Bike Computer Distance Setting

[WhuYu]

Good day people, need some technical info please: If my bike computer is "under-reading" a distance: example = if a distance is measured to be 100kms.............and my bike computer shows 90kms.................what do I need to do on the "wheel size" setting? Increase the wheel size.............or....................decrease the wheel size setting. Hope my question makes sense. I have already measured the wheel size and set the computer setting accordingly; however, when measured against a Garmin....................the distance is less than the Garmin reading. My thinking being the Garmin should be more accurate?? Thank you.

[Bateleur1]

Interresting.  That is a 10% difference which is pretty huge.  Does your garmin use a speed sensor?

 

Maybe do a parallel test with something like Strava, to verify your Garmin but the GPS devices are normally pretty accurate.

 

How did you measure the wheel size?.  The correct way would be to put measuring tape on the ground.  Put your wheel next to it with the valve down at the start of the tape.  Roll forward and let the wheel do once curcimference and there where the valve is on the second point, that is the value you enter into your cycling computer in mm.  Normally something like 2110 mm or something.

[GhostSixFour]

You would need to increase wheel size. By 10% I'd wager.

[seven]

Wheel size should be increased by 11%, it should be 111% of current value...

[Psyrax]

Should it not be decreasing wheel size, so the computer measures the wheel spinning more over same distance? Or something like that

[seven]

Should it not be decreasing wheel size, so the computer measures the wheel spinning more over same distance? Or something like that

It measures the number of revolutions per time interval (RPM), and multiplies that with the wheel circumference...

 

If the RPM stays the same (as it would), increasing the wheel circumference will increase distance traveled.

[WhuYu]

Interresting.  That is a 10% difference which is pretty huge.  Does your garmin use a speed sensor?

 

Maybe do a parallel test with something like Strava, to verify your Garmin but the GPS devices are normally pretty accurate.

 

How did you measure the wheel size?.  The correct way would be to put measuring tape on the ground.  Put your wheel next to it with the valve down at the start of the tape.  Roll forward and let the wheel do once curcimference and there where the valve is on the second point, that is the value you enter into your cycling computer in mm.  Normally something like 2110 mm or something.

Tks Mr "B" for the reply......... I should have been more specific......I use a Sports Tracker app on my phone. Riding with some mates, their bike clocks and apps were accurate...................was just not sure what I need to do to rectify my bike clock. Seems as if there some replies with a solution.........

[WhuYu]

It measures the number of revolutions per time interval (RPM), and multiplies that with the wheel circumference...

 

If the RPM stays the same (as it would), increasing the wheel circumference will increase distance traveled.

Thank guys.............for taking the time to reply. I will do as advised..................tks a wack!!

[Longbarn Killer]

Most of these computers will come with a table of sorts that will tell you what data to insert according to your wheel size. There is also a manual method whereby you measure one full revolution of the wheel and input that data (usually in mm).

 

Remember, if your distance is "under-reading" all your other readings (speed, avg speed etc etc) are also incorrect.

[fabs]

Interresting.  That is a 10% difference which is pretty huge.  Does your garmin use a speed sensor?

 

Maybe do a parallel test with something like Strava, to verify your Garmin but the GPS devices are normally pretty accurate.

 

How did you measure the wheel size?.  The correct way would be to put measuring tape on the ground.  Put your wheel next to it with the valve down at the start of the tape.  Roll forward and let the wheel do once curcimference and there where the valve is on the second point, that is the value you enter into your cycling computer in mm.  Normally something like 2110 mm or something.

 

This is the correct method.

Only thing I would add is, inflate your tyres to the usual pressure you use whilst riding.

You climb on your bike, and do the procedure as detailed above.

[Jaco Steyn]

Interesting and informative information can be read up on here: https://www.sheldonbrown.com/cyclecomputer-calibration.html