15/38 is a popular setup, it's one tooth up on the front sprocket from the stock gearing. Primary drive makes cheap steel sprocket. I don't have experience putting any kind of real hp to them (more than 70 or so) so I can't say how they perform in that situation. But they hold up reasonably well for most machines in recreational riding and occasional grudge racing. If I was going to spend all day launching off a start line I'd spend a bit more money on say a renthal or other brand of sprocket.