You missed my point vascop, the tightest part on many roundabouts seems to be just after the exit when there is usually quite a kink to the left, slightly after the point where one typically starts to accelerate having left the roundabout [apologies if I'm not making myself clear on this!]
Try the Magic Roundabout in Swindon for fast approaches AND fast exits! It's that famous multi-mini one where you're either amongst the quick or the dead .............:)
Here in Birmingham we have many mini roundabouts built at minor road crossroads where nothing existed previously. They are just small bumps in the road. Many motorists completely ignore them by driving straight over them without slowing down at all.
The purpose of roundabouts is to keep the traffic flowing, if you approach a roundabout with caution, you, at times can judge whether you need to stop.