MTB FTP vs. Road/CX FTP

Training
1

Wanted to share my experience with respect to FTP Testing, FTP Results and Observed Results on my CX bike and my MTB.

I recently completed the Ramp Test on my CX bike and scored a number of 253w (reached 337w on the ramp test). This seemed reasonable and inline with my expectations considering the poor season I’ve recently worked through.

Though I haven’t completed any of the TR workouts yet, I have done a number of outside rides on my CX bike and the IF/NP and TSS all seem to be inline with Perceived Exertion and observed HRs. So far so good.

My question comes from my experiences on MTB. Since completing the 253w ramp test, I’ve done two outside rides on my MTB which have caused me to question the accuracy of the Ramp Test number. The first outdoor MTB ride lasted just under 2hrs, and I ended up with an IF of 0.91, a NP of 231w, average power of 218w, and average HR of only 143bpm. High wattage relative to my 253w FTP and low HR relative to my max of 182bpm. The second outdoor ride (2 days later) was more of the same again lasting around 2hrs but this time with a NP of 233w, an average of 214w and an average HR of 153bpm.

Lots of numbers here but the trend I’m observing is that my wattage on MTB is very high for long durations of time relative to my FTP and my HR is fairly low relative to my threshold HR. I should also mention that the above rides were mostly on flat singletrack trails with minimal obstacles (lots of flow).

Has anyone else experienced this discrepancy between wattage they are able to put out on MTB vs. Road Bike? This is nothing new - I’ve observed this same relationship throughout the whole season and all last season as well. Thought I’d post here to see what other people’s experiences have been.

  • yes, the power meters on MTB and CX are different units but both units are very stable in their readings relative to HR and PE
  • yes, both rides were in the same location and completed in the same conditions
  • yes, the obvious way to resolve this issue is to do another ramp test but this time on the MTB - I will do this eventually.

Thoughts?,
eric

2

Sounds like some interesting observations. I think it would be hard to do a fair ramp test comparison with a MTB on a trainer as you’ll either change to a slick, or keep a knobby on. Changing to slicks would not replicate real world use, and a knobby would add a lot of rolling resistance that you’d have to get through, and thus you’d use more effort.

Probably @jonathan would know the answer to your question. I can’t recall him comparing road and mtb readings on his MTBPodcast, but no doubt he will have witnessed something along these lines himself since he is a mtbiker first, road/cx second.

3

Have you ridden your mtb on a few smooth road sections and compared the power readings to the cx bike? Mine actually match up pretty well on the road, bit one i hit the trails average power goes way down, end even normalized power will be about 10-15 watts lower for the measured hr and pe. I think that is more specific to my local trail though, since it is up down, up down, hairpin turn etc… no real flat areas to put down steady power.

4

I think it may also relate to the individual rider’s ability to remain ‘smooth’ and keep putting the power down. As I have improved from a technical ability, I’ve noticed that my singletrack speed has increased (obviously) but also my ability to keep my wattage high and smooth(er).

I’ve ridden my MTB on smooth sections of road and have observed similar to the above - higher wattage than on CX. That said though, I’m pushing 2.25 knobby tires on MTB vs. 30mm slicks on CX.

this might also be down to crank length - 175mm on MTB, 172.5mm on CX. For consistent cadence, wattage would be higher on the 175mm MTB crankset.

the investigation continues!..
eric