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Condensed Answer: In general, a 54cm/21-inch frame can work just fine for an 182cm/5’10” rider, but in some cases, a slightly larger frame (56-58cm) will be needed.

The unique anthropometry of each rider and the non-consistent frame sizing among brands make it more difficult to make such predictions as there are too many variables.

Inseam vs Height

The height of a person is important when it comes to the frame fit, but it’s not the only factor. The proportions of the rider are crucial too.

For example, two riders can be 182cm/5’10” tall but with totally different proportions. One can have long legs in relation to their body while the other has a long torso (and thus shorter legs).

Those two individuals will have different needs despite being the same height.

For that reason, the inseam of a rider is more indicative of the needed frame size.

• What does the inseam stand for?

When it comes to pants sizing, the inseam is the distance between the crotch and the top part of the ankle. In cycling, however, the inseam is measured from the crotch to the floor.

A common method is to use a book between your legs as shown in the video below:

Once you have the inseam data, you can use it to find the recommended frame size for that value.

Conclusion: If your inseam measurement is about 82cm/32.2 inches, then a 54cm/21-inch frame could fit you just fine.

Other Aspects That Affect The Fit

The length of the arms is important too as it has a direct impact on the rider’s reach. The larger the frame, the longer its top tube gets.

As a result, the handlebars get further away from the rider. If the rider has shorter arms and long legs, then the frame may fit his legs just fine but end up being with a less-than-ideal reach.

In that case, it would be wise to consider getting a slightly smaller frame and compensate for it via the adjustments of the saddle and seat post.

FAQ: Is it better to get a frame that’s slightly bigger or smaller?

In general, it’s better for a frame to be slightly smaller than slightly bigger. A smaller frame can be made bigger via the following modifications:

• Elevate the seat post
• Move the saddle backward
• Get a longer stem
• Get a different style of handlebars (if your cycling discipline permits it)

Fun fact: Many professional cyclists ride frames that are smaller than what a classic chart would say. The purpose of this approach is to keep the bicycle more lively and snappier. You can read a full article on the topic here.

FAQ: Where can I find the size of my frame?

In most cases, the size of the frame is indicated on the seat tube. If it’s not, just measure the seat tube itself from the bottom bracket to the connection point with the top tube.

FAQ: Why is MTB frame sizing smaller for the same person?

As you can see in the chart above, a person with an 82cm inseam can fit on a 54cm road frame but needs a 19″ MTB frame.

The reason for the different sizing is found in the use of the two bicycle types. MTBs require a greater standover height than road bikes. 

The standover height is the distance between the rider’s crotch and the frame’s top tube.

MTBs are designed for aggressive riding including technical descents and stunts. The greater distance between the rider’s inseam and the top tube reduces the chance of contact between the rider’s genitals and the top tube. It also makes it easier to lift the front wheel and perform tricks such as manual and bunny hops.

For that reason, MTBs have smaller frames (shorter seat tubes) and have their seat posts sticking out.

At the moment, the common trend is to use a dropper seat post and lower it for technical descents.

During the longer and flatter sections, the seat post is elevated via a control on the bars for more comfortable pedaling.