I have never run out of space.... yet. in winter i usually carry my knees guards, tools, phone & extra jacket, and there is still space for more if you need. the pack is pretty long but comfortable and secure, i don't find that it moves on my back..... provided its strapped on properly. I have a friend who has the 10L and he is able to fit his knee guards and essentials in, but it looks like a tight fit in the main compartment. There is always the helmet mesh which folds up which can become a makeshift compartment is things get full. I purchased the 16L cause i already have a small pack which i could use for short rides if necessary.
