Amazon Customer 4 This is an ideally sized bag. It is big enough to fit in small tools like allen keys and bicycle locks (spiral ones), a large smartphone (5.5 inch screen) and a wallet. At the same time, it is small enough to fit on the bicycle tube, and does not interfere with the knee at all.I haven't tried it on a rainy day so cannot say much about the water resistance.The velcro tape does a good job of holding the bag on to the tube. Very easy to fix.