# Wahoo Elemnt/Wheel Circumference

Hi All
Has anyone come up with a reliable measurement for a 36" Nimbus Oracle wheel?. I have bought a Wahoo Elemnt Bolt and have tried it on auto and inputted my own measurment which was done just by wheeling the uni unloaded. But both ways seem to differ quite considerably from my phones GPS which is what i have used until now. When my phone says 16 miles the Elemnt says 15 Miles. I know my phone could also be wrong but if it is, it is wrong by the same amount consistently because i ride the same route regularly and the phone has always been reasonably consistent. I love the Elemnt so far though just would like to know how accurate the mileage is.

Regards Phil

If there aren’t too many turns in your route, your gps is probably more accurate. Some of the difference will be not so accurate tire circumference due to your weight compressing the tire, some will be because one is always a bit wobbly when riding a unicycle. (look at unicycle tiremarks in snow for example).

What I would do in you case is multiply whatever wheelsize you measured by 15/16=0.9375, then your wahoo elemnts reading will match your gps.
EDIT: actually, multiply it by 16/15=1.06666666667 I messed up.

Do a rollout test - sit on your saddle with your normal tyre pressure and measure the distance of one revolution. I came up with 2785mm for my 36er. These days I just use GPS though.

You should expect some discrepancy between the wheel sensor and GPS, because unlike on a bike our wheels never track perfectly straight. It’s probably such a small difference that you’re unlikely to notice it though. I suppose it comes down to a philosophical decision - whether you want to record how far the wheel has travelled or how far you have travelled.

Even better is to do several revolutions on the uni.
When I get a new tire, I go to the underground car park, mark a spot on the ground and the tire. I get on the uni with both marks aligned, ride 10 revolutions in a straight line then measure the distance to the new mark and divide by 10.
With the 36" I only managed to squeeze 9 revolutions before hitting the wall, but it’s still much more precise than one revolution for sure. Now my Strava rides are identical to what the bike computer says, within a few meters.