Bicycle Mechanics - Blah flats, tire sidwalls repairable?

Toodling along at a brisk pace when suddenly I heard a loud hissing noise, at first I thought I picked up a leaf and it was rubbing the wheel or something, turns out it was air leaking out of the darn tire.

Inspected the front tire and found a nice clean gash (like it was made by a knife), luckily it stopped deflating until it was fully flat and I wasn't too far from home (< 1.5km).

Anyways the gash isn't very long and it only cuts through for less than half a centimeter. Is this repairable or is it time for new tires? I also found a similar small puncture in the tube near the valve. I have a patch kit for that, but would it be safe to ride around on a repaired tube?

Bike computer tells me it was only 500km from the last flat :/

It is not quite as bad as car tires but the risk is moderately high. You can get a large
thick tube patch and put it over the tear on the inside with a bit of rubber cement
and in addition I would get a larger piece of tevdek non woven plastic paper and rubber cement this on top of the patch. This will keep the tube from herniating
through the hole and reinforce it. Keep close check of the tire though and if any
bulging develops chunk the tire. In my experience about half of tire failures are due
to side wall cuts. If there is a bulge there now, I would not waste a patch on it though. I have salvaged a number of sidewall and tread cuts with this approach. Cuts above 6-8mm are in the gray zone for repair, smaller usually works, larger is
a repair once to get home then toss the tire. Steve

When ever I get a sidewall gash I throw the tire away. The side wall flexes a lot during cornering and hitting holes etc, and if you have a repaired gash you stand a chance of opening that gash up again. There is a boot patch available but that is more intended for the tread, but in a emergency you could use it on the sidewall or use Sch's method explained above. So you could fix it in an emergency but I would not keep it as a permenant repair.

As far as the tube goes, if a patch can go on without the stem getting in the way then patch the tube and it's fine.

Just as Sch said, about 50% of tire failures are due to sidewall cuts; this can be avoided if you buy tires that don't have paper thin sidewalls like the Conti's. If your not racing then paper thin sidewalls are a waste of time and money on streets. There are some tires that have very good sidewalls; the Specialize Armadillo as the toughest sidewalls on the market and the toughest tread as well, these tires are virtually flat proof; Conti has just one tire called the 4 Seasons that has a flat resistent ply that extends from the tread (where there are 3 more flat resistent plys) into the sidewall, this tire is not as flat resistent as the Armadillo but it is about 100 grams lighter. The Armadillo cost $30 and the 4 Seasons runs $50 retail but http://www.biketiresdirect.com/continental.htm has them for only $38.