Controller vs GPS mileage

[AzRadtrek]

Hi there,

I am a new Rad Mini owner and I am really enjoying my new ride.  80 miles in 10 days!  I have noticed that my bike controller shows one mileage and my Apple Watch and iPhone show a different mileage.  The difference on my average ride is 6.3 on the bike controller and 6.6 on the watch and phone.  I have also looked at google maps and the mileage aligns to the watch/phone distance.   I have made sure the controller is set on a 20" wheel.  Has anyone else noticed this?  Is there a method to calibrate it?   TIA Bob

[fin_rad]

What does the speed display and GPS speed say while you riding?

I got the 26" RadRhino but since the fat tires are so big, I have to choose 28" in the settings for the wheel size. Otherwise the display on bike will show the range and speed slightly wrong.

[FortunatelyTheMilk]

One of the minor annoyances with the upgraded display I bought is that I can't pick the correct diameter for the wheel and tyre combo on the Runner. 20" is too short, 24"too tall, but closest. I'm guessing it's the same for you?

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[RadJohn]

... Is there a method to calibrate it?   TIA Bob

No.

The difference you noted is within ~5%, which is probably within the design spec. The 2020 RadMini 4 uses different size tires than the previous Minis (20 x 3.3" vs 20 x 4.0"), yet the display compensation setting of 22" didn't change. The difference will also vary with rider weight and tire pressure.

My multiple Garmin stand alone handheld GPS units display similar differences, no big deal.

The Rad controller/display manufacturer could have allowed entering an inflated tire circumference within a cm, but they didn't, probably because most people wouldn't read the instructions or measure or enter it properly, so we're stuck with the inherent errors in their simplified approach.

[AzRadtrek]

I agree it is certainly within a range of tolerance  but based on suggestions I will try adjusting wheel size in the controller to see which one is the most accurate.  I appreciate the insight and guidance.


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[RadJohn]

...I got the 26" RadRhino but since the fat tires are so big, I have to choose 28" in the settings for the wheel size

That's because "26 inch" fat tires are NOT really 26 inches (outside) diameter, but most are closer to 29 inches actual OD unless heavily laden and/or underinflated (technically it's the laden contact patch radius that is important, but that's a bit difficult for most people to measure accurately).

The "20 inch" tires on a RadMini are close to 22 inches actual OD.

The later actual OD numbers are what need to be entered into the controller/display to allow speed/distance to be calculated accurately, assuming the people who programmed the firmware got the maths right.

[AzRadtrek]

Thanks for the additional info. They controller was set at 24" when I received the bike two weeks ago. I changed it to 20" and will test it back at 24".


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[fin_rad]

Here's the good old way to check the wheel size:
https://m.youtube.com/watch?v=lkDnptjAq2o

[RadJohn]

Thanks for the additional info. They controller was set at 24" when I received the bike two weeks ago. I changed it to 20" and will test it back at 24".

My 2020 RadMini 4 came from the factory set to 22 inches (the next closest choices were 20 and 24 inches) , and that is the correct/default setting because it is VERY close to the actual  measured diameter of the mounted/inflated tire.

[RadJohn]

Here's the good old way to check the wheel size:
https://m.youtube.com/watch?v=lkDnptjAq2o

Actually it's the good old way to check wheel circumference, which has to be divided by pi to get the wheel size number that Rad requires us to enter in their display/controller settings menu for proper speed/distance calculation.

[AzRadtrek]

Thanks for the guidance. Started my ride set to 24 and that over estimated first 2 miles. Recalibrated to 22" for next portion of the ride and then as luck would have it tire started going flat :-(  So i managed to limp home and practice my tire patching skills. Will try again tomorrow with controller set to 22".

A small thorn proved to much for the puncture resistant tires. Good thing I bought a patch kit.


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[AzRadtrek]

So the final answer is no setting is exactly correct. Set at 22" it measures the ride at 7.0 miles compared to 6.76 via gps. At 20" it underestimates compared to the gps. I guess it comes down to personal preference. Either way I am loving my new rad mini.  100 miles since I received it two weeks ago.  Thanks everyone for chiming in on this topic.


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[RadJohn]

Keep using your GPS stuff because the Rad trip odometer will fail you completely some day.

If you're on a trip and stop to take a break or chat with someone, if the bike sits too long (seems like about 15 minutes or so), the display will turn off and reset the trip odometer.

Also, if you want to run into a store on the way home and turn off and lock up the bike, the trip odometer gets reset to zero.

So if keeping track of trips is important to you, remember or write down the Rad totalizing odometer reading at the start, or fire up a GPS or GPS app that doesn't reset until you tell it to.

Also, you will probably find that the difference between the Rad and GPS odometers can vary quit a bit on different trips and under different conditions. GPS calculations are influenced by tree cover, GPS constellation azimuth, whether you are traveling in mostly straight segments or zigzaging and other stuff. Mine have been as close as 0.1 mile on a ~50 mile trip, and as much as 0.5 mile off.