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  1. #1
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    Comparing two rider's power.

    I am curious what is a good rule of thumb (nothing too complicated) to compare two riders. I usually ride with my buddy. He blows me away on the climbs. On a recent 3 mile 700 ft elevation climb, I did it in 23 minutes (best time for me). My buddy did it in 15minutes.

    His stats are:
    age: 34
    ht: 5'-2
    wt: 115 lbs
    Bike: All mountain 6" travel ~ 34lbs.

    Me:
    age: 34
    ht: 5'-7"
    wt: 158 lbs
    Bike: All Mountain 6" Travel ~ 27 lbs

    I understand the power to weight concept so thats plays a big role in his time. However is there calculation that attempts to normalize the results by taking into account rider weight, bike weight, time, distance, age, elevation, etc.

    Look forward to hearing others response.

  2. #2
    mtbr member
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    This is a pretty good website to play with for this kind of stuff.

    Analytic Cycling, Interactive Methods for Estimating Cycling Performance Parameters. Tom Compton
    Head Coach, Ben Lomond HS MTB Team
    www.utahmtb.org
    Cycling Team and local Club:
    http://www.roostersbikersedge.com/

  3. #3
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    From your data you can do a quick comparison using the analytic cycling Forces on Rider (Power given Speed) calculator.

    Forces on Rider

    Convert mph to m/s calculator
    Time, Speed and Distance Calculator

    Analytic Cycling entries:
    Frontal area 0.5 m2 (default)
    Drag coefficient 0.5 (default)
    Air density 1.226 kg/m3 (default)
    Rolling Resistance entered as 0.08
    Cadence 90rpm
    Crank length 175mm

    Calculate the gradient of the hill (elevation (ft) / distance travelled in feet x 100)

    700/(5280*3)*100 = 4.4% gradient
    Gradient in the analytic cycling calculator is a decimal so entered as 0.044



    Buddy + bike 115lbs + 34lbs: Weight = 149lbs (67.58kg)
    Time for climb: 15 min
    Average speed 12 mph (5.36m/s)
    Average Power Output estimate from calculator 208.3 watts
    Power to Weight Ratio: 208.3 watts/ 52.16kg = 3.99w/kg

    You + bike 158lbs + 27lbs: Weight = 185lbs (83.92kg)
    Time for climb: 23min
    Average speed 7.82 mph (3.49m/s)
    Average Power Output estimate from calculator 155.9 watts
    Power to Weight Ratio: 155.9 watts/ 71.67kg = 2.17w/kg


    That's a rough estimate of course. It's probably a slight underestimate of your power outputs. If it's climbing a rough track then rolling resistance will be higher. You also need to add in the weight of riding kit and equipment you were carrying. If you had a full backpack that can add quite a bit of additional weight which would make you have to work harder to go the same speed.

    I did a quick check of what the calculator numbers look like using my own figures from a 3 mile 4.5% gradient climb that I rode up earlier this year. Those average power output estimate figures look like they will be fairly close to what you would see riding with a power meter. Give or take 10-20 watts perhaps.

    Me + bike 149lbs + 24lbs: Weight = 173lbs (78.47kg)
    Time for 3 mile 4.5% gradient climb: 17min 54sec
    Average speed 10.1 mph (4.50m/s)
    Average Power Output estimate from calculator 197.5 watts
    Actual power output from my Powertap 212 watts
    Power to Weight Ratio: 212 watts/ 67.59kg = 3.13w/kg

    .
    Last edited by WR304; 10-12-2011 at 03:48 PM.

  4. #4
    Helmetless Crasher
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    Very interesting stuff. I would not have thought the wattages would be so disparate. I would have attributed the time difference to weight and assumed wattage was very similar.

    Just curious, can anyone do the calculations to determine what wattage the OP would need to generate in order to match his buddy's climb time?

    Thanks

  5. #5
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    Quote Originally Posted by Stumpjumpy View Post
    Very interesting stuff. I would not have thought the wattages would be so disparate. I would have attributed the time difference to weight and assumed wattage was very similar.

    Just curious, can anyone do the calculations to determine what wattage the OP would need to generate in order to match his buddy's climb time?

    Thanks
    3.99 w/kg / 2.17 w/kg = 1.84

    1.84 * 155.9watts = 286.9 watts required to have the same w/kg ratio as the other rider (not including bikes, same w/kg metric the post above used).

  6. #6
    more skier than biker
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    Do you guys upload rides to GPS Bike Routes and Cycling Training Log | Strava? It will do the power calculations automatically for you and you can compare your times, power output, and even HR against anyone else who as ever ridden that segment and uploaded their ride to Strava. Totally addicted to that site.

  7. #7
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    Using the calculators you can try different combinations of weight (kg) and speed (m/s) to see how it would affect the results.

    A heavier rider needs to produce more power than a lighter rider in order to go at the same speed uphill. If both riders rode at the same constant power output of 208.3 watts for the climb (on their own bikes) then Lost Biker (83.92kg incl bike) would average 10.1mph (4.53m/s) whilst his buddy (67.58kg incl bike) would average 12mph (5.36m/s). Lost Biker would still be roughly 3 minutes behind at the top of the 3 mile 4.4% gradient climb.

    Riding their own bikes the calculator says that Lost Biker (83.92kg incl bike) would need to produce a power output of 253 watts in order to average the same 12mph (5.36m/s) for the 3 mile 4.4% gradient climb. An additional 44.7 watts compared to his buddy.

    If they were riding identical 27lb bikes then his buddy (64.41kg incl bike) would only need to produce a power output of 199.7 watts in order to average the same 12mph (5.36m/s) for the 3 mile climb. A saving of 8.6 watts over riding the heavier bike. If he maintained the original 208.3 watt power output, riding the lighter bike, then he would be 30 seconds quicker up the 3 mile 4.4% gradient climb on the 27lb bike than the 34lb bike.
    Attached Thumbnails Attached Thumbnails Comparing two rider's power.-forces_on_rider_lost_biker.jpg  

    Last edited by WR304; 10-13-2011 at 09:28 AM.

  8. #8
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    Great stuff WR04! I appreciate your response. The math does justify the results.

    The example above is an easy climb. We rode together on a tougher climb 3 mile 1,600 ft gain (average 10% grade) and the separation time was much greater at 28 minutes. I average about 3-4 mph, per my garmin 305. Based on my math, my buddy conquered this climb at an astonishing 6 mph. Although the average grade is 10%, some parts are close to 20-25% for 1/8 mile or so. Simply amazing how some folks can climb.

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