Forget the weights. You need power, of which the repetitive component in cycling is the key.

Weights will do little for cyclists other than very short track sprinters.

Pro sprint cyclists are bigger and heavier, but don't mistake it that it's because they're doing a lot of high intensity cycle intervals - not just more low-rep weights to get there. It isn't the same. You need a very cycle-specific explosive type power that also will not compromise your endurance significantly, and weights won't get you there. If you're already putting in tons of miles, ok, then throw some weights on for some eccentric type training, but don't be under the illusion that it'll add more than small/miniscule amounts to your sprint.

I'm a pretty good example of why pure leg strength isn't great for bike sprints other than super short ones. I've got very good leg strength genetics - even without lifting any leg weights, and from just playing basketball, I could leg press 1000+ pounds in high school at 140lbs body weight.Only 2-3 guys in HS, each well over 200lbs could match me. Yet when I got on a bike, my sprints, while still pretty respectable, weren't anywhere near that good, and even now, having ridden a fair amount, I only have an 'above average' sprint compared to a competitive cyclist.