Converting 1x12 to 2x9 (or 10)

[Ivan]

Hello, I have Trek Roscoe 7 (2021), which has the following components:

rear derailleur SRAM SX Eagle
cassette SRAM PG-1210 Eagle, 11-50, 12 speed
BB: Truvativ Powerspline, 73mm, threaded cartridge, 118mm spindle
Max chainring size 1x: 32T
measured chainline - about 52.5mm
Rear hub: Boost141, 5mm QR
27.5x2.8" tires
There is an E type mount on the seat tube

So the question is - is it possible to switch to 2x9 or 2x10 and if yes, what components should be used? My main concerns are tire clearance and chainline. When on the biggest cog at the moment there are about 9-10mm between the upper section of the chain and the tire, and about 4-5mm on the lower section.
I want to use 22-36 crankset, probably Shimano CUES FC-U4000-2 Square Crankset and 12-36 9sp cassette, but also opened for hollow spindle (if it's more durable).
My research shows that if I want to use this crankset, probably I need to use 122.5mm Shimano BB-UN300 Square Taper Bottom Bracket. I don't know what should be used in case of hollow spindle. What I also don't know is what front derailleur should be used. It should be E mount, but what model, and will it touch the tire?
The specification says that the frame supports 32t, but this is on 1x, I suppose that on 2x it won't be a problem to use 36mm outer chainring.

 

[BikeGremlin]

Hello, I have Trek Roscoe 7 (2021), which has the following components:

rear derailleur SRAM SX Eagle
cassette SRAM PG-1210 Eagle, 11-50, 12 speed
BB: Truvativ Powerspline, 73mm, threaded cartridge, 118mm spindle
Max chainring size 1x: 32T
measured chainline - about 52.5mm
Rear hub: Boost141, 5mm QR
27.5x2.8" tires
There is an E type mount on the seat tube

So the question is - is it possible to switch to 2x9 or 2x10 and if yes, what components should be used? My main concerns are tire clearance and chainline. When on the biggest cog at the moment there are about 9-10mm between the upper section of the chain and the tire, and about 4-5mm on the lower section.
I want to use 22-36 crankset, probably Shimano CUES FC-U4000-2 Square Crankset and 12-36 9sp cassette, but also opened for hollow spindle (if it's more durable).
My research shows that if I want to use this crankset, probably I need to use 122.5mm Shimano BB-UN300 Square Taper Bottom Bracket. I don't know what should be used in case of hollow spindle. What I also don't know is what front derailleur should be used. It should be E mount, but what model, and will it touch the tire?
The specification says that the frame supports 32t, but this is on 1x, I suppose that on 2x it won't be a problem to use 36mm outer chainring.

Hi,

With the disclaimer that I haven't done such a conversion on that model, here are my 2c:

Front chainrings​

Regarding the frame clearance, briefly put: I don't know.
In detail:
If the chainstays are moving outwards at an angle (to accommodate for the boost hub), a larger front chainring might be more likely to rub against the chainstay. However, on a double, the chainring could be spaced further outwards compared to a 1x system, and also 142 mm hubs aren't really "boost" - just added 3.5 mm on each side compared to a standard 135 mm quick-release hub to accomodate for the thru axle mounting (boost hubs explained). So, the 36 T double chainring might fit - but the only way to be sure is to try it. Especially when you put some load on the pedals and the frame flexes a bit. Looking at the pictures, the Trek Roscoe 7 has the right chainstay goin a bit thicker and wider right after the small factory chainring ends.

Front derailleur (FD)​

For the front derailleur, you could use an E-mount, but depending on the diameter of the seat tube and how far outward the chainrings will go, you might be able to use a standard clamp FD.

A problem is that the frame has no housing stops for the FD. So, you might need to look for a side-swing FD that has a built in housing stop.

• Shimano Deore FD-M4100-E may be a good E-type mount option.
• Shimano Deore FD-M4100-M may be a good clamp mount version.

Either of those is designed for a 10T chainring size difference (26-36), and going with 4 teeth more may cause slower shifting or some chain rubbing in certain gear combinations (especially with modern frames that have relatively short chainstays, well under 45 cm - Roscoe 7 has 43).

You would of course need a matching shifter for the FD you choose.

Cranks and bottom bracket (BB)​

Cues stuff doesn't look like durable, high-quality, but I haven't tested it yet so take this with a grain of salt.
Having said that, steel chainrings are a lot more durable compared to lighter aluminium chainrings that come with most mid and high-end cranks.

Square taper bottom brackets come with different axle lengths, they are relatively cheap and their bearings are quite durable. So that would allow you to play with the chainline.

With Hollowtech II cranks and bottom brackets, you could swap spacers to adjust the chainline to a degreee (Hollowtech II spacers explained).

If the factory info is correct, Roscoe 7 hase a British threaded 73 mm wide bottom bracket shell, so you could use a Shimano Deore SM-BB52 bottom bracket.

With Cues and square taper axle, I would try with the 122-123 mm axle length, and if it turns out to be too short, I'd try a 128 mm long one.

Cues would probably be the only choice if you want the 22 T small chainring (not sure where to find the 22 T Hollowtech II crank apart from using a triple - which is what I opted for on my bike ).

Hope this helps at least a bit. Let me know if you have any other questions.

Relja

 

[Ivan]

Hi,

With the disclaimer that I haven't done such a conversion on that model, here are my 2c:

Front chainrings​

Regarding the frame clearance, briefly put: I don't know.
In detail:
If the chainstays are moving outwards at an angle (to accommodate for the boost hub), a larger front chainring might be more likely to rub against the chainstay. However, on a double, the chainring could be spaced further outwards compared to a 1x system, and also 142 mm hubs aren't really "boost" - just added 3.5 mm on each side compared to a standard 135 mm quick-release hub to accomodate for the thru axle mounting (boost hubs explained). So, the 36 T double chainring might fit - but the only way to be sure is to try it. Especially when you put some load on the pedals and the frame flexes a bit. Looking at the pictures, the Trek Roscoe 7 has the right chainstay goin a bit thicker and wider right after the small factory chainring ends.

Front derailleur (FD)​

For the front derailleur, you could use an E-mount, but depending on the diameter of the seat tube and how far outward the chainrings will go, you might be able to use a standard clamp FD.

A problem is that the frame has no housing stops for the FD. So, you might need to look for a side-swing FD that has a built in housing stop.

• Shimano Deore FD-M4100-E may be a good E-type mount option.
• Shimano Deore FD-M4100-M may be a good clamp mount version.

Either of those is designed for a 10T chainring size difference (26-36), and going with 4 teeth more may cause slower shifting or some chain rubbing in certain gear combinations (especially with modern frames that have relatively short chainstays, well under 45 cm - Roscoe 7 has 43).

You would of course need a matching shifter for the FD you choose.

Cranks and bottom bracket (BB)​

Cues stuff doesn't look like durable, high-quality, but I haven't tested it yet so take this with a grain of salt.
Having said that, steel chainrings are a lot more durable compared to lighter aluminium chainrings that come with most mid and high-end cranks.

Square taper bottom brackets come with different axle lengths, they are relatively cheap and their bearings are quite durable. So that would allow you to play with the chainline.

With Hollowtech II cranks and bottom brackets, you could swap spacers to adjust the chainline to a degreee (Hollowtech II spacers explained).

If the factory info is correct, Roscoe 7 hase a British threaded 73 mm wide bottom bracket shell, so you could use a Shimano Deore SM-BB52 bottom bracket.

With Cues and square taper axle, I would try with the 122-123 mm axle length, and if it turns out to be too short, I'd try a 128 mm long one.

Cues would probably be the only choice if you want the 22 T small chainring (not sure where to find the 22 T Hollowtech II crank apart from using a triple - which is what I opted for on my bike ).

Hope this helps at least a bit. Let me know if you have any other questions.

Relj

Hi,

With the disclaimer that I haven't done such a conversion on that model, here are my 2c:

Front chainrings​

Regarding the frame clearance, briefly put: I don't know.
In detail:
If the chainstays are moving outwards at an angle (to accommodate for the boost hub), a larger front chainring might be more likely to rub against the chainstay. However, on a double, the chainring could be spaced further outwards compared to a 1x system, and also 142 mm hubs aren't really "boost" - just added 3.5 mm on each side compared to a standard 135 mm quick-release hub to accomodate for the thru axle mounting (boost hubs explained). So, the 36 T double chainring might fit - but the only way to be sure is to try it. Especially when you put some load on the pedals and the frame flexes a bit. Looking at the pictures, the Trek Roscoe 7 has the right chainstay goin a bit thicker and wider right after the small factory chainring ends.

Front derailleur (FD)​

For the front derailleur, you could use an E-mount, but depending on the diameter of the seat tube and how far outward the chainrings will go, you might be able to use a standard clamp FD.

A problem is that the frame has no housing stops for the FD. So, you might need to look for a side-swing FD that has a built in housing stop.

• Shimano Deore FD-M4100-E may be a good E-type mount option.
• Shimano Deore FD-M4100-M may be a good clamp mount version.

Either of those is designed for a 10T chainring size difference (26-36), and going with 4 teeth more may cause slower shifting or some chain rubbing in certain gear combinations (especially with modern frames that have relatively short chainstays, well under 45 cm - Roscoe 7 has 43).

You would of course need a matching shifter for the FD you choose.

Cranks and bottom bracket (BB)​

Cues stuff doesn't look like durable, high-quality, but I haven't tested it yet so take this with a grain of salt.
Having said that, steel chainrings are a lot more durable compared to lighter aluminium chainrings that come with most mid and high-end cranks.

Square taper bottom brackets come with different axle lengths, they are relatively cheap and their bearings are quite durable. So that would allow you to play with the chainline.

With Hollowtech II cranks and bottom brackets, you could swap spacers to adjust the chainline to a degreee (Hollowtech II spacers explained).

If the factory info is correct, Roscoe 7 hase a British threaded 73 mm wide bottom bracket shell, so you could use a Shimano Deore SM-BB52 bottom bracket.

With Cues and square taper axle, I would try with the 122-123 mm axle length, and if it turns out to be too short, I'd try a 128 mm long one.

Cues would probably be the only choice if you want the 22 T small chainring (not sure where to find the 22 T Hollowtech II crank apart from using a triple - which is what I opted for on my bike ).

Hope this helps at least a bit. Let me know if you have any other questions.

Relja

Thank you for the reply!
This frame is not 142 boost. It is a little bit odd standart - 141 boost with QR. As far as I know, it has the same flange distance as 148 hubs, but with different end caps.


You are correct about the chainstop. But if I use clamp FD, isn't going to interfere with the E mount on the tube? I suppose that the 10t difference could be avoided by using 3x crankset, but then there could be another problem, or even two - the outermost chainring probably will touch the frame. And the larger derailleur probably will interfere with the tire.

 

[Ivan]

I just realized that I can use Shimano Acera FC-M361 Square Crankset, which is 22-32-42, removing its biggest chainring and using it as only 22-32.
Or I can use the 22-36 crankset with Shimano ALIVIO FD-M3120 2x9-speed Front Derailleur Side-Swing, which has E mount version and supports 22-36 and 51.8mm chainline.