Moving from a 2 ring to 3 ring crank
 

New member here!

My previous 2014 Trek DS8.3 had a 48/38/28 8 speed. I recently moved up to a 2019 Trek DS4 which has a 42/28 10 speed and I really miss the high end. Most of my biking is road biking but with a lot of rough pavement, cobblestone, and some gravel. I'm really wanting to move back to a 3 ring 48/38/28 with the 10 speed . Unfortunately, while I've done plenty of basic bike mechanics over the years, I've never upgraded like this before and I'm not sure what all else is involved - do I need new shifters, derailleur, chain, anything else?

If it helps, my pertinent parts from the spec sheet are:

• Shifters - Shimano Deore M6000, 10 speed
• Front derailleur - Shimano Deore
• Rear derailleur - Shimano Deore M6000, Shadow Plus
• Crank - SRAM S1000, 42/28
• Bottom bracket - Sealed cartridge
• Cassette - SunRace, 11-40, 10 speed

Appreciate any and all input!

Welcome! I saw your post in the hybrid section, and was going to suggest that you ask here as well, and it looks like you've already found the place to be!

When you say that your bike has a "sealed cartridge" bottom bracket, I take that to mean "square taper" (which is commonly called "sealed cartridge"). If you Google "shimano un55", does that resemble what's on your bike (not necessarily the color, but the style, with the square tapered ends)? If so, then you'll need a new square taper crankset, with three chainrings. SRAM's website doesn't seem to indicate that the S-1000 crankset comes with a square taper option, but it's possible, especially for an OEM (which is why I ask that you confirm the bottom bracket type).

You'll need a new left side shifter, one that supports three chainrings. The M6000 series shifters ARE available with 3-speed left shifters, so you should be able to find a left side shifter that will support the change (SL-M6000-L).

Is your front derailer also a Shimano Deore M6000 series? It looks from Shimano's M6000 series website that they have versions optimized for 2-speed and versions optimized for 3-speed. You will likely find best performance from one of the 3-speed versions. They have different mounting styles to accommodate different frame designs. Personally, I'd probably see if I could get your bike set up using extant 2-speed derailer and see how it goes. You may find that you'll want to change it out, but you also may not. That'd be a bridge you might not have to cross.

Your rear drivetrain (derailer and cassette), and chain, will be compatible with a crankset swap. Good luck!

[MENTION=455851]hokiefyd[/MENTION] Thanks for the info, I'll have to take a look at it and see. I also dropped a msg to Trek for more details on the BB.

Now that I'm really thinking this over, I'm wondering if I'd be better suited sticking with a 2 ring but something more like a 50/38. The only time I need the lower gears is when I specifically go off-roading (I'm in Florida, so no mountains - we barely have hills) and I could swap it with my current one if I knew I was going on a trip. Definitely less complicated and cheaper... hmmm.

With 10/11 and even 12 speed cassettes nowadays, I can't think of very many reasons why anyone would want a triple anymore, especially in Florida. Do your ratio chart for 2 and 3 rings and you'll see that adding another ring will not give you very many more gears. Add a bigger ring to your double and go riding.

Bicycle Gear Calculator

with a suggested 48/34 (14T difference).. Front derailleurs are sensitive to the difference in the number of teeth between adjacent chain rings.

To switch to a road crank (the most common option is 50/34, other options are 48/32, 50/36, and more rarely 48/32 and 46/30) you'll need a road compatible flat bar front shifter and front derailleur in addition to the crankset. Don't worry about the BB--your bike uses a threaded BB shell and you can buy a BB to match whatever crank--it's a relatively minor cost in comparison to the crank itself and potentially the labor if you're paying for the work.

Also check out your shifter--is there a small switch on the underside? It may be a 3x compatible shifter as is, as they'll work with a double FD. If so you can get a 3x crank and derailleur.

I don't know what cadence you ride at and the speeds you need. If I were in Florida, I'd probably either keep the bike as is (as you can go faster than 25MPH if you can pedal 100RPM) or run it as a 1x with perhaps a slightly larger ring.

With that additional information, I certainly agree with sticking with a double in any of the popular configurations noted by others above.

I'm thinking you're right...

I've already done the calcs and was hoping to bump from my prev 48 top to a 50 but see from others (below) that crank vs. derailleur size matters too, hmmm. Good info on the teeth differences though, didn't know that...

Geez, hadn't even thought about the derailleur size being an issue; I haven't gotten to give it a good look over yet but will keep that in mind too!

Hmmm, more good info to chew on, thanks!

My cadence could get just get ahead of my prev 48 occasionally in good flats and I'm definitely overpedalling the 42 I'm on now. I'm a little out of my depth here since I know nothing about road bikes, but keep in mind I'm riding on 29s which I ~think~ changes the cadence comparison if you're thinking about it from road bike sized tires.

Agree, I'm very much leaning towards upping my double and forgetting about the three.

Still, even though that simplifies things, it looks like I still have a bit of homework to do. I'll spend some more time looking her over tomorrow and will get back here for more input, stay tuned!

1, realize 10 speeds is referring to the back.. not the front

42 28 I expect is functionally a single ring with a bail out gear.. lower 2/3 of a triple

DS4 specs

i have a 52,42,26 triple from way before the external bearing thing took off.. and freewheels were 13t.
>42:11 is 3.8:1... 52:13 is 4:1< so 44t is as high with an 11 as a 52, with a 13..
specs are for a Sram crank , consider;
look for a Shimano, Trekking crankset BB and all ?

https://bike.shimano.com/en-US/produ.../FC-T8000.html (a 48-36-26t)

"Just putting on a bigger ring" I'd (also) suggest means putting a bigger inner chainring on too
(unless, as above, just adding 2 teeth)

to keep the 14t~16 gap.. that will be somewhat expensive.

[econ of scale] as bike factories buy whole truckloads of components ,

your buying 1 chain ring has all the distribution costs to cover.. on its own..

​​​​​​​ good luck, with your choice..



....

1. more things to go wrong.
2. more weight.

It turns out I have a Shimano FD-M610 which is a clamp-on. Interestingly, it's 3-ring capable but at this point I think I'm sticking with a bigger 2 ring. Specs say that it's max ring size is 42T (what I'm running right now) but you're saying I can just raise it and it'll be fine for a 48T?

No switch on the shifter unless it's supremely hidden, but I think I'm going to stick with a bigger 2 ring anyway. Interestingly, I found (above) that my front derailleur is 3-ring capable even if the shifters aren't.

Once I got the specs on my FD it looks like it's got an 18T difference - I'm presuming that's larger than what you expected since it's actually 3-ring capable. I'm still expecting to be in the 14T range, but I'm assuming that 18T limit is still the same regardless of whether I'm running a 3ring or a 2ring, right?

"It turns out I have a Shimano FD-M610 which is a clamp-on. Interestingly, it's 3-ring capable but at this point I think I'm sticking with a bigger 2 ring. Specs say that it's max ring size is 42T (what I'm running right now) but you're saying I can just raise it and it'll be fine for a 48T?"

Bit of a crap shoot. Many FD's are shaped to specific chain ring sizes, with a cage shape that is matched to the curve of the largest chainring. Your's is likely matched to the 42 ring, but I've no clue with SRAM gear. When the FD shape doesn't well match the ring, or there's a huge difference in rings, you can't get the FD into a prime shifting position of 1-2mm. The bottom/rar of the cage may be close, but the upper section won't be. Thus index shifting can suffer. What most folks do is try it and if not, then change the FD to a model matched to the larger ring. FD's are cheap, relatively. .

Good info and exactly what I was thinking, appreciate the input!

Thanks again! Geez, wow ... deep topics within deep topics; so much to learn.

So, after deciding to stick with a bigger 2-ring instead of moving to a 3, I think I've settled on going for a Shimano 105 5750 50/34 Compact w/175mm - which is a 10 speed like the rest of my train. But I still have a couple of small dangling questions...

Hmmm, what do you mean by "flat bar" front shifter?

Since my FD is a clamp on and I'm sticking with a two-ring, I'm going to risk just adjusting it as-is and see if I can get it sorted to the new height. If not, then I'll get another proper FD for it - sound good?

Which path do you think is better/easier/less-likely-to-be-problematic - switching the BB to match the crank or getting adapters for the sram BB that I've got now? Note that I haven't taken the crank off yet to see exactly what it is yet and I haven't more detailed info from trek about it yet either...

Even though I'm sticking with a 2 this point was really bugging me - since I earlier said I had M6000's per the specs and everything I've seen says that those have a 2x-3x mode. Since I couldn't find the 2-3x switch, it worried me that I was wrong about the part (and maybe other things?) so I went hunting... After more inspection, it turns out mine are a SL-M6000 which specifically don't have the 2-3 ring switch. Ok, now I'm on point..

Thanks again to you and everyone else!

.For some markets , Shimano EU , and Australia , there is a Fitness Bike Sector.
Road bike wheels and drivetrains , but flat/straight handlebars.

It is for those customers, they made a flat bar left indexed shifter which matches the cable pull needs of the
Road, front Derailleur , like 105.