GPS-Based Speedometer Apps

**rionapo** · 08-19-2012, 09:01 AM

Can't decide whether our odometer works with the bigger tires or not. Measured against mile markers, we're about 1/10 of a mile slow while the speedometer agrees with those roadside speed control gauges. I've tried a couple of GPS-based apps to measure speed and odometer readings. (Methodology: Set cruise on a flat road section, verify speed on app and track miles.) None of them agree with each other. Seems to me there are a few explanations. Could be the iPhone GPS isn't sensitive enough. Could be the error in the odometer reading is trivial or falls within the margin of error of the app or the phone's GPS. Could be the apps do something funky with their GPS readings. Any ideas or comments?

woodbee · 08-19-2012, 10:55 AM

rionapo,

I think the most accurate way is to use a hand held GPS mounted on your dash. I have done it many times and compared it to my topo software in my computer, it seems quite close.

Hope the info helps,
Woody

**rionapo** · 08-19-2012, 11:04 AM

Quote:

Originally Posted by woodbee

rionapo,

I think the most accurate way is to use a hand held GPS mounted on your dash. I have done it many times and compared it to my topo software in my computer, it seems quite close.

Hope the info helps,
Woody

THat's where I'm headed. Can't imagine the phone's GPS is sensitive enough at highway speeds.

Ultrasport12 · 08-19-2012, 01:43 PM

Seems to me that if the Speedometer (mph) is close the Odometer would be as well. To me 1/10 per mile is a lot. I did a 3,000 plus mile cross country trip last year and my gps vs odometer readings were less than 20 miles different at the end of the trip.

I think you will find when you check with a gps unit (I would think depending on your phone and carrier it would work as well) they both are close or they are both off. Depending on what year your van is you can get it adjusted to be more accurate once you find out how much its off.

**rionapo** · 08-19-2012, 05:48 PM

Quote:

Originally Posted by Ultrasport12

Seems to me that if the Speedometer (mph) is close the Odometer would be as well. To me 1/10 per mile is a lot. I did a 3,000 plus mile cross country trip last year and my gps vs odometer readings were less than 20 miles different at the end of the trip.

I think you will find when you check with a gps unit (I would think depending on your phone and carrier it would work as well) they both are close or they are both off. Depending on what year your van is you can get it adjusted to be more accurate once you find out how much its off.

We're heading towards Crested Butte in a few days. Not exactly 3k miles but an opportunity to check over a longer distance.