I bit of common sense here. Think- if you approach said mini roundabout at 30mph and another like-minded wizzi does the same at 3 o'clock or 9 o'clock entry then there is likely to be an almighty bang - the intention being that no-one is anticipating to give way.Just a question re roundabouts especially ones with white spot circle in the middle. if the road you are on and the one you are to go on to is a 30 mph speed limit what maximum speed should people be travelling at as they approach the roundabout and whilst on it???
As for maximum speed you can go around said roundabout - this depends on mechanics of motion - the centripetal force generated by your velocity. If the force does not balance the inward friction force of tyres in contact with the road you'll end up somewhere did not want to be, or toppling depending on centre of gravity and centre-line spacing between your offside and nearside wheels.