rough roads -- wattage drops

[doofus]

on some stretches of really rotten stuff around here, I notice that the watts displayed will drop by as much a 100+w -- from old power tap files, I know that if my speed holds constant on those stretches, I actually have to put out 10-20w more than on the smooth surface before the pavement changes (on a tempo ride, it would go from 270-280 on the smooth surface up to 290-300 on the rough patches -- on the iSport it drops from 270-280 to 150-170).


I assume its just vibration messing with the unit. I can live with it -- its not a deal breaker with this computer. But, is Velocomp still working on this?

Boyd -- what was your Battenkill file like? This York Co. SC crap is about like that....

[Velocomp]

Please send a ride file to jhamann@velocomp.com

We no longer have issues with rough roads so something else may be going on.

I saw Boyd's Battenkill file and it was within 5W of his DFPM...

[doofus]

john --

its still an iSport right now -- I'll upgrade it with the next week (ordered the upgrade last thurs), and we'll see after that

[rruff]

We no longer have issues with rough roads so something else may be going on.

My Gen 2 and Gen 3 both get confused when the road is rough. They display much lower wattage than usual because the accelerometer thinks you are going down a hill but you aren't. I'm not talking about the crazy spikes that occurred with previous units... that problem has mostly been fixed (though my Gen 3 still has them occasionally).

Last weekend my wife and I did the TT in Moriarty. The pavement itself was fairly smooth (ie not chipseal) but there were a lot of cracks. She had the Gen2 and her power was severely under reported for the whole race. The tilt was checked before and after and it was fine. Power was way low on my Gen3 until the tilt correction occurred at 5 minutes, and after that it fluctuated up and down since the degree of roughness was variable. On smoother roads they both work ok.

[Velocomp]

I'd very much appreciate getting some ride files that show this phenomenon.

[djconnel]

Of course, in theory the iBike should report low on rough roads, due to the assumption of constant rolling resistance coefficient. Obviously it's harder to ride at the same speed on rough roads, yet the iBike will report the same power on any surface as long as the speed and gradient and headwind are the same. Similarly, it has no way to know if your tire is flat, so if it is, it will also report low.

The only question is how low this will be. For example, if Crr = 0.5% on a smooth road, and increases to 1% on a rough road, for a total system mass of 75 kg, moving at 9 m/sec, this represents an additional 34 watts (assuming 98% drivetrain efficiency) from the road surface which the iBike can't possibly know about.

[rruff]

What you say is true, but what I'm talking about is an under-reported power because the tilt reads negative due to vibration.