Why are CT watts so much flippin harder then the SRM watts.
My threshold watts are around 275. Last week i did a 2hour ride at 220 watts. Both tested outside. Now today i get on the CT for a interval workout i’m doing a 200-250 watt increase over 8 mins. I get up to 220 watts and it feels like i can’t even spin the tire over. I’m in the 39x17 and am just dying.
FYI, everything on the SRM was zeroed out along with the CT. Am i doing something wrong with the erg program. or do i need to adjust my wattage by a lot to get it to equal the outside wattage?
CT measures, I believe, power at the wheel, so you have all the losses from your drivetrain to make up for. I think it compensates for Crr (isn’t that what the calibration is at the beginning?). BUT, CT are notorious for being imprecise. They are consistent, but they are definitely imprecise. I.e., each computrainer will be equally hard day to day, but computrainer 1 will not show the same watts as computrainer 2. That’s the rumor anyway… I think gregclimbs had some posts about this a while back… Anyway, the short answer is what you are experiencing is not uncommon…
The CT watts and the SRM watts are at opposite ends of the measurement points. SRM measures watts at the engine (you) and the CT measures watts at the final drive. Your drive train, crank, bb, hub, wheels and tires will lose watts along the way.
Since you have both, you can make adjustments to your drive train and see what effects that will have.
If you were into cars, the horsepower that an engine generates and the horsepower measured on a dyno would be totally different. The dyno would read significantly less than the rated horsepower of the engine. All the losses are coming from the drivetrain.
Drivetrain losses shouldn’t be that large. It only makes sense if the CT doesn’t in fact account for power lost to rolling resistance, which would be silly, but possible…
So essentially i should do a FTP test on the CT and use those wattages for only the CT. Because its quite on the frustrating side when you can’t even get up to 230 watts with out standing up and mashing the pedals.
I would recommend you ensure your RR Calibration for the CT is at least 2.7. Do not use the 2.00 value. Also, make sure you recalibrate multiple times through your warmup.
One thing to be careful of, if you were riding at a speed prior to calibration that was higher than what you ended up doing your intervals at, then your RR might have gone back up. At a higher speed the tires will warm up more, and you will have a lower RR calibration. Most folks believe speed is irrelavant in ERG mode, and that is true to a certain degree; however, you want the speed you ride at to be similar to the speed you were riding in the few minutes before calibrating. With that said, a difference of 40-50 watts is pretty darn large.
If this didn’t make sense, then I appologize. Its late…
Yup. Don’t forget that your FTP will be lower inside anyway due to core temperature increases that you don’t see outside. Riding inside, even with a fan, your waste heat will raise your core temp much faster than it would outside. To a certain extent, inside watts are inside watts, and outside watts are outside watts. Adding a different power-measuring device into the equation forces you to realize this, so perhaps it’s a good thing. This is when using a HRM to double check yourself is a good idea.
I understand what you are saying but i also agree with rappstar. If you think about it i should thoretically be able to run even like 270+ watts for that 8 mins easy. If thats true you’re looking at like over a 20percent drivetrain loss which is definitly not possible.
Erg watts, combined with a low flywheel effect, are always harder anyway. Even when I’ve had my Powertap and CT matched up very nicely, I can always hold more watts for a given duration on a real road than on a CT in erg mode. I once did a 45-minute duathlon bike leg at 255 avg. watts at a time when I couldn’t do 235 watts on a 2x20’ CT workout. I think the difference lies in the fact that the CT gives you almost no flywheel effect, and that somehow puts a bigger strain on the ability to hold high power levels.
The problem is that, at the end of the day, the CT is still just a trainer and one with a light flywheel. Though its ability to vary resistance mitigates it to some extent, trainers with light flywheels don’t have enough inertia to sufficiently simulate outdoor pedaling. People only apply power during part of the pedal stroke but trainers apply resistance countering that at all angles. The sensation that you are pushing over the top and pulling through the bottom (pedaling more in “circles”) is very real. Outdoors, you have the momentum of the wheels and drivetrain and your body to carry your legs through the “dead spots.” On a high inertia trainer, you have a large flywheel (~55 lbs) to do that.
If you’re not generating as much power, you’re not getting as good a workout despite equivalent or higher perceived exertion. In addition, I’ve long suspected that there are specificty issues with low inertia trainers which have been confirmed by studies:
The type of road riding condition that these trainers most closely emulate would be considered “low inertia” - i.e. slower speeds, climbing or riding against a stiff headwind. The higher priced trainers tend to use a larger flywheel and more closely replicate the feel of road riding under “high inertia” conditions - i.e. faster speeds, road racing or time trial. There have been a few studies on stationary trainers that suggest that the inertia of the trainer affects the muscle fibers and how they are trained. Low inertia trainers require more use of fast-twitch fibers while high inertia trainers more effectively train slow-twitch fibers. A few more popular trainers that would be considered “high inertia” trainers include Velo Equipe’s Chaindriver, Velodyne Sport’s Velodyne, Racermate’s Velotron, and most “spin” bikes.
On a Velotron, I can generate as much power in erg mode as I can outdoors once I account for the 15W difference between it and the SRM.
You’re using 39x17 in erg mode? Sounds like you are shifting to an easier gear to try to keep your cadence/torque in a comfortable range. That works in “grade” mode but not in erg mode.
Try using just one gear and keeping your wheel speed up at 20mph or higher. If you are tempted to shift to a lower gear then increase cadence so that the CT will reduce the required torque. (This requires a temporary increase in power.) If you let your cadence get too low you will bog down on the wrong side of your cadence/torque curve.