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The road bike I'm planning on buying is only available in 49cm and 50cm. Will that be okay given that my height is 5'8/9?

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    Too small, don't do it, lower back pain, inefficient, awkward. – Lamar Latrell Sep 11 '20 at 22:18
  • Have you tried it out in person? Buying a new bike sight-unseen is a recipe for pain and a bike that won't be ridden. – Criggie Sep 11 '20 at 22:57
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    One very important bit of information you should add is exactly how the "size" measurement is done on the bike you are considering. Commonly, size refers to the distance measured along the line of the seat tube from the bottom bracket to a point in space where the top tube would meet the line if the top tube were horizontal. But some bikes will measure to the point where the actual sloping top tube meets the seat tube, so the "size" is much smaller for a given bike. Thus 49 and 50 may be sizes comparable to a typical 54 or so. – Andrew Sep 13 '20 at 11:24
  • In the end it’s all about stack and reach, the size (whether in virtual seatpost height or S/M/L etc.) is meaningless. – Michael Sep 13 '20 at 16:03
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Very unlikely a 50cm (small?) bike will fit you. I'm about the same height and fit a 54/medium in most road bike models.

Some people about the same height with short legs fit a 52cm frame with a long stem fitted.

The manufacturer of the bike you are looking at should have a sizing guide that takes height and inseam measurements into account.

Don't compromise on bike size, get the bike you want that fits you. A frame that is much too small will be a pain to ride.

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    A frame that is much too small will be a pain to ride. Literally. – Andrew Henle Sep 11 '20 at 14:00
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    This, definitely. 50cm is a child's bike - my seven year old rides that. Can't imagine riding it as a road bike as an adult (as opposed to a trick, BMX bike). – Joe Sep 11 '20 at 22:43
  • @Joe: 50cm frame height can easily be the right size for a 165cm woman. That’s not a child. – Michael Sep 13 '20 at 8:13
  • With a long stem it could work. A 140mm stem adds 5cm of reach compared to a default 90mm stem. That’s like going from a size XS to M. If the frame has a lot of reach to begin with it can work just fine. – Michael Sep 13 '20 at 8:16
  • @Michael A long stem will adjust reach, but there are other issues: the seatpost may not be long enough and toe-front wheel interference may be excessive due to too-short wheelbase – Argenti Apparatus Sep 13 '20 at 14:39
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While it's likely that a 50 cm frame is smaller than you'd like (as others have said), there is one situation in which it would be what you want, and that is if you want a really aggressive aerodynamic position.

If you watch competitive cyclists, you will see that they generally position their handlebars quite a bit below the saddle height, especially for events where aerodynamics are very important such as time trials and draft-illegal du/triathlons.

If you are interested in having a very aerodynamic position with a large saddle to bar drop, you will need a bike with a short "stack", and a 50 cm might be about right for you. It depends somewhat on how long your legs are for your height.

That said, even pros often find aggressive aero positions uncomfortable to ride for long periods of time, and just getting into such a position requires that you be pretty flexible, so I wouldn't recommend it if you are just getting into road biking for the first time.

For reference, I'm a short-legged 5'6" and have regularly ridden frames as small as 47 cm, but for a comfortable touring bike (almost zero saddle to bar drop) I ride a 53-54 cm.

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  • Agreed - note in OP's other question they've asked about an entry level bike, so getting riding is more likely than getting very aero. – Criggie Sep 13 '20 at 1:07

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