Some time ago I had a good friend explain to me how GPS works. It seems that it uses the CPU to create a mesh of the signals from the various GPS satellites tracking around the Earth. The signal is very faint, so it has to use DSP to improve the quality of the signal, and then begin to tighten down the mesh until the grid square that the device is in is small enough to provide reasonable accuracy. To obtain altitude, the device has to find a signal from a 4th satellite that is at something of a horizontal to you to figure out how high you are relative to sea level. Finding this satellite takes a while which is why current GPS devices are so terrible and take so long to determine altitude.
The iPhone, and other phones, get a boost in speed by using the cellular network to get a rough location, and to download the locations of the satellites instead of trying to get it from the satellite network itself. This is called aGPS, which is what the iPhone uses.
Another piece of information I discovered with a few friends a while back was that when the iPhone is either on a congested Wi-Fi network, or is hunting for Wi-Fi, in addition to draining the battery, the performance of the CPU is degraded, especially on 3D gaming.
Recently on my last ride, I put these things together and turned off 3G ( leaving EDGE on ), turned off Wi-Fi, in addition to disabling push notification and setting fetching for email to manual, turned off bluetooth, and disabled auto-lock. This left my iPhone in a near airplane mode state. After my ride, I reviewed the map and to my surprise all of the inaccuracies I was blaming on my iPhone having subpar GPS went away. The tracking was perfect, the best I’ve seen as well as having fairly little battery consumption. I’m not sure what impact 3G has on the CPU, but it is likely significant as I had done some of these other things in the past and not had such rock solid GPS tracking before.
I think I’ve found a new riding configuration, if only Apple would update the settings application to give me custom settings bundles so that I could drop it into my riding configuration with one tap. Maybe for iPhone OS 4.0?
I had always known about how Lance Armstrong continuously advocates riding with a higher cadence and in a higher gear for maximum speed on a bike. I never really appreciated how that worked until today.
I was on one of my usual rides today, but I had left my bike in a higher gear than I usually ride. I decided to stay in the gear throughout my ride. What I found is that I dropped 0.2 watts per kilo, and was off about 40 watts from my typical average power output. It could be that it was cold, but I don’t think so. I have done that ride many, many times and I am typically at around 2 watts per kilo or a little better and 200 ~ 220 watts average. I dropped to 1.6 watts per kilo, and 175 average or so.
What I expected was a minor drop in watts per kilo and average, but what I didn’t expect was the magnitude of the drop in average and max output. On my next ride, I’ll drop into my usual gear and see how it compares. It is really cool to have access to all this data.
Over the winter months, it tends to rain in my part of the world. It is often during this time of the year that people think that a Garmin or a Polar have the advantage.
I have figured a way in which I can still bring my iPhone out in the rain and have it stay dry as a whistle. You may already know it, but a Ziplock baggie is your best friend in the wet winter months.
The baggie keeps the phone dry, make sure that you seal it and push out the air, and the best part is that you can still use it while it is in the bag. The screen is completely workable! Anyway, I hope this winter tip keeps you riding with your iPhone through the winter months, assuming the temperatures cooperate.
The other day, an annoying thing happened to me during my ride. The thing I have been trying everywhere to fix is still there.
Basically when someone calls you during a ride, whether or not you answer the call it cancels the application’s call to tell the phone to stay awake. This is a bug in the iPhone OS 3.1.2 as best as I can tell.
When this happens, the ride data gets screwed up, your moving time and total time may, or may be generally correct, but the power and speed graphs will look nuts.
Whatever the case, the best workaround is to turn off “Auto Lock” in your settings on the iPhone under the general preferences section. The caveat is to turn it back on after you have finished your ride.
I’m hoping for a Juice Pack for Xmas so that I can extend my rides past 3:30 minutes, or the longest I’ve been able to ride before my stock 3GS battery dies.
I know with the weather out there it’s tough, but even in the cold it’s good to get out for a ride in the real world and leave the fluid trainer for when it’s particularly nasty out there.
Anyway, Good Riding!