Condensed answer: A 17-inch MTB frame will fit a person with an inseam measurement of about 82cm or 32.3 inches. In a specific context, taller individuals with a longer inseam can also use a 17-17.5″ frame.
The Effect of Height and Proportions on Frame Sizing
It’s obvious that taller people tend to ride larger frames, but height is not the only factor. The bodily proportions of a rider have a strong influence too.
Two people can have the same height but a different skeletal structure. One can have a long torso and short femurs while another could have a short torso and long femurs. Others will be somewhere in between.
If you have a long torso and short legs, you will probably need a smaller frame than someone of the same height but with long legs and a shorter torso.
Arm length is important too because it directly influences the back angle of the rider.
Longer arms make the back angle more horizontal whereas shorter arms force the rider to bend over more and thus flatten the back angle.
The Inseam = Crucial Measurement
Because of the factors explained above, the standard way to come up with a frame size estimate is to use the so-called inseam measurement rather than the rider’s height.
The cycling inseam is the distance between the rider’s crotch and the floor. The inseam should be measured on a flat surface with straight legs and without shoes.
One of the options is to use the book method which goes like this:
1. Put a book between your legs all the way to the crotch (there should be a very slight contact)
2. Measure the distance between the higher book edge and the floor with a tape measure.
Once you have your inseam, find it in the chart below.
Conclusion: If your inseam is about 82cm/32.3 inches, then a 17″ frame will probably fit you just fine.
The next table shows frame sizes based on height. (As already mentioned, the inseam method is more accurate, but it’s still helpful to study the relation between frame size and height.)
If your height is about 5’6″-5’10”/168-178cm, then a 17″ frame could be an acceptable fit for you.
FAQ: Is there a way to make a 17″ frame feel larger?
The classic method of making a smaller frame feel larger is:
- Slide the saddle maximally towards the rear wheel to artificially elongate the top tube.
- Get a longer stem to increase the reach.
If those adjustments are not enough to put you in a comfortable pedaling position, then a frame of a larger size will have to be provided.
MTB Sizing Doesn’t Have to Be Extremely Precise
I am about 6′ tall and have long femurs. According to the charts I should be using a 19-20″ frame. However, the frame of my hardtail is about 17.5″.
I chose this size intentionally because I wanted to use my bike not only for commuting but for tricks too.
I can’t complain. The frame worked just fine for me. I learned the bunny hop and used the same bike for a long 110km tour with zero issues.
That said, I have no doubt that a slightly larger frame would have been more optimal for me if pedaling was the only goal.
My experience taught me that MTB sizing doesn’t have to be brutally precise. As long as the frame isn’t insanely small for your height, you will be able to find an acceptable (maybe not ideal, though) setup.
Road bikes are different, however, as they are meant to be aero-efficient pedaling machines. For that reason, road cyclists obsess over getting the most ideal bike fit. The goal is minimal drag and maximum power output – those cannot be obtained on a frame that doesn’t fit you precisely.