Riding through dust on an otherwise hard road (or marking the tires with chalk before riding) can give a good visual indication of the contact patch of the tire, too. If it's just a narrow strip down the middle of the tire, you're probably running too much pressure. Ditto if you find that your rear tires wear thin at the centers when there is still thick rubber at the shoulders of the tread.
From
https://janheine.wordpress.com/2016/...ompass-tires/:
The rear tire is a bit more worn. The wear is almost entirely in the center of the tread – an indication that Andreas is running slightly higher tire pressures than we’d recommend. He might be more comfortable and even faster if he let out a tiny bit of air.