This is a great tire for mixed terrain riding. It's not so knobby that it feels sluggish on the road and it still corners fine, but there's enough side knob that you don't have to worry as much about washing out your front wheel.
There's a less knobby version out there, the Terra Speed, but it's basically just a worn out version of these ones. You'll get more bang for your buck going with the slightly knobbier one.
The 700c x 40s are 455 grams. The 700c x 45s are 495 grams.
