[Overdrive]

My sister's 99 Boxster's brake booster failed last year, leaving her without brake control, but it was the opposite effect. If she applied the brakes even lightly the pressure would sometimes hold like you were trying to put your foot through the floor, and they would not disengage for anything. Very unsafe, and I'm sure quite scary for her nearly getting stuck in the streeet not being able to move the car when the brakes did this.

I would think your booster may have just decided to give up the ghost around the same time you did the wheel swap, and in your case instead of the brakes locking up big time you're instead getting a delay in braking and a loss of braking power...failing closed instead of open, if you will, and not giving you the additional braking force it's supposed to.

I'm certainly no expert, but to me your issue doesn't sound like it's related to the wheel change. I think you're dealing with something strictly in the braking system.

And those wheels are quite nice.