I would guess that would slow you down. Bailed in the PP race today not too far from the end, rear tire felt mushy, looked down and it was very low to the point where I saw no point in continuing (this was lap 8 of 10 in Prospect this AM). I was actually fearful of the 35mph+ descent on a tire with <50lbs of air.
I would guess that semi flat would go a long way towards explaining why that race felt so hard for me today, although I think it was a fast pace, I'm pretty sure no breakaways succeeded. I would imagine it's harder going 30mph with 50lbs instead of 160 in the rear tire. I was even more fearful of trying to continue and losing all remaining pressure on my pricey Zipp rim at the wrong time. That would suck. Oh well.
Pcad's Bag of Excuses always has room for one more.