How to Measure Your Sit Bones for the Perfect Saddle Fit (It’s Easy)
Try before you buy. That’s the advice bike saddle buyers have been hearing for years, and in an ideal world, it’s definitely the way to go. However, unless your local bike shop has a wall full of saddles and a generous return policy, the next best thing is to measure your sit bones and choose a saddle that’s your size. But how do you know how wide your sit bones are?
There are a few good methods you can use at home to estimate your sit bone width, and knowing this number can help you narrow down the correct saddle fit. If you have time, we recommend using more than one method of verification.
What is a sit bone?
Your sit bone, officially known as the sit bone, is “the V-shaped bone at the bottom of the pelvis that makes contact with a surface when a person sits,” according to Dictionary.com. If you’ve ever sat in a hard seat for any length of time, you’re no doubt familiar with these stiff bones that transmit body weight from our skeleton through muscle and skin to the surface.
Bicycle saddles are designed to provide optimal support for the sit bones and maximum comfort. Too narrow sit bones and sit bones are completely unsupported, resulting in excessive muscle and tissue stress on the rider. Sitting bones that are too wide can rest uncomfortably on the edge of the central channel, where saddles offer little to no padding.
How to measure sit bones with cardboard
This is both the low-tech and most accurate home method. Take a flat piece of corrugated cardboard – you know, from one of your countless online purchases – and lay it out on a flat surface. Sit on the box and make yourself really comfortable so that your sit bones form a hollow. You can even pull up on the chair to really push your butt and set bones into the surface.
Hop up and use a pen to circle the indentations. Mark the approximate centers with a plus sign and use a ruler to find the distance between the center marks. Most sit bone and saddle width measurements are given in millimeters, so convert from inches to make shopping easier. I keep a spreadsheet of all my measurements for future use.
things to see: Make sure your clothes don’t give a false result; For example, jeans rivets that pierce the cardboard instead of your sit bones. A firm chair works best, so don’t bother doing this test on the couch. If you’re not sure you did the test correctly, grab a fresh piece of cardboard and repeat it just to be sure.
The cardboard sit bone test works similarly to the high-tech, pressure-sensitive devices that saddle brands have available, so the results are generally quite accurate.
How to indirectly estimate sit bone width
Besides direct measurement, there are a few other methods to estimate saddle size and sit bone width.
WTB developed the Fit Right system to estimate men’s and women’s widths based on wrist size. Their free online tool shows you how to measure your wrist and asks questions about your riding style, body shape and padding preferences. I found the WTB result to be quite close to my cardboard sit bone test, even though my wife Leah’s WTB estimate was much lower than her actual one. One thing we found is that selecting a “Recreational” riding position compared to “Performance” increases the width estimate significantly.
With seating position in mind, SQLab strongly recommends adding up to 40mm to your sitbone measurement in its saddle sizing system. In particular, for a typical mountain bike position, they suggest adding 20mm.
Ergon uses a different set of measurements if you don’t know your sit bone width—height, weight, and hip measurement—to recommend proper saddle fit. The Ergon tool doesn’t give an exact number, but it does give a range that you can use to determine if you’re on the left or right side of “medium.” Again, the results I got seemed pretty accurate, but for Leah they weren’t, as they underestimated by a fairly significant amount compared to the cardboard test.
things to see: It’s tempting to equate body shape and height with sit bone measurements, but experts say there’s no connection. In a podcast interview about bike saddles, Sean Madsen, WTB Saddle Category Manager, said, “One of the widest people I’ve ever measured at 165mm [sit bone measurement], was an elite runner who had this boyish build, like a 12-year-old boy. So very slim, very narrow, but their sit bones are very wide. I’ve also measured NFL football players who were massive individuals who had sit bones that were about 90mm tall that were very narrow. So you really can’t tell.”
Also, keep in mind that these tools provide an estimate, not an exact measurement, of your sit bone width.
How do I use my sit bone width to find the right saddle fit?
Each brand gives slightly different specifications for saddle width. Some like WTB offer a range of sit bone widths for each size, while others like Velo simply specify the overall width of the saddle. In the latter case, be sure your The sit bone width is at least 15mm narrower than the width of the saddle to ensure you aren’t standing squarely on the edge or, worse, your sit bones are unsupported.
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If after purchasing you find that a saddle is uncomfortable, even though it is the right size, check that you have positioned the saddle correctly. For example, if the saddle is mounted too far from the bars, your sit bones could be closer to the nose of the saddle, where it tapers. Saddle angle can cause similar problems if the tilt causes you to slide forward or backward on the saddle and away from the widest point where your sit bones are supposed to rest.