Javier

Good evening,

It seems there are a few ways to measure your inseam (to discern frame size). Some methods ask for measuring while wearing the (potential) bicycle shoes, other methods ask for measuring while barefooted. And some methods are not clear about how wide to keep your feet apart while measuring inseam.

Is there a "tried-and-true" method of measuring inseam?

Thank you in advance!!

Carbonfiberboy 

One measures inseam to get a number to put into a calculation for something. Therefore use the method specified for the calculation. If no method is specified for the calculation, do some more research. There's a method prescribed for every fit calculation, or if no method is prescribed, don't use that calculation - waste of time.

I think the most used calculation is the Competitive Cyclist Bike Fit Calculator, though it often raises more questions than it answers, i.e. there's no one correct formula for all bikes and riders. It does give very good directions for how to take the measurements.

Road Fan

OP is asking about a measurement. There are old ways and there are new ways, but one I've seen a lot is as follows.

Stand barefoot on a hard floor with your back against a wall. Don't wear bulky trousers like blue jeans: compression shorts, cycling shorts, yoga shorts or ... be creative. Pull a large book up between your legs as hard as possible so it presses against your sit bones. Press the book against the wall and have an assistant measure carefully (to the sixteenth of an inch or a millimeter would not be bad) from the top of the book to the floor. Write it down. Measure several more times and use the largest value. That is your cycling inseam length, a best-estimate of the distance from your sit bones to the hard bottom of your heels with straight, locked knees.

Many bike shops have a few apparatus around for helping with this measurement. You can do it that way, or at home using the above procedure and a family member, friend, or significant other as an assistant. Cats and dogs tend not to contribute very well.

This is just one way to measure your cycling inseam. It isn't a fit calculation method or a fitting system. You need a bunch of numbers for those, and this gives you only one of them. But, it is essential.

Wildwood

+1 on the @Road Fan technique, but i use a yard stick instead of a book, the long extention between my legs (ooopps...) lets me make sure the measurement is taken perpendicular to the vertical. No assistant needed .

Carbonfiberboy 

OTOH, the Comp. Cyclist system specifically says to do it in cycling shorts and apparently, in socks, feet 8" apart. It's like I said: do what the calculation requires. Garbage in, garbage out.

Road Fan

lots of variations! Zinn had one where he used a 2” dowel as a pull up, with a line level glued to it to sense levelness. I don’t recall how he did the vertical measurement, which is the key point of the assistant, make the measurement while I hold everything together! With a big enough book I can mark the wall with a pencil or use a plumb line to capture the vertical distance, then measure it with a tape.

Road Fan

The 8" spacing would tend to mimic the stance while feet are on the pedals, so I like this approach - if you have to pick an arbitrary criterion, it's probably better if it mimics the actual riding position. If you instead assume you should place your feet shoulder width apart that might be a little wider. If you set up the triangles on paper and calculate the error introduced by making it shoulder width versus 8" (or vice versa) I'm sure the difference will be very small and for my fitting I would neglect it. I also suspect the difference found with actual cycling socks versus barefoot is less than 1 mm, but ... I don't really know. I don't fit other people so I don't have to be Right and Correct. I just have to make my body happy. One reason I take such a lax attitude is that after I have computed the starting point for saddle height, I'm going to (following Carbonfiberboy's often-stated and excellent advice) adjust the height based on riding, to optimize my hip rocking and whether I am stable on the sit bone platforms of the saddle, and have managed pressure distribution against my undercarriage.

john m flores 

The book, if placed flat against the wall, ensures that the measuring device is horizontal. A yard stick can be inadvertently tilted upwards or downwards.

Road Fan

Yes, indeed! Those problems are why Lennard Zinn's technique uses a thick dowel that will be hard to bend, and a sensitive level on the dowel to see when it's level. A very resourceful person could rig up a device to perhaps allow a plumb line to be attached so that you could capture the vertical distance without an assistant and then measure the length of string with the bob and get the PBH. But, more steps allows for more errors.