Hey guys,

Help me think through this please, I need a physics check.
I’m trying to set the wheel circumference for my Wahoo speed sensor for my Wahoo Bolt because I recently switched to a 32mm rear tire that I inflate to 63psi per the Silca calculator.
If I measure my inflated tire circumference with the roll out method and the wheel off method I get 2152mm BUT if I sit on the bike and do the roll out method I only get 2120mm… a 3cm difference!

My mind says that since my weight is compressing the low pressure, wide tire it results in a shorter rotating circumference but the other half of me says the same amount of tire material is being covered in the rotation.

Ran the test twice both ways, exact same results to the mm as noted above. Is the sit on test the most accurate and does it make sense that it is shorter? Just need a check because I haven’t found anywhere online that discusses this. Also at 3cm difference I don’t think I’m overthinking this, that can make a big difference over a day’s ride. Thanks!