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MTB Fit
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Does anyone have interest in/information about mountain bike fit protocol? I have been working with several local triathletes in The Woodlands, TX and many of them compete in the X-terra events as well. I am very confident with my triathlon/tt fit skills and learning more every day on road fit, but I'm weak when it comes to MTB fit. I would love to share resources and discuss if anyone else is interested.

Audaci Favet Fortuna
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Re: MTB Fit [Austentx] [ In reply to ]
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Some of this may be obvious but here goes… Knee angle stays about the same for road and mtb. Generally, the rider is set up a little further aft (however you may measure that) than a road position. Reach is much shorter, and bar drop is far less aggressive; therefore, hip angle is more open. The key is allowing the rider to position themselves not only for climbing, but also for technical downhills where they may need to move their center of gravity off the back of the bike.

That’s all pretty general, but there are a few keys to keep in mind. Mountain Bikers experience many extremes during a ride or race, both in terrain and position on the bike. Cadence can vary substantially depending on terrain, and foot position through the pedal stroke will also tend to have more variability depending on the steepness of a climb. If a rider pushes his/her heel down more to power up a steep incline, than knee extension will increase as well. Of course, position on the saddle also varies more on an mtb both fore and aft; these extremes will also create different knee angles.

Whether or not you’re fitting a hardtail or full suspension bike must certainly be taken into consideration. A full suspension bike, depending on how active the suspension, will have a constantly changing saddle height and fore/aft position as the rear shock works through its stroke under power and over terrain. This, in turn, changes the rider’s position.

An mtb position is anything but static, and fitting in a controlled environment will simply not provide enough changes in position to mimic what a rider will experience on the trail. You have to prepare for less accuracy, and more of a general position, unless you go out in the field and work with an athlete in an mtb environment. It’s a little more trial and error.

In the past few years we’ve seen an explosion of mountain bikers coming in as the sport has seemingly “discovered” bike fit all of the sudden. A couple of things we’ve consistently learned and/or experienced. 1. Elite mtb’rs always want to try a lower bar position, but rarely stick with it; it simply does not allow for a good overall position for technical riding. 2. Measuring power while an athlete rides over a short pre-determined course over and over again can be beneficial as it allows you to track and evaluate positional changes. 3. It will likely take a few sessions to dial in an mtb position as the athlete rides with the new changes and assesses their effectiveness. 4. With this new interest for bike fit from the mtb community, getting experience fitting mtb’s is very beneficial for a fitter as very few understand it as well as road, tri, and tt. There isn’t as much data on the position, and most simply make general adjustments to position rather than try to find a truly optimized fit for their client. Hope that helps.

Jim Manton / ERO Sports

Aero Tidbits posted on Instagram & Facebook
Last edited by: JM3: Jul 27, 11 17:16
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Re: MTB Fit [JM3] [ In reply to ]
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Thanks for posting this, I've always wondered a bit about the nuances about MTB fit.

Jonathan Blyer,
ACME Bicycle Co., Brooklyn, NY
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Re: MTB Fit [JM3] [ In reply to ]
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JM3, Though I agree with most of what you said, in my experience a slightly more forward saddle position (compared to a road bike) is more appropriate for a MTB racer (recreational riding is different) The more forward position creates a more solid platform for the rider while climbing. (when descending technical terrain they are off the saddle anyways and the forward saddle position doesn't make any difference). If you look at a mtb racer while climbing, they always slide forward on the saddle to create a more stable position. From there you "stack" the rider (shoulder, knee, and ball of foot) like in other sports where stability is required - think weight lifting, or playing defense in basketball etc...
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Re: MTB Fit [jeremysimmons] [ In reply to ]
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I have to both agree and disagree to both JM3 and jeremysimmons.

Yes, MTBs are a much more dynamic fit than road and especially TT, meaning the rider is constantly moving and adjusting for stability and traction.

JM3 -- except in the case of poor suspension designs, the saddle height is static--it does not change with suspension sag. The wheels move, the bottom bracket does not. Therefore, that aspect of fit is static. The caution, however, is to fit the bike in a suspension sagged position (under rider weight) and since MTB tires sag quite a bit more than road, the fitter must level the bike under weight.

jeremysimmons -- have to disagree on the forward position. Riders leaning forward on climbs (except the most steep climbs) are moving forward for traction rather than balance, as a more aft position is more powerful but the front wheel will lift or the rear can spin or slide. The normal knee position is 5-10mm further aft on an MTB than a road bike, the hip angle is more open (more upright for dynamic stability) and the bars are set closer to accomodate the wider grip.

Brian Grasky
RETUL fitter, biomechanist, USAT Level II coach
former Pro MTB/XTERRA, elite triathlete
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Re: MTB Fit [seebritri] [ In reply to ]
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Curious, if the more rearward position generates more power, why is the position refered to as "on the rivet" when you are in a position on the bike trying to generate the most power by sliding forward on the saddle? (historically a road term, where traction is not an issue) I know from personal experience (and analyzing pro Mtb racers that this is where they sit when producing "maximum effort". I agree with the more open hip angle (relative to a road fit) but am wondering why the theory on the more rearward saddle position other than the "more power" argument. More power when? On the flats? On the descents? As mountain biking is more dynamic as far as terrain, when do you need to produce this power? On the climbs when the bike is rotated underneath you, pushing the seat back.
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Re: MTB Fit [jeremysimmons] [ In reply to ]
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When you're on the rivet you're in an aerodynamic position (road or TT/tri) and the forward pull on the saddle is your body trying to open the hip angle to produce power or to open the lungs/chest cavity.
Plus, I slightly mis-spoke--back on the saddle produces more torque (vs power) and is therefor a power position. Power can be applied in the forward position as well, but not as much torque. You'll also notice on flat terrain, just as many cyclists ride aft as those who ride forward in their power position (depends on their power profile and muscle type). And watch the pros again, on the rivet while climbing is primarily aft. Way aft. TT/tri, it's a forward position for on the rivet.


Brian Grasky
Grasky Endurance: World Championship Triathlon Coaching; Professional Training Camps
RETUL fitter, Biomechanist, USAT Level 3 Coach, USAC Level 2 Coach
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Re: MTB Fit [seebritri] [ In reply to ]
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Here's some photos of a couple of world cup racers on a moderate pitch climb riding in the saddle. They look pretty far forward. They are also way faster than most people I fit.

http://www.canadiancyclist.com/...images//_DSC0805.jpg
http://www.canadiancyclist.com/...images//_DSC0842.jpg
http://www.canadiancyclist.com/...images//_DSC0826.jpg
http://www.canadiancyclist.com/...images//_DSC0870.jpg
http://www.canadiancyclist.com/...images//_DSC0822.jpg
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Re: MTB Fit [jeremysimmons] [ In reply to ]
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That's a steeper hill and they are forward for weight distribution, not for effort/power. Go back to what I said about balance and bringing the front wheel up on steep hills and how that dictates being forward. You can also see that they are shifting for weight balance in how they hold the bars wide and elbows low and the low gearing.


Brian Grasky
Grasky Endurance: World Championship Triathlon Coaching; Professional Training Camps
RETUL fitter, Biomechanist, USAT Level 3 Coach, USAC Level 2 Coach
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Re: MTB Fit [seebritri] [ In reply to ]
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Ok, so for a minute, let's disregard why (physiologically) they are forward on the seat. The fact is that they are forward. When you conceder time, climbing takes up the majority of a Mtb race course (and even more so the time when they are actually putting power to the pedals) Why not fit the rider to be in a better position on the climbs?
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Re: MTB Fit [jeremysimmons] [ In reply to ]
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We're talking steep climbs for forward position. Forward is MUCH less stable on descents and while maneuvering, and I'd argue the rider is on shallow climbs, descents, and is maneuvering the bike a bit more than he's on steep climbs.
Again, the MTB fit is a dynamic fit. You're fitting him neutrally, knowing that he will be shifting weight and moving all the time on the bike. Movement is the normal case in MTB. It happens on a road fit as well, but not as much. ON a TT/tri fit it is the exception.


Brian Grasky
Grasky Endurance: World Championship Triathlon Coaching; Professional Training Camps
RETUL fitter, Biomechanist, USAT Level 3 Coach, USAC Level 2 Coach
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Re: MTB Fit [seebritri] [ In reply to ]
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I really agree that forward position is much less stable on descents and riding technical sections. This is why riders are out of the saddle for these sections of the race. Being seated would put you at a very distinct disadvantage in these sections, regardless of where the saddle is positioned. Having the saddle forward (for people riding out of the saddle) in these situations is actually an advantage as it makes it much easier for the rider to get "behind the saddle" to increase stability. You are also correct in saying that Mtb fit is dynamic, that is why you want to place them in a position on the saddle that will give them an advantage in sections where they are actually sitting on then saddle. (usually while climbing). Moving back and off the saddle is a pretty programmed movement for most racers while descending and riding technical terrain.
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Re: MTB Fit [jeremysimmons] [ In reply to ]
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No, based on power production, cadence differentials, and movement, the neutral position on the MTB is 5-10mm further aft than a road bike, the hip angle is more open (more upright for dynamic stability) and the bars are set closer to accommodate the wider grip. This is the neutral position, it does not cover all instances. Some people will move more forward on steep climbs, but to say that's the majority of rides and that the fit should center on that is limiting.



Brian Grasky
Grasky Endurance: World Championship Triathlon Coaching; Professional Training Camps
RETUL fitter, Biomechanist, USAT Level 3 Coach, USAC Level 2 Coach
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Re: MTB Fit [seebritri] [ In reply to ]
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I guess we agree on everything except saddle position, though it is clear to me that it's not "some" riders that move forward on typical mtb climbs but most, if not all. Again, when you call it neutral, are we talking about while descending or climbing? I think you can agree with me that most descending on mtb courses is done out of the saddle and shouldn't be a consideration when talking about saddle position. We'll see how the guys with a more forward postition do in some big races over the next few months (Leadville, Trans Rockies, and MTB Worlds).
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Re: MTB Fit [jeremysimmons] [ In reply to ]
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Again, you're talking steep climbs, not all climbs. Not the primary terrain, but yes, an important one. And riders will move back on climbs when on technical terrain. Fitting a neutral position for maneuverability, power production and balance is more important that optimizing for one specific part of the race.
We'll agree to disagree. There are different ways to skin the cat, but I'll stand by my statements and belief. It's the belief of most major fit schools including Retul, the one I follow primarily.


Brian Grasky
Grasky Endurance: World Championship Triathlon Coaching; Professional Training Camps
RETUL fitter, Biomechanist, USAT Level 3 Coach, USAC Level 2 Coach
Last edited by: seebritri: Aug 3, 11 15:30
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Re: MTB Fit [Austentx] [ In reply to ]
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OK, I'll chime in an go out on a limb. In my opinion you cannot fully fit a mountain bike in a studio. My reason for this is mountain bike position is maintaining traction and handling. The main issue is that there is a large variation in geometry differences and bottom bracket heights, suspension rates which can make a difference in handling and demand some weight shifting from the rider. Lets take an example of two popular full suspension bikes, Cannondale's Scalpel and Giant Anthem X 29'er. The Scalpel has a 16.7 inch chainstay, the Giant an 18.2 inch chainstay. If you add that to the increased bottom bracket drop of the Giant to accomodate the larger wheels a rider position that would have the Scalpel doing a wheelie up the slope would be solid on the Giant. You can then throw in front center, trail, stem length and bar width to the equation.
I have found myself that changing to a new bike with different geometry will cause me to make changes to my position, for example switching from a setback to offset seatpost. Perhaps something that involves runs on a consistent track?

Kevin
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Re: MTB Fit [Austentx] [ In reply to ]
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I'm glad you brought this subject up, found out that my fit for my bike is a little off.


Electrolyte Replacement
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Re: MTB Fit [mythekx] [ In reply to ]
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Let's keep this going in hopes that I (we), will learn more about this subject. Yes geometry differences no doubt cause different saddle set back. Here is a case in point. A Cannondale Flash 3 hardtail with app.72 degree seat tube angle has the bottom bracket in line with the seat tube. A Trek Superfly full suspension with the same seat tube angle has the bottom bracket app. 2 cm rearward of the seat tube. With the saddles jammed all the way rearward on both bikes you end up with app. 73 deg. seat angle on the Cannondale and app. 75 deg. seat angle on the Trek. What to do?


By the way the Cannondale comes stock with a 2 cm offset seat post. The Trek comes stock with a zero offset seat post. I assume this means that the manufactures believe this to give a correct fit. I also notice that not many mountain bikes have the bottom bracket located rearward of the seat tube. Does this mean that hartails should be ridden with slacker seat angle than full suspension bikes?


Also researching the subject I have found some information to suggest that we should set the saddle set back in line with the proper balance technic, ie: saddle forward as far as possible while being able to remove the hands from the bars without doing a nose dive as with a road bike.


I understand you cannot give a complete fitting on a mountain bike while in a stand because of all the variables of the trail but we should be able to develop a system that gets riders to a generic point in space that gets them very close.


PS. Dont give me any of that drop a plum bob from the knee crap!!!

Cap
http://www.fulltiltfitting.com



http://www.fulltiltfitting.com
Last edited by: gcappy: Jun 25, 12 3:48
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Re: MTB Fit [Flying Wombat] [ In reply to ]
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Taking the fit from the studio to the trail is an essential part of helping clients. I've been working on a protocol that clients leave the fit studio with for things to try, observe then report back to me on. For example, and in Cliff's Notes' format, on the MTB, I want feedback on contact point pressure and comfort under varying workload and terrain. Flat, smooth and fast. Flat, rocky and fast. Flat, rooted and fast. Etc Etc.

Then with this info, two things happen: 1) the customer becomes more aware of their balance etc on their bike and 2) I can make any fit tweaks that weren't able to be identified in the studio. Ideally, after a while, the customer realizes that some things tools can address and other things their personal riding style can address.


Brian - Chief Fitter
Velocraft Bike Fit Studio
Phoenix Metro, Arizona
http://www.velocraftcycling.com
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Re: MTB Fit [seebritri] [ In reply to ]
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Agree with the concept of 'finding a neutral position for maneuverability', but if I may add a few thoughts from my mtb xc racing experience as well as fitting xc racers:

Suspension, particularly in the front (plus tire pressure) can adversely affect handling and maneuvering almost more so than poor fit; head tube angle changes during compression and rebound can wreck your timing and balance on technical sections. Therefore, where the saddle is in space is moot as you aren't on the saddle at all. When climbing,however, a too-far forward saddle nose will catch the back of your leg (or baggy shorts) if you get out of the saddle.

Trust me, riding 'on the rivet' in mtb is not a comfy thing! Yes, coming forward slightly on super steep stuff can help if you are 'throwing' your upper body forward to propel yourself. The photos may show them on the rivet, but these are static images. If you watch them in video you get a better idea of the dynamics of the momentum generated by the rider:

http://www.youtube.com/...&feature=related

A XC rider will go from a range of motion more similar to a stair-climber to that of a roadie; trying to put a saddle 'forward' or 'further back' can just confuse the issue. Saddle shape may help them more than moving the saddle itself. The dropped nose and 'shaved' rear area of the thigh glides (see Fizik Tundra or WTB) reduce the 'hooking' on the nose or enable the move off the back of the saddle.

Anne Barnes
ABBikefit, Ltd
FIST/SICI/FIST DOWN DEEP
X/Y Coordinator
abbikefit@gmail.com
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Re: MTB Fit [jeremysimmons] [ In reply to ]
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The riders appear more forward because the frames are small. With easier gears while climbing your weight needs to be forward or the bike will come back over on you. The small frame allows you to be back for power while over the bars for climbing stability.
The third pic of the guy on the specialized, that stem has to be 110 or longer. They look a little upright to me. All this on the forum is great info!

http://www.mybicyclefit.com
Last edited by: Ron Hacker: Oct 22, 12 19:37
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