matthewayres

Friends, looking for a bit of assistance/advice.

Looking at picking up a new 650b, but need help with the sizing... Nashbar has a seemingly well appointed 650b with a X9/7 mix for $1000, full specs below. I am 5'5", with a standover of 29.5. This is my first mtn bike in a decade, so I not sure about how best to fit it, and I am having trouble finding a 650b at a LBS to size.

My "48cm" small bmc road bike fits like a glove, with a 440 seat tube, 510 effective top, stack of 508 and reach of 369.

THis 15" 650b has a c-c top tube of 555, c-t seat tube of 380, but doesn't offer a lot of other info... the bike is listed here: https://goo.gl/MNeJL



So what do you think, good bike? Size works? I have been looking at 29ers, but just feel like I am too small to get a good fit....

I appreciate all input, even snarky. Thanks!



FRAME: 650b Alloy, tapered 1 1/4" head tube, trail tuned chain and seat stays, replaceable rear derailleur hanger, disc tabs and double water bottle mounts
FORK: Rock Shox Revelation RL with Remote Lockout and 100mm of travel, Tapered 1 1/4" steerer, 15mm Thru-Axle
REAR SHOCK: None
HEADSET: FSA, TH-875
CRANKSET: SRAM X5, 38/24 chainrings
BOTTOM BRACKET: SRAM External Bearing
SHIFTERS: SRAM X9 trigger, 2x10
LEVERS: Avid Elixir 3
HANDLEBAR: Alloy Oversized, 31.8mm clamp, 620mm width, 15mm rise
STEM: Alloy, 80mm
FRONT DERAILLEUR: SRAM X7, 34.9mm clamp
REAR DERAILLEUR: SRAM X9, Medium Cage, 10-speed
CASSETTE: SRAM PG-1070, 10-speed, 11/36 range
BRAKES: Avid Elixir 3 Hydraulic
WHEELSET: Alex 650b XD-Lite, 6-bolt IS disc,sealed bearing hubs
TIRES: Kenda Nevegal, K-1010, 27.5x2.1 (650b)
PEDALS: None
SEATPOST: Aluminum, 31.6x400mm
SADDLE: Prologo Kappa Evo
CHAIN: SRAM PC-1071, 10-speed
GRIPS/TAPE: Lock Ring, black

Zephyr11

Mountain bike fitting is an art, not a science. Very different beast from sizing a road bike. I'd say at 5'5, you're likely looking at a small frame (especially with big wheels), but there's a lot of preference in there. This is why it's kind of tough to buy online...you don't get to test ride at all.

tkehler

Try the bike you will buy.

If you can't do this, try a bike by the same manufacturer.

If you can't do that either, for sure figure out who is making bikes with a similar geometry and then try one of those bikes.

As you know, bike fit has various stages. i) loosely figuring out if you need a S or M or L or whatever. ii) next fit is initially done by seller, fiddling with stem length, and seat position. Maybe later, iii) either get a good fitter to help with shoe inserts etc., and fine tuning position. An experienced friend can help too.

Svr

A 650B wheel is only 25mm larger than a 26" wheel. That's about 12.5mm in radius.

The only change in frame geometry required is to slightly lengthen the chainstays to accomodate a slightly larger wheel.

What I'm trying to say is if you fit on a small sized 26" bike, you'll fit fine on a similar sized 650B bike.