During a recent Deja Vu breakdown (SFGAm) a ride attendant came out to chat with the people in the front of the line. Somebody asked, "How fast does this go?" Citing the signs at the front of the ride, I said "65". The ride attendant said, "No, 57. Our supervisor sets it at 57." I asked if this was to prevent too much wear-and-tear. He said, "Yes, but mostly it's so that people won't get sick. You don't want this thing going 65."
This may be a stupid question, but how does one "set" a coaster to run a certain speed. It would seem that gravity determines the speed. Is this why the trains stops 6-7 below the top of the tower before it is dropped? Or is there another way to control the speed? Or is the ride attendant full of it?
Actually even the weight doesn't make as much of a difference as you might think. In an ideal case, Vmax = 60/11 * sqr(h) where h is the height of the drop in feet, Vmax is the top speed in MPH. That's for a frictionless coaster in a vacuum, but it's a reasonable baseline for a ball-park estimate. What added weight will do is to increase losses due to rolling friction, but increase total momentum, thus making the system more resistant to losses due to, say, wind resistance.
That said, some coasters can have their speeds manipulated a little at particular points on the ride through the use of different wheel and track lubricants, application of trim brakes, and occasionally other tricks like gauge manipulation, feed wheels, and lift chain speed. But apart from the brakes, the changes you get from these things tend to be fairly minor.
I personally find it hard to believe that Deja Vu actually goes 65, but what do I know? I also don't believe that Tatsu has a 273' differential. Again, all assumptions.
Speaking of. Assuming that (on a steel coaster) the wheels never break contact (or traction) with the track, greasing the track will do not good. Greasing the wheel behrings, on the other hand, will lower friction, and improve speed.
One of my friends went to Cedar Point a while back and Millennium Force was closed. He was told the reason was because it was "going too fast" and they couldn't keep it below 110mph, so they had to shut it down.
I explained to him that this is physically impossible and that the top possible speed is 93mph, or possible a couple more, but he didn't believe me.
The effects of grease in various places also depends on what kind of coaster you're talking about. A steel coaster typically has wheel carriers and axles that can actually steer around the course, so lubrication on the track is not required for proper function (except as Rob noted). In the wheel bearings, packing the bearings full of grease will tend to slow the ride down, cleaning them out and using a lighter load will speed them up. On a wood coaster (except for those few that use GCI or Prior & Church trains) the cars can't steer, so lubricant on the track is necessary to allow the cars to take corners without grinding away at the track steel and making horrible screeching noises. In this case, the lubricant will also tend to increase speeds, as the speed doesn't get bled off by the grinding and screeching.
Since we're talking about people who are full of it - here are a few comments from the Fark.com thread on the SFGAm death:
I decided against top thrill dragster after the incident where the train got stuck at the top of the tower for 15 minutes. I don't mind heights so much, but there's only so much of sitting on top of a 410-foot tower that I could handle.
It happened on Space Mountain, at DL for one. Guy got past without pulling down the bar and was clowning in the ride. Decapitation was the end of his clown career. Now they have a guy checking to see that everybody pulls down the bar, duh.
Millenium Force is an Intamin coaster, Kingda Ka isn't. I think Intamin is the best.
Well, the second 2 are probably garbage, but I think the first has some truth to it. At one time, one of TTD's trains actually did get stuck at the top, perfectly balanced. A mechanic had to ride the elevator to the top and give it a push. I think there may have actually been a photo that someone took of the train sitting there with people.
Someone should send a memo to Parc Asterix. Remind them that not greasing the track is not the proper way to slow down the ride! Tonnerre de Zeus screeches horribly all during the ride and it must have an effect, cause in 2004, one of the PTC train died. They picked up a used train to repair it.