dont know if this any use to u but it works for me anyway:if you dont like having heavy downhill tubes in like most people do try drilling another hole in your rim and fit 2 inner tubes so if you get a puncture you have another to ride with.Its so much easier cos i dont like downhill tubes in and i kept getting punctures so i came up with this soloution because if your out on a ride and you do get a puncture it ruins your whole day.