1.9 and 2.2 refer to the wheel diameter. Your CR01 comes with 2.2 wheels and tires. If you want to change to 1.9 tires then you'll need to also get a set of 1.9 wheels. The hexes on the back of the wheels are the same so they should just bolt right onto your truck.

Also just realize that the smaller the tires you use the less capable your truck will be. Its just a trade off that you'll have to decide if it is worth it for you. 1.9" wheels/tires look more scale but aren't as capable. 2.2 tires are larger and more capable but dont look as scale. I'd say to decide what you're looking for and go with that. If you're looking to build a competition crawler then you'll definitely want to go with the 2.2s. If you're looking to build something scale looking then the 1.9s may be better.