How to size up a Mountain Bike – girl’s quick and dirty version

Who would ever think that you would hear those words put together: Women’s Geometry Mountain Bike. It is sweet music to the ears of women who have been riding their ill-fitting mountain bikes for years, and enjoying mountain biking in spite of problems like endo-ing off a bike that’s too big. But it seems as if all of a sudden, for 2010 many manufacturers have created real, “made for a woman’s  three dimensional body” proportioned bikes. There are many to speak of, but how do you figure out your size?

First, you should ask yourself

What are you using this bike for?

What kind of terrain is in your area?

Here are a few things to think about:

If you live in an area with a lot of quick up and downs, consider rapid rise shifters.

If your live in an area with roots, and rocks, and flowy singletrack, full suspension can be a godsend.

If you plan to shuttle, and/or live in a very steep area, consider a bike with a bit more travel (4-5 inches of suspension), and a more slack geometry.

If you have sustained sometimes never ending hill climbs, mostly smooth trail or fire road, or if budget is a big concern, then consider a hardtail.

Weight Matters

Tips for Light Riders (150-120 lbs) and Very Light Riders (under 120 lbs)

Don’t let anyone tell you that the weight of the bike is not the most important thing to you;  you on average, weigh two thirds to one half of the guy standing next to you. For controlling the front end, you only have (again, on average), about one third of his upper body strength. That front end has to be lighter for you, otherwise your shoulders will ache unreasonably, (and in a group you’ll probably be the first to tire). Steer clear of bikes that are over 30 lbs., unless it is a downhill bike.

If you are 120 lbs. or less,

Be sure to research which forks and rear-end suspension systems allow fine adjustments for your weight. This is VERY important, as there are still many that do not cater to the 120-90 lb. range.

Unless you have unbelievable strong shoulders, try to stay under the 25 lb mark. Yes, do ask for it to be weighed in front of you. Or better yet, bring your own scale. (Yes it’s true; bike shops guys love me.)

Size Matters (or not)

The labels are at best confusing, and at worst, deceiving. For instance, most men who are 5’10” have no problem finding a bike: since they are average height for a guy, they pick out a medium. OK, that makes sense.

But if you are a woman of average height (5’4″), EVEN IF IT IS A WOMAN’S bike, you will most probably fit a small or XS. But it’s possible that even the women’s small will be far too large for you. I can think of at least two women’s mtb bikes that cannot sell to 53% of the women’s market because they don’t make their women’s bikes small enough to fit women average height or shorter.

So how can I tell if it’s my  size? The best and easiest way that I have found, is with a secret weapon: with my imaginary friend, the Effective Top Tube (or EFF).

Effective Top Tube is the horizontal distance between the center of the head tube, and the center of the seat tube. Much like fitting a backpack, If you measure your torso from C7 down to the Sacrum (which is a few inches longer than the backpack measurement), you’ll have a wonderful guide to which bike will likely fit you well.

So this Woman’s Specialized Era fits a woman of average height in a Small; in fact, this size would statistically fit the majority of women. Do the buyers in local bike shops take note of this when ordering? One would hope so.

Have a friend measure your back with a cloth measuring tape, so that the measurement hugs the contours of your back. They can locate your C7 vertebra, because it is the big lump at the base of you neck, when you tilt your head forward. Then have them contour straight down to the bottom of the spine (there should be a little protuberance at the bottom, that’s the Sacrum). Cut a piece of non-stretchable string exactly this length. and take it with you when going to the bike shop. If you see a bike that you think will fit you, use the string to make sure it is the same size as the effective top tube. The Effective Top Tube measurement of each bike is also available under the “geometry” section of the bike information, and most brands list them online, usually in centimeters. Using this as a simple measuring tool can keep you clear of bikes that are not your size.

A Few Choice Words About Standover Height

Unless you ride your bike with both feet on the ground, it’s really not that important, and much less important than spine measurement.  Just make sure you can stand over your bike.

Geometry Matters

This is the easy part. Your geometry depends upon where you live, or the terrain where you will ride. Not sure? Check out what bikes other women ride in your area. Or go to, and look up your state or country. If you search around, you’re bound to find out some information about what bikes (i.e., light cross country, single speed, downhill bikes, etc.) people are riding in your area.

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12 Responses to “How to size up a Mountain Bike – girl’s quick and dirty version”

  1. Tweets that mention How to size up a Mountain Bike – girl’s quick and dirty version « Girl meets Bike, Girl on bike -- Says:

    […] This post was mentioned on Twitter by girl meets bike, Lorri Lee Lown. Lorri Lee Lown said: RT @girlmeetsbike: How to size up a Mountain Bike: Girl's quick & dirty version: […]

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  6. jane flax Says:

    What do you mean by standover? I feel like my bike is too tall for me. I have to jump forward to get off the seat. Help

    • girl meets bike Says:

      Standover height is a dimension of the bike: it is the height of the top tube, generally measured where one “stand’s over” the bike (with feet on the ground). Acording to Sheldon Brown

      Standover Height
      One of the prime dimensions of a bicycle, this refers to the height of the top tube above the ground. If the standover height is too tall for a given rider, mounting and dismounting are awkward and dangerous.

      Conventional wisdom is that the standover height should permit 1-3 inches (2-8 cm) of clearance between the top tube and the crotch of a rider straddling the frame, for road use. For off-road riding, considerably more clearance is required.

      But it’s also possible that you have a tall Bottom Bracket height, especially if you’re on a mtb.

  7. Mountain Bike Review: Specialized Safire Comp Women’s Full Suspension MTB « Girl meets Bike, Girl on bike Says:

    […] Size: 5’4″  Back Length: 545mm (find out why that’s important HERE). Weight: 120lbs (135lbs with […]

  8. Another Blog Title Says:


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  9. Garrett Says:

    Thanks for the info! I am building a bike for my fiancee and want to make sure I get the sizing right. Very helpful!!

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