Looking to get a MTB...stem length and trainer compatibility help needed

I’m thinking about getting a mountain bike and I’m 6’5" so definitely need an XL. The reach numbers seem to range from 475mm-ish to 510mm depending on brand. How long of a stem is too long for a mountain bike? I have 110/120mm on my road/gravel bikes but I know MTB is typically shorter. I know seat the angle has alot to do with it, but is it ok to run a 70-90mm stem if I need to get the reach right or is that too much?

Also, can I get away with putting a bike with SRAM Eagle on a trainer with a Shimano 11-34 cassette? I’m sure it would shift like crap but maybe I can find one gear that works and just run the trainer in ERG mode.


Probably gonna take a little trial and error with reach and stem length. Just a guess but at 6’5" I’d gravitate towards the longest reach available. Tons of other things to consider when buying a bike, but when I talk to my taller MTB friends they all say that fit is the hardest thing to dial in. Luckily more companies are making bikes that will actually fit you. Stem length is going to be more a personal choice too and unlike drop bar bikes you’ll want to match that up with riding style as well as ergonomics. Personally I don’t like super short stems that are very fashionable in MTB now say 40-60mm, 60 maybe - so I don’t think going to a 70 would be bad. That said longer than than and you’ll give up some handling.

Your trainer is wheel off I assume? I’d be shocked if you could even find a single gear that would work with that set up. Not sure there’s an easy answer there, but as a MTB rider/racer I use my road bike exclusively for the trainer. I don’t see any advantage of training indoors on a MTB. I’m sure there’ll be a counter opinion to that, but getting modern MTB on trainers usually requires some adapters / etc.

1 Like

Thanks so much for the input! From what I’ve been reading it seems like MTB and road fits are so different it doesn’t make sense to try to match your road fit on the mountain bike. I’m just always nervous about getting the right reach and you might not know how well it fits after doing just a few loops in the LBS parking lot.

One more question if I could…seems like the whole idea of setting your seat to a “knee over pedal spindle” position might be very hard with a steep seat tube angle and 0 set back on the dropper posts. Is this relevant in MTB? If not should my knee be behind or in front of the spindle or is it more about riding style/what’s comfortable?

As far as the trainer goes, I was wondering if it would make sense to try some TR workouts on it to make sure I can get decent power out in a different position. Im running a Kickr Core. Sounds like it’s not worth the trouble though.

Thanks again!!

1 Like

This is a tricky one for me as I have tried to use the classic KOP position, even for my mountain bike set ups, but I’m not sure how important that aspect is for mountain biking, I have to claim ignorance on that one in general actually and seem to remember that it may not be as crucial as once imagined. I used to be very particular about fit, down to the mm but now I go more by feel, even on my road bike. I know my saddle height down to the mm but beyond that, and especially on the MTB, I just know what feels right for me at this point. This isn’t super helpful I realize but some of this will need to be trial and error for you. I do subscribe to running the exact saddle height on all my bikes for what ever that’s worth. Also, I’ve yet to run a bike with a steep seat angle but I do have on order, and can’t to try it!

With the steep SA and non offset post is your concern being too far forward?

1 Like

I planned to run the same seat height that I’ve dialed in pretty well on my road and gravel bikes. I forget the exact numbers but my gravel bike is more slack and I can get away with the seat set back a bit on a 0 offset post. My road bike is more upright (but not as much as some mountain bikes) and I had push my seat back close to the max on a 20mm offset post. I think a steeper seat tube on a modern geo mountain bike, especially with a 0 offset dropper, might put my knee a little in front of the spindles.

I was able to sort out some prior knee pain issues with cleat wedges so I don’t honestly know how much that will affect me, but then again, MTB riding is probably more dynamic rather than getting in a relatively set position and pedalling away like on the road.

1 Like

This is a very interesting brand for me as well. They have 26" ETT on the Trail Pistol (120mm bike, and the closest they make for a pedaling race bike), that seems LONG, but good. This is a very blanket statement but horst link bikes (which is the suspension design layout GG uses) tends to be very active. That usually equates to some very nice descending bikes, but they tend to rely heavily on a pedaling platform in the way of a shock “lock out” or firm mode. Not to distract from the original topic, and yeah so much to consider when buying a mtb.

I have an Ibis Ripley on order and cannot wait to try out this steeper STA thing. Even my current XC bike is slack by today’s trail bike standards.

1 Like

Yeah, that’s kind of my thought too. I actually had a V1, and it was really good uphill, maybe the best climbing bike I’ve ever had. I’m on a SC Blur now and I’ll keep the Blur until I determine that the Ripley will work for me on race day. I’m not doing much XCO style events (as originally planned) so the Ripley might actually be faster for me overall. A little more stability and travel on the techy DH is what I’m looking for, without giving too much up on the climbs.

Sorry, don’t mean to derail the thread. @FrankTuna - let us know how the bike shopping goes.

1 Like

9point8 has a great offset (setback) dropper post I’ve been running for over a year (FallLine R).