Yesterday I did a 20 minute of what seemed like an all out effort on my trainer to determine my FTP on my new power meter. The last couple of weeks have been rough so riding has been limited. But my FTP measured at 186 (192 NP). Then today I road 20 miles for about an hour and my highest 20 minute average was 186 (189 NP). I didn’t go all out, but there was 20+ MPH and a couple high bridges. What gives? Is it just a mental barrier to go all out on a trainer?
By the way, I weigh 215 lbs and my trainer is fan powerd if that matters.
Many people have trouble making the same power on the trainer as they can outside, for two primary reasons
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heat - your body produces a lot of heat when you go hard, outside you immediately leave this heat behind because you are moving. Indoors, you just sit in it. You need a bing strong fan and somewhere for the air to go. Turn the heat off, open a window if it is cold outside, get a big fan
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inertial loading - most trainers have a pretty small flywheel and the inertia is much less than real riding. if your muacles are used to the outdoors, you may make less power
Very normal to have a drop on trainer.
Various explanations, none perfect, but likely in combination, explaining it.
- Cooling. Even with a big fan, it’s not as whole-body as being outdoors
- Position. Even having position changes in angle from terrain elevation changes can offload some muscle work to slightly different muscles, so you in effect get more muscles activated outdoors on varied terrain, leading to higher FTP. If one is tested in aero and one on climbs, that increases the discrepancy even more.
- Fun factor. Outdoor stimulation >> trainer, every time.
Thanks, have an industrial fan and it was cool last night, so no. 2 sounds close to what I had in mind I think, though I didn’t know the technics. Trainers have always felt harder to me. So which is a better measure for setting FTP?
Well the purpose of FTP is primarily to set training zones, so if you train mostly indoors, test it indoors.
If you train mostly outside, test it outside.
If you are about a 50/50 split, it might be good to know your FTP on each.
Or, find a way to fix it. You might get better on the trainer with practice, or you might be able to add some mass to the flywheel or get a trainer with a bigger flywheel.
Thanks, have an industrial fan and it was cool last night, so no. 2 sounds close to what I had in mind I think, though I didn’t know the technics. Trainers have always felt harder to me. So which is a better measure for setting FTP?
Jack is right on. I believe the fan trainer has the lightest flywheel of all, but I could be wrong. I find with a little time on the trainer and some power targets, I can make the same power inside as out.
Jack is right on. I believe the fan trainer has the lightest flywheel of all, but I could be wrong. I find with a little time on the trainer and some power targets, I can make the same power inside as out.
depends on the fan, the Lemond had a big ass iron fan that was real heavy.
Jack a usual is spot on. I find that leg fatigue seems to occur a lot faster at a lower HR. But on the flip side, I did a “pwoer test” (no power meter yet) to try and determine LTHR, and I actually went higher than anticipated.
Well the purpose of FTP is primarily to set training zones, so if you train mostly indoors, test it indoors.
If you train mostly outside, test it outside.
If you are about a 50/50 split, it might be good to know your FTP on each.
Or, find a way to fix it. You might get better on the trainer with practice, or you might be able to add some mass to the flywheel or get a trainer with a bigger flywheel.
Thanks, have an industrial fan and it was cool last night, so no. 2 sounds close to what I had in mind I think, though I didn’t know the technics. Trainers have always felt harder to me. So which is a better measure for setting FTP?
I go through the motions or do hard intervals indoors, but get most of my mileage outdoors (Florida), so it is in my interest to do it outdoors. I’ll do an all out on a trail I often ride with few stops and flat, that will be the FTP I use for racing, etc. Like I said, since my ironman (injuries and personal challenges) have reduced my training to 4-6 hours a week. Just make the most out of what I do, so I’ll probably have to do a few tests as I find the fitness comes back.
I’m no guru at this stuff, but I feel like these numbers are not saying what the OP thinks they are saying.
If FTP is measured at 186 on a 20 minute test, then wasn’t the actual power output on the test 196, since FTP is 95% of 20 minute max power, or 196*.95=an FTP of 186. If you did 186 average then your calculated FTP is only 177 and maybe there is an issue.
Depending on which is the case, while perhaps the 20 minute max average was 186, he hasn’t given us his average for the whole hour. He presumes he could go harder for the whole hour because he didn’t go all out for the hour btu that seems like a big stretch. It seems highly likely to me that his max output for the hour, if he had been going hard, may be really close to 186 if he that was his hardest 20 minute average and the rest of the ride was somewhat lower. In which case, the trainer FTP test looks awfully valid.
Not trying to be a jerk to the OP, but I just don’t see how your numbers are telling you your outside FTP is way higher than your indoor FTP test. And if I am way off here, happy to be corrected since I am trying to learn all this stuff too.
…Is it just a mental barrier to go all out on a trainer?
I find that I struggle quite a bit on the trainer as well. The only thing I can accomplish with certainty are my recovery rides. Harder intervals I’m normally 20% lower than I would be outdoors. For me I find it to be more of a mental game, lack of motivation.
- inertial loading - most trainers have a pretty small flywheel and the inertia is much less than real riding. if your muacles are used to the outdoors, you may make less power
I’ve heard this explanation before, but it doesn’t completely make sense. Inertia should play a very large factor in speed, but not necessarily power… Except for overcoming the dead spots of your pedal rotation. I use oval (Q-Ring) chainrings to help reduce this during day to day riding, but still find a very large discrepancy between indoor and outdoor.
Got any further explanation?
Also, I’m using a very cheap fluid trainer that does not have a flywheel. Was originally purchased for my wife and I was going to use the rollers. Now I use the trainer and she quilts… go figure!
I’ve heard this explanation before, but it doesn’t completely make sense. Inertia should play a very large factor in speed, but not necessarily power… Except for overcoming the dead spots of your pedal rotation. I use oval (Q-Ring) chainrings to help reduce this during day to day riding, but still find a very large discrepancy between indoor and outdoor.
Got any further explanation?
Also, I’m using a very cheap fluid trainer that does not have a flywheel. Was originally purchased for my wife and I was going to use the rollers. Now I use the trainer and she quilts… go figure!
If you could look at your instant power output shown in relation to crank arm position, you’d see power climb rapidly as you reach 90 degrees then it slowly drops off as you reach the bottom and finally gets ot nearly zero as you get to 270 util probbly around 340 degrees. Near the top you’re able to generate power again if you’re seat isn’t too low.
The difference is that while on the trainer and outdoors drag is still constant, but out on the road, a 160lb ride and bike has 180lbs of force moving down the road. That’s a lot of inertia. When you coast on a flat road, it takes what, almost 2 minutes to reach zero mph. On a trainer that’s probably 15-30 seconds. So between those peaks in power your wheel is slowing down. You legs will attempt to compensate somewhat by pushing harder than they might normally during the less powerful ranges of motion. So you have your actual cadence varying somethimes significantly within each crank rotation.
My trainer has a pretty minimal flywheel weight. I’m tempted to get a much heavier one machined for it. Although as weight increases, you may have to get it balanced. Although, static balancing might be good enough. Ideally all trainers would have an options of a big cast iron flyweel that you could bolt on.
I think the most important thing is to do the test either indoors or outdoors depending on where you’ll use it most to guide training.
So if you’ll be doing mostly outdoor power-based rides (note this doesn’t mean outdoor riding alone, it means using power to GUIDE training, not just using it as a recording tool and doing your regular rides as previously), get your outdoor FTP and base on that.
If you’ll be on the trainer mostly , or using it for trainer-rides (like Trainerroad), suck up your manly ego, take the FTP hit, and go by your indoor (lower) test numbers.
Now this is more like it. Hooked up the virtual trainer and with a screen in front of me I averaged 209W in my best 20 minutes in a 40 minute trainer ride np was a little higher at 211. Does it matter I had motivation. All the literature says do it without to not bias the data. But I still felt good after could have gone higher if I was doing a test. Can’t wait to get on that flat trail I know.