MTB bike sizing general question

CrankAddictRich

CrankAddictRich

Well-Known Member
If someone were buying a new bike and they were right on the line between a medium and a large, what size would you recommend? On the road side of things, I'd say go with the smaller bike, if both can be fit the same.... but it seems like the MTB trend is longer reach across all sizes, as it promotes more stability? correct? So if someone could ride either, is the larger size the better choice?

This is all hypothetical.... thoughts?
 
CrankAddictRich said:
If someone were buying a new bike and they were right on the line between a medium and a large, what size would you recommend? On the road side of things, I'd say go with the smaller bike, if both can be fit the same.... but it seems like the MTB trend is longer reach across all sizes, as it promotes more stability? correct? So if someone could ride either, is the larger size the better choice?

This is all hypothetical.... thoughts?
Click to expand...

This is a big part of my daily life when selling bikes. I’ll typically have them ride both sizes and take into consideration which size the customer generally gravitates toward. There is not a cut and dry answer.

Personally, I’m about 5-10”. I buy jean in a 30” length. I do a ton of yoga and I have a naturally forward rotated pelvis (which is to say that most flat saddles feel nose up when they are actually level.. this is why smp works well for me). My legs are short for my height, but I have a long-ish torso and arms. When I go to any demo event, they always want to put me on a med. I always buy large bikes and a 56cm on the road. The trick here is I’m honoring the combined reach of my torso and arms, while giving little thought to my inseam / stand over height. This keeps my center of mass between my wheels and not heavily over the front wheel. On a med I often feel that I’m overweighting the front end and bike almost feels like it’s behind me.

The steeper seattube angles on modern bike work well for me as I run my cleats all the way back, plus I have shortish femurs. The combo make me slam the saddles all the way forward on many bikes. Less so on modern bikes. In reality I’ve been running a 77degree seattube angle on my mtbs for years. This forward seat posture eats up around 2 cm for me and on med the reach numbers aren’t there to give up. The longer reach in a lg makes up for the dismissed reach from running saddles more forward as well. It’s important to note that the modern geos actually are worse for some body types.

On DH bikes you are basically standing the whole time and so the med bikes can work for me. That said I still like the longer front center on longer bikes so it never feels like you will go over the bars on the really steep stuff.


I can ramble on for hours about fit as it’s what I do all day every day. There is no onsize fits all approach here. Trial and error and experience goes a looooong way.
 
CrankAddictRich said:
If someone were buying a new bike and they were right on the line between a medium and a large, what size would you recommend? On the road side of things, I'd say go with the smaller bike, if both can be fit the same.... but it seems like the MTB trend is longer reach across all sizes, as it promotes more stability? correct? So if someone could ride either, is the larger size the better choice?

This is all hypothetical.... thoughts?
Click to expand...
Have someone test ride both bikes, L&Med. Have someone choose the bike they feel more comfortable on.
I can go either way, no ACDC. I go Large.
 
AS it happens I'm always on the line between a medium and a large according to the manufacturer specs. I've always gone with the large and not regretting it. For reference, I am 5' 11" and 32" inseam.
 
I'm 5'10" with a 32" measured inseam (not pants size). I'm right between a M and L. My first bike was a L and didn't have adequate standover and I couldn't get a 150mm dropper to fit with my saddle height. Say what you want about standover but when it isn't there you will become aware of it, or the lack of it. My current bike is a M but I had to lengthen the stem to get comfortable. I love the new trend of shorter seat tubes and lower top tubes. I'ts a lot easier to go up a size than it used to be.

Take all that with a grain of salt. I've only been riding again for 3 years so I am just starting to "get it."
 
CrankAddictRich said:
If someone were buying a new bike and they were right on the line between a medium and a large, what size would you recommend? On the road side of things, I'd say go with the smaller bike, if both can be fit the same.... but it seems like the MTB trend is longer reach across all sizes, as it promotes more stability? correct? So if someone could ride either, is the larger size the better choice?

This is all hypothetical.... thoughts?
Click to expand...

So the thing not asked here is, how experienced is the rider?

New riders tend to not like being stretched out. And new riders do not know how to use a dropper. So a large is a potentially bad direction there.
 
Go large. If you’re on the cusp, you can always get a shorter stem, mess with the stack height, try different bar widths. If it’s too short, it’s very difficult to comfortably add length. Confirm with both sizes on your favorite ride first.
 
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