Elevation "Instability"
Posted: Mon Sep 08, 2008 11:51 pm
For some time I have been seeing my elevation data jumping erratically throughout the ride. I have attached a recent ride file. I live in south Louisiana, and the areas I typically ride (such as this ride) are 100% F__L__A__T. A five foot elevation change would seem like the Galibier here. Looking at the ride data, I have no idea what occurred between miles 7.5 to 8.5. To see this much slope I would have had to accidently ride up the face of the Mississippi River levee and back down three times. But this is not even the effect I am talking about. I am looking at all the points where the elevation curve will suddenly 'drop out' and go instantly from +25 feet to -25 feet of elevation, and then back up a few seconds later. When I look at the actual data in the table these jumps are instantaneous from one data point to the next. Reviewing a sampling of my rides, it did not do this for the first couple of months after I installed the iBike. This started in about June.
Other data: I have the old iBike Pro model, wireless stem mount. Mount seems quite solid to me, but I did need to add some tape to the battery cover to assure good contact was maintained with the mount (without the tape I was occasionally getting wirless fail in the middle of rides). I see pretty much the same effect whether logging at one second or five seconds. I have Rotor elliptical chainwheels and originally I was concerned that perhaps these could screw up the power readings due to pulsations from variable effective chainwheel size around the pedal cycle, but I've never been able to see any ill effects. The attached file was for a solo ride, but I see the same effect for a ride in a paceline. I did a couple of rides in Austin TX a month or so ago and on hilly terrain I still see this 'ragged' effect on the elevation data with the momentary shifts down and back.
There is not a huge amount of traffic where I ride but I am wondering if vehicles overtaking me at fairly high speed could suck down the altimeter reading or a similar effect. When I shift the x axis to time and blow the curve up to 2 mins full scale, it appears these drops last between 20-25 seconds each time. At the speeds I ride and the speed of the traffic, it does not take them this long to get by me! But perhaps if the altimeter response is fairly slow to abrupt changes?? Any ideas would be appreciated.
P.J. Boyle
Other data: I have the old iBike Pro model, wireless stem mount. Mount seems quite solid to me, but I did need to add some tape to the battery cover to assure good contact was maintained with the mount (without the tape I was occasionally getting wirless fail in the middle of rides). I see pretty much the same effect whether logging at one second or five seconds. I have Rotor elliptical chainwheels and originally I was concerned that perhaps these could screw up the power readings due to pulsations from variable effective chainwheel size around the pedal cycle, but I've never been able to see any ill effects. The attached file was for a solo ride, but I see the same effect for a ride in a paceline. I did a couple of rides in Austin TX a month or so ago and on hilly terrain I still see this 'ragged' effect on the elevation data with the momentary shifts down and back.
There is not a huge amount of traffic where I ride but I am wondering if vehicles overtaking me at fairly high speed could suck down the altimeter reading or a similar effect. When I shift the x axis to time and blow the curve up to 2 mins full scale, it appears these drops last between 20-25 seconds each time. At the speeds I ride and the speed of the traffic, it does not take them this long to get by me! But perhaps if the altimeter response is fairly slow to abrupt changes?? Any ideas would be appreciated.
P.J. Boyle