MTB Geometry Comfort / Ergonomics

bike

#1

I have pretty much left the geometry on my new race bike alone except for a good “ShockWIZ” tune on the suspension, set the saddle height, and knee to spindle alignment.

In the quest of putting it on a small diet I have ordered a small pile of carbon parts.

How many MTB peeps ride with zero stem spacers, mine came with a 20mm shim stack and yesterday before a ride I removed them and dropped the stem down thus changing the geometry, in turn I also have a stem that is 50mm shorter on order which strange enough will almost put me back to my initial geometry…

I know to each person what is comfortable is going to be different but what if we look at it from a lower body profile on a MTB and compare it to the aero position on a Roadie?


#2

So you are asking about setting up a potentially long and low bar drop (relative to the saddle) to mimic road bike setup?


#3

We need some clarification on your goals and what kind of riding and racing you do.


#4

In the Spring I race XC , mid summer to fall I race 24 hour solo endurance events. Goal is to drop my profile slightly, which I did when I removed the 20mm stack thus saving a few watts from wind drag?


#5

If you listen to the Aero Deep Dive podcast, you will learn that aero is not a direct or 1:1 relationship.

Generalities may be true, but also false. Meaning that the “low and narrow = aero” is an oversimplification that is right sometimes, and wrong sometimes. Frontal area matters, but so does the profile behind it.

Sadly, without aero testing via a couple of defined methods, we are simply guessing and applying rules of thumb, which may or may not prove correct in any given instance. Likely, your drop of the bars may prove effective in reducing overall drag, but it is a guess at best without looking at the other implications of that change (i.e. body profile).


#6

I race XC Cat 2 and MTB 100s. My setup is a flipped stem to give it a negative rise (-6 degrees) and I have one spacer above and one below on my Scott Spark RC 900 WC. I also tried the stem slammed (no spacers below) for about a month but didn’t like the feel. A slammed stem is what most pro XC racer do, but I wouldn’t try to mimic theirs or any other’s setup.

Regarding XC racing, wind drag and becoming more aero should be about the last thing you should worry about concerning most (if not all) MTB racing events. Becoming more aero would be at the utmost end of marginal gains once you have optimized everything else. Slammed positions on XC bikes are generally about handling steep and technical uphills, not about getting more aero. Conversely, that slammed position makes it more difficult on technical descents. So the trade off becomes the benefit of keeping more weight “on” the front wheel going up, but being able to handle that somewhat compromised position going down. However, since XC races are generally won on the accents that compromise is worth it if you have good handling skills.

The priority of your cockpit setup for XC racing should be handing, as you’ll lose far more time being inefficient in that aspect than you’d ever gain by having World Class CDA. Furthermore, the nature of XC racing and the actual speeds for those events, further minimize aerodynamics benefits and are far less of a factor (when comparing to road). I just looked at my last five XC races from 2018 and my average speeds for those races (where I placed between 2nd - 4th) were 13 mph, 15 mph, 12.2 mph, 14.2 mph and 13.7 mph, for an average of 13.6 mph.

Lastly, for 24 hour races and MTB 100s (8+ hours) comfort will be especially more important than typical XC races that last 1:15-1:45. Being on the bike for a relative extreme long duration, and being beat up my rocks, roots and drops, is far closer to survival than being optimized for aerodynamic drag. Anything that can be done to ease that survival (comfort) will have far greater impact on your outcome than any perceived watts gained improving CDA.


#7

This is the best article I have seen regarding MTB setup. Some of what you see in the World Cup fits are absolutely awful.

Excerpt:
Wider bars also allow you to keep your arms bent and chest down allowing you to ride in a more athletic, neutral position. Perfect for riding smoothly and adjusting to anything and everything the trail throws at you.

Your stem is a not a bike fit device, it greatly effects the control of your bike. Motorcycles don’t have stems for a reason, a long stem puts you out of balance (too much weight forward) straightens your arms (taking you out of a neutral position) and the long lever of a stem more than 90 millimeters long makes your steering “flop” to the side instead of being precise.

So for a more controlled ride go with a 50 to 80mm stem and 27″-32″ wide bars. I know this goes against tradition so please try this set up for a week before commenting. If you understand correct body position, how bikes turn and how to manual or wheelie correctly (using no upper body strength) you will love the control this gives you.


#8

You’ll change your weight distribution when you’re adjusting how forward or not your weight is, which will affect whether or not your front wheel has enough weight on it to maintain traction. You can certainly compensate for this while standing by shifting around on the bike. But IMO, it still matters how your weight is distributed when seating, and that’s much more fixed by the fit.

Regarding spacers, that has a lot more to do with the stack on your bike, than the number of spacers. I swapped forks and increased my axle to crown a while back. I ended up dropping my spacers and switching from a riser to a flat bar. The front end looks different, but fits similarly.

I think the shorter and lower specs you listed sound pretty drastic. If you think that’s what you need for the bike to fit you, that’s fine, but it looks like that should make the bike fit like it’s a lot smaller. I would be inclined to try smaller changes to see if that helps improve fit. But that’s mostly my .02 thinking with my bike as a point of reference. I don’t know how your bike fits you currently.


#9

I disagree regarding the stem, it is both.

He races XC and 24 hour solo events, I’m guessing his priority is not wheelies and manuals. I think we’re discussing two different things, optimizing for racing XC versus handling for general trail riding. True, the narrow handlebars (700 mm and under) and long stems (100+ mm) of previous XC geometry of just a few years ago are proving to be not ideal. The XC race community has moved towards 720 mm - 740 mm handlebars with 70 mm - 90 mm stems (frame size dependent). However, that is still outside of the general all mountain/trail riders with 780 mm - 800 mm handlebars and 30 mm - 50 mm stems. There are benefits and drawbacks for both setups.

If I had 32" wide bars I wouldn’t even be able to make it through the trees in some of my trails, lol. I guess this is dependent on where you live though.


#10

Pretty much all of this.

My setup is similar. Comfort is number one and aero should be the last thing on your radar. You’re not going to win a race because you saved 2 watts on the flats. You’ll win/podium if you can climb and be smooth when it gets technical/descend.


#11

I agree with all of the @MI-XC comments above.

The article and comments are too short in their scope. The “it must be this size” idea is flawed. It ignores looking at the specific rider, bike and events.

  • A change to a any component mentioned will affect handling AND fit. You can’t decouple the two aspects.
  • Rider: Depending on skill, one setup may be better than another for handling and comfort.
  • Bike: There are a wide range of current “XC” bikes that may be more like the older style geometry and other new models with more “Down Country” tendencies. That makes a HUGE difference when it comes to selecting component sizes and positions.
  • Events: Duration, course profile, trail difficulty and such will all impact what may be “ideal” for the rider/bike combo.

In short, there are no easy answers. No single solution (or mindset) rules all. I have done enough fits to know that every “rule” is meant to be broken. The trick is knowing the right time to break it (or not) :stuck_out_tongue:


#12

Hmm. To each their own. I find the advice very accurate. I think bike handling and comfort is paramount to MTB racing. It isn’t about aero unless you’re talking about Leadville which is basically a gravel race. Even more so in longer events where your concentration can deteriorate as the race goes on. If you can’t wheelie or manual you can’t ride smoothly on the trail and have to work much harder to get over obstacles and be fast on descending.

It has been way more productive for me to be on a 60-75mm stem and 740mm bars. If I have to dodge a few trees during a 2-5 hour race it is well worth it. I think of it as having your bike set up for the 95% of the race course vs the 5% you may have to squeeze through a tree on one trail.


#13

Good gosh what did I miss today while I was out playing…lol

1st off, I have never been the person to do something because it looks cool or so and so did it, so lets toss that idea all together…

  1. I am very much a person who will make changes to be more comfortable and fit my riding style better.

  2. If said changes enhance performance I consider that a bonus…

I know that changes in regards to stem length will effect both handling and personal geometry… my current bars are 740mm and work fine, I’m more apt to clip a elbow or shoulder on a tree than I am a handlebar the way I ride . I have been called a lot of things on downhill segments, slow is not one of them, I love technical climbs so tight twitchy steering is something I like. Flats are all about going quickly…

So…today in the mail …yeap the wrong stem came in but what the hell, I tossed it on there anyway. 30mm Renthal, zero shims below the stem.

I will give it a try and see how it handles and to see how the body geometry feels, is it comfortable, etc.

If its a bit to twitchy is a super simple fix, just move my Ride9 setup over one space to rake out the front a bit and presto, give it another try…

On the topic of watts gained, it might be better said in relation to 24 hour endurance race as watts saved…


#14

+1 to that, and part of the reason is, I believe, that XC is becoming more technical. I recently sold my cannondale scalpel which despite being quite the weapon, was just too focussed for more technical stuff with narrow flat bars, a negative rise 90mm stem and super steep HA. I’m currently running a more modern alloy hardtail and despite being a lower spec on paper it’s a faster bike for me.

I’m currently running a 60mm stem with 720mm bars and it’s perfect. My enduro bike which is actually lighter than the HT is way slower through twisty stuff but obviously much more fun!


#15

I use Bike Fast Fit to keep track of my bike fits


#16

I’m rolling a 60 mm stem 0*, 720 bars, dropper, and 2.4 and 2.35 rubber on my xc race bike. It’s a Felt Nine 1, weighs under 20.5 pounds and with the larger tires it just rolls through and over most stuff easily on xc tracks. Super fun to just shred too.