downhill tubes are thicker, and I've found tend to be bouncier.. don't really know what to suggest but I use try all stickys, when I moved to them i've used nothing else..
I'm sure someone will back me up on that, they're really grippy.. there could be bouncier tyres out there, but i've never tried them...
I bet that makes no sense.. i'm rambling a bit...
EDIT: just realised you asked one question I gave you a completely different answer
sorry about that...