I've been looking at the BMC TM01 geometry, and I see the tt and reach length of the M-S is shorter than the S. What am I missing? I was thinking I would be the M-S or M-L, but the M-S looks so different in the numbers. Any thoughts? Thanks.
You are not missing anything. The MS is shorter than the S. The numbers on the geometry chart are correct.
I am 5'9" and ride a MS TM01. I previously rode a Cervelo P2 in a size 54, which has a stack/reach of around 51 and 42 cm. I rode it with a 90mm stem and a Visiontech basebar and extensions with 2.5mm spacers under the pads, so I was riding with a pretty standard stem and a very low aerobar setup. On paper, I should have been a near-perfect match for a ML, but the ML was too long for me and the MS ended up being the right fit. IMO/IME, bikes with bayonet style front ends can fit differently in reality than they may appear on paper. It is a great bike, with really good stiffness, handling, and ride as far as TT bikes go. Given its geometry and the way the TM01 fits and also its mechanical quirks, particularly with the cabling and brakes, it would help a lot to visit a shop with a lot of experience fitting and wrenching this bike. Also, if you get one, brake levers with barrel adjusters are a must.