mountain bike sizing

Mountain Bike Sizing and Fitting (Ultimate Guide)

mountain bike sizing

No matter which mountain bike you choose it has to match your bodies measurements as closely as possible. This mountain bike sizing and fitting guide will help you do just that.

If you get this wrong and start riding a bike that does not fit you then you will not be able to reach your full potential as a rider. Having the wrong size bike for your body will not only be uncomfortable but your riding performance will be lower.

Size and Fit For an Assembled Mountain Bike

Stand-Over Height

  • All mountain bikes have a top tube, but not all top tubes are designed exactly the same way. It is important that there is enough stand-over height so that if you need to jump off your bike you will not hit your crotch and injure yourself.
  • The best way to determine stand-over height is to stand flat foot over your bike’s top tube. From this position lift up the bike straight up until the top tube touches your crotch.
  • Then make sure that the wheels are at least 2 inches off the ground. Two inches would be the minimum. But if you jump off you will probably bend your knees. So a stand-over height of up to 5 inches or more is good as well. There is no maximum limit.
  • It is a good idea to also ride the mountain bike slowly and then jump off to a standing position as you straddle the top tube. Make sure to bend your knees as you land. Do this a few times and bend your knees more or less each time so you get a good feel for how much room you have above the top tube.
  • You will need to do this for every bike you are interested in. This is because one bike from a particular manufacturer with a listed frame size of medium will have a different stand-over height when compared to another bike manufacturer with a listed frame size of medium.
  • This happens because manufacturers usually measure frame size in different ways. Also different manufacturers have various ways of designing the top tube of their mountain bikes. Some have a slope or are curved differently. They also use different bottom bracket heights. All of these variables will cause a different stand over height for each bike.
  • All manufacturers measure the frame size from the center of the bottom bracket up to the top of the seat tube. But the measurement changes at the top end of the location.
  • Some measure to the top of the seat tube, some measure to the top of the top tube, and some measure to the center of the top tube. You can see now that each of these methods will give you a different frame size for the same frame.
  • The stand-over height of a particular mountain bike is determined by the slope and design of the top tube and the bottom bracket height, no matter how the frame size is measured.
  • Because of this, where you stand over the top tube is very important. Most top tubes slant up from the seat post to the headset. It is a good idea to straddle the top tube 1 or 2 inches ahead of the nose of the seat if the top tube has an upward slant.
  • You also have to consider the different levels of travel that mountain bikes have. A bike with suspension fork travel of 80mm or 100mm will have a lower front end than a bike with a 125mm travel suspension fork. Even a bike with a rigid fork will be lower because the frame has to accommodate the rising and falling of the front wheel.
  • On a full suspension bike the pedals need to be higher off the ground to make sure that the pedals and bottom bracket clear obstacles when compression of the suspension occurs. This makes a full suspension bike the tallest type of bike by design.
  • Finally, different wheel sizes will play a part in determining the stand over height. A 29er bike will have a higher front end than a bike with 26 inch wheels even though they have the same fork travel.  This makes it hard to determine stand-over height even from the same manufacturer when you are comparing listed frame sizes.
  • If you are looking at one bike manufacturer and two frames which are listed as large but the wheel size and or the top tube design is different then the stand-over height will be different.
  • The only way to be sure is to actually go and stand over the bike yourself. If you have stood over a few different bikes and the stand-over height is not at least 2 inches, then try standing over bikes with a smaller wheel size.

Do Your Knees Clear the Handlebars

Even when you are in the most awkward pedaling position, check that your knees will not hit the handlebars. The best way to check this is while you are seated in the saddle.

You should turn the front wheel slightly to the left and to the right and check your knees. Also be sure the balls of your feet are on the pedals and not your heels.

Handlebar Reach and Comfort

  • As you ride the bike notice how you are holding the handlebars and bar ends. Does it feel comfortable, can you reach them easily, while maintaining a slight bend in your elbows.
  • Make sure while holding the handlebars that your knees do not hit your elbows as you pedal. You should also be able to grab the brake levers easily. Check that you can lower and raise the stem so that you can set it to a level that is comfortable for you.
  • Stem height can be adjusted but only up to a certain limit. If it can not be adjusted so that it is comfortable then you may want to replace the stem with another one. Another option is if the stem is too short because you are tall then try a bike with larger wheels.
  • A bike with 29 inch wheels will have a longer fork and higher handlebars than a bike with 27.5 wheels or a bike with 26 inch wheels. Mountain bikes with larger wheels have longer forks, which therefore will give you higher handlebars. If you are shorter then go down in wheel size.

Toe Overlap

Toe overlap is the situation when you are riding slowly and you make a sharp turn and your toe hits the front tire. This can be avoided by doing a toe overlap check. Begin by sitting on the bike and pedal the crankarms until they are horizontal. Now turn the handlebars and see if your toe hits the front tire or not.

Making sure there is no toe overlap is especially important when riding slowly, such as during technical riding. When pedaling up rough terrain slowly the front wheel can turn quickly back and forth as your toes pass by while pedaling.

When you are riding at faster speeds toe overlap is not a problem because the front wheel can not be turned right or left enough at an angle to be at risk of hitting the foot. If you turned the front wheel sharply while going fast you would probably crash.

Use Body Measurements to Determine Frame Size

In order to figure out which frame is right for you, you will need to take 3 measurements. These measurements are your inseam, your inseam plus torso length, and your arm length.

Inseam Length

Stand barefoot with your feet about 3 inches apart and firmly hold one end of a tape measure up into your crotch on the right or left side. Then have another person bring the tape measure straight down to the floor.

You can also firmly pull a book up into your crotch so it is pushing on the pelvic bone. Then mark the top level of the book onto a wall. Finally, measure from the floor up to the mark on the wall.

Inseam Plus Torso Length

While standing up straight place the eraser end of a pencil horizontally against the u-shaped bone indentation just under your Adam’s apple. Then face a wall and mark the wall with the horizontal pencil. Now measure from the floor up to the mark.

Arm Length

With your elbow straight, raise your arm out away from your body at a 45 degree angle pointing downward. Have someone help you if you are using a tape measure. Measure from the wrist bone on your little finger side up to the sharp bone point, which is directly behind and above your joint.

Find Your Frame Size

  • Now that you have your measurements subtract 36 to 42cm or 13.5 to 16.5 inches from your inseam length. This length represents measuring from the top of a horizontal top tube to the center of the bottom bracket. If you want an estimated center to center size, subtract 3/4th of an inch.
  • You should subtract closer to 36cm if you are a shorter rider. Subtract closer to 42cm if you are a taller rider. Remember full-suspension bikes usually have higher bottom brackets which lower the stand-over height. So the more suspension travel your bike has the shorter the seat tube length you will want.
  • Never subtract less than 36cm from your inseam to get your seat tube length because you want to make sure you have at least 2 inches of stand-over clearance.
  • On the other hand look for a bike with 27.5 inch wheels or 29 inch wheels if you are a taller rider. You could also use a very long seat post which would seat you further back out over the rear wheel.
  • For females who have a step through bike which means it has a very long slanted top-tube upward beginning near the bottom bracket. This type of top tube makes stand over clearance a non issue.

Top Tube Length

To find your top tube length you need to know your torso length. Begin by subtracting your inseam which you found before from your inseam plus torso measurement, also found before. Now add the torso length to the arm length.

Finally, multiply the arm plus torso length by 0.47 if you are a casual rider. If you are more of an aggressive rider use 0.5. If you are in between casual and aggressive use 0.48 or 0.49.

The top tube length on a bike is measured horizontally from the center of the head tube to the center of the seat tube. This line is an imaginary line, it does not measure anything physical.

Don’t measure along a sloping top tube because your body position will not follow this measurement. Your body position goes horizontally from your butt seated on the saddle going forward with your hands reaching the handlebars.

Stem Length

If you are a casual rider multiply the arm plus torso length by 0.085. If you are a more aggressive rider then multiply closer to 0.115. If you are in between casual and aggressive then multiply somewhere in the middle. Use this as a guide. The only way to be certain is to actually sit on the bike.

Crankarm Length

In general tall riders should use a crankarm length of 180mm or longer. Shorter riders should use a crankarm length of 170mm or shorter. Usually mountain bikes are designed with a crankarm length somewhere in the middle, normally 175mm measured hole to hole.

Position of Saddle and Handlebar

We are going to determine the correct position for the saddle height, saddle setback, handlebar height, and handlebar reach.
If your saddle and handlebars are not set properly then it does not matter how good of a frame size you have chosen. You will be uncomfortable and your performance will be reduced.

Saddle Height

  • There are two easy ways to determine the proper saddle height. The first is to sit on your bike while it is mounted on a stationary trainer stand or you can have someone hold you up and keep the bike straight.
  • Now pedal forwards until one of your feet is at the bottom of the pedal stroke. Be sure to lock out your knee and put your heel on the pedal, not the ball of your foot.
  • The reason for this is when you do put the ball of your foot on the pedal at the bottom of the pedal stroke your knee will be slightly bent, as it should be. The next way to get the right seat height is by using your inseam measurement.
  • Take 1.09 and multiply this number by your inseam measurement. The number 1.09 is the length from the top of the saddle where it makes contact to your sit bones also called your ischial tuberosities, to the center of the pedal spindle at the bottom of the pedal stroke. Once the calculation is made and you have the result, adjust the seat height so it matches the resulting number you got.
  • Both of the above methods will give you similar results and they are for matching your body size to your bike. But if you are more of a technical rider you should get a dropper post. For this type of riding you will want better bike handling so a lower saddle is better for this.

Saddle Setback

Saddle setback has to do with how far forward or backward the seat is set. When this happens it will move your knees more forward or backward when you pedal which changes where the pedal power is focused.

Begin by putting your mountain bike on to a stationary trainer. Then sit on your bike and pedal the crankarms until they are horizontal. Make sure your feet are at their normal position on the pedals.

From a point just below your kneecap on the front of your knee have a person drop a plumb line. You can try using a washer or a heavy ring tied to a string for the plumb line.

The bottom end of the plumb line should make contact with the end of the crankarm. This approximates the center of rotation of the knee over the center of rotation of the pedal.

Following the plumb line down from a point just below your kneecap, your kneecap should be lined up, up to 2cm behind the end of the crankarm.

A saddle positioned at this location promotes smooth pedaling at a fast pedal stroke per minute. If the knee position is set up 2cm farther back this will promote powerful seated climbing uphill.

If the saddle position is pushed farther forward this will help to keep the front wheel on the ground while on steeper climbs. The best foot position is to make sure the ball of your foot is right over the pedal spindle or up to 2cm ahead of the pedal spindle.

If you have larger feet, position your cleats further back, as far back as possible while keeping the ball of your foot over the pedal spindle. Same thing if you have short feet but in reverse. Position your cleats further forward.

Handlebar Height

  • In order to determine the handlebar height you need to measure the handlebar height from the ground up to your handlebars. Then determine the saddle height by measuring the vertical distance from the ground up to the saddle.
  • Once you have both numbers subtract one from the other. How much higher or lower you set the saddle compared to the handlebars depends on your body’s flexibility, your riding style, overall size and the type of riding you prefer.
  • You can start by setting your saddle 10cm higher than your handlebars if you are a taller rider. Short riders will want to set their saddle lower when compared to their handlebars.
  • Raise your handlebars higher if you do lots of downhill riding or slalom riding. Beginner mountain bikers should start with handlebars and then lower them later as they become more experienced and comfortable on their bike. To start you can have the saddle 4cm lower than the handlebars, and make adjustments from there.
  • Remember, the front wheel will have a greater chance of pulling up off the ground when climbing if the handlebars are higher. Higher handlebars also mean more wind resistance at times, but you will have more comfort and control riding down on technical terrain with drop offs.

Handlebar Reach

An easy way to begin determining handlebar reach is to use a plumb line. Put your mountain bike in a stationary trainer. Then sit on your saddle and grab your handlebars as you would when riding. Pedal forward so the crankarms are horizontal.

You should be in a comfortable riding position. Have a friend drop a plumb line from the back of your elbow with your arms bent. The plumb line should go down past your knees. The plumb line should be 2 to 4cm ahead of your front knee.

Generally, more aggressive riders will want a more out stretched position than more casual type riders. The correct handlebar reach is more dependent on person preference, but the elbow plumb line measurement is a good starting point.  It is up to you from there to experiment a little and see what works best for you.

Bar End Position

  • Bar ends are not as popular on bike today but they are beneficial for those riders that choose to use them. They are usually found on cross country bike. Bar ends can be used by both performance riders as well as casual riders.
  • Performance riders use bar ends in order to increase their pulling power when they are climbing uphill out of the saddle. The most effective position for the bar end is at a 15 degree angle up from horizontal.
  • This angle increases pulling power because the bar ends are perpendicular to the forearms when you are standing on the pedals while pedaling. It also makes for a lower, more extended position when you are seated. This is more aerodynamic and reduces wind resistance.
  • The bar end angle for casual riders should be 45 degrees. This allows riders to pull with a straight wrist and a closed fist while remaining seated. You can begin with a 45 degree position, keep the nuts loose, then adjust the angle to your liking and tighten the nuts.

Inner Bar End Position

Inner bar ends are more commonly used than outer bar ends. They should be placed more inward than the grips. They are more effective when placed on wide riser bars, as opposed to standard handlebars.

You will find that your shoulders are supported more, and your arms are in a more relaxed comfortable position when using inner bar ends. The correct position of the inner bar ends is up to you and your personal preference. Determine what is most comfortable and effective by experimenting with various angles.

You can place your hands on the brakes while riding on the inner bar ends. Inner bar ends are most effective on non technical terrain. The narrow position of it allows for enhanced comfort, as well as efficient aerodynamic riding.

Mountain Bike Sizing Chart and Guide

Your Height Inseam Length Frame Size
4’11” – 5’3″ 25″ – 27″ 13 – 15″
5’3″ – 5’7″ 27″ – 29″ 15 to 17″
5’7″ – 5’11” 29″ – 31″ 17 to 19″
5’11” – 6’2″ 31″ – 33″ 19 to 21″
6’2″ – 6’4″ 33″ – 35″ 21 to 23″
6’4″ and up 35″ and up

Stand Over Heights From Manufacturers

Cannondale Trail Bike

Extra small frame, wheels 27.5, standover 71.0cm
Small frame, wheels 27.5 standover 74.6cm
Medium frame, wheels 27.5, standover 77.4cm
Large frame, wheels 29 inches, standover 82.0cm
Extra large frame, wheels 29 inches, standover 85.0cm
Extra extra large frame, wheels 29 inches, standover 88.0cm

Trek Marlin 2019

13.5 inch frame size number, wheels 27.5, standover 70.5cm
15.5 inch frame size number, wheels 27.5, standover 72.8cm
17.5 inch frame size number, wheels 29, standover 74.3cm
19.5 inch frame size number, wheels 29, standover 74.7cm
21.5 inch frame size number, wheels 29, standover 75.0cm
23.0 inch frame size number, wheels 29, standover 78.3cm

Whenever you find the stand over height for a mountain bike listed by the manufacturer make sure that your inseam is at least 2 to 4 inches or 5.08 to 10.16cm above the stand over height listed. This is a good starting point for determining which size bike you should consider first.