Here's a table of Crr's from 2010: http://www.biketechreview.com/...ire_testing_rev9.pdf
The best in that table was 0.00220
The worst in the main table was 0.00448.
Rolling resistance force is <your mass in kg> * Crr * 9.81
Rolling resistance power loss is <your speed in m/s> * <your mass in kg> * Crr * 9.81
So for a 85kg bike+rider @ 25mph:
The best tire would take 20.3W to keep rolling.
The worst tire would take 41.5W.
A 20W loss is pretty substantial.
"How would it affect you over 20 miles?"
We can figure this out by looking at how much energy your tires waste over 20 miles, which is actually completely constant and not affected by your speed.
Work = Force * Distance
Force = <your mass in kg> * Crr * 9.81 = 1.83N or 3.73N
Work needed = <force> * <distance = 20 miles> = 58.8kJ or 120.0kJ
So the amount of time added would completely depend on your actual power output. The worse tire would require 61 extra kJ of work to be done to keep those tires turning. At 300W, that'd add 3m 20s to your ride. Which seems high, so feel free to find an error in my calculations.
That table, though, seems confined to plausible race tires. I imagine gatorskins or cheapo no-name tires could be even worse.
STAC Zero Trainer - Zero noise, zero tire contact, zero moving parts. Suffer in Silence starting fall 2016
The best in that table was 0.00220
The worst in the main table was 0.00448.
Rolling resistance force is <your mass in kg> * Crr * 9.81
Rolling resistance power loss is <your speed in m/s> * <your mass in kg> * Crr * 9.81
So for a 85kg bike+rider @ 25mph:
The best tire would take 20.3W to keep rolling.
The worst tire would take 41.5W.
A 20W loss is pretty substantial.
"How would it affect you over 20 miles?"
We can figure this out by looking at how much energy your tires waste over 20 miles, which is actually completely constant and not affected by your speed.
Work = Force * Distance
Force = <your mass in kg> * Crr * 9.81 = 1.83N or 3.73N
Work needed = <force> * <distance = 20 miles> = 58.8kJ or 120.0kJ
So the amount of time added would completely depend on your actual power output. The worse tire would require 61 extra kJ of work to be done to keep those tires turning. At 300W, that'd add 3m 20s to your ride. Which seems high, so feel free to find an error in my calculations.
That table, though, seems confined to plausible race tires. I imagine gatorskins or cheapo no-name tires could be even worse.
STAC Zero Trainer - Zero noise, zero tire contact, zero moving parts. Suffer in Silence starting fall 2016