Holding league night in the open lobby would be oh so painful.
Your plan only works if the number in the room remains stable throughout the evening, but that doesn't happen. Four out of five rooms lost at least one racer during the course of the night. If that happens in an open lobby, think about how many people would have to be booted between races.
Think about what happens when some random guy logs into the room during the middle of the race and causes a painful lag spike.
Think about the heartache when the guy who opens the room mis-types one number when posting the room number on the thread.
We do all we can to minimize the trouble caused by the un-stable-ness of the internet and GT5's servers. If there are more than 12 people in a room, it is commonly advised/required that everyone shut off their mics during the races. We try to put someone with a known good connection and low ping as the room host.
I think things will be much smoother and safer in loungesprovided the host has no known network issues with other racers. Who hosted D1 last night?
That said, I don't entirely believe that the speed of the host has much to do with anything. The ping, possibly. The network compatibility, definitely. Hell, I was host of D3 for a while last night and there were no problems. (6mb download, 600k upload quoted, but a ping in the teens.)
Race tires? I agree.
Suggestion? Sure.
Road Cars:
below 400 PP -> Comfort Mediums
400-449 PP ---> Comfort Softs
450-499 PP ---> Sports Hards
500-549 PP ---> Sports Mediums
550-599 PP ---> Sports Softs
Race Cars:
Below 550 PP -> Race Hards
550-699 PP ---> Race Mediums
700PP and up -> Race Softs (should it ever come to this, Race Mediums may still be in order, lest we be forced to pit or cruise to preserve tires.)
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OR
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Stock tires for every vehicle. Or one softer than stock. Use a similar system to above for RM cars since they'll have sports tires as stock.