I'm about to install my e-bike kit onto a mountain bike with rear suspension. I understand if you tighten the spring, this will make the bike more rigid to make the bike go faster when pedaling.

Q1: I don't really use suspension because I mostly travel in the city on flat streets. Would tightening the suspension all the way also improve the speed I get with a hub motor?

Q2: Also, some rear rack (for mounting batteries) instructions tell you not to mount the rack to the rear axle and the seat post with rear suspension because if you mount an immovable object to a movable object then there is a chance you could break your rack. I assume that I should be fine if I tighten my rear suspension all the way making the bike as rigid as possible. Does anyone have any experience along these lines?