Okay, time for everybody's TTD Train History lesson:
Yes, TTD did start with 4-car trains for press previews, and that was only two trains (red and green I believe). Almost IMMEDIATELY after that, the fifth car was added to those two trains and all the trains ran with all the cars.
By the way, the fins up front are NOT brake fins. They're strictly for theming. All the brake mechanics (magnets on train, copper fins on track) are below the train.
The weekend of May 16, the tires were removed. I was there that weekend, I got two trips with the tires, one without. Also, all the trains had five cars.
When TTD was shut down for most of June, they removed the engine and rear spoiler, which were replaced by two additional seats. I think the front spoilers have since been removed, but I'm not entirely sure.