Wheel size for Radrunner 1 display upgrade

[Grizzly Granny]

 Hello!  I am new here.  I just received a new display upgrade for my year old Radrunner 1 for Mother's Day.   In the display settings for wheel size, it was preset to 22.  RR1 has 20 wheels, which really measure to 22 inches on the stock tires. I am not needing to increase the speed setting, just want to have the most accurate wheel size.  Rad customer service unsure, and after checking said to change to 20. Other advice given on FB and other sites recommend increasing it to 22.  Thanks for any advice!

[Eric7]

It is really hard to say. The only way is to find 2 markers on a road that are exactly a known distance apart, ride it, and see the measurement.

I am not trying to be difficult.  It is hard to say what 20 means on the controller.  Because the controller may have been programmed for a 20 inch wheel with a fat tire - meaning 20 inch on the controller may mean 21.5 inches.  22 inch on the controller may mean 24 inches.  Nobody really knows.  And there are probably many versions of the software.  After production of the controller, they probably updated the software a few times to adjust other things and the wheel size may have been adjusted. So probably by now, nobody knows for sure.  And if you hound the support guy and he/she says something - how can you be sure?

Maybe the best is just to choose something and not worry too much.  I am sympathetic but I see no solution.

The car speedometer is not any better.  People change tire sizes and diameters all the time without reprogramming.  You see car magazines testing cars and they hook up a calibrated bicycle wheel in the back to make actual speed and performance measurements because the car magazines don't trust the car speedometer.

To further show these measurements are just in the ballpark, the batteries are probably made with a 5% to 10% tolerance.  One battery may be 10% better than another - they just all have to meet the minimum requirement.  So it is probably the luck of the draw.  A lot of electronics are in the 10% range (things like resistors). 

And you know the battery meter is not linear.  There are 5 bars.  The first bar, in theory, should represent 20% of the charge.  It is actually closer to 30% or slightly more. This is to give you the illusion that the battery is better than it is.

All brands do this, not just Rad.

Digital accuracy is really an illusion.

[Si1Dia]

Your best bet for the most accurate measurement to enter into the display is to measure the outside diameter of your tire. Then enter that measurement or the closes match.

Remember that we are dealing with entry-level bikes using the cheapest available parts. The displays will never be GPS accurate.

[Ddaybc]

What Si1Dia has said is as close as one can get without going to crazy lengths to be "accurate."

If one wants to be as accurate as possible then set your tire size and test it compared to a GPS unit. Change your tire size and test it again. Keep doing it until you get the closest setting to your GPS unit. That's about all one can do.

What Eric7 said about car speedometers is also true and something to keep in mind. I remember some of my cars were accurate at lower speeds but at cruising speeds they were off by as much as 10 mph (I never cared enough about it to check on my metric vehicles when I got older.) Other vehicles I've had were never accurate. That's also why the police usually "allow" up to a 10 mph difference before they react to speeding based on what their radar guns show.

[Kapfish]

I set mine to 22 and increased max speed. I used my phone with a speedometer app and I believe this is the correct setting

[Grizzly Granny]

Thanks, everyone!  Great words.  I am going with 22 and not looking back, LOL!

[Radding Along]

The factory setting for the Runner 1, Runner 2 and Runner plus is 22". There were some early runners also set at 21". Either size works fine.