Mtn sizing help

[kookmyers]

Mountain bike sizing is confusing me. Please help.
I reached out to the forum about a 19.5 trek pro caliber and was told it was too small.
I rode a size large BMC team elite 02 and it seemed to feel fine. Just rode for 3 minutes in a parking lot in flip flops.
It’s stack is larger than the trek 19.5 but the reach is less. Compared to the 20.5....

Trek 20.5 stack = 628, reach = 457
BMC size large stack = 628, reach = 442
What’s more important? Would I need a longer stem? Again, on my 3 minute ride, it felt fine.

Full geometry here:
https://www.racycles.com/product/detail/9832

Thanks all!

Edit:
I’m 6’3.5 with a 35.25 inseam. I will be riding the local San Diego canyons. Most likely un aggressively.

[NHAero]

There isn't much of a standard in MTB sizing as far as I can see. When I bought my Pivot 429 used 3-1/2 years ago I was looking for either that bike or an Ibis Ripley and the small 429 had almost the same stack/reach as the medium Ripley. Gotta look at the numbers, and best to try it out (though I bought my bike off of Pinkbike sight unseen from across the country!)

[kookmyers]

Bump for early AM and other time zones. My GF bought one Sunday and if I act fast I can get a better price than if I lag.

[KonaSS]

Well, you are asking the impossible - internet fitting with a zero details. Don't know anything about your size or how and where you intend to use the bike.

The BMC is a pretty classic XC type hardtail with geometry, that believe it or not, is starting to look dated. Yes, changes are moving quickly in the mtb world.

Doesn't make it bad, just is. Probably a nice bike. Anyway, without details, the large would be good from some around 6 ft ish to 6'2" ish.

[kookmyers]

Originally Posted by KonaSS

Well, you are asking the impossible - internet fitting with a zero details. Don't know anything about your size or how and where you intend to use the bike.

The BMC is a pretty classic XC type hardtail with geometry, that believe it or not, is starting to look dated. Yes, changes are moving quickly in the mtb world.

Doesn't make it bad, just is. Probably a nice bike. Anyway, without details, the large would be good from some around 6 ft ish to 6'2" ish.

Wait...all you paceliners don’t know me? Edited first post.

[Mark McM]

I' don't think you'll find a simple answer. The range of different terrains and riding styles can be vastly larger off-road than on pavement, so it is as much a matter of fitting the bike to the terrain/style as it is to fitting the bike to the rider.

On the plus side though, The range of good MTB bike fit can be a bit wider than for road bikes. On a road bike, one typically sits in one position for a long period of time, so getting that position right is important. On an MTB, the rider is constantly moving around on the bike, so there may not be a single "sweet spot" as far as rider fit.

The best bet is to find an LBS that will let you try out bikes on actual trails, to find the bike geometry that best fits your style of riding.

[tombtfslpk]

I hope this isn't too long. If so, I'll apologize now.
Mountain bike fit does cover a pretty broad range. I can offer some thoughts based on my personal preferences and experiences.
I have a Trek Top Fuel 29er. Mine is a 19.5, Trek calls that a 19.5 "actual" 18.5 "virtual". The ProCalibers seem to be sized similarly, I'm assuming someone feels they fit and ride a little smaller than a "real" 19.5.
Just this weekend, I rode a 20.5 Procaliber Allow me to share some observations with some input from my personal preferences. I don't prefer the latest generation of slacker, shorter stem, long travel fork bikes. I don't consider the ProCaliber to fit that genre. I like shorter forks, steeper head angles, and longer stems. I put my saddle height at 770mm (crank centerline to saddle top). On my Top Fuel that only leaves around 55mm seatpost before the minimum insertion. On the ProCaliber it was just past the 80 mark.
Another thing to consider is your preference for bar drop. I like flat-ish bars and prefer to put the bar tops (at the stem) around 30mm below saddle level. That makes the stem pretty low on the 20.5 bike. Low enough that the shifter can strike the top tube. That's an issue on a carbon frame to me.
So.....I expect you could ride the 19.5. If the saddle height will work out. If the saddle won't be too far forward. If the bars are high enough for you. My biggest concern for you is the seatpost, will it go high enough? Can the saddle slide back that far?
I'm not as tall as you, only 6ft on a good day. It seems that you already compared the numbers between the frames and the 20.5 Trek compared closely to the large (19ish) BMC. If you don't anticipate dropping the stem a bunch, I'd look at a 20.5.

[kookmyers]

Thank you everyone. I’ve decided to hold off on this one. It’s too expensive to not be what I would expect to be “perfect”.
Though, I second guessed my decision when I rode around my GF’s size medium. It felt fine. I was just chasing my son around the cul-de-sac a few minutes.
Not to mention I think I need something more multipurpose than a carbon race frame.....
There’s way too many choices out there.

[Ken Robb]

What saddle height do you like?

[andeww]

I think you should test an xl, a standard large seems tiny for someone with your dims. I am 6 ft 2.5 and a modern 29 cannondale and specialized both feel on the smaller side in xl