Blueflikk04

Can I use MTB cassette with my current 11s Shimano 105. May current cassette is 11-34t.

to be honest, i'm having hard time to go uphill with current cassette (newbie here).

So i'm planning to put the Deore XT cs M8000 (11-42t) but i'm still gonna use my crankset of 50-34t.

i would really appreciate if you can advise me if this is okay before I order the cassette.

if this is not possible, any suggestion you can share with me? Thank you so much.

c_m_shooter

Your rear derailer may not clear the big cassette, it is hard to know. You will need a new longer chain. If you can deal with these obsticles, as long as the cassette has the same number of gears you have now, you are good.

Paul Barnard

Assuming you have a 105 medium cage length rear derailleur, the answer is no. The derailleur does not have the "wrap capacity."

chain wrap capacity ? CanooterValve

The answer to all of your follow up questions is no as well. You can't get what you want with road shifters and derailleurs and that front crankset.

Bryan C. 

It is possible but you will need a new rear derailleur as well.

It has been done before with an Ultegra RX derailleur and also with the GRX 810 derailleur. Both of these are compatible with your 105 11 speed shifters. You will need a longer chain, and some free time to adjust your b-screw and chain length so it all works ok.

You may not be able to use the small/small gear combination but that wouldn't be a deal breaker for me.

cxwrench

I'm sure people have 'made it work' but it's definitely not correct. The 812 will work w/ the 42t cassette, but it's for a 1x crank...it doesn't wrap enough chain for a double. The 810 derailleur does wrap more chain, it's capacity is 41t, but it will only work w/ a 34t cassette. Same w/ the RX derailleur. You might be able to get a 36 to work but a 42 is wayyyy past the spec of both those derailleurs. Adjusting the b-tension screw so the derailleur will shift to an overly large cog will mess up the shifting on the small cog side of the cassette as the upper pulley is too far away to shift accurately.
It would be great if people understood derailleur specs in general and capacity in particular before posting advice like the above. This thread should also be posted in 'bicycle mechanics' for obvious reasons and not GD.

Bryan C. 

Just because Shimano says it won't work doesn't actually mean it won't work. Their super conservative specs are designed around optimal operating ranges. Not necessarily real world specs.

Maybe the problem is people like you who see the specifications as hard limits? So if it works, and works pretty well, then it's still not ok? Give me a break....

BTW, I do practice what I preach....

cxwrench

I'm a professional mechanic, I work in a shop. We have certain liabilities to consider. Where do you suggest I draw the line? Is the line blurry? What works on one bike may obviously not work on another. I'll stick with Shimano spec and not have to worry about it. In your case I would preface any advice you give that involves not sticking to spec by saying: 'This is my personal experience. I realize that I'm not doing this according to the manufacturer's recommendations...your results may vary'.

Bryan C. 

Lol, ok.

Elvo

Yes you can make it work with a road link and mid cage derailleur. You probably will not have enough chain wrap to use the 11/13T with your 34T front though

cxwrench

Definitely not great advice. See previous posts.

HTupolev

I'm assuming that you have the mid-cage (GS) derailleur.

It goes well beyond the wrap of your derailleur, so assuming you use the Shimano chain sizing method (big-big plus an inch), the drivetrain is going to go slack if you try to use your small cogs while in the small chainring.
It also goes beyond the max cog of your rear derailleur, which means that you may end up needing a hanger extender, depending on the bike. Or maybe it'll work if you merely screw the b-screw pretty far in.
The drivetrain also might end up more prone to baulky shifting, but this is hard to predict and also depends on your pedaling and shifting style.

In terms of liability, no. In terms of functionality, yes. And importantly...

...Shimano doesn't spec a drivetrain that does what the OP wants. No manufacturer does. A zero-compromise "not have to worry about it" option does not exist.

That's a fair concern, but an RD-RX810 isn't necessarily a bad option. It's got a very wide range of b-screw adjustment and an impressive ability to tolerate nonsense. I have one friend using it on their Cervelo Aspero with a 48-32 crankset and an 11-50 (!!!) cassette, with seemingly reasonable shifting.

katsup

Op did not specify that he wishes to stay within Shimano's specifications. The mentioned rear dérailleurs will clear a 42t cassette, whether it's recommended or not.



However, I was never using those gears, so the bike now has a 36t cassette.

Bryan C. 

So your opinion is the only one that counts? Get real. The question was asked and answered by people who have actually done what the OP asked. It's fine to put forth your opinion, but stop acting like you're an expert. You claim you are a "professional." Yet all you do is follow the directions in the dealer manual explicitly?

cxwrench

Wanna compare resumes sometime? Part of being 'professional' is making things work. Part of it is not taking chances in certain instances. I will definitely stick to the manual/spec when the differences are so big. Pairing a medium cage RD 8000 w/ a 36t cog? Probably gonna work fine every time. Pairing that same derailleur w/ a 42? Not even gonna try. I don't give a rats ass if that's what the customer wants. If they want it that bad they can do it themselves.

Kapusta

Could the OP just get a 30/46 crankset instead? Sound like the most straight forward thing to me.

FWIW, I believe are ways to get what the OP wants to work - isn’t this what a goat link does? Folks were getting MTB RDs to work with 42t cogs for quite a while before Shimano and SRAM started making RDs rated for anything over 36t. but these can be finicky and not the best idea for a self-professed newb to take on.

But like others have said, you will likely lose one or more of your small/small combos. And I would not care for the wider gear ratio spacing for a road bike.

Bryan C. 

HTupolev

Due to the liability issue, I think it's reasonable for bike shops to turn away this sort of work. But I'm not sure what that has to do with this thread: the OP isn't asking you to work on their bike, they're asking if the thing they want to do can be done.

If the OP doesn't need the top-end, smaller chainrings can be a great alternative. Less stress to drivetrain specs, and tighter gear spacing. A 30-34 is still a 10% higher gear that the 34-42 that the OP wants, though. Changing to a 46-30 would also likely more expensive than the cassette change, and availability of road-width sub-compact cranks just isn't very good.

I wish that itsy-bitsy subcompact road-width cranks were better-supported in the market, because a lot of cyclists don't need anything close to the top-end gears that modern road bikes use.

Kapusta

30/46 cranksets options have greatly expanded over the past year.

HTupolev

Yes, but cranks that support it still aren't standard, and smaller chainring options remain very sparse.

Kapusta

Yes, standard (or compact) cranks do not support it. That is why I was suggesting the OP get a 30/46 CRANKSET.

Shimano GRX FC-RX600-2

30/46, just under $150, and widely available.

HTupolev

Yes, I know. When I said "standard", I wasn't referring to 53-39, I was referring to cranks that road bikes generally come with. I was pointing out that a new crankset would be required, my point being that this...



...is far more expensive than a new cassette. And, furthermore, that the OP would still have to get a new cassette anyway to achieve the low-end that they want, because 30-34 is significantly higher than 34-42.

Kapusta

How much more expensive are we talking about? The cassette the OP is looking at is at least $80, plus $22 for a Roadlink, plus ~$25 for a new chain because the old one will be too short, So that is ~$127 (a whopping $23 savings) for a setup that has big ratio jumps and does not have the chain wrap capacity needed, so he loses some combos.

You are correct that 30/34 is a higher than 34/42. HoweverI think in reality that even the 30/34 is enough of a change that the OP is going to really notice it on a climb. And heck, if that is not enough (which is unlikely, IMO), then he can probably get a cassette with a 36t cog to work with his RD. Yes it is more money overall, but the RD will likely not run into chain wrap issues, nor will he need to deal with stuff like RoadLinks. And he keeps the gear ratio jumps the way they are.

Anyway, If I were in the OPs position and wanted lower gears, I'd just get the sub-compact crank. And that is exactly what I did when my wife wanted lower gears, and that is what I am likely going to do with my own gravel bike soon.

To each his own, I guess.

HTupolev

A roadlink sometimes isn't necessary, and a new cassette would kick the cost difference back up by another $50+.

Ultimately it depends on the use case. If the 46-30 with an 11-34 covers adequate range, in most cases it'll be a better setup than swapping to the 11-42. But 50-34 11-42 has a higher top-end and a lower low-end, if you have use for those gears it might be a better drivetrain (and cheaper) than swapping out the cranks.
(Granted, the OP most likely isn't in dire need of their 50-11 top-end.)

Kapusta

I am having a hard time seeing a RoadLink (or something similar) NOT being needed to get a 11sp 105 RD to work with a 42t cog.

Yes, that would be an extra $50, making this ~$75 more total. But well worth it, IMO. With a 30/36 low gear, that is getting reasonably close to 34/42 without the drawbacks (wide spacing, lost ratios,).

Agreed. Hey, some people don't mind wider gear ratio spacing, anyway. And they learn not to cross chain into small-small combos.

HTupolev

I know someone who does it.

TimothyH here did it with an Ultegra RX derailleur which has basically the same wrap and cog ratings:
https://www.bikeforums.net/20989426-post13.html
https://www.bikeforums.net/20990016-post16.html