Mountain Bike Help for a Roadie

Hey all, bought a mountain bike this fall after riding only road and CX for the last 5 years. I bought a 2019 Trek Fuel EX 5 29er. I am 5’6” and the Sizing chart had me in the middle of the range for a medium and I bought it used online. I am now finding my bike feels big and a not particularly agile. Wondering if I would be better served by a smaller frame and/27.5 wheels?? Or both?? The bike feels properly sized while riding but it feels big standing over it.

In general I think the specs and travel of the bike suit my needs (on paper) but would like something a bit more playful and agile. Thoughts on where to start looking would appreciated as I expect to buy used and demos are hard to come by right now. Thanks!

Well, that’s kinda expected, IMO. It’s going to be slower until you go at speed. Most of the riding is on leans at speed.

If you want more agile, I would’ve looked at the Top Fuel or the Supercaliber.

Playful, it’s not going to be the same definition of what you’re thinking of, unless you like to jump and whip.

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I’ve got the same bike but in a Lg 29’er. I’m also 6’1". I riding buddy of mine who is about your size, maybe an inch or two taller always goes 27.5. He says he feels more ‘in’ the wheels rather than over them which he likes. And conventional wisdom is that smaller wheels are more maneuverable. The fuel ex will take 27.5+ wheels, so theoretically, you could get some 27.5 wheels and put regular tires on them and it would at least be compatible, not sure what that would do to handling though

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Not too “regular” as the BB will be too low. It’s already a bit of a drop to go from 29 to a 2.8 27.5 (somewhere between 0.5 to 0.75 inches). A 2.6 might work, but would be loathe to go to a 2.1 or anything like that.


“More playful and agile” = go with a 27.5. Also the frame might be a tiny bit big for you but close enough it shouldn’t matter too much. I ride a Pivot Firebird XO1 Eagle and have a M and left the 29 on (Im 5’9") My riding buddy is about your height and he got the same bike as me and road the 29 for a bit and decided to switch to 27.5 and loves it. Smaller wheels will help with the cornering and being more agile but you just give up the monster truck feel of just bombing over everything in your path the 29 gives. Id say if you can fit 27.5 on the bike just do a wheel swap and see how you like it. Probably can find someone online to do a swap with or sell them for the same price as buying some used 27.5s.

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Dont discount that the latest crop of mtn bikes has “relaxed” geometry which makes it feel lazy as well. Coming from my old ~2009 26er to a '21 epic evo, it took a while to get used to the “lazy” feeling. As stated above, it allows you to go faster, and then everything starts to feel more alive.

Also, this is a great thread title to dump all of the “help me what I am doing on a mtn bike” questions for all of us new mtn bikers.

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Fit is obviously a personal thing, but FWIW, I’m also 5’6", and while I don’t ride a Trek currently, my bike’s measurements are roughly equivalent to a M Trek, and the bike I had previously was a M Trek (albeit not a 29er), so you probably aren’t that far off the mark on sizing unless you have particularly unusual proportions.

What kind of riding are you doing? People do often go 27.5 when looking for playful and agile, but short travel 29ers can also fit that bill quite nicely. If you’re not riding particularly aggressive trails, your issue may be more that the Fuel EX has more travel than you need for what you ride rather than needing to go with smaller wheels. If that’s the case, I might lean more toward the Top Fuel from Trek’s lineup or any of the numerous competitors in that travel bracket.

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OP’s first MTB.

I want to revisit my first remark. It’s not going to be what a roadie thinks it’s going to be. Those terms mean something different in the MTB world. Compared to a road bike, everything is going to be sluggish. There’s ALOT to learn before you even get to that part of discerning if a MTB is playful, and if it’s just being a dirt roadie, then a 29er is better.

I don’t mean to come off as snarky, but there’s context when you read reviews and they talk about being playful and agile. It’s the way they ride and how hard it is for them to maneuver the bike. I’d gather, for the average beginner, unless you are coming from BMX, you will not be able to discern this.


I got that it was OP’s first MTB, or at least first MTB in a while, but even so, local terrain can make a difference, and people also advance at different rates. That said, I actually do agree with you. I also think it’s more likely that OP is overbiked in terms of travel rather than on the wrong size bike or the wrong size wheels. Unless OP is riding aggressive terrain, which seems unlikely for a beginner, I think a short travel 29er is probably the best fit.

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You might give that new bike a chance to grow on you. Mountain bikes, especially 29’ers, feel enormous compared to an equivalent sized road bike. I ride both, but often go long periods between MTB rides when the trails are too muddy during the winter. When I do get back on the MTB, the bars feel comically wide and the wheelbase makes me feel like there’s no way I’ll make it around a switchback. The suspension sucks up my watts, and it feels so hard to get moving. Then after an autumn of back-to-back MTB rides, my road bike feels skittish and twitchy, and the skinny tires roll so easy I’d swear the bike grew a motor.


A medium sounds big especially with a 29er. Personally I rolll a medium giant anthem 27.5, I’m 5’8". I went from old school 26 to 29 to 27.5 and realize I love how nimble a 26 and 27.5 is. My 2 cents.

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So much of bike sizing for mountain bikes is personal preference (in my experience), and it can be tough to separate sizing from being “over-biked” in regards to suspension.
Best idea would be to try to demo a few different bikes, but obviously that’s currently difficult.
Maybe explore some varieties of terrain that you haven’t yet? Often what seems like a cumbersome bike on tame stuff comes to life on more challenging trail or if pointed downhill.

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I’m 5’10 and on a medium 26er pivot mach 4 (100mm f/r). I don’t care that its super old-school, I love throwing it around!

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Only way you will truly know is to try a small…seems at 5-6 you would be borderline small/med in most brands…I am 5-10.5 and am right on the med/lrg threshold…I always gravitate towards the large because I like the seat to bar distance with a short 50/60mm stem.

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Being mostly a roadie, 29ers have always felt like getting on a horse or something. Because of the tall tires, you are sitting up higher than you are used to. To me it sounds like you have the right sized frame. I’d just go with it and get used to it.

A 27.5 wheel may not even be all that much smaller than a 29er. Finding the right mountain bike takes some experience of just knowing what you like. I ride mountain bikes like a roadie. I don’t do jumps and stuff so I’ll stick with the 29er. I’ve been through a few mountain bikes. I was dead set on getting full suspension so now I have a Specialized Camber with 140mm of travel. It’s a fantastic FS bike and faster over most terrain but I kind of miss the hard tail I had before. The hardtail was a XC race bike. It was pretty light and a lot of fun to ride.


What you are experiencing is likely a fatal combination of all three factors, frame geometry, frame size and wheel size. Wheel size is a matter of taste, and frame size depends on too many variables like arm and leg length in addition to height. I reckon you could make S and M fit, but S might have a geometry that is more to your liking.

Geometry for sure plays a big role. The Trek Fuel is a trail bike, and trail bikes have become significantly longer and slacker than what mountain bikes were about 5-10 years ago. Just think of the difference between a relaxed endurance road bike and an aggressive race bike. Now multiply the difference by a factor of 2 or 3.

Trail bikes are nowadays designed to be stable and capable at fast speeds. Hence, the slack head angle. That also makes them more sluggish in slow-speed maneuvers.

If you want a bike that handles more quickly, you need to look at XC bikes, although even they have gotten quite slack. If I were you, I’d keep the bike for half a season or so and then I’d go to a LBS and try out a bunch of different bikes. If you find one you like, sell the Trek and buy a new one. Mountain bikes — especially trail bikes — are significantly larger and heavier beasts than svelte road bikes. So you need to get used to that. The slack geometry, which you currently perceive as lazy, actually serves a purpose that is anything but lazy. It makes your bike more stable at speed, so in a sense, you may be just going too slowly :wink:


A couple things come to mind that might help you out.

Does the 2019 FEX5 have the Mino-Link? If so you may want to switch the setting to see how that feels. I prefer my top fuel in “party Mode”, but I think the taller/short mode may feel more agile.

Also does it have the adjustable dropout? There maybe some room to make it more agile feeling there.

Another thought are the suspension settings, and since you bought it used, the suspension system may need a proper servicing. If you bought it used and didn’t make adjustments to the fork and rear shock it may be set up for someone that weighs drastically different than you or prefers a different ride feel. The Trek Suspension Calculator is an alright place to start, but you may need to do some trial and error for your trails and how you like to ride.

Have fun on the MTB


I have a 2017 Medium Fuel. I think that’s the same geometry as yours. A few thoughts:

  1. I’m 5’9”. I’m on the upper end of the size range for a medium. I’ve ridden a Large Fuel and could probably be just as comfortable on that. At 5’6”, you’re on the lower end of the size range for medium, but still within the recommended size, so you should be fine - see following points.

  2. If this is your first MTB, give it time. I am able to move the bike around a whole lot better now than I was when I started MTB.

  3. What stem length do you have? Try a 50mm or shorter.

  4. How is your saddle positioning? Maybe move it forward a little so you’re not a stretched out.

  5. Wheel weight makes a difference in how agile the bike feels - especially the front. Go tubeless, and use a reasonably light front tire e.g. no need for a heavy Maxxis Minion. The Team Issue XR4s I really like.
    I wouldn’t go 27.5 on the Fuel, as that will lower the BB below what the bike is designed for, and you’ll end up with a ton of pedal strikes. And if you use a big tire to give you more diameter, you could end up with a heavier wheel than the 29er in the first place.

  6. On the rear, I’d use a lower rolling resistance tire than the XR4. This will help the bike feel a little faster. The XR3 isn’t bad, but I’ve found they wear down quickly. My current choice is a continental cross king.

  7. Check your suspension setup. Make sure you have enough pressure, and not too much rebound damping.


This is super good advice. I run tubeless and cross king on my rear, I think trail king on my front (which is slightly more aggressive than the cross king but nothing like a minion).
I’m guessing your wheels are tubeless ready, but if not I hacked mine using gorilla tape. Couldn’t have been easier and I haven’t flatted since. Occasionally I’ll burp some air because I run the pressure so low, but those are only on big hits that would’ve pinch flatted me in the past.