Top speed is not that big a deal, as tanks would rarely travel at rate cross country at top speed, and are usually limited to the slowest vehicle (probably something wheeled, or the AVLB).
Now, if you want a speed measurement that means something for an AFV, look for its ability to cross a 100m distance from a stop. The time it takes to dart across an open defile to cover is more important than overall top speed, and while it is not often cited in Jane's as a stat, it is usually defined somehwere in the statement of operational requirements.
GD |