Of course, a MTB is meant for riding off road, but with the lack of good trails and good weather in Singapore, off road sessions are rare for me. Unless you stay near a trail or really enjoy riding off road, most people will choose to ride on the road as you can start your ride as soon as you are downstairs.
Nevertheless, I will still jump at the chance to upgrade the MTB if there are suitable components that constitutes an upgrade. The current setup is a 3x10 speed drivetrain with a mixture of Deore XT, SLX, and Deore grade components. All of them work well together as they are all from the Dynasys 10 generation of components.
Current setup of 3x10 speed drivetrain on the MTB. I found that the chain is a bit slack in the front low - rear top combination, but I did not notice it before as I don't ride in this gear combination.
Deore XT Trekking shifters SL-T780 with Deore brake levers BL-M615.
With a 3x10 setup, the gear range is wide. The Deore XT M780 triple crankset has a combination of 42/32/24T, while the rear 10 speed cassette is 11-34T. With a 26" wheel, this gives a low gear of 18.4 gear inches and a top gear of 99.3 gear inches. Having a low gear that is easy enough is always important for off road riding, where the terrain can be slow and steep.
However, the top gear of 99.3 gear inch is quite redundant on a MTB, especially if you only consider off road riding. My Java Freccia mini velo, which is a fast bike with drop bars, has a top gear of 88 gear inches. This is sufficient for 99% of the time except when I want to pedal downslope. With a cadence of 100 rpm at the highest gear, 37km/h is achievable on the mini velo. The gear range on the mini velo is perfect for me as I don't need a lower or higher gear ratio.
On this MTB, there is no need for such a high gear ratio, unless you plan to cycle fast on road. It is redundant to have higher gear ratios on the MTB than the mini velo, especially when the mini velo can go faster and yet rides perfectly fine with a lower top gear ratio.
Therefore, there are hardly any downsides to using a front double or even front single drivetrain on the MTB, as long as you can get a sufficiently low and high gear range that is suitable for off road riding.
Changing to a front single drivetrain is easy. The idea is to use just a single front chainring, and use a wide range cassette to get the range of gears you want. Increasing or decreasing the size of the front chainring shifts the whole gear range up or down respectively, depending on your riding ability.
With a front single setup, the front derailleur and front shifter is no longer required. However, you do need a special front single chainring to prevent chain drops, and a capable rear derailleur to shift properly across the wide range cassette.
The more speeds you have, the wider the gear range possible, without making the gear steps too big. At this point in time, the SRAM Eagle 12 speed system has the widest gear range, with a gigantic 10-50T cassette. However, it is also very expensive and requires a special XD driver freehub to use the XD cassette.
Going to 11 speeds is quite sufficient. With a 1x11 speed setup, you can also get a wide gear range that should be suitable for most conditions. A 3x10 drivetrain has about 14 unique gears, while the 1x11 speed drivetrain obviously has 11 unique gears.
After doing some calculations, I found that a front single chainring size of 34T, together with a rear cassette size of 11-46T will give me a suitable gear range. With this setup on a 26" wheel, the low gear is 19.2 gear inches, while the high gear is 80.4 gear inches. This range can be shifted upwards or downwards by using a bigger or smaller chainring.
3x10 drivetrain: 18.4 - 99.3 gear inches
1x11 drivetrain: 19.2 - 80.4 gear inches
With this 1x11 speed drivetrain, I have a low gear range that is almost similar to the one on the 3x10 drivetrain. At the other end, I lose 2 higher gears of 84 and 99.3 gear inches.
3x10 speed drivetrain on the MTB
1x11 speed drivetrain on the MTB
As Shimano MTB 11 speed cassettes can be fitted directly on 8/9/10 speed freehub bodies, there is no need to change the rear wheel. Just remove the 10 speed cassette and install the 11 speed cassette!
Changing the crankset is also easy as the Hollowtech II system makes it so convenient to swap the entire crankset effortlessly. As for the rear derailleur, the mounting method is the same, using the Direct Mount rear derailleur hanger that is found on this frame.
1x11 speed drivetrain!
SLX M7000 crankset with 34T chainring
The gigantic 11-46T M8000 cassette! With a big jump of 37T to 46T in the lowest gear, it is more like a bailout gear when the terrain gets really steep.
Top level XTR M9000 11 speed rear derailleur to cope with the extra large cassette. Adjustment of the B tension screw is required to get the setting dialed in.
XTR M9000 11 speed shifter, with the super slim clamp band. Still using the Deore brakes as there is no need to change it.
Chain path when using the largest 46T sprocket. Looks really stretched out.
The rear derailleur looks almost straightened out! However, the chain cannot be lengthened any more...
When using the smallest 11T sprocket, the rear derailleur is almost fully contracted.
The chain is almost touching the guide pulley when using the 11T sprocket.
With this super wide range 11-46T cassette, the rear derailleur just manages to cover the whole range. The chain length is also just nice. It cannot be lengthened as there will be chain slack when in the 11T sprocket, and yet it cannot be shortened or the rear derailleur will be overstretched when in the 46T sprocket.
This 1x11 speed drivetrain setup simplifies everything. Shifting is easy as there is only the rear shifter to operate. With the low gear of 19 gear inches, it is sufficient for off road riding. As for the top gear of 80 gear inches, it has been tested and is also OK for road riding. At a cadence of 100 RPM, in the highest gear combination of front 34T and rear 11T, it will give a speed of about 38 km/h which is enough. On a mountain bike, this speed is only attainable on down slopes and is not sustainable on flat roads.
As for the gear steps, it is larger compared to using a road cassette. However, I did not feel that it was a big issue as compared to on a road bike. Not sure the exact reason why, but I guess it is because I am mostly using only the highest 3 or 4 gears when riding on road.