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I found an old racing road bike with a 50 cm frame. I would like to build it out and use it, but I am concerned it may be too small for me. I'm 5' 7.5" and I think I should be riding a 54 cm frame, but I'm not sure. Would that 4 cm difference be an issue?

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  • If it's any help I'm the same height but ride 56cm. – Dan K May 29 '20 at 8:49
  • Do you have an existing bike that you find comfortable to ride? If so, use a tape and measure from the BB axle up to the top of the saddle, staying parallel to the seattube on your known-good bike. See if the other bike can replicate this measurement without exceeding the "minimum insert" mark on the seat post. Mine's 83cm, anything less than 81cm is uncomfortably small. – Criggie May 29 '20 at 12:11
  • I'm the same height and rode a 50cm frame. I had the longest seat post & stem I could find to get a good position on the bike. It worked OK for me for many years, but as I got older, it got less and less comfortable. – FreeMan May 29 '20 at 16:07
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I'd say "proceed with caution." The main question is whether you can get your contact points where you need them. And you probably can, but there may be compromises.

  • A smaller main triangle, ridden by someone with bigger feet, will increase the likelihood of toe overlap.
  • You'll obviously need to jack up the seatpost, and if you're past the limit line, you may need to get a new seatpost.
  • You may need to put a longer stem on the bike in order to get the right "reach," and this can have consequences for handling. You'll probably want to put on a stem that has a fair amount of rise, to make of for the frame's smaller "stack." Otherwise you'll either need very good hip and torso flexibility or a willingness to ride with discomfort.

Also, for whatever it's worth, small bikes (such as 50 cm) often have innate geometry compromises in order to fit the frame around 700C wheels.

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