After a long season of training for road racing, I’ve switched over to just riding my MTB for the fall/off season and I’ve been stunned by how much lower my power numbers are on the MTB. I’ve pulled a couple of efforts from road and mtb from the last month or so below, listed out below. Comparing the 50 minute road effort and the 20 min mtb effort, both felt like high tempo efforts, the road power was ~100W higher with a lower HR for over twice as long. Comparing the two 15/18 min max efforts, the road NP was 57W higher. The implication here seems to be that my endurance zone on the mtb is something like 80-100W lower and threshold is 60W lower.
I’ve ruled out a few of the obvious reasons my power might be so different. 1) I did a test on my indoor trainer at 200W and 300W with both my road PM (assioma duo) and mtb PM (garmin rally double sided). Both read about 3-5W higher than the trainer as you would expect for pedal based power. 2) It also isn’t the big power surges and drops required to climb on singletrack. One of the power tests I did, noted here, was conducted on my mtb on a smooth steady paved bike path with my suspension locked out. 3) I measured and matched the saddle height and seat setback on my mtb to my road bike, on which I did a professional bike fit at the beginning of the season.
Has anyone had any similar experiences or have any ideas why the power might be so wildly different? There are obviously some differences in the position (stack, reach, q-factor), but can those really make that much of a difference? Anything I can do to pull my power up on the mtb?
Road Bike Efforts
-20 mins, 249W avg, 250WNP, 153W avg HR (snippet of endurance training ride)
-50mins, 303W avg, 319W NP, 161 avg HR (long climb in a race)
-15mins, 367W avg, 368W NP, 181 avg HR (near max effort)
-20mins, 206W avg, 208W NP, 167 avg HR (paved bike path, felt quite hard)
-18mins, 300W avg, 311W NP, 181 avg HR (single track climb, near max effort)