Apps that let you set wheel size
 

I've tried a bunch of different IOS apps and the data is always wrong because I have 20" wheels, so big difference in the speed reported. Anyone use an app that actually lets you set the wheel size (not just the bike type)? I don't need anything fancy, I just want speed/distance/calories burned. I've got a wired cadence sensor I mostly rely on.
thanks in advance

An app that uses GPS for speed should not need wheel size. You could be jogging or on a skateboard and it would still be able to tell what speed you are going.

Ride with GPS should work.

What apps are you using now?


-Tim-

Cyclemeter lets you enter specific wheel sizes. It's not confined to a few presets like some apps. It's compatible with at least some sensor devices, but I don't use any.

+1 on the GPS. Strava is easy and fun as well.

I've got a cateye speed and cadence meter mounted to the bike - and runtastic/mapmyride and several others are way off compared to my meter (which is set correctly for 406 wheels). A difference of around 2-4mph depending on the app compared to my physical sensors. Just to be sure, I rode along side my son yesterday (he has a 700c bike) and we compared sensor speeds to make sure mine was reading properly.
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GPS accuracy should be better than 2-4 mph off, however your phone's GPS may not be that accurate as phones are usually designed for longer battery life rather than accurately measuring your speed.

All of the phone apps use GPS to obtain speed and distance unless there is a sensor connected to it, in which case they use sensor over GPS. Setting wheel diameter to a phone app without a speed sensor connected won't make a difference since it has no sensor data to calculate speed and distance with. Every time I have compared any GPS computer (not connected to a sensor) to a stand alone computer, there is always a difference.

Ah, okay. I actually tried 3 apps yesterday and they ALL gave me different readings, lol. I will stick with my cateye data and just log it manually.

How different were the readings? My wife started using a cheap wired computer on her bike. I calibrated and installed it. I did the calibration by doing a rollout test, so it might be 1 or 2% off. It agrees pretty well with my ridewithgps recordings.

I compared Wahoo Fitness using GPS for speed to my friends using dedicated garmin with wheel sensor and the difference is negligible when riding. The GPS takes a couple seconds more to adjust for increase/decrease in speed. We also compared distance logged at the end of the ride and again its negligible in the big scheme. I know wahoo lets you set the wheel circumference if you're using a sensor. I would guess the model phone/OS is the blame if there's big reading descrepencies if using popular apps like STRAVA, WAHOO, RIDEWGPS, etc. regardless of using GPS or sesnsors. Those apps are popular for a reason.