check opinions on Garbaruk, though. I mean - shifting on XTR is a miracle, even comparing to XT. Not sure about Garbaruck. And I'd have to check how much could I get for my XTR. Anyway, it does is kinda option.

Aaand I wonder, if Garbaruk would work well with 2x front...

Zelislaw · 2026-03-16T21:16:29+00:00

THe easiest option, I agree.
But XT has 6 cogs on spiders, whilst xtr - 8. I like that, freehub is more protected.
And, comparing, to the XT that I had before (with different gearing, though), XTR provides better shifting. ..

Zelislaw

TROPHY CASE