getting trainer wheel up to speed...trainer feature

[nreimche]

Doesn't it take more watts then 300 to get the wheel up to 300 watts on the trainer? It would be a good feature if those numbers could be figured out by the Ibike. For instance, I'm sure getting the wheel to spin fast enough, to read 300 watts, in 5 seconds would require a spike in watts greater then if I got up to 300 watts (on the trainer) in a minute. IS there information or statements, somewhere on this topic, like "On a road machine it would take, an average of x amount of watts to reach 900 watts in 4 seconds"? Where would a 5 second average power on a trainer stand in a power profile chart if the extra watts were considered? Thus, sprint workouts, on a trainer, w/ an Ibike would omit the MAXIMAL instantaneous power spikes, one really generates. Thanks!

[lorduintah]

The same holds true for getting the space shuttle into orbit. Not just because of the extra power required to carry the depletion of mass (expended fuel and tanks) as it is accelerated to 18,000 mph.

There is inertial resistance that is needed to be overcome to get the wheels spinning - same is true for regular, aero and disc wheels on a bike or a trainer for that matter. It will depend on the mass and resistance and how fast you want to accelerate.

On average how much time do you want to take? How much time are you going to be spinning? If the latter is much greater than the former, then it is very likely that the spike of Watts will have an extremely small influence on the total Watts (and of course average) expended during a spin.

Tom

[nreimche]

so can we see a logirhythm(or some formula) in the future for an Ibike firmware that calculates instantaneous watts? Instantaneous watts that are indicative of rate of accelration to get up to speed? Just curious. Perhaps it is too complicated, but it seems doable w/ a DFPM! I don't have a DFPM to use myself, but it could make the overall use of the product more interesting! Thanks.

[MultiRider]

I'm not a physicist, so I may be wrong, but you'd probably have to enter the weight of your wheel into the iBike and they would have to do additional calculations for that. And you'd have to enter the weight of each wheel. So you could have trainer profiles based on wheel weight just like outdoor profiles with all the other parameters. My guess is that this won't be high on the iBike list of desired enhancements. It would be cool, for sure, because it would then accurately measure watts for sprints on the trainer, but that is a tiny percentage of iBike usage.

[nreimche]

Thanks for that insight! I did not consider wheel weight, but you're right about all the little factors, that would have go into 100% accuracy. Rolling resistance ofthe tire used, tube type, bladed or non bladed spokes, are a few more details that would have be accounted for. I was thinking in general terms anyhow. I get curious about such little things once in a while, and I don't know anybody w/ a powertap, computrainer, or DFPM to test some of these things. I shall never give up my persuit anyway(Lord willing!). Grrrrr!

[racerfern]

Instaneous watts are roughly shown in the bar graph under the wattage display number. Actual (instantaneous) wattage is probably too wildly fluctuating to display.

The amount of energy required to get you up to say 18mph in 20 seconds is phenomenal. It's probably enough to keep you going steady state for a minute or so. So after a half dozen or so hard accelerations towards the end of a long ride I feel wasted and there's good reason why.

On any given ride try zooming way in to a hard standing start. You'll see a significant jump in wattage until you're up to speed. Highlight that section and look at the corresponding energy. For me it's about 6-7kj per acceleration. That's enough energy to carry me for 50-60 seconds of steady state riding.

WKO has a feature called Fast Find to show you where you burned your matches. http://home.trainingpeaks.com/articles/ ... match.aspx

[rruff]

I'm not a physicist, so I may be wrong, but you'd probably have to enter the weight of your wheel into the iBike and they would have to do additional calculations for that.

Worse than that... you not only need the rotational inertia (not weight) of the wheel, cranks, pedals, shoes, and legs (if you want to be picky) but also the inertia of the trainer. Good traners have a big flywheel to supply extra inertia. But the inertia of a typical trainer will still be a lot less than what you have on the road... in most cases trivial enough to ignore.

[lorduintah]

This may not be up to the complexity and standards of rocket science and putting a spacecraft in orbit around Saturn, But I think it is illustrating that there are a number of factors that could be considered. That said, I don't think a DFPM or the iBike has quite the level of sensors to accommodate the instantaneous accuracy that appeals to the true Watt freak - in an OCD sense, anyway. Suffice it to say that neither the iBike nor any of the DFPM units also take into account the Watts used for a beating heart, pumping lungs and a myriad of other factors that might add a few more fractions of a Watt to this endeavor.

I write this with tongue in cheek. But the reality is one can always find sources of error by omission, it is just how much is good enough and I think the iBike has met that requirement.

Tom

[nreimche]

I concur. Maybe I am a watt freak or a bit picky, but not really. Rhetorically/sarcastically speaking! Sprinting is just one of my weaknesses, and I wanted a general (but a LITTLE more specific) estimate of my power to work with. I guess when I'm fresh I can just do short maximal repeats and I'll improve (w/ proper rest, diet, etc).

Interesting to know that space shuttles have such things. As far as accelerations requiring so much more energy to get up to speed(s), I guess that's why it is best to take a minute to reach Time Trialing speed in a race or test. It saps you quicker then you realize. Anyways, thanks for the replies (I feel like I put myself on the spot here). I can work w/ the Ibike as is! Now I just got to get it fixed, Lol!

[rruff]

iBike nor any of the DFPM units also take into account the Watts used for a beating heart, pumping lungs and a myriad of other factors that might add a few more fractions of a Watt to this endeavor.

They measure output rather than input... or in the iBike's case it is more like measuring demand. The human body tends to be ~20% efficient at cycling... so in other words if you are pedaling at 300W your body is burning energy at a rate of ~1500W.

On a trainer we are talking about something else entirely. The iBike assumes zero inertia... it merely uses the power vs speed curve of the trainer. A DFPM works as it normally does while on a trainer... it measures torque and speed, so it doesn't need to make assumptions about inertia.

It would be possible to calculate the degree of error that would occur by neglecting inertia on the trainer, but I'll leave that as an exercise for those who are interested. I've been able to do NP busters with 1 min intervals on my KK, so I don't think inertia is a big deal. One thing that makes it tough to do sprint intervals on a trainer is the slippage of the tire.