orbano

Hi there!

Finally I got myself a 2019 Toughroad SLR 2 (or something like it: a 2019 SLR1 frame with SLR2 specs, but with deore rear hw).
Question is: can I do the conversion in two steps:
First leave the rear alone and change the Altus M371 to any Hollowtech stuff (BB-M801 and M8100 36T)?

This modification seem to me like a low hanging fruit, but don't know if there are dependencies between the front chainring, the chain and the rear derailleur that I don't know about.

Thanks

hokiefyd 

I would have a long think about what your end goal for such a conversion is...specifically, what gearing range you want or need. Calculating the gear inches of the lowest gear you use regularly, and the highest gear you use regularly, will give you an idea of what range you need to cover with a 1x conversion. For example, I regularly use about 20 gear inches (at the lowest) to about 100 gear inches (at the highest). This is a 500% gear range. If you use only 30 gear inches at the lowest to 90 gear inches at the highest, that's a 300% gear range. Your riding may be, and probably is, different from mine (as is your riding style, fitness, cadence preference, etc.). All of that comes into play when deciding the right gearing for you.

Then, your second decision point is deciding how large of a step between gears are you willing to put up with. The cassette on a 3x9 can have pretty closely-spaced sprockets (in terms of gearing) because you have three chainrings on the front to give you the range...you don't need the range back at the cassette. With only one chainring, your cassette must handle the entire gear range. A 9-speed cassette that can handle a 500% gear range will have very wide spacing between the ratios. A 500% 10-speed will have slightly smaller spacing. A 500% 11-speed even smaller spacing, etc. As you pack more gears into the same gear range, your ratio steps are smaller, which some people prefer.

Unfortunately, this isn't a "just give me the easy answer" type of question, because there are so many variables and what works for one person well might be a terrible experience for another person.

Also consider your hub. You mentioned a 9-speed drivetrain now...I'm not sure if all 12-speed cassettes will fit onto an 8/9/10-speed hub. Others can probably speak better to that.

poiuyt

Technically, the chainring is the least "chain dependent" part: the inside width of the chain is the same from 9 to 12 speed. https://bike.bikegremlin.com/3555/bi...sion-standards

I see however one dependency between chainring and rear derailleur: the clutch. 1x require some retention mechanisms to avoid derailment, clutch derailleurs are the most common ways, along with narrow-wide chainrings. The XT chainring has a narrow-wide teeth pattern, but it may be not sufficient.

But if the modification is not urgent, might be good to wait for a wider availability of Shimano CUES parts: they are targeted for trekking bikes. I personally find 36T to be too limiting for a bike that has a road focus, and it's hard to find larger chainrings with 73mm bottom brackets. Note that if your bike has a 68 bottom bracket shell, you can also have a look at gravel cranks.

If they have a smaller sprocket that has 11 teeth and a large sprocket larger than 34T, they should fit. 10-teeth small sprockets require other hubs (XD or Microspline), but I have never seen a 11T small sprocket cassette that doesn't require a standard Shimano hub.

orbano

Thanks guys for the insight.


I cannot think in gear inches, only in gear ratios (my other bike I'm used to has the same wheel size and crank length). I had the same thought process, and came up with this:

I rarely use my current 3x8 above 36x11, maybe on bigger descents, but thats a rare occasion, 90% of the time I'm on the 36T chainwheel so I think that's a sacrifice I could make (so I need ratios south of 3.3).

This is why I was thinking about keeping the current 11-34 9 speed until I find out whether I want a new hub/wheel for the sake of the 10T cassettes, the extra headroom would be nice, but my main focus is not the roads, I'm just commuting there, or being on a small casual tour with friends who are in worse shape than me .

Probably I'm fine with a 11-46 11s cassette (would mean a randge from 3.27-0.78 instead of my current 0.69 minium): I checked the ratios and it seems to me that at higher gears the gear spacing is not that different.


So if I understand correctly, from a technical point of view, with the current rear 9 speed setup (11-34T with 9s Deore derailleur and "regular width" chains) I might have a higher tendency of derailling if I use the M8100SM series 36T 12s NW chainwheel (SM.CRM85)? If it's not a dealbreaker, and could happen only occasionally, I'm okay with it, the rear 11-12s conversion will happen in the near future, I just want to upgrade in smaller increments if possible (that would help me decide whether I need 10T or not)..

poiuyt

The reasons I experienced chain drops at the chainring with a 1x without clutch (to be correct: because I forgot to activate the clutch after unmounting the wheel) is on flat at higher speed when I stopped pedalling: because the inertia of the cassette, the cassette keeps rotating. The lack of clutch means that the derailleur can take the slack on the lower part of the drive train which decreases the tension on the upper part of the chain and causes the derailment (hard to explain). But this may not be a problem with a 11-34 cassette, that is lighter (in my case: a steel 11-42 cassette).

orbano

We will see, I'm committed now I just have to figure out chainring clearance, whether M7100 crank is good, or I need M7120. My frame is 68mm so I have a little headroom with a 73mm BB and also an extra 2mm compared to my current ~50mm chainline for the mid 34T chainring, which is 3mm away (from tip to the nearest point on the fork, so effective distance is more if I consider the constrained movement of the chainring on a circle).
Still a bit nervous, the crank is pretty expensive, hopefully the 52mm version will be enough

DorkDisk

7120 is for modern MTB boost frames, you have a basic QR frame so 7100 is what you need.

orbano

Thanks for confirming, I'm pulling the trigger. Just to be sure, this is my shopping list:
SLX FC-M7100-1 (52/172/175) cranks
XT SM-CRM85 36T direct mount chainring
XT BB-MT801 68-73 bottom bracket