12 Speed Drivetrain Durability

Hi @alunjr , 1400 miles sounds good to me.

On a variety of mtbs with 9 & 10 speed I was averaging about 650 miles per chain and 3 chains per cassette. When I had 3x and 2x, the front rings seemed to obey no law known to me as to when they would need replacing, I just had to keep an eye on them. I used to wipe the chain down after every ride and lube before every ride too. When the bike was washed I'd wipe and lube afterwards. I used wet lube and dry lube appropriate to the seasons.

Then I converted a 2x10 Shimano to 1x11 Sram. That set up did almost a 1000 miles without fault and I sold the bike as was and received no complaints, although I did get a moan about the rear pads needing replacing after a month! The bike I bought to replace that one came with Sram Eagle 1x12. It just ran and ran, again without fault. OK, I had to realign the rear mech three times (those mech arms hang really low!), but no problems with wear in any part of the transmission. The last time I checked before selling that bike I'd done 1403 miles with chain "stretch" measured at 0.25%. That would indicate (possibly) that I'd get over 4200 miles before I got to 0.75% the normally recommended place to change the chain. Apart from rub marks on the ring and cassette, I could detect no signs of wear on the gears. There were no extended troughs, no hollowing out of the faces of the teeth, no shark finning, nothing!

How do I account for this? My theory is that the 11 and 12-speed chains were of a very good quality and with hardened pins. Because the chains didn't wear quite so fast, neither did the gears. A worn chain rapidly wears the gears it comes into contact with and the more worn it is, the faster it wears the gears.

My current bike is a 1x11. And it is an emtb. Whatever your thoughts are about emtbs, the one thing everyone who has one will tell you is that they wear out the transmission quite rapidly. This is said to be for two main reasons: 1) they are heavier by 10-15 kg than mtbs. 2) There is more power going through the transmission. The peak torque can be whatever you apply x3.
I suspect that the consequences of poor shifting technique with that amount of extra torque is "snapped" chains. (They never "snap" the side plates peel off).

So what life am I actually getting on my emtb?
First chain,1706m at 0.4%. I changed because the 11-46 SLX cassette was looking a bit worn. I fitted a new XT cassette, so I fitted a new chain to go with it. I kept the old chain and cassette for later.
Second chain, 1006m at 0.375% so far. The XT cassette appears unworn. I will let the chain run until it gets to 0.6% and then I will refit the old chain and let that run until 0.75%. Then I'll refit the second chain and run that until 0.75%. At some point the second cassette may start to look worse than the first cassette, in which case I'll swap that over. The chain ring looks scuffed but unworn and that's after 2748 miles.

I freely admit that this is an experiment that I have never tried before. But the key thing is that coincident with moving to 11-speed and above, I got significantly improved chain life and subsequently the rest of the transmission.

Throughout this period I have maintained the same maintenance and cleaning methods. My riding style has not altered, nor the type of places I ride. The place I ride the most is very sandy and is notorious for eating bikes.

@alunjr There are many riders that are adamant that 1x10 is the best transmission to ride because it is cheap to run (and it is). My problem with 1x10 is the lack of range. I have to decide whether I want to go up steep hills and run out of gears on the flat, or to be able to go fast, but fail to get up the steep bits. I have that problem because I am almost 70 and have arthritic knees. But many riders are just not fit enough anyway to run 1x10 and still have no problems with steep hills. They (and me) need a wider range. A 1x12 will give you almost the same range as a 2x10. That 1x will also give you a cleaner bar and allow the dropper remote to fit on the left of the bar, so that both hands have an equal duty. Nice!

You can buy special add-ons for the cassette to improve your range, but they compromise with the gear spacing and can leave holes in your shifting caused by big gaps between gears. But it is a solution that some have embraced.

When I last had an mtb, I needed my 1x12, with its 10-50t cassette. I also swapped out the 34t ring for a 30t, just to get up the steep bits that I needed to. Eventually even that wasn't enough so I bought an emtb and the 1x11, 11-46t with a 34t ring suits me just fine (better than fine in fact!)

The key to transmission longevity is mechanical sympathy. No nasty bangs or clunks when you change gear. Back off the pedal pressure momentarily just before you shift. It is a skill you have to learn and once you learn it, you will find yourself physically incapable of shifting under load. Anticipate the trail ahead and try to get into gear before you need it. Once you are almost stalling on the steep bit is no time to be shifting into a bigger gear!