I've been riding road bikes for years but just got a mountain bike earlier this year. I've been riding the Canal trail and Bartram several times each, as well as kicking around in the woods out at Mistletoe State Park.
I was a bit surprised this morning to get two flats on while riding FATS; I took a hard right turn just after the trail head, and road a bit past Hopewell Church to where it turned from obviously cleared trail to uncleared trail; I turned back at that point to go back and try the other loops. When I crossed back over Hopewell Church Road I got two flats. On my slow way back to the parking lot I noticed there was a lot of broken glass on the trail. I'm a pretty inexperienced mountain biker but I know that much glass in the road would be a problem for my road bike. Do mountain bike tires tend to be less susceptible to that type of damage? I'm not sure yet if it was the glass or something else that gave me those flats. I was running about 45 PSI in my tires. Is that too low? The tires are rated for 40-60 and I was thinking since it was off-road I didn't want them to be at their max pressure in order to help with traction.
As for the glass, is this something we should look to clean up? I can help.
I've ridden my mountain bike on mostly singletrack but occasionally roads as well (between 1200 and 3000 miles per year) and have probably averaged two to three flats per year. I normally run about 45 - 47 psi. I think you just had some bad luck!
I have had about 5 flats on my road bike in my past 2 rides (and I hardly ever ride it!), but rarely have flats on my mountain bike. Now that's bad luck!
Make sure you check your tire carefully for thorns, etc. when you change out a flat. Sometimes those thorns are so small that they are hard to find. I have always been told to keep track of the tire and tube orientation, so you know where the hole was on the tube and can search the tire in that location for the culprit.
One of my friends has been getting flats when riding the canal trail lately.
No help here on the flats, but 45psi may be a little high actually. Lower pressures increase traction and cush, both of which are good, so you want as little air as possible. Typically the drill is to keep letting out air until you start to pinch flat regularly, then add a couple of pounds. For an example, I weigh 165 and ride with 38psi in back and 35 in front. I may vary that depending on the trail I'm riding and how I'm riding, but in general that's where I start.
Another tip: sometimes something will get imbedded in the tire and you wont be able to see it even when you get the tire off and inspect it. But, when the tire flexes, like when you run over a rock or root, the object will protrude enough to puncture the tire. I use to get little pieces of glass like that in my bmx tires at college. The best way to find them is to bend the tire (almost like you're trying to turn it inside out) and run you fingers over that inside surface of the tire. Just don't press down too hard!
But if you're getting flats repeatedly, that might be what's happening. Also check to make sure you don't have any produding spokes.
you can also get a protective lining that goes between the tire and tube. it won't prevent pinch-flats, but it'll help quite a bit with thorns.
like dgaddis1 said, make sure you feel along the inside of the tire to find anything that may still be stuck in it. as soon as you put in your new tube, it'll be wasted if there's anything still in the tire.