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Unless he (or she?) has a very unusually proportioned body, and the bike has some very unusual fit adjustments made, it is HIGHLY unlikely -- impossible, in my view. 180 cm is 5 feet 11 inches in "American" units. A normally proportioned male rider that tall would normally ride a frame sized at least 60 cm, maybe bigger. I'm about 5' 7" (170 cm) and a 50 cm bike would usually be a little small for me -- I ride a 52 or so.
 

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I was 5'11" in my prime and closer to 5'10" today. I have ridden comfortably on bikes from 55cm to 57cm by using longer or shorter stems and raising or lowering the seatposts. I tried my wife's 54cm Pinarello with a 13.5 cm stem; didn't get enough reach and my body weight felt too far forward. She's 5'9" and rides a 52cm with a long top tube as comfortably as she rides the Pinarello.

With an mtb seatpost and a long, riser stem you could probably get the dimensions pretty close, but I doubt you could be well centered and balanced on the bike. Not only that you run the risk of looking like a kid wearing the suit his mom got him 2 years ago.
 

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It depends on the geometry. You have to look at your effective top tube length. I know of guys who are 5'7" riding 48-49cm bikes because it is a semi-compact or compact frame. My bike is a compact frame at 49cm. It definitely stretches me out but I like the feel. I thought it may have been too big for me at 5'5"
 

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Being clear

bardeleben said:
Can anyone tell me if a 180 cm rider can ride a 50cm frame without being too uncomfortable.
Assuming that 50 cm is a horizontal top tube frame, the answer would generally be no, absent a very long and steeply angled stem and a mountain bike seat post. For a compact frame, 50cm is reasonable if it is measured to the seat post clamp. Also recognize that different manufacturers measure frames differently, ranging from center to center, to center to top (of the top tube), to center to top of the seat post clamp. That might represent 3cm or so difference in measurement for three identical frames.

For someone of your height, a "typical" frame size might be 57-60 cm, measured center to center and dependent on your flexibility, your preferences, and your specific body measurements (leg length, arm length, torso length).
 

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I'm 5'11" and riding a 54cm with a 100mm stem... I can use a bit larger. I'd think you'd be too cramped and risk injury. Maybe you can get a 160mm stem?
 

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I'm 5'11" with a 32" inseam and ride everything from 54-56cm. Anything smaller or larger than that just feels uncomfortable and awkward.
 

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I'm 5'10.5" - 5'11" tall with a short inseam length 32.5"

In reality I'm best fitted to a 56-58, but with the shorter legs and short femurs I ride smaller bikes for racing to get a racier position on the bike (it helps that I'm flexible enough to do so).

Smaller bikes tend to have steeper seat tube angles, shorter head tubes and shorter top tubes than bigger bikes. With shorter legs the shorter head tube helps in being able to get the front end low enough...though I still run a -17 degree stem and an 11cm saddle to bar drop. The steeper STA allows me to get the seat more centered on the rails, though I still use a 0 degree post and am most of the way forward on the rails (also run 170mm cranks).

However....with all that said...you can get some length back with a longer stem (I run 120mm stems) and lower bars...think of arcing your arms from a forward position to a downward position.

So my current race bike is sized as a 53cm frame, but is actually a 55cm due to top tube length. In an ideal world all the dimensions would be the same but the TT would be 1.5cm longer. However, the shorter bike also puts more weight on the front wheel and makes for a very quick steering bike :)
 

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I'm 180cm and 56cm bike is the sweet spot. But +1 or 2 in either direction can be okay, as long as proper adjustments are made. But 50cm is out of the question.
 

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I'm 180cm and have riden 56cm frame for years, now I'm on a 57cm

my ex had a 50cm bike and I simply couldn't ride it. It is too small.
 

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I have a 31inch inseam and one of the bikes in my stable is 52cm and it's really too short, especially when I ride out of the saddle. My other bikes are 54cm and they feel comfortable. I'd think 50 would be much too small.
 

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i hear a lot of numbers being bandied about, but no one specified what those numbers are. are those top tube measurements or seat tube? are they center to center or center to top? are those top tubes virtual or actual? what size stem with those top tubes?

not enough info ...
 

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I took the "small bike" approach since I've been used to it for the longest time. Standing 5'11 and riding on a 48.3cm(19in) frame. Most of the space-making is done with a longer stem but ironically (to some...or most), I have a Profile Design Fast Forward seatpost because I get along with riding more over my bottom bracket.

But to respond to the original question: riding a smaller bike comfortably is a matter of getting used to it. I am in no way cramped nor have disproportional body. A longer stem is a necessity as well as getting used to the handlng with it. If it's strictly for performance riding, don't consider it a weapon or advantage. Best fit always prevails over weight.
 
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