I've found tire temperature (i.e. first few miles when the outside temperature is 40F vs. 70F) makes a big difference. This winter I took my bike out a couple times when it was 40-45Fand accidentally locked the rear tire several separate times coming to a stop. It got my heart beating a little faster but not a huge deal. Never locked my front tire and NOT looking forward to the first time. From what I hear it invariably leads to a low-side.