Every time I ride down this one road I notice my 30s power increases for seemingly no reason. It's in the first 2 minutes of my ride, I'm in a residential neighborhood so there's stop signs & traffic & I'm not trying to go hard. Now that I've noticed it I intentionally don't try to push harder & yet my power increases for about 15 seconds & the returns to normal. I looked at the power curve for that section & in every single ride I notice that my power spikes from 200w up to about 600w at the same point on the ride. After 15-20 seconds it returns to normal. Any ideas what would cause that? I'm using a Powertap Pro+ hub with a Garmin 500.