Another variable that may be at play here is the fact that roller coasters actually tend to go faster as the day goes on. This has nothing to do with being day or night or the park turning up the speed somehow, but rather the length of time the ride has been continuously operating since sitting idle for an extended period of time; i.e., overnight between park opening and the previous day's closing. When the ride first opens for the day, the wheels/lubricant/bearings are cold (at room temperature in this case) which causes additional friction losses during the ride. So the average speed of the coaster cars will be slightly less than later in the day when the wheels have heated up from continuous use. It's not uncommon for a roller coaster to shave off 5-10 seconds or more in ride time (leaving the chain lift to hitting the final brakes) from the time it opens until the time it closes during an operating day. This is due to the cars maintaining a higher speed throughout the dynamic portion of the ride compared to earlier in the day when wheels are cool. Thus, the ride imparts slightly higher forces on you which makes it feel faster (because it is faster). I've personally experienced a tremendous difference in ride experience on Space Mountain (and hundreds of other roller coasters) from around opening time at 9am to riding on the same track a few hours later.
Some roller coasters go fast enough their wheels have to be cooled down by water to prevent them from overheating and needing more frequent replacement (example Intimidator 305 at Kings Dominion in Doswell, VA).
When it's too cold, the wheels have too much resistance to maintain enough speed to complete the course, so it's rare for most roller coasters to operate in temperatures much less than 35-40 degrees Fahrenheit.
Some roller coasters go fast enough their wheels have to be cooled down by water to prevent them from overheating and needing more frequent replacement (example Intimidator 305 at Kings Dominion in Doswell, VA).
When it's too cold, the wheels have too much resistance to maintain enough speed to complete the course, so it's rare for most roller coasters to operate in temperatures much less than 35-40 degrees Fahrenheit.
