I was thinking about running two ultralite tubes this season and was wondering what everyone's thoughts were. I'm between running diy tubeless and two tubes. A guy on Instructables did this with a commuter bike so this plan isn't to my credit. I'd drill another hole in the rim for another presta valve. One tube would be empty and the other inflated. In the event of a flat, simply hop off bike, finish deflating the flat tube and hook CO2 up to the spare. You'd never have to take the wheel off and could keep you in a race that would otherwise be lost. The drawbacks would be the weight of the extra tube, (I wonder if running the extralite tubes would cause much more frequent flats), and the cost of the light tubes. The hole would be negligible as trials bikes have drilled rims frequently and seem to be strong enough. I'd be racing XC in Southwest Virginia.