The Importance of Mountain Bike Fitting: Benefits and Design Factors That Influence Fit

Introduction and Bike Characteristics

As a bike fitter, I see many cyclists on a lot of different types of bikes, and predictably these bikes are more often road, gravel, or tri bikes.  But what about mountain bikes?  Yes, I fit for those too, and am always delighted when someone comes in with a mountain bike for a fit session.  But it is infuriating when I hear from clients in the fit studio that when they ask their LBS about getting fitted on their mountain bike, they are laughed at and told it’s not relevant or necessary.  If you are in a local bike shop selling mountain bikes, please do your customers a favor and come up with a more respectful and helpful response!  Mountain bike fitting is a thing and can significantly improve a rider’s experience, helping them stay on their bike and avoid crashing out of the sport.

Why is Mountain Bike Fitting Important?

I first rode a mountain bike over 30 years ago and immediately fell in love with the sport.  One other guy I rode with on that first day fell off his bike and broke an arm within 5 minutes  (and that was just in the parking lot), so although not everyone takes to it easily, it can be made safer and more enjoyable with practice, skill development, and in many cases, a bike fit.

The need for skills development and practice may be obvious. The need for a bike fit, however, is not. The nature of mountain biking often disguises a lot of mis-fits.  Cushy suspension, dropper posts, wide low pressure tires, rest and scenery appreciation breaks, and the dynamic nature of the riding with more time off the saddle can all hide the symptoms of a poor fit.

Although mountain bikes and mountain biking are more fit-forgiving than other types of bikes, this doesn’t mean that mountain bike fitting is irrelevant. Add to this the mentality that if you don’t hurt, you didn’t ride hard enough, and it’s easy to see why the average LBS (local bike shop) employee laughs at the idea of getting fitted on a mountain bike. Some years ago I pulled the trigger on a new mountain bike purchase after much research, evaluation, and careful selection.  The bike handled like a crazed pig.  I was, shall we say, “disappointed”. However a fit session on this bike from a colleague literally transformed the bike into sheer riding pleasure and joy.  The difference in ride experience the fit session made was a true revelation.

So, what benefits can mountain bike fitting provide?  There are three broad areas (the 3 C’s):  Control, Confidence, and Comfort.

Control

A good relationship between the bike and the rider will translate into improved bike control a.k.a bike handling.  This is the single biggest benefit and outcome for most mountain bike fits.

• Uphill and downhill cornering is easier
• Traction is improved
• Weighting or unweighting hands or feet is easier when appropriate
• Weighting or unweighting the front or rear wheel to negotiate technical terrain is easier
• Intuitive access to the handlebar controls: brake levers, gear paddles, and dropper trigger keeps mental focus on the trail and not the equipment operation
• More durability and less fatigue on longer / harder rides

Confidence

Novice mountain bike riders in particular often lack confidence, and this is made worse if the bike feels awkward to maneuver.  Improving the ability to control the bike does wonders to improve confidence riding the bike. While this needs to go hand in hand with skill development, it’s difficult to learn and practice mountain bike skills on an ill-fitted bike.

Better control and more confidence = fewer unintended dismounts (aka crashes).

Comfort

Although the aforementioned characteristics of mountain biking bring more intrinsic comfort than other types of bikes, discomfort often drives a mountain biker in for a fit.  Common complaints include:

• Tight and achy lower back
• Upper shoulder or neck tension
• Numb hands: which may show up on long descents, or long flat rides
• Knee aches and twinges
• Quad or hamstring overload

These are the sort of issues that can usually be resolved with a bike fit, provided they primarily only show up during or immediately after rides.

Factors Influencing Mountain Bike Fit

Before examining the specifics of mountain bike fit, it helps to step back and consider some of the influencing factors:

• Bike design/geometry
• Body size and proportions
• Physical considerations: injury history, aches and pains, strength, mobility

In this article I’ll focus on the first point, as the other two apply to all types of bike fit.

Mountain Bike Design and Geometry

Since their inception, mountain bikes have changed and diverged into a multitude of categories based on primary use intention: dirt jump, trials, cross country, trail, all mountain, enduro, slopestyle, free ride, and downhill.  There are probably more!  However, for most recreational riders, the all purpose mountain bike is a “trail” bike.  Want to bias to less weight, easier to ride uphill, and maybe race? Then cross country it is.  Prefer to bomb the downhills?  Enduro bikes cater to this crowd.  I’ll focus on these 3 main categories and look at the RELATIVE differences between them.

The below tables present some generalizations, for which exceptions can always be found.  With that in mind, let’s look at some important features and geometry metrics.

Quick summary: As the bike design moves towards enhanced downhill performance, the frame reach gets longer, the stem shorter, the seat tube angle steeper, the head tube angle more relaxed (slacker), the suspension travel longer and beefier, and the bike heavier.  Here is an example from mountain bike brand Pivot, and their current lineup, showing 3 models across these 3 categories.

For a web browser view, click here

In the above comparison notice how the frame reach gets longer, the stack gets higher, the head angle gets slacker (smaller number), and the seat tube angle gets steeper (bigger number).  Although Pivot (and other brands) have done a bit of a wobble here, as the XC bike has a steeper STA (seat tube angle) than the Trail bike.  We’ll talk about that in a moment.

All of these design variables are intended to change how the bike handles and how you ride it.

Design changes in mountain bikes have been driven by several factors:

• Improve descending capability.  Riders can go downhill faster, with more control, and the bike has more intrinsic ability to forgive mistakes in line choices and weight distribution, translating to fewer accidents.  This has been achieved by a combination of a slacker head tube angle and a longer travel front suspension. The taller frame stack is partly a result of having to accommodate more suspension, but a consequence of both is to push the bars back toward the rider.
• Maintain climbing capability. Keeping the front wheel planted and steering controlled while getting body weight over the pedals and bottom bracket (BB) is crucial for propulsion without having to move onto the nose of the saddle. This has been achieved by steepening the seat tube angle to bring the saddle forward when the bike tilts uphill, which in turn brings the rider closer to the bars.

In any given size both these “drivers” shorten the saddle-to-bar distance. The solution has been to increase the length of the top tube and frame reach.

However, a slacker head tube angle also slows steering input. To counter that, stems get shorter as head tube angle gets slacker, resulting in more saddle-to-bar distance in the frame and less in the stem.  The design variations between these three categories of mountain bikes mean they all ride a bit differently, as summarized below.

None
None of these are absolutes, but are terms of relative comparison.  Speed of travel also affects this.  A longer travel bike comes more alive and responsive the faster it is ridden, and can feel cumbersome at low speeds.

Bike Fit Implications of Geometry

What’s all this got to do with fit?  Well, the bike category and its underlying geometry significantly influences rider position, how you ride the bike, and how you pedal the bike.  You don’t ride an enduro bike in quite the same way you ride a cross country bike, as the bike geometry and handling characteristics will demand a somewhat different body position and riding skills.

Hence the style of bike, the style of riding, and the types of trails the rider prefers must be factored into an understanding of the bike-to-body relationship, the mountain biker’s fit issues, and the achievable fit position.

For charging along the flats and uphill, a cross country bike requires more hip hinge and a forward leaning torso, relative to a trail bike, in which the rider is more upright, and more so again on an enduro bike.  Try and ride an enduro bike like a cross country bike and it isn’t going to feel the same.  In the land of cross country race bikes, bike design has been heavily influenced by the increasingly technical world cup courses, featuring short punchy climbs and rock and drop infested descents. This has led to the enduro-fication of cross country bikes, and this is likely why an XC bike like the Pivot Mach 4 SL has a steeper seat tube angle than the trail bike from the same brand.  Although this will work for riders charging the aforementioned courses, this design backfires when it comes to general trail riding and 50 and 100 mile marathon events like the Leadville 100, and Chequamegon as it does not facilitate a more endurance orientated riding position.  It’s increasingly difficult to find a cross country bike designed for, well, cross country!

As mountain bike designs appear to be driven by marketing, you would have to be living in a remote Himalayan cave not to have been subjected to pitch phrases like  “modern”, “progressive geometry”, “longer and slacker”, ad nauseam over the past few years.  All of these marketing phrases are designed to convey “newer and better – buy now!”

To be sure, there have been some great advances in bike and equipment design, but not all that is new is better, and not all that is old is obsolete.  Current mountain bike designs remind me of the ski industry 15 years ago, when wider skis were found to be easier to ski, leading to yet wider skis.  The design mentality seemed to be, “Well, if wider is better, more wider must surely be more better!” (For you nonskiers, it’s not).  Things got way out of hand there for a while but eventually settled down as designers and skiers realized there wasn’t one design solution to all ski terrain and styles.

Mountain bike designers don’t seem to have had that realization yet, so we are seeing some truly mongrel contraptions trying to be all things to all people – and failing.  Not that there is any admission of that, but Joe and Jane average weekend riders who make up the bulk of the market are too often riding bikes too heavy, with too much suspension, with not enough fit adjustability, that are hard to push uphill and boring to ride downhill.  And this is one reason gravel riding is thriving – It’s akin to 1990’s mountain biking. Sketchy and Fun!

To be continued with a follow-up article on the Practical Implications of How to Fit a Mountain Bike!