How to Fit a Mountain Bike: Practical Techniques and Essential Adjustments

This is the second part of a two-part series on the importance of mountain bike fitting.  In Part A we explored the reasons a mountain bike fit can be beneficial and took a dive into the categories of mountain bikes and the design implications for bike fit. In this article, we will focus on the rider and the practical considerations when it comes to how to fit a mountain bike.  This article is primarily intended for bike fitters, but riders may find relevant insights as well.

Assessing the Rider’s Needs and Preferences

“Know your client” is not only a recommendation in the financial industry for assessing investment risk tolerance, it applies to bike fitters working with cyclists as well. During the pre-fit interview, I want to learn more about the rider’s experience, ability, terrain and trail preferences, riding motivations, and any pain points or bike handling concerns they may have.  Things like:

• How long have they been mountain biking?
• What is their experience level and self-assessed competency?
• Are they riding for social fun or fitness?
• Are they competing?  For personal challenges or podium places?
• Do they prefer uphill or downhill?
• What types of trails do they enjoy vs. avoid?
• Do they have multiple bikes?

The reality of mountain bike design and fitting is that you cannot optimize the fit for both uphill and downhill.  You can either bias the fit toward one or the other or strive for a suitable all-around compromise – which will be the case for most recreational mountain bikers.  As a bike fitter, we have to marry together an understanding of the rider and an understanding of the bike. That’s easier if the two are simpatico than if they are not.

Time to get out of the background briefing and into the nitty gritty of actually doing a fit.

Setting up the Mountain Bike on a Trainer

This is not always the easiest thing to do with mountain bikes.  Because I often simulate climbing and descending during a fit, I use a wheel-on trainer placed on a platform. For a climbing simulation, I support the front wheel with a wheel riser. For descending, I remove the wheel riser and move the whole setup forward so the front wheel is off the platform and lower down.

Dealing with thru axles on trainers presents its own challenges, as you need multiple lengths and pitches.  Rear derailleur hanger mounts can add confusion, and the new SRAM Transmission rear derailleur is a beast best left untouched. The best way to deal with it and anything with a rear axle endcap with a big enough center hole is to use a Robert Axle Project axle of the same length as the rear wheel axle, and a longer (20-30mm) than supplied 5mm bolt through the RAP mounting nut.  Tighten the RAP end nut into the axle, over the pre-existing end cap or Transmission arm.

Axle hole for inserting trainer mounting nut on a bike with SRAM Transmission.

Longer than standard bolt through RAP mounting nut passes through Derailleur hanger hole and inserts into RAP axle.

Other fitters use Wahoo Kickr Roller trainers with the front MTB tire deflated to get past the front arm width limitation; or a Feedback Sports Omnium trainer, which is one of the most unstable and high risk (of toppling over) trainers to use in my experience.

Understanding and Checking the Bike Geometry

A bike from the same brand with the same model name may be completely different from one year to the next. There is far more variation in mountain bike geometry than there is with road, gravel, or tri bikes, and this is an important consideration in the fit.  Know the key geometry numbers for the bike you are working on, as this will help inform you of both the possibilities and constraints with equipment changes and body positioning.

You can go to the manufacturer’s website for current models, or search geometrygeeks.bike or 99spokes.com for current or older models, and run side-by-side model comparisons.

Check the Suspension Settings

If the suspension sag is set for the rider, don’t proceed with the fit until this is addressed. Front or rear suspension either too firm or too soft will have unintended consequences on the fit outcomes and ride quality. It doesn’t have to be perfectly dialed for the rider, but it should be close, with a sag of around 25% of the suspension travel, give or take. You’ll want to have a shock pump in your equipment arsenal for this. Sometimes I’ve solved a rider’s hand problems by simply paying attention to the front suspension sag and getting that set. Suspension sag influences and affects head tube angle, handlebar height, seat tube angle, and saddle angle.

Ensure both front and rear (where applicable) suspension are unlocked. If the rear has three options(locked, firm, soft), I’ll run the middle setting.

Feet, Shoes, and Cleat Adjustments

Although quite a few mountain bikers ride on flat pedals, attention still needs to be paid to foot size, shoe choice and fit, and foot placement on the pedals.  Achy feet when riding on flat pedals can often be linked to using regular fitness sneakers which are too soft and flexible.  MTB-specific shoes for use on flat pedals are highly recommended.

For riders using cleats, I’ve often seen them take to heart the advice to “slam them all the way back,” which, for some MTB shoes, places the cleats under the arch.  This can make the feet feel blocky on the pedals, and reduce the range and control of the foot flexion while riding  However, this can be more stable for riders with a strong preference for downhill-style riding. A short-course XC (cross country) rider may prefer a more forward position for quicker accelerations.  For recreational riders, I’ll err to a rearward bias with cleat adjustments, which means cleats closer to 5^th met head than 1^st met head. The rider should feel stable on the pedals but be able to pivot their feet freely to toe point and heel drop as needed.

Speaking of stability, stance width is something to pay attention to. Not all cleat types allow for lateral adjustment, but the more common Shimano SPD and Crank Bros cleats do. Remember that mountain bikes have a wider pedal stance width than road bikes to accommodate the wider rear tire. I personally prefer a narrower stance width and have to adjust the cleats laterally to achieve that, or I get some knee protest. However larger riders, especially those who have significant upper body bulk, often feel unstable on a mountain bike in technical terrain because their feet are too close together to feel stable and balanced. Think of an inverted triangle trying to balance on a mountain bike. A wider stance through lateral cleat adjustment, adding in a 2mm pedal washer, or going all out with pedal extenders (with caution), can provide these riders a much greater sense of stability on the bike, which translates into more riding confidence and capability.

Expect mountain bikers to show up with cleats caked in dirt.  A small pick to remove mud and grit embedded in the cleat screws and surrounds will see heavy use.

Crank Length Considerations

Yes, crank length is important in mountain bike fitting.  It’s not as critical for the average-sized and able-bodied rider, but more significant for the vertically challenged or joint impaired.  I have a whole separate post on this, so if interested check it out here.

A recurring issue with mountain bikes is that the designers and product managers are not giving sufficient attention to proportionality, and the impact (often negative) of their equipment specifications on the end user, most notably for smaller riders. This applies to crank length, handlebar width, dropper post travel, suspension travel, and bike weight.  There is far too much of a “one size fits all” approach, and one size does not fit all.

A crank length too long for the rider makes climbing harder, not easier, despite the longer lever. If a rider is suffering from recurring cycling-induced hip pain (often one side only), knee pain, or back pain, it’s likely the primary culprit is the crank length being too long. I recently had a NICA high school mtb athlete with chronic recurring hip pain who spent months off the bike and getting PT treatment, only to experience the same pain when returning to cycling. Testing crank length and switching from 170mm to 155mm resulted in an instant “cure”, and a physically and emotionally much happier cyclist.

Saddles and Saddle Adjustments 

Choosing the Right Saddle

The saddle itself is a critical component.  Far fewer mountain bikers suffer from saddle pressure issues compared to road cyclists, simply because they spend less time seated. But saddle discomfort can still occur, especially when the saddle isn’t a good match. Hence saddle testing and selection may be part of a fit. Here are a few common questions about mountain bike saddles answered:

• Are there specific mountain bike saddles?  Yes.
• Can you use a road saddle on a mountain bike?  Yes.
• Can you use the same saddle on a road and mountain bike?  Maybe. The pelvic angle and therefore pressure distribution will be different.
• Can a mountain bike saddle be too narrow or too wide for the rider?  Yes.  A saddle too narrow won’t offer good pelvic support and stability for seated riding and climbing and a saddle that’s too wide may interfere with leg clearance while moving around on the bike descending.
• What about padding? I prefer a bit more padding on the saddle for mountain bikes, as it provides a small amount of extra passive suspension.

Saddle Height and Overcoming Dropper Post Issues

All the usual rules apply—not too high, not too low… just right! However, it’s easy to over-extend your legs on a mountain bike, due to rougher trails causing upward thrust into the bike leading to micro levitation off the saddle, effectively raising the saddle height. This is more noticeable on a hardtail than a full-cush bike, but it warrants going a little lower with the saddle height on a mountain bike (and gravel bike for that matter), than what the same rider might prefer on a road bike.

But there is one major issue that often complicates setting an appropriate saddle height on a mountain bike: the dropper post design and travel range. This issue rarely shows up on medium to extra-large frames but is an ongoing problem on extra-small to small frames. Due to either ignorance or cost-saving decisions, mountain bikes used to come with the same dropper post travel across all sizes. Proportionality anyone?  A 160 cm tall rider does not use the same amount of drop that a 180 cm tall rider might use. While there’s no harm in having more dropper travel than needed, the problem occurs when the saddle is too high for the rider when the post is fully extended, and the dropper post is already bottomed out. This typically means the rider needs to install a different dropper post, often at a cost of $300-$500.

THE SEAT TUBE LENGTH IS NOT THE PROBLEM! It’s the Dropper travel.

Thankfully, most brands seem to have learned from these mistakes, but by no means is this issue entirely behind us, as demonstrated by this recent MTB review! I’m guessing this was an extra-small or small frame size.

If the dropper post is fully inserted into the frame and the seat is still too high for the rider, this is a clear sign of poor product design and spec. It’s not the rider’s responsibility to constantly struggle with their dropper post to find an approximate seat height with a partially compressed post. Mountain bike designers—take note: You can and should do better to cater to your shorter customers! Go all out with 200mm of travel on XL frames, but scale it down to 100mm on XS frames.

Saddle Setback and It’s Relevance

Bike and equipment design limit the range of setback adjustment on a mountain bike. As most bikes will have a dropper post, the post setback is zero and with no other options, whereas with road, gravel and tri, there are usually a couple of post setback options. Mountain bike saddles seem to have shorter rails as well, which further limits the adjustment range.  This is becoming a bigger issue as seat tube angles on mountain bikes continue to steepen. This forces the rider into quite an upright body position. This is fine for chugging uphill, but not ideal for racing uphill, or for endurance-style events where the rider will want more hip hinge for power production (glute and hamstring activation) and even marginal gain aero advantages.

Why is saddle setback important? The saddle’s role is to support the pelvis in a position where the rider is balanced against gravity and positioned functionally to produce force through the legs, as well as weight shift to control the bike. Without the ability to adjust the saddle properly, this can lead to a chain of compensations that sap performance. Increasingly, it’s the seat tube angle on mountain bikes that determines the rider’s position and function.

An unintended consequence of steeper seat tube angles and reduced saddle setback is that riders are often forced into a quad-dominant mode of force production. This may not be noticeable on short, steep climbs, but it becomes more apparent on gradual terrain and during long-distance or endurance-style riding. If you’re looking for a bike for long days in the saddle versus an hour or two of maximum-intensity riding, pay particular attention to the seat tube angle.

Saddle Angle: Adjusting for Terrain and Riding Style

The ideal saddle angle on a mountain bike is up for debate, opinion, and experimentation, as it also depends on the bike’s suspension, bike style, and the terrain. For descending with the saddle lowered, the saddle angle doesn’t matter much, but for seated riding(especially on side country and upcountry trails), it does.

As a baseline for a full suspension XC or trail bike, a reasonably level saddle works reasonably well. But switch to a hardtail, and with suspension sag in the front but not the rear, the saddle can turn into a nose-down saddle when weighed. This shifts more weight into the hands and can create tension in the arms and shoulders, as the rider presses into the bars to stay on the saddle instead of sliding forward. To counter this, adjust the saddle slightly nose-up on a hardtail.

For riders tackling steep climbs and then descending, they may prefer a nose-down saddle so it feels flatter and more comfortable when doing hard, seated climbing efforts. Change the bike to an enduro or downhill bike, and the rider may prefer a saddle aggressively nose-up so that they can stay on it and not slip forward for any seated pedal sections when descending.

Hand Positioning and Control Adjustments

I was originally going to call this handlebar positioning, but it’s really about the hands: where they are, what they’re holding, and how they interact with the bike’s controls.

Handlebar Width: Adjusting for Rider Sizer

Rule #1. Just because a bike ships with a bar 800mm wide doesn’t mean it has to stay that wide. Cutting down handlebars (with careful consideration) is a thing in mountain bike fitting.  Again, smaller bikes with smaller riders who have narrower shoulders and shorter arms often have trouble controlling a bike with a bar proportionally too wide.  A common cause of tension between the shoulder blades in the traps (rear neck muscles) and difficulty cornering and feeling nimble with the bike can often be traced to an overly wide bar, for the rider.

A certain amount of bar width is required to control a 29er, but I wouldn’t go narrower than 720mm and only that short on an XC bike, but 740 – 780 mm is a common viable range for those who find a stock 800mm bar too wide. Handlebar width does have a correlation with head tube angle, suspension travel, and wheelbase. For longer travel bikes (150mm and up) and slacker (under 67 degrees HTA), a wider bar is needed for steering input. However, don’t be afraid to trim bars on bikes with shorter travel (100–140mm) and steeper head tube angles (67° and up).

Handlebar or Grip Height

Where should the grips be in relation to the saddle? More important perhaps is where the hands are in relation to the feet, and for lengthy thoughts on this, I’ll refer you to Lee McCormack and his book on mountain bike fit called Dialed.  However, where the bars are in relation to the saddle is a common reference. On a road bike, this is referred to as saddle-to-bar drop. On a mountain bike, I’m looking at a saddle-to-grip drop, which is commonly a rise and not a drop.

If the bars are too low, there’s too much weight on the hands, making it difficult to lighten or loft the front end when needed to clear obstacles. A low bar position also contributes to lower back tension, fatigue, and aches, which can show up on long, grinding climbs. Too low can also pull the rider’s weight too far forward when descending steep terrain, making it harder to keep centered on the bike without overextending both arms and spine, compromising responsiveness and handling. A higher bar helps move weight back to counter steep descent angles.

On the flip side, if the bars are too high, it can make it harder to keep the front end down for grip and turn control when climbing. Too high when descending makes it harder to get weight over the front wheel for cornering traction and feeling fluid flicking the bike in and out of corners.

Finding the sweet spot is the art of the mountain bike fit and is where the rider has a good seated riding position, a range of upper body positions through hip hinging, good spinal posture, relaxed shoulder and elbows, and hands light on the grips. Bike design, riding style, body proportions, rider strength, and mobility all factor into this.

I use grips level with saddle as a starting reference point, and evaluate from there, typically using a stem sizer and testing both stem length and angle and/or spacer height under the stem.

Factors that play into this include the following:

Note that these are mostly relative terms, not absolute terms.  It’s not formula fitting, it’s evaluating a bunch of variables and seeing what shakes out as most appropriate.  Not all of these things may line up for a particular rider, so it’s deciding where the tradeoffs are for the best overall experience.

Depending on all of the above I expect to see the grip height relative to saddle height in the range of 4cm below saddle height to 8 cm above saddle height.

Handlebar Height Adjustment Considerations

How is height change achieved? There are 3 equipment things to tinker with:

• Stem angle:  This is often the least influential, as the shorter the stem the less influence a change in angle has.
• Headset spacers:  Way too many bikes have the steerer tube cut down too low when the bike is assembled, so it looks cool, but there should be at least 15 – 20mm of headset spacers to play with, and ideally up to 40mm. I’ll often see mountain bikes with only 10 or 15mm of spacer height to adjust, which is better than nothing, but not much.
• Bar Rise:  This is the big one! Bar rise can vary from 0-80mm, which is a large amount of height adjustment. Also, the most expensive fit adjustment of the three, if a new bar needs installing. XC bikes often come with a flat bar (0-10mm or rise) to encourage a more aggressive riding position. This might be too low for some, and if spacers and stem angle are used up, then a bar with more rise can make the position more upright and relaxed. Trail bikes often have 20-30mm of bar rise. This is great for many, but not for the human outliers. Riders with a lot of leg length relative to height often need a higher rise bar to counter the high saddle height. On the other hand, extra short riders on XS and small frames and overly generous front suspension travel (which increase frame stack) might feel like they are riding a bike equipped with ape hangers and need less rise so it is easier to get on top of the bars.

I’ll mention bar sweep, as this can be an important consideration for older riders with arthritic wrist joints, or riders with injury history such that wrist articulation is constrained.  A bar with a more exaggerated sweep can be helpful in these cases.

Reach Adjustments

One of the downsides of “modern geometry” on mountain bikes is that there is less available reach adjustment. Top tubes are longer, and stems are shorter for the same overall bike length. As a result, the range of adjustment is narrower compared to drop bar bikes, where you have an effective 60mm of reach adjustment. For flat bar mountain bikes, it’s now half that at most, so we can only do what can with the available adjustments. The same factors that influence bar (grip) height noted in the table above, also largely apply to reach. A lower bar often goes hand in hand with a longer reach, and a higher bar goes hand in hand (literally!) with a shorter reach. This all affects torso angle, weight distribution, and maneuverability, as relevant to the terrain and style of riding.

Regardless of the rider and their preference, the bike design is dictating the rider’s body position. Those most negatively impacted by this are the torso-dominant riders, who find themselves cramped up on the bike, or too front-heavy (due to the steep seat tube angle jacking them forward in relation to the bottom bracket). The symptoms can include increased hand pressure, shoulder tension, backaches, and difficulty breathing under exertion. The rider’s spine wants more space to open up into, but this can only be achieved by sitting more upright (and losing pedaling efficiency) not by lengthening out over the bike. That said, I’m not averse to throwing a 60 or 70mm stem on a bike that came equipped with a 40 or 50mm stem. The designers can roll their eyes. The riders thank me for it.

Speaking of stems, 35mm is the most common stem diameter now, thanks to 35mm diameter handlebars (opinion withheld), and these are only available in extremely limited lengths and angles. RaceFace offers the largest range. To solve one fit issue recently, which required both a handlebar and stem change, we changed from a 35mm diameter bar/stem to a 31.8mm to get the specs needed (more bar rise, and more stem angle).

Handlebar Rotation

The handlebar rise, reach, and sweep are all affected by the rotational position of the stem. I like to have the rider find the rotation that feels most natural for them by slightly loosening the stem bar clamp and having the rider test different bar angles. Too much rotation up or down usually feels “wrong”. A suitable rotation makes for happy wrists and even pressure across the hand grip. Having the logos of the bar brand facing forward usually indicates a neutral position, which might be perfectly fine, or the rider may like a slight deviation up or down from that. Rolling the bars forward and away from the rider serves to raise the grip position and raise the shoulders and elbows, encouraging a more aggressive turning input favored by riders charging downhill and/or working through technical terrain. Rolling the bars back toward the rider lowers the grips, and relaxes the elbows down, favored by riders on smoother trails, with more emphasis on speed and endurance, and on bikes where less steering input is needed.

To increase sensitivity to bar rotation I will remove the grips if that is easily done, and then reinstall them once the bar rotation is set.

Grip Style

It’s imperative to know that not all grips are the same, and the differences are not just in color, material, and pattern. Yes, grips should be grippy. There are also different diameter grips, and it is reasonable to suggest that a rider with gigantic hands might prefer a larger diameter grip, and a rider with small hands may prefer a smaller diameter for improved grip security.

Although most mountain bike grips are round, I’ve had great success personally and with clients using ergonomic grips with a slight support bulge under the ulnar pad (heel) of the hand. The most popular brand is Ergon. I’m not suggesting the commuter grips with huge wings, but the more nuanced mountain bike-specific models like the GA-3. These can be an important contributor to resolving numb hands on a mtb. Numb hands may come from being over gripped, or not having enough shock absorption, but the shape of the grip can be more significant than padding.  A round grip will be preferred by a more aggressive rider tackling technical terrain, while an ergo grip may appeal to general trail cruisers on single or doubletrack.

Control Positioning:  Brakes, Shifters, Dropper Trigger

Without even looking I know there will be literally hundreds of YouTube videos on how to set up the controls on a mountain bike because it is important.  All the controls should “fall to hand” (fingers actually) without either physical compensation to reach and operate them, or mental distraction to find them. That means attending to brake lever position along the bars, lever reach (yes, it is adjustable), shifter paddle positioning, and dropper trigger positioning. I like to set the bike up going downhill and have the rider in descending mode (seat down; body hinged down in the bike, elbows bent, eyeballs looking ahead) to refine the brake lever position. After all, that is when the brakes are going to see the most use.

I start with brake levers, then do shifter paddles, and finish up with the dropper trigger. Sometimes a bell is involved as well.

Because all of these ergonomic adjustments are made in a static simulated riding position in the fit studio, I always advise riders to go ahead and tweak any of these once they are out on singletrack. What can feel right in the studio doesn’t always translate the same way on the trail.

The Wrap

Although mountain bikes are fit-forgiving in many ways, mountain bike fits are some of the hardest to “get right” for many reasons, including bike and equipment design constraints coupled with the dynamic nature of mountain biking.  Many bike fitters also have a stronger background in road racing or triathlon than mountain biking and perhaps haven’t experienced the difference between a good and bad fit on a mountain bike. Let me assure those fitters that a mountain bike fit can transform the ride quality of a mountain bike in a hard-to-describe way. It can make a bike feel like a whole different bike. However, this is not obvious to mountain bikers either. Things usually have to be pretty dire for a mountain biker to get a fit. Either the bike just feels “off” and “not as good as my last bike”, or there is a recurring pain point that seems bike related. The same principles of fitting apply to mountain bikes as any other bike, but consideration needs to be given to the category of the mountain bike and the type of riding the bike is designed for, what the rider is actually using it for, and what their riding experience and intent is. More than any other type of cycling, mountain biking is about having fun and getting into a flow state – which can only happen with excellent harmony between the bike and the rider.  Fit – Fun – Flow!