Originally Posted by
vcand
Ok, I think Im starting to understand their sizes.
I "should" be a 56cm from what I am being told. Now if I understand sizing, 56cm "should" be the length of the seat tube, correct? If that is the case, in the Motobecane specs for the bike that I am looking at, a 56cm bike has a 53.3cm tube. A 58cm bike has a 55.3cm tube. So technically, the 58cm bike actually has a seat tube of about 56cm, which is a 56cm in a normal bike, which is where I should be, or did I butcher all that?
This is where all the confusion from BD comes into play, they have "general guidelines" all over the place which contradict the bikes actual specs.
On the bikes page under "General Sizing", I should be a 56cm, based upon height. On the "Sizing Tips" page (
http://www.bikesdirect.com/products/roadsizing.html) it wants me to measure my standover height, which is 33inches. It then says get a bike with a minimum of 32inches (one inch less), which is 58cm on their chart. The bikes specs align with be being a 58cm
Now for crankset, I am told I should be about 170mm. On the bike I'm looking at the sizes are:
47-52 = 170
54-56 = 172.5
58-64cm = 175mm
The bike Im looking at is:
http://www.bikesdirect.com/products/.../mirage_sl.htm
(specs and sizing link is under the images)
They only have a 58cm left, so I want to be completely sure to rule that size out. I'm also emailing them my specs and seeing what they recommend, maybe they will be able to bypass all the conflicting information.
Common confusion for new buyers.
Most sizing systems, when they speak of 'seattube' (ST), are referring to the length of the seat tube from bottom Bracket (BB) to the 'center' or 'top of where the top tube (TT) joins the ST. This is done in a HORIZONTAL PLANE (relative to flat ground) from where the TT contacts the Head Tube (HT). This using Traditional Diamond Frame geometry... Think of older style bike, with horizontal TT...
The bike you're looking at has 'compact' design, so the actual seat tube is shorter because the TT is sloping from horizontal (measurement they've given you on the chart). but the size is designated '56', BECAUSE if you extend an imaginery horizontal line from the TT/HT contact , back to where the ST would go (where the seat post actually goes) - The length of the ST would be close to 56 cm...
Forget standover, you'll have plenty on a compact frame.
Don;t fret on crank size. You'll be able to ride well whether its 170, 172.5 or 175. There was a time when getting anything other than 170 was a special order item.
It's good to be thorough, but stressful to be anal. In the end there are other things which will have a greater effect, but best not to worry about that now - get the bike, go ride a bunch.
Don;t worry, be happy. Pick the right color!