Animations are managed by a quite complex file tree structure within anim.wad. You have main file that lists all the other files (
animsetup.set), a main scene script
normalchange.ssc, a set of events (
pc00.evt,
pc01.evt, etc.) that call individual animation scripts for each pitcrew member, with these scripts then calling the actual animations for pitcrews and props. The scripts are all text files, with what I believe are time delays. The animation files are binary files, much more difficult to properly edit. As far as I can remember, the overall tyre change time is not controlled only by the animation though. I know32BOBO32 did quite a bit of testing about this some time ago, maybe he'll have some more info