When I take turns, my rear wheel is sliding to the outside of the turn. I'm riding a 2012 Norco Heart, brand new stock tires, single-speed. I'm not carrying much weight, or taking turns too tightly. Any ideas?
Try adjusting the tire pressure you may be to high or to low. If it is low the sidewall can squirm inturns making handling inconsistant, too high and the tire can be so hard it bounces off the surface when hitting any imperfection.
You may want to check that the rear wheel isn't coming loose on the axle. If the nuts that hold the bearings in have come a bit loose, the wheel might slip a little in the corners. If they are very loose, the wheel will wobble even when you're riding in a straight line.
Your body position may be an issue. When the terrein is loose, you need more weight on top of the bike. So as you lean and carve into the corner, you may need to lean the bike, and your body at different angles. Essentially leaning your body less, and shifting weight to still provide downward pressure vs all lateral pressure relying too much on grip and inertia.
And tire pressure for the right terrain is key. If its loose, 32psi and above will break loose faster than say 28psi. If you have to go by feel, you need it to press in a bit if you squeezed it with your thumb, or if you are on it, guess 20% compression squish would be a best guess for your weight.