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road_vs_mtb

I’ve been mountain biking for decades, and as far back as I can remember, mountain bikers have always taken pride in how much more difficult MTB is compared to road riding. I’ve heard rules of thumb like multiplying the length of a mountain bike ride by two or three to get the equivalent road ride, and based on my own experience, I’d say something close to the two-times rule seems about right. But how much more difficult is mountain biking, really? I decided to see if science could get me closer to an answer to that question.

I’ve been testing a fancy power meter from PowerTap, and I used it to set up a controlled test to isolate the factors that make mountain biking more difficult than road biking. These are the three main factors I considered:

  • Obstacles on the trail. The number and size of trail obstacles can vary wildly, and generally come in the form of rocks and roots. Paved roads, by comparison, are generally smooth and obstacle-free. Trail obstacles slow riders down and increase the amount of physical effort required.
  • The trail surface itself. Dirt and vegetation slow riders down compared to solid, high-traction pavement.
  • Tire resistance and aerodynamics. Fat, squishy tires add resistance over skinny, high pressure road tires. Road bikes place riders into a more aero position and generally cut a narrower overall profile as well.

Factors I decided not to consider because they are not unique to road or MTB riding:

  • Mountain bike trails often have sharp, steep climbs, while roads usually stick to milder, more consistent grades. However, roads can have steep grades and quick reversals, just like mountain bike trails can be flat. If we’re truly looking at what makes MTB harder than road riding, we have to normalize for elevation gains and losses. A road ride in the mountains is certainly more difficult than a MTB ride on a railroad-grade trail. For my test, I kept the surface grade the same.
  • Road bikes are generally lighter than mountain bikes but every bike (and every rider) is different. Plus it’s pretty obvious that pedaling a lightweight bike will be easier than pedaling a heavy one, and this isn’t unique to road biking. One could make mountain biking easier by dropping a few pounds off the bike and/or rider, too. For my test I kept the overall weights of the test bikes the same, adding weights to the road bike to normalize weight between the two bikes.
  • Trails typically have more twists and turns than roads, and believe me, cornering definitely takes an energy toll during a ride! But a lack of turns isn’t unique to riding a road bike just like twists and turns aren’t unique to mountain biking. Some MTB trails can run straight as an arrow for long sections while riding a greenway path on a road bike can involve a significant amount of turning.
  • Stop-and-go riding due to traffic signals can take a real toll on road rides, just like dismounting for hike-a-bike can for MTB rides. Roads and trails can vary wildly from this perspective, so comparing the two might just be a matter of counting the number of times the rider has to accelerate from a stop or near stop. Some road rides might have a lot of acceleration points while a MTB ride on a flow trail could have relatively few.
  • Suspension, even when properly tuned, sucks energy during a ride. I want to test this separately but for now, I stuck with a hardtail with the front suspension locked out. Not all mountain bikes have suspension, anyway.
  • Decision making–that is, choosing lines–is mentally taxing which can, in turn, exact a physical toll. Really technical trails require more frequent decisions but then again, riding in traffic can be equally stressing. For that reason, I decided not to test this factor.

Testing the effort to clear obstacles

A 4x4 inch block of wood.

A 4×4 inch block of wood.

I set up a 0.10-mile test track right outside the Singletracks office, which happens to be on a hill with a decent grade. For the control test, I pedaled up the concrete path on my mountain bike three times at the same speed each time, and measured the overall power I expended.

Next, I set up ten obstacles along the same path at even intervals: 6 two-by-four and 4 four-by-four pieces of lumber. I figure the two-by-fours, at 1.5 inches tall, roughly simulate trail roots, while the four-by-fours, at 3.5 inches tall, are more like the rocks one might find on a trail. I pedaled this course three times again, keeping the same speed as I did in the control test.

The result: the obstacles required a 9% increase in power to keep the same pace as in the control test. Now, if the obstacles had been larger or spaced more closely together like a rock garden, that number would obviously rise. Now I understand why it’s impossible to form an exact comparison between the difficulty of road and mountain bike riding! Every trail is different.

Testing a natural surface

Natural surface beside the paved bike path.

Natural surface beside the paved bike path.

Admittedly my test track for this one wasn’t perfect. I really wanted to test hardpack, but it was important to keep the exact same grade as in my pavement test. Instead, I ended up testing in patchy grass and leaves. Sure, this isn’t ideal but then again, few trails have consistent surfaces along their length anyway. Riders can encounter pretty much anything on the trail including sand, rocks, packed dirt, mud, weeds, grass, and fallen leaves.

Surprisingly, I found the patchy grass and leaf surface required nearly 31% more power than in my control test! Personally I’ve always hated riding on grass and I’ve long suspected that it was more difficult to ride on grass than other trail surfaces. But still, 31% is a big jump. I suspect hardpack or even loose-over-hard would add far less than 31% to the effort required.

It might be interesting to set up a separate test on trail surfaces alone to understand how much difficulty each one adds. But even within surface types we’re sure to find variations. For example, “sugar sand” seems to add more resistance than, say, course river sand. And muddy clay will slow tires way more than organic black dirt.

Testing tires plus aerodynamics

The PowerTap hub I’m testing is built into an MTB wheel, so I didn’t have a way to mount it to my road bike. However, from my tire pressure tests a while back, I learned that downhill speeds are a pretty good proxy for uphill climbing power changes, at least for the purposes of this test. I added 8.5 pounds to my setup to even up the weight between the road and mountain bikes I used in the test. For those who are interested, the mountain bike was a 29er running 2.3″ MTB tires at about 30psi. The road bike was running standard road bike tires at about 80psi.

Based on the speed test, I found the road bike rolled, on average, about 11% faster than the mountain bike. One interesting thing to note is that a lot of the speed difference in the test seemed to come in the first 10 yards along the test track as the bikes accelerated up to speed. The increased rolling mass of an MTB tire compared to a road wheel makes a big difference here.

Bottom Line

Based on the factors I was able to test, I found a 51% increase in the effort needed to ride a mountain bike on a grassy, leafy trail with obstacles, compared to a road bike on a paved surface. Remember, that assumes a mountain bike course with grades and turns that are similar to what one would ride on the road.  It also assumes riding a mountain bike without suspension. For bikes with suspension, there will be additional energy expended on the trail.

Adding in all the additional factors I mentioned above, it’s easy to see how the percentage increase in effort could get to 100% or beyond, which would match up with the 2-times estimate I mentioned at the beginning. I don’t know what the upper limit might be (if there even is one), but if I were pressed, I would say mountain biking requires 50-150% more effort than a road ride of equivalent distance. So, I would say a 10-mile mountain bike ride is roughly the same (physically) as a 15-25 mile road ride.

Of course, another quick way to estimate is to look at average speeds. If a rider averages 8mph on an MTB ride and 18mph on a road ride, that means the equivalent road ride is about 125% longer than the MTB ride, assuming the same total moving time and average heart rate for both rides. This fits nicely within the range I estimated based on my tests.

Your turn: What did I miss? What is the factor you use to estimate the road ride equivalent of your MTB rides?

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# Comments

  • ahtannerii

    Great article! The energy for obstacles touch on this, but there’s much more energy expenditure due to isometric contractions of arms/legs to stabilize/maneuver mountain-bike over rough terrain. Further, MTB trails generally are at higher altitude, and undoubtedly riders are above lactate threshold more quickly.

    • WesternSLP

      Before you start throwing out terms like isometric and lactate threshold you should know what you are talking about. MTB is a much more Dynamic effort vs road riding. Dynamic = eccentric and concentric muscle contractions, as you are active (dynamic) with the bike. A hill descent on a road bike (holding a position on a flat service) would get you close to isometric. Rarely does one spend any time iso when trail riding. In fact, this is an entirely different level of whole body “effort” that fits into the equation this article is discussing.

  • MTBrent

    Good stuff, Jeff. I wish the “decision making” factor was quantifiable, ’cause it’s gotta be one of the most substantial energy-consuming aspects of mountain biking.

  • Michael Paul

    Great article! I’d love to be able to test this on some of the steeper, rocky front range trails like Apex, Chimney Gulch, or Mt Falcon, where occasionally I see crazy/enthusiastic individuals riding up on cross bikes. They are hard enough on a full sus mountain bike…and seem 5x harder than riding up roads that often parallel them.

  • paulmacdermid

    The only true way to know is to control speed and measure work and forces at a number of positions on the bike. Here’s a real simple study we published in 2015 (https://www.researchgate.net/publication/277666661_The_Effects_of_Vibrations_Experienced_during_Road_vs_Off-road_Cycling) where speed was set while riding up a single track and tarmac road. While we envisioned that the rider would be dealing with a whole lot more vibrations (you have to dampen these to protect the central nervous system) it seems likely that drag played the biggest part. You’ll notice that our mean data reported the MTB trial to have a 32W greater power output (only about 10%) while the physiological intensity was about 6% greater.

    For more science type stuff on MTB follow: P.W.Macdermid and Co on http://www.researchgate.net

    • Jeff Barber

      Thanks Paul. I didn’t go into the full details of our test but it sounds like we used a similar method to your study for the surface and obstacle tests. Speed was held constant over multiple trials (to get an average) and we measured work and forces using a power meter.

    • paulmacdermid

      I guess the limitation is that we are all only measuring work in the propulsive sense i.e. force and velocity at the cranks or rear hub and this may be alright in road cycling but the static forces being applied to the bike during MTB’ing would contribute considerably you’d assume. Especially on a technical climb. I guess that’s why we included the overall physiological response with the metabolic cart measurements.

  • kaistenseth

    if you go at your maximum wattage both should mean the same effort really.

    but for me subjectively the more variable power put in when mountainbiking suits my body better than the more continuous effort when roadbiking. air resistance is a formidable enemy.

  • paulmacdermid

    HI, Effort and work done are different and understanding the extra effort is important as any of the peer reviewed publications reviewing MTB and Rd that look at rider efficiency will tell you per W that Rd rider are more efficient. As you say you’d have to compare both types of rider in both situations. The problem is finding people that don’t do it all i guess.

    As for not being able to cope with the constant effort of Rd i fully agree. Ask a marathon runner to play a game of soccer. It will kill their legs pretty quickly!

    • GTXC4

      Great point, loved playing soccer and I remember the 5k’s and 13’s seemed like cake compared to it. When you’re supposed to be hitting 40m/week, throwing in “recreational”, well ughhh…. anyway. I will say, off road is always more work no matter where you are. However, off road is hands down where it’s at.

  • RobertD

    Thanks for taking the time to do this. I do a lot of gravel rides on my Sunday longer rides. Depending on the number of creek crossings, I feel that in 4 hours at 12.5 mph or whatever, I would average about 3 miles per hour faster on a similar road ride with the same bike and slicks. I know that road rides are very nice but seem easier. When I ride my SS set up for my hometown routes, I can average around 15 to 17 mph and on the gravel or trails maybe 8 to 10 depending on the technical difficulty and climbing on said trail.

  • BSAphex

    Thanks, Jeff. Great article. Always wondered this myself (as we all have). Definitely tough to calculate. Some trails are a non stop battering of rocks and roots. Some not so much. Either way I like the data you collected. Gives a great general guide.

  • rushrider6

    what about standing versus sitting?
    as a BMXer & MTBer i almost never sit…

  • GTXC4

    Maybe it’s just me, but I don’t see the mental “taxation” on picking lines, where your pedals are, and such. Perhaps at first, but when you’ve been riding for a while and pretty much daily, it becomes second nature. When you love something, the effort doesn’t seem like it, just pure enjoyment.

    One thing to consider is that if you an advanced trail rider, throwing the bike around also requires more physical effort. But as before stated, when you’re having a great time doing something you love, those things aren’t even noticed as effort, just relaxing, therapeutic, smiles.

    High five on the science to put values to what we know, nice to see some numbers! Take care.

    -GT

  • paulmacdermid

    The more you know about this kind of stuff the greater advances can be made in technology and training to alleviate the extra stresses which ultimately leads to more smiles as you spend more time on the tracks.

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