I know some difference is normal, but this makes me wonder if there isn’t something really wrong with my fit, technique, or something else I can’t figure out. I went pretty hard on a climb on Saturday on my MTB and was only able to do 262w average / 269w NP for 41 minutes, with an average HR of 163 which is right around my LTHR. The climb is a kind of chunky fire road, but smooth enough that I never have to stop pedaling or really take any additional effort to handle the bike. I rode it in with my suspension in the middle of three positions.
One thought is that the grade isn’t constant, and the micro-accelerations where it kicks up wear me down, and then I don’t keep power up when it briefly flattens. The only other things I can come up with is that my fit is bad (although it doesn’t feel that way, but I am going to see a fitter soon) or my pedaling technique is bad and I mash too much. There shouldn’t be any significant difference in power meters, I’ve “triangulated” with my KICKR bike.
A sorta-hard MTB for 3 hours and I end up with 190w average / 228w NP at 148bpm, where that wattage on the road would feel very easy:
After seeing your post, I looked at my data and sure enough, road/gravel rides have significantly higher power than my mtb rides despite feeling equally tough, or sometimes tougher on the mtb rides. I haven’t analyzed it further, but my mtb rides have a lot of quickly varying climbing grades, so have a lot of variation in power. At first I might think NP would account for this, but no, it too is lower for MTB despite the climbs feeling similarly hard. Now I want to do some investigation and experimentation and see if I can figure anything out.
I’ll add that ~5 years ago I had put my mtb on the trainer instead of a road bike for a while and did some workouts on it. Results weren’t notably different then.
Unless you’re using the exact same powermeter then I’d bet it is just a difference between the two powermeters. They can be pretty different sometimes.
The OP said, “There shouldn’t be any significant difference in power meters, I’ve “triangulated” with my KICKR bike.” I’ve done similar in that I ran my Assioma power pedals on my mtb with a spider PM and put that on my trainer. They were all within a 5 Watts.
Yeah, I’m pretty confident it’s not that. I have Favero pedals on both bikes, both dual sided, and they both measure within a few watts of my KCKR bike.
MTBing often involves much steeper climbing than typically done on road. Not sure of your exact situation, but doing the same wattage at much lower cadence climbing something steep is much harder - more force per pedal stroke, muscle burn, psychologically much more difficult.
Those look like pretty significant differences, but there are three things I can think of in addition to what others have said (some of which overlap my points).
MTBs tend to have a significantly different fit than gravel and road bikes, and you may be weaker in that position. If I’m doing a long sustained climb on a MTB, I almost always wish my saddle was higher and further forward. Occasionally if I know my day will involve sustained steep-ish and non-technical MTB climbs, I’ll move my dropper post up by maybe 1 or 1.5cm. When I hit the long climbs I fully extend the dropper, and the rest of the time I know I’ll need to restrict how far the dropper extends.
Additionally, MTB cassettes tend to have significant jumps, reducing the amount of time you’ll be at your preferred cadence.
The more inconsistent the gradient and bumpy the terrain, the more difficult is to stay on the power smoothly. For gradient, think about doing a 5min VO2 effort on a hill which keeps changing gradient… it’s going to be more difficult to sustain your target power. For bumps, I find it sometimes feels difficult to hold onto upper Z2 power on a rough gravel road.
Daily variations in glycogen stores and training fatigue could also contribute.
My MTB is always much lower too - but more for real trails with undulations - I’d say on long gravel climbs they’re about the same. But, I think MTBing probably takes a lot more ‘micro’ movements (don’t know what else to call them) from your whole body than road biking. And I bet they add up. Have you ever compared your HR when you sit up straight on the trainer vs have your hands on your hoods? At least for me, just using my core muscles - on a stationary bike - to sit up straight will cause a 5-10 bpm jump. So I’d think all of the core/stability muscles you use to constantly handle the slight variations in terrain - even just from loose gravel - could potentially cause a higher effort for lower watts. I’d say in general - even hard trail rides that leave me feeling totally beat will often be (significantly) lower than endurance power on the roads where I feel like I had a nice refreshing spin.
To me it’s just an accepted fact that I can accumulate appreciably more TSS per unit time on road than MTB.
Others have said it, but the steepness of the terrain and the undulations are the main driver of this for me. Both of these things affect cadence. One moment you’re slogging in your 52 tooth going up some 20% grade, then you’re spinning your legs when it levels off, then back to steep.
In contrast in erg or on a long sustained road climb I can just get into my optimal cadence, actively focus on smooth 4 quadrant power and lay down the watts.
This is not something I lose sleep over. MTB still >> road.
First of all, Kudos for a 4h MTB ride. RPE is usually much higher on the MTB for me as well - reasons are manifold. For one I work much harder with my upper body on the MTB on berms, jumps, hopping over obstacles. This certainly has an effect on HR or general strain. I can easily ride 30min at LTHR on my local XC loop without touching NP anywhere close to FTP.
If you think there is something off fit-wise. I’d check saddle height and set back from the BB and compare that to your roadbike. A good fit can have substantial effect on RPE at a given output in my experience.
I can´t comp with road, as I only do MTB & gravel. But what I can confirm is that descending costs me significant power on the following climbs.
One of my home trails takes 15..20min to descend and it shakes you up from start to finish. And on the climb before I am worlds stronger than on the climb back up.
I preface this by saying that I don’t have a power meter on my MTB, my observations are based on a climb that I’ve done on mtb, road and gravel bikes. This climb is fairly smooth gravel, and takes me ~21-22 minutes on the roadie or gravel bike, but I’m happy to break 28 if I do it on the MTB. My MTB is a ~26 pound FS Epic Evo, so its fairly efficient for a mountain bike, and my gravel bike and road bike both hover around 18 pounds. So weight could be a factor, but I really think its the MTB position that is robbing some power.
The kicker is, I just don’t think that my road position would work on the MTB, the seat is too far back for technical climbs. “Modern” MTB geometry dictates a long front center, and if you put your saddle where it would be on your road bike, you’re not going to have enough weight on the front wheel.
My power on the MTB is always 10% or more lower. I blame it on less time on the MTB, the years it has been closest between the two were when I did a ride or two a week with my wife just cruising fat bikes on the tar trail around our house. I think that couple hours a week just cruising got my body more used to that position.
I get maybe 8 hours a week on a road or gravel bike and maybe 4 on the mtb, and the mtb time is on trails with less sustained (20+ minutes) just rolling on the power.
Thanks all for your responses. I have an appointment with my fitter in a few weeks. Not expecting any miracles, but I want to be sure there’s nothing major that’s holding me back.
@Sulliesbrew that’s a really good point about just spending more time on the MTB. I was looking at my training history a little more, and my numbers were closer last year when I was able to spend more time on the MTB early in the season. This year was cold and wet, so I ended up on the trainer and road bike more.
Take your MTB on smooth tarmac and see what you find. I can generally put out nearly the same numbers on paved road (as long as I haven’t run out of gear lol). I find on anything loose, like a steep chunky fire road climb, I lose some pedal efficiency as the tire doesn’t grip perfectly and I can’t relax my upper body the same way I can on the road bike. 20% loss seems like a lot, but 10% wouldn’t surprise me depending on how loose or rocky it is.
If I do that, without any upfront descends, I indeed would also see similar if not equal power, given that it´s on a climb. Modern MTB geo is not good on flat due to the steep seat angles and rather high fronts.
But I also run the same P2M PM on all my bikes.
I’m the same and always have tested lower power (esp average…disgustingly low). Once i tested my FS (115mm) vs hardtail with the same PM (stages-RIP), same parkour (different tires but close and diff fit and day) and the HT def was about 5-10 more. Not sure what type of PM or FS you have but the suspension may be taking some of that away. As others here have said all the micro adjustments and more use of your core/upper body with MTB’n makes the TSS more even if your TSS-ometer say differently on a road bike.
Now i dont have a PM on any of my MTB’s(SS, FS,HT) and really don’t miss it. Like the OP i’m in the mid Atlantic and there are no real sustained climbs, super punchy and cant really check out power while riding because of the typical east coast trees (you take your eyes off the trail and you hit a tree, that simple). I’m from the west originally and having a PM there is more relevant because of long sustained fireroad climbs and wider trails. I’m always dying to check out my power after a XCO or XCM but can’t do that now but otherwise don’t miss it and just have power on my rd, grvl and tacx. I use HR for MTB and its fine.
I’m going to say it doesn’t matter. You can’t expect your power levels on the trainer to match up what you can do on the and then also somehow triangulate that to the off road. Different bikes, terrain, temperatures, etc all come into play. What really matters is what your RPE is if you are trying to gauge effort. Tell me 2, 3 or 400 watts feels the same when you are on the trainer, on a track, on the sand or washboard fire road but you most likely can’t because they are all different. Personally, when I’m riding off road, I’m not doing intervals, and I only glance at my power to keep myself in check but I usually just go by RPE. I save the training and and nailing my wattages for workouts on the road or trainer. I will say, that I think it’s important to train on all the bikes that you have, and switching things up keeps me flexible and gives me the confidence that regardless of what bike I’m on, I can get my workout in. With that said, I have a road bike and gravel bike and I routinely train on my gravel bike on the road. My position is similar on both bikes and I swap my pedals over.
By triangulate what I mean is that I have power meter pedals on my road bike and MTB (both Favero). I can’t run them both at the same time obviously, so I tested each separately against my KICKR bike and everything tests within a few watts of each other. So the point is that the discrepancy isn’t due to PM differences.
EDIT: What really matters is not the RPE, but the power I can put down on my MTB. I don’t race on the road or really even do group rides, it’s only training for MTB racing. If I could close the gap between what I can do on my road bike and MTB, I’d be climbing about 10% faster in the example I posted, which would be huge. Maybe it’s not possible though, that’s why I was asking for others experience and opinions.
I get what you are saying, and I understand your triangulation. Riding on the dirt is so different when it comes to how the power is put down. Like you said, when the terrain flattens you power could dip and that may be cause for what you are seeing. For sure, if you could replicate the power output that would hopefully translate to quicker climbing and ten minutes would be huge. If it were me, and I was motivated to close the gap in terms of power, then I’d dedicate some regular training on certain course and consciously try and duplicate the power outputs for a given time on that course, whether it be single climb, a series of intervals on a climb, or what have you. Perhaps there are some gains to be made there with practice and you can get better at putting out more power on the MTB. Hopefully your bike fit helps and you can squeeze out some more watts because of it.