MTB power meter thread.
Anyone got any MTB power meter files from a Powertap or SRM or whatever they can share on here?
I have seen plenty of road bike files but not as many from mountain bike rides. Thanks.
what are you specifically looking for? I have probably 30-40 from the last 9 months or so
Originally Posted by Johnny K
I would like to see a normal XC race and a hard group ride. See how they compare.
Originally Posted by fsrftc
And with that, time in Zones. (aerobic, tempo, threshold, AC, etc. if possible).
Also, TSS, and IF. That way it gets normalized to your power level. (Which is a lot higher than the rest of us )
hah, well I'm a bigger guy so its all relative?
Originally Posted by Poncharelli
I don't really do group rides, maybe 1 or 2 a year. I do almost all my long training rides solo, so my data may be a bit off from what you are looking for.
this was my best recorded "tempo-ish" ride of last season: http://www.trainingpeaks.com/sw/KOWH...QWC45OFNA2FR5E and one of the few rides I did last year chasing a particular number, in this case 300 watts.
and this was the only "short" XC race I had recorded with power for last season, I placed 3rd in Expert, less than 11 seconds from 1st. http://www.trainingpeaks.com/sw/OV5W...XLH47QEENBFBS4 (interval 2 is the race)
The XC race was King of the Rockies in Winter Park, CO which is nearly all between 9-11,000 feet elevation (probably a 5-6% power loss from me at my normal 5000ish foot rides) and my 1st good race after my late summer crack (I got completely overtrained/tired/whatever you want to call it). I was about 182 pounds for both of these files and my 20 minute interval power was at least 400 watts, hope that helps.
Man!! And I thought I was OCD!!
Originally Posted by WR304
How did you label all those intervals? (road, byway, track, etc.). Did you just start an new interval real time, and rename later?
I've been thinking about getting a powermeter for my MTB, so this thread is interesting to me. Its difficult to go from having power on the road to me and not having it on the MTB.
For those that have road and mtb power, do you find a 100TSS road ride feels like a 100TSS MTB ride?
How about NP compared to AP, I find on the road, my NP is generally within 20W of AP, is there a bigger gap due the the coasting thats neccessary on the MTB?
maybe you guys said already - but is everyone using powertap?? i'm interested in a quarq or srm but gosh i'd have to sell some other bikes to get one... thanks in advance. jg
[QUOTE=wetpaint]For those that have road and mtb power, do you find a 100TSS road ride feels like a 100TSS MTB ride?
No TSS seems to be always much lower on a MTB ride for a given effort.
When mountain biking you do a lot of work is done that that power meter doesn't count.
A good example is on a pump track, I can have my heart rate at threshold without ever turning the pedals.
"The best pace is suicide pace, and today is a good day to die." Steve Prefontaine
Oldie but a goodie
MTB power overlaid with Road Power at Same hear rate on similar climbs Mtb power spikes much moreso, but road power average is clearly higher....
I'm sure you've seen this study of the rolling resistance of different Schwalbe tyres offroad before.
The study was originally carried out by Peter Nilges, for his graduate dissertation at the German College of Physical Education, Cologne.
He used a SRM power meter to try and evaluate how power varies offroad depending upon factors such as surface, tyre pressure and tyre tread.
It's a good demonstration of how you can use a power meter on the mountain bike to help with decisions such as tyre choice.
(The graph on Page 7 of the study is mislabelled. I've corrected the key of the graph posted below.)
Pictured below: Extract from rolling resistance study.
Bumping this thread because I ended up ordering a powertap. TSS and IF end up feeling about the same as the road, but the power distribution is different. I'm quite happy to be getting power data from road and mountain now.
My road power files end up being fairly smooth and the power distribution is mostly Z2, Z3 for an easy ride. The mountain bike data is really spikey, lots of time in Z1 and then threshold or above.
Here's a lap from a smooth flowing single track
Work: 371 kJ
TSS: 27.6 (intensity factor 0.726)
Norm Power: 214
Distance: 6.545 mi
Elevation Gain: 517 ft
Elevation Loss: 521 ft
Grade: -0.0 % (-6 ft)
Min Max Avg
Power: 0 637 197 watts
Heart Rate: 80 161 137 bpm
Cadence: 30 212 88 rpm
Speed: 0 35.5 12.5 mph
Pace 1:41 0:00 4:49 min/mi
Altitude: 732 774 754 ft
Crank Torque: 0 800 191 lb-in
Last edited by WR304; 04-24-2011 at 01:12 PM.
Average power doesn't include stopped time, just coasting time, so the time you spend stopped won't affect your average, only the time coasting to a stop. There were some small rollers in that course, but it is fairly flat. The entire ride ended up having an IF of ~.7, it felt similar to what a .7 road ride would feel like, except the graph showed alot of spikes in power and coasting. On my typical road files, there is virtually no coasting and the power is quite constant.
Last edited by WR304; 04-25-2011 at 01:53 PM.
My 23T Rotor granny chainring snapped on a climb today. It was riding up the horse trail climb through the woods which is loose rocks and dirt. Suddenly the bike lost drive and I couldn't pedal any more. I got both feet unclipped and down but my left leg isn't strong enough and gave way. That was that, another mechanical related fall. That's two falls in two weeks due to mechanical issues.
I've attached the power data just before the chainring broke as it provides some clues as to why it broke when it did. You can see from the power data that there was a heavy load on the chainring immediately before it failed. I'd been in bottom gear averaging 410 watts at 83rpm (virtual cadence) up the steepest 18.5% gradient section of the rocky track.
Being as low as 79rpm is quite a low cadence for me as I was really fighting the bike to keep going over the rocks. A comfortable climbing cadence for me is usually very close to my normal cadence of 90rpm+. On this particular climb I'd run out of gears so couldn't downshift anymore. Offroad I often tend to ride at lower cadences though. When it's very bumpy I often find that my cadence can drop significantly.
When climbing a track like this one at low speed with very little momentum there are short spikes of effort that don't appear on the recorded data as you have to try and get the wheels to roll over each individual rock in turn. You can tell it's happening at the time but it usually doesn't show on the graph.
Power output up climb immediately before chainring broke. You can see how I had put in a short burst of hard effort to get up the steepest part of the climb immediately before the chainring broke. The sudden drop in speed and abrupt stop is when the chainring has broken and I'm trying to work out why I can't pedal anymore.
Rotor 23T granny chainring snapped on climb.
I doubt it broke just because of that one effort. Granted, the torque is pretty high with a ring that small and I'd rather see your torque numbers than your watts for something like this but I'd venture to guess a manufacturing defect or defect in heat treatment made itself known at that time. Maybe a steel or ti inner ring would be a better choice?
Can you screenshot your WKO+ graph with the torque channel turned on and the rest of them turned off? View > Torque.
Here's the graph showing hub and crank torque for the same climb. The maximum torque figure recorded just before the chainring broke was: hub 60 lb-in, crank 488 lb-in.
The data is from a Powertap hub with no smoothing applied. I'd guess that "crank torque" from a Powertap is going to be a virtual value (like cadence) rather than the exact figure?
The Rotor chainrings aren't new. I've been using them since July 2009. In total they've done about 13,000 miles. Most of that mileage would have been on the middle or big ring instead of the granny ring. 10-15% perhaps climbing on the granny ring 1300 - 1950 miles approx over almost two years. Most hills around here involve using the granny ring.
So far as I can tell the chainring bolts were tight. There had been some odd clunking noises from the drive train whilst climbing on the granny ring for a few weeks before hand though. That was obviously a warning sign which I should have paid attention to. Possibly the ring had cracked a while ago and the steep climb today just finished it off.
Pictured below: Torque output up climb immediately before chainring broke.
Yeah I wouldn't think 70 ft-lbs on the ring would be enough to break it but over the course of a couple of years it's definitely possible. I replace my rings once a year although those rotor rings are horribly expensive to replace, I can understand waiting.
A bit late, but I finally have a race file. The graph and time in zones looks a lot like my power files from crits, lots of big spikes in power. The power profile is U shaped with recovery zone and Anaerobic being the highest times (about 20minutes in each of those zones)
Originally Posted by Poncharelli
Work: 1301 kJ
TSS: 128.9 (intensity factor 0.953)
Norm Power: 281
Distance: 21.029 mi
Elevation Gain: 2306 ft
Elevation Loss: 2325 ft
Grade: -0.0 % (-18 ft)
Min Max Avg
Power: 0 881 255 watts
Heart Rate: 106 187 176 bpm
Cadence: 45 246 90 rpm
Speed: 0.6 31.2 15.6 mph
Pace 1:55 96:34 3:51 min/mi
Altitude: 603 920 817 ft
Crank Torque: 0 843 248 lb-in
One thing to compare as mward pointed out is the torque values. Looking at my offroad files I'm generating much higher maximum torque values for offroad rides, even though the maximum power and average power may be higher on the road ride.
Originally Posted by wetpaint
Power = Torque x Cadence
09 May 2011 Road ride (mountain bike with knobbly tyres pumped up to 60psi)
Maximum power 546 watts
Average power 183 watts
Maximum hub torque 44 lb-in
26 April 2011 hilly Offroad ride (Trainingpeaks file is a few posts up)
Maximum power 492 watts
Average power 141 watts
Maximum hub torque 63 lb-in
Here's the Training Peaks power file from today's mountain bike ride. It has a few descents in where I wasn't going too badly. It covers some of the same tracks as in the 26 April 2011 ride but I was quicker today on the offroad sections.
My descending in particular has been getting better. I've been letting the bike run more and trying to relax instead of riding on the brakes as much. Once the speeds get over 14-15mph then the benefits of a full suspension bike really start to show as at higher speeds the suspension increasingly smooths out the bumps, making it easier to go fast than riding down the same tracks slowly. The second half of Interval 15 (Byway behind golf course) is a good example. It's a fairly straight but rocky byway descent with lots of ruts cut by water running across the trail. On 26 April 2011 I averaged 14mph (max 19.5mph) down it but on 21 August 2011 I improved to an average of 18.2 mph (max 26.1mph) for the same downhill section. There's still a lot of room for further improvements though.
The offroad sections which are the same between the power files are these ones:
26 April 2011 = 21 August 2011
Int 4 = Int 5 (Track)
Int 15 = Int 15 (Byway behind golf course)
Int 17 = Int 17 (Track up to woods)
Int 21 & 23 = Int 19 (Singletrack descent)
Int 28 = Int21 (Byway through farm)
If you look at the climbs on 21 August 2011 then you can see how I rode the first climb as a gentle warmup at only 208 watts. I twiddled up in bottom gear as I'd only just set off.
Training Peaks 21 August 2011 MTB Ride
As part of the ride there's a section of flat twisting woodland singletrack which I know quite well. It has some exposed roots and weaves through the trees. The picture below shows this section of the ride. The altitude trace isn't as detailed as on previous graphs because I'm using a Garmin Edge 500 now. Its barometric altimeter doesn't seem to work as well as my CycleOps Joule 2.0 did.
When you look at the power output and speed for this section you can see how both traces jump around quite a bit but there isn't much actual freewheeling. Unlike the singletrack descent in post #18 I was pedalling most of the time. I was only stopping pedalling momentarily whilst cornering, as opposed to the singletrack descent which was spent largely freewheeling.
The short bursts of power are accelerating over roots and up some small rises. You can see how although the power output overall is quite low (average of 101 watts) there are sections where I need to produce 300 watts plus for short periods of time, mostly to power over roots.
The gap in the trace near the end is because it was a Sunday and there was a pony trekking event on. I had to stop, pull off the trail and stand in a nettle patch in order to let some horse riders past.
Pictured below: Flat Woodland Singletrack Power and Speed Traces
Last edited by WR304; 08-21-2011 at 02:57 PM.