I'm considering getting a bike for my friend; she is interested in riding road/gravel with me, doesn't own a bike of her own, and doesn't know too much about what's available.

She is about 5 feet tall (1.5 meters) and 100 pounds (45 kilos). I believe a 47-49cm frame would be a good fit for her. Considering her small stature and the small frame size I was thinking about a set of 650b wheels.

It seems there has been a trend of 650b fitted bikes recently and that the wheel size is slowly creeping back into the market. One of the advantages is that one can fit a wider, taller tire without worrying about clearance or modifying frame geometry. I got to thinking that outfitting her with a 650b wheel set might be a viable option with some advantages over a 700c wheel set.

My question is what are the advantages and disadvantages of fitting a petite rider with a 650b wheel set, in comparison to a 700c set. I'm especially interested in bike handling, tire fitting, and frame geometry implications and considerations.

  • 1
    The main problem will be tyre availability, huge with 700, narrow with 650. There are many bicycles around with a frame size and geometry adapted to smaller riders without the need for exotic wheel sizes.
    – Carel
    Commented Apr 23, 2016 at 16:13
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    @Carel I think thats a good point and probably one of, if not the, most important decision factors. I was thinking the bike handling characteristics of a 650b would be better for someone of that stature, and that the size was becoming more common, but the availability is still pretty slim.
    – ebrohman
    Commented Apr 26, 2016 at 14:05
  • Availability depends on where you are, and your willingness to order online. There is a decent variety of 650b tyres made, and the bigger online shops tend to stock or at least list everything the manufacturers can supply. It might just take a couple of weeks longer than you expect to actually get them if they have to come from the manufacturer. My 150cm tall partner has a 24" kids BSO/MTB which has similar tyre availability issues, but I've bought tyres for it online without issues.
    – Móż
    Commented Jun 11, 2016 at 23:22
  • As a trial - do it cheap, with a used bike first. Don't go spending a lot straight up because she may not like it, and we don't need another unloved bike stored in the garage.
    – Criggie
    Commented Jun 3, 2017 at 5:59

1 Answer 1


I personally am a fan of the 650b movement. With a 650x47b tire, you get approximately the same rollout diameter that you get with a 700x28c. So as far as the distance per revolution, you are about the same with a 650bx47 as you would be on most road bikes. The benefits start with increased air volume. This leads to a much softer ride.

If you are talking about a conversion from a 700c to a 650b on a bike, there are very interesting things that happen to the geometry. Your bb drop will be greater, so clearance could become an issue. with a lower bb, however, comes a lower center of gravity. This could increase stability through corners. Another consideration is that most bikes designed for a certain sized tire. By changing that, you could affect things such as trail. A decrease in trail would help in low speed handling, but could greatly hinder higher speed stability.

One last consideration for converting a 700c to 650b is braking. If the bike has discs, then no worries. If they are v or canti brakes, then the reach may not be great enough to have the pads make contact with the braking surface on the wheel.


There are some bikes road type bikes that are designed with the 650b in mind. Some are children's bikes, but if the rider is small, a children's bike could be easier to control.

  • Extremely minor point: I believe the BB drop is defined as the vertical distance between center of hub axles and the center of the BB. Converting a bike to 650B won't change that parameter. It will change the ground clearance, however.
    – Weiwen Ng
    Commented Jan 11, 2023 at 13:03

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