GPS Madness

In an attempt to dial in our bike computers to match each other we spent most of our ride yesterday fiddling and diddling with our settings. We have a "measured mile" on our road (pays to have runners in the family). We kept riding up and down trying to get it right and then worked on it more during the ride. Most maddening is that no matter how we tried we had a difference of 4 hundredths of a mile for every 3/10ths of a mile. Miniscule, right? Except as you extrapolate that to longer and longer rides the differences pile up. If you are trying to coordinate together on a cue sheet or you have a mechanical or medical problem, and you need to know how far away your help is it can really mess things up.

We even pulled out our phones and tracked our bike computers along with our GPS based Map My Ride App. Closer to Marsha's bike computer, but sometimes matching mine and then going back to being closer to hers. There was not one consistent pattern we could zero in on. My computer actually would run ahead of Marsha's quickly climbing to .09 and then mysteriously dropping back to .06 to match her for a while.

There are many reasons why bike computers will vary from each other. Different tire pressure, some type of interference between the cadence sensor and the handlebar unit, or with the cell phone some type of interference between the phone and GPS satellites and/or cell towers. The fact that I out weight Marsha by 100 pounds can change the diameter of my tires as I push them down more.

So, we decided that we will live with it, or perhaps spin my wheel a few hundredths to catch up to Marsha's computer before we start a ride so we even out. The GPS based phone apps we usually hold in reserve as it really sucks down the battery and even with our extra battery packs, the ability to have juice to call for help is more important than recording the ride. Around home for a workout ride or to measure a new route, fine, but out on our western wanderings, an extra layer of security in battery life is a trump card.