School me on MTB sizing

[Onno]

I've owned lots of road bikes over the years, and feel I understand sizing issues with them fairly well. When I'm shopping for a new road bike, I know what I need and want. However, with mountain bikes, I don't have a clue. The numbers make no sense to me, except that I assume (because I'm 6 feet tall, and have a fairly big inseam of 34 inches) that I need a Large or X-Large. But I also assume that there is lots of variation in mountain bike fit. The only mountain bike I bought, about 20 years ago, fit me terribly--there was way too much drop between saddle and bar, about twice as much as my road bike.

So how should I read mountain bike geometry? Are there some basic tips, guidelines, anyone can give? Are there differences (in terms of geometry/fit) between all the different types (29ers, fat bikes, etc.)?

Thanks!

[CMiller]

I find myself MUCH less sensitive on mountain bike fit compared to road. I can get on any medium ~17" bike and adapt fine.

You are shifting body weight all over the place more often offroad, you are elevating yourself off the seat, you are experiencing much more extreme slopes, overall the couple cm differences disappear a bit.

I'd go to a favorite shop and take a few on a test ride. Do sudden stops and hard turns. Do your elbows feel too crunched in? Does your crotch hit the top tube? New bikes are in the trend for short stems and long top tubes, so don't worry too much about how it looks, especially if you are used to 100mm+ road stems.

[ofcounsel]

I'm no expert on MTB fitting, but I do ride them a lot. But you being 6 feet, I would recommend you start with a large frame in virtually any brand's model line.

Getting the "right geometry fit" isn't as critical for MTBs as it is for road. For one thing, you'll be moving back and forth on the saddle, and getting off of the saddle quite often. You're rarely a static pedaling mode for very long on an MTB.

Geometry on the bike can instead be a more telling indicator of the type of use the bike will be good for. For example, hardtails and full suspension cross country bikes are typically going to see 69-70 degree head tube angles. Something that is more trail-enduro focused will see head tube angles in the 69-67 degree range.

Typical modern MTB frames are focusing on shorter chain stays for nimbleness/playful feeling, and longer top tubes combined with shorter stems, also to encourage a quicker/confident feel associated with shorter stems, in particular when descending.

I would say that if you are in between sizes, when in doubt, go with a larger frame, and work with seatposts and stems to get comfortable.

[ofcounsel]

I find myself MUCH less sensitive on mountain bike fit compared to road. I can get on any medium ~17" bike and adapt fine.

You are shifting body weight all over the place more often offroad, you are elevating yourself off the seat, you are experiencing much more extreme slopes, overall the couple cm differences disappear a bit.

I'd go to a favorite shop and take a few on a test ride. Do sudden stops and hard turns. Do your elbows feel too crunched in? Does your crotch hit the top tube? New bikes are in the trend for short stems and long top tubes, so don't worry too much about how it looks, especially if you are used to 100mm+ road stems.

Haha! typing at the same time. Agree 100%

[ofcounsel]

What kind of riding do you envision doing? Cross-country racing? Fire roads and some single track? Technical uphills climbs and steep downhills with large boulder rock gardens? Riding for 3+ hours in varying terrain? Chairlift assisted resort riding? A little bit of everything? Depending on the style of riding you're doing, we can point you to some examples, and you can start to see the similarities/differences in geometry for bikes with similar/different purposes.

[p nut]

What type of bike are you looking at? XC, AM, DH? HT, FS? What type of riding will you be doing? I think fit will largely depend on those factors.

Edit: got beat

[christian]

You're a Large.

(If you are going to be racing enduro and getting a Santa Cruz Nomad, you might want to try an XL. If you are getting a Giant Glory Advanced DH, but are not a professional rider and are getting it for "free-riding" not World Cup racing, you might want to downsize to a Medium, but probably not.)

But short of those specific scenarios, you're definitely a size Large. :)

[d_douglas]

You're a Large.

(If you are going to be racing enduro and getting a Santa Cruz Nomad, you might want to try an XL. If you are getting a Giant Glory Advanced DH, but are not a professional rider and are getting it for "free-riding" not World Cup racing, you might want to downsize to a Medium, but probably not.)

But short of those specific scenarios, you're definitely a size Large. :)

Correct - that is your baseline and go from there.

I am 6'1" and 33" inseam and ride a L AM hardtail and an XL XC full sus bike. I tend to like my bikes fitting a bit big, and the Chromag HT feels smallish, but I *know* its the correct size. I would guess that a bike like that would fit you perfectly.

[dustyrider]

Correct - that is your baseline and go from there.

I am 6'1" and 33" inseam and ride a L AM hardtail and an XL XC full sus bike. I tend to like my bikes fitting a bit big, and the Chromag HT feels smallish, but I *know* its the correct size. I would guess that a bike like that would fit you perfectly.

What chromag HT do you have? I love my old Sakura!

I'm chiming in to say go for a couple demo rides with folks you see yourself riding with. This will let you know what "kind" of bike you want to get. Try to pay attention to the groups and setup especially if there are guys who don't buy stock or have upgraded. Sometimes manufacturers do demo days at a trail head in conjunction with local shops, or you can try to time it right with a bike festival where multiple manufacturers are demoing their bikes.
Opinions on sizing norms are going through a flux right now. There's this whole sizing up the frame and shrinking the contact points going on. In the end, your individual fit and feel trump all if you want to find your flow on the trail. I like a large in almost every bike I've ridden, but know guys who size up and size down that are my size. Really you see it with all people sizes and riding styles.

[d_douglas]

I bought a Rootdown 29er. It is great. I went to all the trouble and fun of building it up, rode it and liked it. Then I took my somewhat dated FS 29er out and realized that I think I like FS bikes more :(.

I am ashamed to admit it, as I want to be a purist, but riding an FS bike in rough conditions is a pleasure (with the exception of my shrieking brakes)

[Onno]

Thanks for the help, everyone. There are lots of single-track trails around where I live (mostly recently made by a core of bikers). I'm a keen x-c skier, and those are the kinds of trails I imagine riding--not super technical, not super hilly, no long downhills. So I'm guessing an XC or Fat bike (which lots of people around here have, and seem to love). My uninformed biases run towards lightness (I hate lifting heavy bikes into cars, etc.) and simplicity (don't want a bike with more parts, bells, whistles, shocks, adjustable bits, etc. than necessary).

[p nut]

If there are lots of fat bikers, I'm assuming shops around there have demos. Rent them for a weekend and see how you like it. Some love it, others don't. I love my fat bikes but there are quirks, such as weight (they're heavy, unless you spend $$$), steering is funky, and Q factor (super wide bb). But man, they're fun. Good thing about fat bikes: you can buy a second wheelset to run regular 29er tires. Or "Plus" tires. Very versatile.

[Schmed]

Biased towards light and simple, you say?

One is all you need.

http://fcdn.mtbr.com/attachments/singlespeed/653644d1321428187-question-best-rear-hub-ss-dsc_0006.jpg

[benb]

There's a lot of what has been said that I don't disagree with but I do think mountain bike fit is more important than what the roadie biased response here seems to indicate.

You can throw me on just about any road bike, if it doesn't fit right it will be uncomfortable and/or cause injury and loss of power but it won't make me crash the bike, spin the rear tire, lose traction, or wash out the tires in a hard corner.

Mountain biking my impression has been that I can get away with a lot more from a comfort and power standpoint but way way less from a handling/cornering/traction standpoint. Get the weight distribution between the wheels wrong and you've got a bike that pulls wheelies when you don't want it to, spins the rear tire when you don't want to, refuses to corner tightly when you need it to, washes out the rear wheel easily, or worst of all washes out the front tire first. Having to actually get off your bike slows you down way more than anything you encounter on the road.

That said I agree mountain bike fit seems to be more tolerant of different body types.. I'm 6'1" with long legs and road bikes seem to be biased towards long reach and it's pretty hard for me to get fit right. Mountain bikes don't seem to have this issue, although I don't really know how the new ultra short stem thing effects that. If the bikes don't handle right if you have to lengthen the stem maybe I could end up being between sizes on current MTBs the same way I seem to be on most stock road bikes.

The other thing is not as many shops have a clue about how to perform mountain bike fits. They seem to admit it too, it doesn't seem like any of the fitting programs really work on training them. Personally I run the same saddle position as the road, it doesn't seem to be high enough to cause issues mountain biking. I put the center of the bars in about the same place too and let the mountain bike bar take care of reducing the reach and drop as necessary. That's for X/C style riding though (perhaps with a more technical bias than you see in X/C racing though), I have little experience with how I'd want the bike to fit for more gravity oriented types of riding.

[ofcounsel]

Thanks for the help, everyone. There are lots of single-track trails around where I live (mostly recently made by a core of bikers). I'm a keen x-c skier, and those are the kinds of trails I imagine riding--not super technical, not super hilly, no long downhills. So I'm guessing an XC or Fat bike (which lots of people around here have, and seem to love). My uninformed biases run towards lightness (I hate lifting heavy bikes into cars, etc.) and simplicity (don't want a bike with more parts, bells, whistles, shocks, adjustable bits, etc. than necessary).

Well, for lightness and simplicity, you can always go with a single speed, fully rigid MTB. Something like a Niner SIR 9 single speed. http://www.bikebling.com/Niner-SIR-9-2-Star-Single-Speed-2016-p/niner16-sir9-ss.htm?gclid=CM2bvLKvzc0CFQiqaQodUp4HdA&utm_source=google&utm_medium=cpc_feed&utm_campaign=comparison_shopping_feeds

In my opinion, fat bikes are fun for the occasional ride/winter ride.I wouldn't get one as my "only" mountain bike, but rather the 2nd or 3rd bike in my quiver. Generally, fat bikes are a bit heavy, lumbering, and just flat out not as versatile in varying trail conditions, IMHO. Of course, there are exceptions. I'm speaking generally.

At a minimum, for versatility's sake, consider looking at hardtail mountain bikes (consider 29" wheel size) with 1x11 gearing (simpler than a 2x10 or 3x10 gearing set up) and about 100-120 mm of suspension in the front fork.

Edit: In response to the post by bend, I'm not a roadie. I'm a mountain biker and "occasional" road rider who admires the classic steel aesthetic. But when I do ride road, it's on a carbon framed, disc braked, di2'ed machine.

[benb]

I wasn't trying to imply any one person here was roadie biased, I meant overall forum tendency, myself included.

[Tony]

Thanks for the help, everyone. There are lots of single-track trails around where I live (mostly recently made by a core of bikers). I'm a keen x-c skier, and those are the kinds of trails I imagine riding--not super technical, not super hilly, no long downhills. So I'm guessing an XC or Fat bike (which lots of people around here have, and seem to love). My uninformed biases run towards lightness (I hate lifting heavy bikes into cars, etc.) and simplicity (don't want a bike with more parts, bells, whistles, shocks, adjustable bits, etc. than necessary).

I switch off between my Ibis Mojo 650b and my Lynskey ti hardtail 29er. On not so rough conditions and longer rides I really prefer the 29er hardtail. Both are set up 1x. The hardtail comes in at 23.5 lbs compared to 27.5 lbs for the FS. I would also recommend a 29er hardtail for you needs, a large maybe even an XL depending on model.

[CampyorBust]

You're a big guy and I am not so take my advice with that in mind. Generally I think this is a key rule of thumb, size up if you want stability and be in the bike, size down if you want flickability/maneuverability and ride on the bike.

Up if you want the bike to work for you, down if you want to work the bike.

Stem size also plays a big role. Recently the trend is towards longer top tubes with short stemz and slacker head angles. Generaly short chainstays benefit handling at the cost of stability and climbing. Lower BB = lower center of gravity and better handling, then you come up a downed tree and have to suffer the shame of dismounting your steed and walking your bike over it.

Try as many bikes of various sizes and wheel sizes as possible, buy the one that speaks to you.

[Onno]

What's the advantage/disadvantage of a 29er? I know what it is, but not why it's a recent development, and why some people love them, and some don't.

[Schmed]

What's the advantage/disadvantage of a 29er? I know what it is, but not why it's a recent development, and why some people love them, and some don't.

"Rolls" better over rocks/roots given the approach angle of a bigger wheel. Can be a bit "sluggish" feeling with some geometries, but personally, I prefer it WAY more than a 26er. You might try a 26.5" / 650B, but for your description of riding, a 29er sounds about right. Especially if you are on a hard tail.

[benb]

I don't own a 29er MTB, I have a 26er and then I have a gravel bike which has the 700c/29er size wheel.. but I can take a stab at it.

At least around here there are roots that appear at certain frequencies (distances between roots).. when you get in then right terrain the 29er wheel will not fall into the gaps between the roots the same way. The 26er will go into each depression and then have to ride back up the surface of each root. The 29er will skim over the tops of some of them providing a nicer ride and more control. In my case my 26er has way bigger tires and suspension and yet I think there are some sections I still get a better ride through those roots on the rigid gravel bike. (Other cases the MTB is still miles ahead regardless of wheel size)

To me that seems like one of the biggest differences... if I have to get a new MTB I'd definitely get a 29er, particularly in my case I'm tall and I think it may be advantageous for sizing too.

As the roots/rocks spread out the difference seems to be negated but that is still not really a negative for the 29er. As they spread out you should be able to ride around them on either wheel size anyway.

[CampyorBust]

What's the advantage/disadvantage of a 29er? I know what it is, but not why it's a recent development, and why some people love them, and some don't.

If you hear a blood curdling scream followed by ungodly cursing in foreign tongues in the woods chances are I flipped my 650b again. I would go 29er especially at your size, at least I have a feeling you might like that size best. Some consider it cheating.:D

[christian]

29er wheels have better rollover, but have more rotating mass and thus have slower acceleration and turn in a bit more leisurely. I tested a lot of bikes before buying my Santa Cruz, but I ended up with a 27.5 bike. Didn't like 29ers at all.

[p nut]

Rotational mass was a big concern 10 years ago, but now with carbon rims and light tires, not as big of an issue and personally, tips the scale to overall benefit for me for 29ers (and c'mon, euro's are also going 29 (http://www.bikeradar.com/us/mtb/gear/article/julien-absalon-bike-bmc-fourstroke-01-with-shimano-di2-and-dropper-post-2016-46913/)). Also, geometry has come a long way. My 29er feels just as responsive (if not more) than my old 26.

This just tells you that even given the same wheelsize, bikes can ride totally different. Just demo as many as you can. As Campy said above, you would be best on a 29er given your size.

[ofcounsel]

Rotational mass was a big concern 10 years ago, but now with carbon rims and light tires, not as big of an issue and personally, tips the scale to overall benefit for me for 29ers (and c'mon, euro's are also going 29 (http://www.bikeradar.com/us/mtb/gear/article/julien-absalon-bike-bmc-fourstroke-01-with-shimano-di2-and-dropper-post-2016-46913/)). Also, geometry has come a long way. My 29er feels just as responsive (if not more) than my old 26.

This just tells you that even given the same wheelsize, bikes can ride totally different. Just demo as many as you can. As Campy said above, you would be best on a 29er given your size.

Agreed. Rotational mass is not necessarily a huge concern. Now and days, you might see an extra 100-200 gram penalty per set, on the same brand of 29er wheel/tire combo verus a 27.5 (I don't mention 26" the because 26" wheel size is effective dead for new bikes) For example, the wheels on my short travel, full suspension 29er weight only 1510 grams, and my tires are not any heavier than most 27.5" tires (and I'm a 240 lbs guy when in full gear, but no concerns with wheels as light as mine).

I would also say that the variation in ride/feel of mountain bikes between brands, and even between models of the same brand, is hugely different over what you would experience on road bikes. SO I agree, give as many as you can a try.

Now, this is a very general statement, but "generally" a 27.5ers tend to be a little more playful and nimble. 29ers tend to be a little faster and roll over stuff better. But based on what you described, a 29er might be a better fit. But it comes down to personal preference.

My personal preference is for 29ers. My current stable consists of: (1) Niner Air 9 RDO hardtail, which I sometimes use for shorter rides and days with lots of climbing on fire roads and light singletrack (2), Pivot Mach 429SL which is short-travel full suspension bike. The Pivot sees the most use in my stable, and could handle everything I ride if I were limited to one bike, and (3) a Stumpjumper FSR Evo 29er, which my longer-travel full suspension bike. I use the stumpy when the ride I plan on might get a bit rough and rocky.

[Fatty]

Just go buy this. Be Happy.

https://ithaca.craigslist.org/bik/5613690288.html

http://images.craigslist.org/01010_koJUY8cH1Zw_600x450.jpg

[invertedhog]

borrow some size L MTBs from friends and try them out. Most cities have a higher end or bigger shop that does demo days with different brands. Ride as many different setups as you can on the type of trail you plan to ride.

Depending on your torso length maybe XL with short stem and zero setback post.