This application of cavalry is suicidal
It doesn't matter whether you have horses, lizards, or elephants. You do not charge into pike formations head-on unless you can out-range them with your own lances, concentrating the momentum from the animal's charge into the lance's head to punch through the enemy's armor...and then pull back before you get bogged down in the melee and slaughtered.
When attacking infantry, cavalry does not want to stop: a horse is a huge target and a cavalryman – even an armored one – at a stop is a terribly vulnerable target. Since (say it with me), horses are not battering rams, that means you need space in the enemy formation to ride in and around the enemy infantry, spearing and slashing as you go (you can trample a lone infantryman, but not a dozen in a pack).
If your strategy is to have your mount headbutt the enemy's pikes away, you are too close.
Which brings us to density. Pike formations look something like this:
Pikemen are heavy infantry, standing shoulder-to-shoulder, in multiple rows. They are numerous, largely because they are cheap. By comparison, cavalry is expensive and loosely packed (since each animal needs room to maneuver). Your lizards will be far looser than horse cavalry because of the way their legs are - lizards splay out their legs when they stand, meaning that they cannot stand shoulder-to-shoulder like horses would.
Each individual lizard will be facing twice as many pikes as a horse due to the width it takes up (and the space it will need for its tail when it turns around), and will not be able to headbutt all of them away. The pikes will catch on its splayed-out legs before the head reaches the pikemen's bodies, breaking the charge.
The only application of cavalry that stands a chance at a frontal assault is to scatter the formation of pikes, either by breaking their morale with a fearsome charge, or by feinting a retreat to get them to advance (or by skirmishing with ranged weapons).
But what you should actually be doing is flanking them, because the best way to break a formation is to strike it from the side or rear. Cavalry can move faster than infantry can pivot, unless the pikes have formed square.