Mountain Bike Size Chart, Fit & Frame Geometry

Mountain Bike Size Chart

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How Are Mountain Bikes Sized?

Sizing Up Or Sizing Down Your Mountain Bike

So you’ve matched your height to a manufacturers mountain bike size chart, and you’re right on the edge - what do you do now? Sometimes you’re in between mountain bike sizes. Here’s a few tips on when to size up or size down your mountain bike when you don't quite fit on the mountain bike frame size chart.

What You Get for Sizing Up

When it comes to mountain bike sizing, Reach tends to be what changes more from Small to Large than Stack. Almost all mountain bikes are trying to get as low as possible to buy the rider range of motion in the cockpit of the bike so you’ll see a lot of bikes with an increase in Reach.There’s also a minor corresponding increase in Wheelbase as the whole bike itself gets a little bit longer, so you get the benefits (and pitfalls) of a longer mountain bike.

Also, if you happen to have a proportionally longer torso, you’ll want to size up in order to get a neutral fit, since Reach is primarily what’s affected by the size.

Flexibility and range of motion in your hips is also something to consider. If bending over and touching your toes sounds like a tall order, a longer bike is going to be a bit more taxing to maintain a low and aggressive riding position. On the other hand, if you know the difference between your Tadasana Pose and your Lotus Pose (AKA: you’re a supple yoga leopard), a larger size will reward you with a more aggressive riding position.

To sum up: If you’re flexible, longer in the torso and like to monster-truck over your terrain rather than whip or flick your way around it, size up your mountain bike.

What You Get for Sizing Down

Conversely, a smaller sized mountain bike will have a shorter Reach and a slightly shorter Wheelbase. Stand-over height will be a tad lower and you might have to extend your seat-post a bit in order to get to your pedaling position, but it’s a pretty minor consideration when it comes to being between sizes.

If you’ve got proportionally longer legs than average, lack a bit of flexibility or generally like to be more upright , you may be a bit more comfortable on a shorter size.

Additionally, a shorter Wheelbase will ride more nimbly and while the longer cockpit provides a really aggressive riding position, low and aggressive riding positions are tiring to be in, so consider your fitness, endurance and ride length. Shorter bikes are easier to be on for long periods of time.

To sum up: If you like a more nimble and whippy ride, are a bit less flexible, are shorter in the torso or are looking for a more casual riding position, size down your mountain bike.

Demoing Mountain Bikes

Now that you know what happens when you size up and down, go test ride some bikes! Just like 2 medium shirts from different brands don't fit the same, similar bikes from different brands will also fit and feel differently. You may size up with one brand and size down for another so go out there with an open mind, a good idea of your riding style and how you’ll use the bike, and find the best fitting bike for you!

Mountain Bike Geometry Measurements

Mountain bike geometry is literally the shape of the bike. The overall shape and geometry of your mountain bike is made up by several different and important measurements. These measurements are important when discussing the fit, feel, and style of a mountain bike, and are often proportional to the style and terrain your bike was intended to perform on.

The two main measurements that will affect the way that your bike will fit are Reach and Stack. Keep in mind that while these terms come from the road, triathlon & time trial world, those numbers won’t port over from your tri-bike to your mountain bike.

• Reach
• Stack
• Head (Tube) Angle
• Chainstay Length
• Bottom Bracket Height
• Wheelbase

Mountain Bike Reach

The reach measurement on a mountain bike is the horizontal distance between the bottom bracket and the center of the head tube. This is arguably the most important figure for mountain bike fit because it affects the length of your bike’s cockpit when you’re standing on the pedals and how much range of motion in your hips you’ll use up in order to achieve a good, strong riding position. Too long of a reach and you’ll be stuck leaned over and stretched out, too short of a cockpit and your weight bias will shift too quickly and leave you in a position that’s overly upright.

Mountain Bike Stack

The next important mountain bike geometry measurement is stack, the vertical distance between the bottom bracket and the center of the head tube. This is primarily a gauge of seated pedaling position and relative handlebar height. This can be adjusted to a degree, with headset spacers & handlebar rise for increased stack height. For mountain bikes, where geometry is based on the aggressive riding (standing) position with the seat down, Reach trumps Stack as the primary mountain bike fit dimension.

Mountain Bike Head Tube Angle

Head angle, or head tube angle, is the angle between the front fork of your mountain bike and the ground. Although there are other parameters that go into what makes the front wheel behave, (fork offset, trail, etc) this is the key metric that the industry uses to determine front-wheel characteristics.

A “slack” mountain bike head angle is a lower number (eg: 65°) relative to a “steep” head angle (eg. 70°). A slacker head angle will, in general, be more stable at high speeds as well as feel more comfortable on steeper (downhill) terrain. Conversely, your bike will steer lazily and flop from side to side on uphill terrain - you will need to make more body position changes in order to tackle steep up hills, such as keeping your weight on the front tire so you don't wheelie yourself off the trail.

Mountain bikes with steep head angles feel like the front wheel is planted and steer nimbly on uphill terrain, while feeling twitchy and unstable on fast downhill terrain. If your inclinations (no pun intended) are towards pedaling uphill, you’ll pick a bike with a steeper head angle and vice-versa if you like to head down.

Mountain Bike Chainstay Length

Chainstay length preference is personal to each rider. This measurement effectively determines the distance between the rider’s center of mass and the rear axle. Bikes with short chainstays have the rear wheel closer to being “under” the rider. Short chainstays allow the rider to be more dynamic with their weight. This means easier manuals & wheelies and a general ease of getting the front wheel off the ground.

This comes at the expense of overall Wheelbase length, which contributes to stability at speed and over rough terrain. (Consider that unintentional wheelies while going uphill aren’t generally a desired trait.) If you want your bike to ride nimbly and like wheelies & manuals, short chainstays are your friend. If you prefer stability, go for a bike with longer chainstays.

Mountain Bike Bottom Bracket Height

The bottom bracket height on your mountain bike is the distance between the ground and the center of your cranks. Some manufacturers refer to “Bottom Bracket Drop,” which is the vertical distance between the wheel axles and the bottom bracket. They effectively measure the same trait of the mountain bike, which is how low your center of mass is.

Just like your lowered sports car, bikes with low bottom brackets corner like they’re on rails and transition from turn to turn effortlessly. The tradeoff here is that the earth isn’t flat and trails aren’t typically paved smooth; the lower your bottom bracket, the more likely you’ll clip rocks, roots or logs you’re trying to hop over.

If you’re a skilled and savvy rider, you can make sure your pedals aren’t down when passing over obstacles, but that means not pedaling over rough terrain and can be difficult to do when you’re brain’s starved for oxygen on a climb or you’re traveling at blinding speeds.

Mountain Bike Wheelbase

There are a lot of factors that contribute to the wheelbase length on a mountain bike including Head Tube Angle, Reach, and Chainstay Length, which we’ve discussed previously. Total wheelbase is something of a culmination of all of these factors.

The gist of wheelbase is that increasing the distance between your front and rear axles will increase stability, whereas shortening wheelbase will make a bike more maneuverable. Take note of where that increased wheelbase is coming from (Head tube angle? Chainstays?) and reference the above measurements to see how that’ll additionally affect the overall ride of your bike.

Conclusion

That’s a lot of information and though we've only covered the basics, this should give you enough background to pick the right size mountain bike and figure out how a mountain bike should fit.

That said, there is still no substitute for getting out there and test riding some bikes. When it comes to choosing a mountain bike, there’s always a little bit of an unexplainable, intangible connection to a particular ride. It just fits and feels right. So take this info with a grain of salt, throw your leg over a couple of bikes, and go ride! If you’re in the area of one of our locations, check us out and come in for a test ride!

Need a tune up? Bring your bike in for maintenance at any of our flagship locations for assistance:

• Seattle Bike Services
• Portland Bike Services
• Denver Bike Services
• Salt Lake City Bike Services
• Snoqualmie Pass Bike Services
• Whistler Bike Services

Learn More With Our Other Bike Guides:

• Mountain Bikes - How to Choose
• Mountain Bikes - Size and Fit Guide
• Mountain Bikes - How to Get Started Mountain Biking
• Mountain Bikes - How to Choose a Wheel Size
• Mountain Bikes - Suspension Basics
• Mountain Bikes - How to Choose a Mountian Bike Dropper Post
• Mountain Bikes - How to Choose MTB Handlebars
• Mountain Bikes - How to Choose MTB Pedals
• Mountain Bikes - How to Change Bike Pedals
• Mountain Bikes - How to Clean
• Mountain Bikes - How to Bleed SRAM Brakes
• Mountain Bikes - How to Bleed Shimano Brakes
• Mountain Bikes - How to Convert to Tubeless Tires
• Mountain Bikes - How to Replace Internal Cable Housing
• Mountain Bikes - How to Adjust Your Rear Derailleur
• Mountain Bikes - How to Bleed a RockShox Reverb Seatpost
• Mountain Bikes - How to Service Fox and RockShox Fork Lowers
• Mountain Biking - What to Bring Mountain Biking
• Mountain Biking - What to Wear Mountain Biking
• Mountain Biking - How to Choose Knee Pads
• Bikes - Size and Fit Guide
• Gravel Bikes - How To Get Started Gravel Biking
• eBikes - Classes, Features & More
• eBikes - Where to Ride eBikes
• Bike Accessories - Helmet Size & Fit Guide
• Bike Accessories - How to Choose Bike Shoes
• Bikes - How to Choose Bike Tires
• Bikes - How to Change Bike Pedals
• Bikes - How to Repair & Replace a Bike Chain
• Bikes - How to Choose Accessories
• Bikes - Urban Riding Tips
• Travel & Destination Guides - Where to Mountain Bike

Learn About our Favorite Bike Gear:

This is evo. We are a ski, snowboard, wake, skate, bike, surf, camp, and clothing online retailer with physical stores in Seattle, Portland, Denver, Salt Lake City, Whistler, and Snoqualmie Pass. Our goal is to provide you with great information to make both your purchase and upkeep easy.

evo also likes to travel to remote places across the globe in search of world-class powder turns, epic waves, or legendary mountain biking locations through evoTrip Adventure Travel Trips. Or, if you prefer to travel on your own, check out our ski & snowboard resort travel guides and mountain bike trail guides.

Still have questions? Please call our customer care team at 1.866.386.1590 during Customer Care Hours. They can help you find the right setup to fit your needs.