Condensed answer: If your inseam is about 88cm/34.7in, then a 58cm frame won’t be too large. The final fit, however, depends on a number of factors and the best approach is to test a frame or a model similar to it before buying it.
Height and Bodily Proportions
The factors that determine a rider’s frame size are:
- Bodily proportions
Many people focus only on the height as its influence is obvious. However, analyzing height without taking into account the proportions of the body, does not result in a maximally accurate setup.
Consider the following situations:
- Rider A is 175cm tall with long legs and a short torso.
- Rider B is also 175cm tall but has a long torso and short legs.
Even though the two riders have the same height, they have different proportions that change the way a frame feels.
The length of the arms has an impact too. Longer arms may require a frame with a longer top tube if the goal is to assume a maximally aerodynamic position.
Meanwhile, shorter arms could make an otherwise acceptable frame size feel uncomfortable due to the stretched position. (This issue can be fixed by installing a shorter stem and/or sliding the saddle forward.)
Using The Inseam To Determine The Possible Frame Sizes
Due to the mechanics discussed above, the most common method to determine an estimated frame size is to rely on the so-called inseam.
The inseam is the distance between the rider’s crotch and the floor. It can be calculated by placing a book between your legs and then measuring the distance between the book edge that’s closer to the crotch and the ground.
The measuring requires a flat surface and should be done without socks or shoes for accurate results.
For a visual guide, consider watching the clip below.
Compare the inseam data to the table below:
|Inseam||Road Bike Frame||MTB Frame|
Conclusion: If your inseam is about 88cm/34.7in,, then a 58cm frame is considered an acceptable fit. If your inseam is 84cm or less, then a 58cm frame is probably too large for you.
That said, the following factors should be taken into consideration too.
- Variations Between Brands
Brands often measure frames differently. Thus, a 58cm frame from one brand could be larger or smaller than a 58cm model from another. For that reason, the safest approach is to test the frame before purchasing.
If that’s not an option, you can search for information about the frame from previous users. Some may indicate that the frame rides “smaller” or “bigger”.
Even though the table above is quite useful for general direction, it cannot possibly account for all the factors of the equation (frame variation, rider flexibility, anthropometry, riding style….etc.)
- A Good Fit Cannot Always Be Found In a Table
If you base your entire bike fit on tables, the real-world result could be less than ideal.
FAQ: What can I do if my frame feels too big for me?
Other than getting another frame, the options are:
- Lower the seat post to the point where your knee is ever so slightly bent when the pedal is the closest to the ground.
- Take an Allen key (usually 8mm), unscrew the clamp under the saddle, and slide the saddle closer to the handlebars.
- Get a shorter stem if you feel “stretched when reaching for the handlebars.
- Replace the handlebars with one of the following – butterfly, North road (swept back handlebars), or flat bars/risers.
The above changes can definitely make a difference, but only when the frame size is inappropriate within reason.
If you are built for a very small frame, the adjustments will not be effective.
FAQ: How tall are the professionals who ride 58cm frames?
Usually, the pros ride slightly smaller frames (sometimes surprisingly small) than what one might expect for their height (learn more). The purpose of small frames is to keep the handling snappy and the overall bike agile and easy to control.
Very few professionals ride 58cm frames. 54cm and 56cm are more common. Usually, the height of professional cyclists with 58cm frames is 6’2″/188cm or above.