I am getting myself a hardtail mountain bike for racing this year, and I have a choice of equipping the bike with either Shimano XTR M9100 (mech) or SRAM X01 AXS (electronic, not XX1).
I have exclusively positive experiences with Shimano on the road, both with mechanical and Di2 groupsets, while my experiences with SRAM have been very good so long as there is no front shifter involved.
My main concern with XTR is that, while Shimano is superb, the M9100 is a relatively old groupset, and I fear that I end up with a “last gen” bike very quickly. SRAM X01 AXS, on the other hand, may help retain more of the second hand value of the bike + probably works just as well as Shimano (if not better, although I find that unlikely given how well Shimano works).
Either way, are there folks in here with experiences from both groupsets or with other valuable insights that they care to share?
I have a full sus mtb with XTR M9100 mech and a hardtail mtb I mixed Shimano and Sram. With an XTR crank, Shimano chain and cassette and Sram Eagle AXS GX rd.
Generally I like electronic shifting more. The full sus mtb is my “adventure” bike for stuff like Atlas Mountain Race. But I also would run AXS in such races.
I wouldn’t fear Shimano XTR ending up last gen. Microdrive hubs are here to stay, it’s 12x and now the brand new GRX 12x adopted the cassettes and stuff, too.
OTOH, Sram Eagle AXS is now definitely last gen since Eagle Transmission came to market. So go figure. But maybe you meant the Transmission x01 already. So I would more look what type of shifting (electronic or mechanical) you prefer. And maybe which brakes - but gladly we can run totally different ones as the shifting group set we chose.
Hey @sykkelerik,
I think many know my opinion on this one. 
It’s hard to beat Shimano’s functionality in terms of shifting and braking. I’ll always choose them over Sram.
I’d rather not have to charge my bicycle if I don’t have to. Save the lithium for where it’s actually needed. 
If you’re looking for resale value, Sram might have an edge there, given how well they market their stuff, but they also roll out new products pretty often, so who knows if what you choose will be current when you decide to sell. XTR has been known to hold its value pretty well too though!
If you want to enjoy your bike while you own it, pick Shimano. It sounds like that’s where your heart is. 
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eagle axs mech will shift a 12 speed shimano mtb cassette wonderfully 
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Hard to go wrong. I haven’t used XTR or X01, but have used the lower groups from both and zero issues with either.
If going SRAM, I’d go Transmission (not Eagle AXS) since that’s the hot new stuff. But I wouldn’t have any concerns with current gen XTR - I imagine Shimano will be keeping to 12s and Microdrive for a few more generations.
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I don’t have AXS or Transmission experience, but I have used etap in the past. My current hardtail is Deore/XT 12s and I have no want or need to change that; it’s been a flawless performer and the shifting is buttery smooth, even under load.
I’m also terribly forgetful and have in the past found myself single-speeding my etap bike.
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In terms of racing, and assuming it’s not the new T-Type, I’d 100% go for XTR.
Yes, it’s been out a while now, but it’s lighter, shifts more smoothly, and should run quieter on your hardtail due to a better clutch than SRAM.
It’s still a very flash group set with appeal to a lot of people. It’s hard to fully gauge where resale value sits, but that’s my 2c.
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There is one very clear solution here: TWO BIKES!
One mechanical with Shimano XTR and the other with Sram XO1 AXS. Why limit yourself when you can enjoy both! 
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I have massively unpopular opinions here. My bike came with 9100. I replaced the shifting with XX1 AXS.
I don’t like either of them.
XTR shifts absolutely vague. It just feels soft and wishy washy. I never got comfortable with it. I bought XX1 and a Garbaruk cassette, and that is absolutely…fine. I find that I just don’t like electronic shifting. I had at the same time put GX AXS on my trail bike and have a worse opinion. I absolutely hate having to be sure I charged my battery for every ride, and really hate when it dies mid ride (I can put in some big miles). It eventually broke, no idea why, just quit shifting (something in the electronics) and I picked up mechanical X01 to put back on, and now I’m happy. It just works. Clean, crisp shifts, always, no batteries, no vagueness.
Microspline is bullshit and I hope it dies. Money grab from Shimano. XD already existed and works great. Shimano doesn’t even use it on their 12 speed road groups.
Ideally, I would run XX1 mechanical with a SRAM cassette, but don’t want to spend more money on a bike that only gets used for racing, so I’ll just suffer with electronic crap until it dies, then go back to the XTR that I didn’t like.
I also have new Di2 on my road bike because you can’t get a decent bike that is mechanical anymore, and I hate it there too. I don’t get the love for electronic shifting, it just sucks. Absolutely no tactile feedback and I hate that I have to wonder “did I remember to charge this junk?”
I have XTR M9000 (11-speed 1x) on my road bike and SRAM Force AXS eTap on my road bike. Had Shimano (105/Ultegra mix and several gens of XT) on my previous bikes. I have used SRAM X01 or XX1 mechanical on a high-spec rental bike in Chile.
- All of them shift fine, you initiate a gear change and it shifts. I personally prefer the feel of SRAM shifts, but that’s just feel. SRAM shifts feel more crisp are more consistent to me, Shimano shifts are smoother but when you give it the beans, they can get very crunchy. Shift feel is like engine noise, I prefer a high revving Porsche 6-cylinder boxer engine, you might prefer a burbly V8 in a muscle car.
- Ditto for the trigger shifter: Shimano’s XTR and XT trigger shifters are either super smooth or vague, depending on your preference. Likewise, SRAM’s mechanical shifters are either crisp or unrefined. (My preference is crisp, but it isn’t super strong.) Shimano’s road Di2 buttons are unbearable to me. Just the buttons alone make me never want to have a Di2 drivetrain on a dropbar bike.
- I found no difference in reliability (N = 1): my SRAM shifter levers broke because my sweat is corrosive AF. My Shimano shift levers rusted internally because my sweat is corrosive AF. And my XT front derailleur trigger shifter broke after ~1 year of use on my last bike. Just use wax-based lube to extend the life of all your drivetrain components.
- If you want a power meter, get SRAM. Shimano has nothing here. And I’d want a crank-based power meter on a mountain bike, and Quarq power meters just work. (Shimano, come on, you are not even trying. Although probably if you did, the power meter would likely have the same accuracy problems as on the road.)
- Shimano always seems 1–2 steps behind SRAM. They were very late to 1x. (I remember that they threatened reviewers to remove the front derailleur when they sent out test bikes equipped with XTR M9000.) They are late to electronic shifting on mountain bikes, because they seem to want to base their tech on road Di2. Unfortunately, there is no good place to put the giant Di2 battery (dropper posts are a thing). They still have no power meters for any of their mountain biking cranks.
- Electronic shifting is very nice to have, but not a must. I’m not sad that my mountain bike has XTR mechanical. But then again, I think my inner cable needs replacing, I have trouble shifting into the hardest gear …
- Shift speed is likewise a non-issue in my opinion (also on the road … I don’t have a FD on my road bike either, so I don’t know whether SRAM front shifting is actually as horrible as people claim it is
)