Hello,

Im another lost soul when it comes to bike fitting. Originally I went to this site to find my size:

https://www.ebicycles.com/bicycle-too....5&b=Calculate

This site said I should be a 56cm frame with a 170mm crank. I thought I was good until I went to purchase a bike and I posted on this forum to find out if the price was right. Someone responded and said that for my height and size I should be a 58cm bike, even a 60cm to be comfortable.

So I thought I was set on size. So I ended up finding a Motobecane I liked on BD and I was looking at their sizing charts and they says this:

47cm - 5'0" to 5'3"
50cm - 5'3" to 5'6"
52cm - 5'6 to 5'8"
54cm - 5'8" to 5'10"
56cm - 5'10" to 6'0"
58cm - 6'0" to 6'1"
60cm - 6'1" to 6'2"
62cm - 6'3" to 6'4"
64cm - 6'4" +

and the 58cm bike has a 175mm crank.

So this recommends that I get a 56cm bike and that a 58cm would be too big for me. I am completely lost on what to do, everytime I think I understand bike fitting, it changes.

I am 5' 10.5" and my leg length is 32.5". Are Motobecane bikes size different? What size should I look at as I am unable to try it out when ordering online? My assumption was I should get a 58cm, which would be slightly bigger than what the link and BD suggests, yet on par or slightly smaller than what a poster on here told me.

Thanks.

For what it's worth, we are of similar size; I'm 5'11" and have an inseam of 32". I ride a 56 cm that has a 172.5 mm crank. I tested many 58 cm's before, and there were all to large for me.

Lots could be said here, but probably the most helpful tip for you would be to buy a bike from a local shop where you can test ride and get help adjusting if you need it.

Sizing a bike isn't that hard for most riders' needs, but without having a basic understanding of the numbers at issue, you're making it too hard on yourself, and I'd say, getting ahead of things.

But, if you're insistent on continuing with the Bikesdirect thing, I'd suggest you follow the vendor's sizing guide, not some joe-schmoe on the internet, like me, who may or may not know what they're talking about. A second tip is that erring on the small side is much better than erring on the too large.

Good luck.

leg length is a very important part of bike sizing and 'fit'. Most of the 'charts' refer to the average human for all the assorted measurements, but very few of us are avg...
Your leg length measurement is dependent on how you actually measure it. Bike convention is to get the measurement from barefoot standing up to the sitzbones - easiest way to do that is to stand against a wall, slide a book with some thickness up the crotch as FAR as it will go - I mean PUSH! past any equipment... If the book is hardbound and one side is square against the wall, then the book will be perpendicular to the wall - measure from the floor to that top book edge - that's your cycling inseam...

I'm 5' 10.5" and have longer legs/arms, shorter torso, my cycling inseam is 34.85 in or 88.5 cm - i prefer a 56/57 in the modern frames with a 56.5 to max 57 Top tube... and with a 73 ish seattube angle will use a 110-120 stem on a std reach (not compact reach) bar. Old school bikes from decades ago I rode 59cm, with occassional 60 and down to 58. But there's really no need to go there anymore.

IMO, If you're inseam is less than mine, then I would suggest staying with 56 or smaller (if cycling inseam significantly shorter) to 54 and using stem length to get proper reach for your torso and arm lenght. IMO

+ the Purpose you have intended ,,Fast in a Racing tuck , versus touring and sitting up more ..

Stand over height is best judged, physically standing over the Bike. ahead of/off the saddle , feet flat on the ground.



If you use trouser leg length that is not a useful number ..

how high can you pull a tube, big Book etc up between your legs before you say "Ouch".. measure that maximum.

FWIW I'm 5'11" (33.75 inseam) and if I were ordering a Motobecane from BD I'd go for the 56 - based on both their height recommendation chart and the fact that I currently ride a bike with a 56 Top Tube that fits me well.

It'd be nice if they also told you the head tube length for a given size, as that would help give an indication of type of fit and whether a certain bike will work for you. ie a short head tube=geared toward a more aggressive position with deeper seat to top of bars drop, one would need to set up stem/fork with lots of spacers for a less drop; vs longer head tube = geared toward less aggressive more upright position, someone racing would be limited by the amount they could drop the bars to suit a more aggressive riding position.

As an aside those new 2014 Motobecane Le Champion CF PRO look pretty nice - may put this one on my short list

UPDATE: I wrote them asking the head tube length of a size 56, and Chris from BD wrote me back - it's 170mm if anyone is interested.

Yeah, Im starting to think their height guideline is wrong (see my next post).

You ride a 56cm, is it a motobecane? From what I see a 56cm motobecane is NOT a 56cm tube, a 58 is.

They do, if you click on a bikes specific "sizing chart" (under the image), they tell you all those goodies... like this is the one for the bike Im looking at:
https://www.bikesdirect.com/products/...mot_al_geo.jpg
[/QUOTE]

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 (https://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:
https://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.

I would use this calculator.

GET A HELPER, measure several times (in cm-metric for road bike) and average results.

Go to BD geometry sizing chart and order according to top tube length.

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!

Yeah confusing is the fact that they say actual frame size is 56, but then seat tube length is 53.3 without seeing a diagram it's hard to say what they're measuring from, I think the size 56 is more of a virtual size because the bike does have a sloping top tube.

In any case I ride an older pinarello which has a seat tube that, measures 55.5 c-c; a 56 top tube and a 160mm head tube. Based on that info since I like that fit I would select the 56 motobecane for my height as it most closely corresponds to geometry of my current frame, even though my frame has traditional horizontal top tube (non sloping) geometry-the effective TT is the same, and the head tube is close.

I think BDs height chart seems pretty accurate to me. I would check your measurements again, but am fairly certain the 58 will be too big. Also remember these frames look like they have a fairly tall head tube (170 on a size 56) so if you are more inclined to racing or fast sport riding, the 54 may even work for you.

I see they also provide seat post height recommendations, which is nice. Work out your seat post height with an online calculator and see where it falls in the range of recommended min/max heights, that might help you as we'll. if your at the extreme max/min end of that range you may want to look at next size up/down. Standover is less of an issue with most road frames today, provided your junk clears top tube, stand over clearance is a more critical factor with track, cyclocross and mountain bikes.

See my thread for another aspect, where some of these measurements are not even taken in the same place on different bikes.

I too tried to do it "by the numbers" and found a huge discrepency when I actually rode the bikes. Bikes that spec'd out as the right size were too small, and one that was supposed to be too big felt just right (why do I feel like Goldilocks all of a sudden?). Two with very similar specs felt completely different.

BTW, I'm about your size too (5' 10", 175#, 32" inseam) and ended up on a bike with a TT length of 565cm (22.24") and a standover height of 772cm (30.39"). Also, I have long arms, and this bike has a long handlebar clamp.

-- Sam

Dude, you really need to do more reading before you link any of what you think you know to a purchase decision. I'm not trying to be mean, but you're just all over the place, and don't at all have a solid understanding of the basics on which to stand. And the way you ask questions, well, if you get to where you want to be, it will be due to luck and not rigor. My best advice to you is to read 3 books or articles on bicycle fit, and then come back with questions. There are lots of well-intentioned folks here, but this thread is a hot mess.