You've heard it before and you'll hear it again. It happens all over the country with a carbon copy of the same clueless individual at the climbing shop. "Dude, you need shoes that hurt," he tells you. "They should be at least two sizes too small for your feet!"
Two sizes too small...? Is there any truth to this?
The answer is yes and no. What the yahoo behind the counter forgot to do was to ask what you're going to do with your rock shoes. Are you going to boulder a lot? Are you trying to do hard sport climbs? Or are you headed out to do long multi-pitch trad routes? Each answer should lead the clerk to a different recommendation...not to the generic two sizes too small answer.
To understand rock shoes, one must understand that the shoes are tools. And different tools are constructed differently for a different job. There are two major styles of rock shoe, board-lasted and slip-lasted.
These are shoes that feel literally stiffer than the alternative. The midsole of these shoes are particularly stiff. This stiffness comes from an internal structure on the bottom of the shoe called a last. In this style of shoe the last is rigid, but it is important to note that this is not the case with all lasts.
Board-lasted models are excellent all-around shoes for two major reasons. First, they work equally well in all environments. They work well for edging and friction as well as for cracks. Second, they do not require a super tight fit to perform well. As a result, this style of shoe is recommended as an all day shoe for all levels of climbers and as a first shoe for beginners.
When it comes to fit, all shoes should be somewhat tight. I often buy board-lasted shoes that are a half size to a full size too small. A half size is good if you plan to wear them in the alpine with socks and a full size is good if your plan is to go go barefoot in them. Don't forget that your shoes will stretch and that if your toes are moving around it will be hard focus force where you want it to be.
These shoes are designed for sensitivity. They are built around a sock-like last that allows a climber to focus his foot strength on the smallest of edges. Slip-lasted shoes have little support, require a tight fit and are not recommended for those who have not yet developed the prerequisite foot strength.
Slip-lasted shoes were designed primarily for bouldering and sport climbing. In these endeavors a climber might only wear his shoes for a very short period of time and thus a tight fit is more tolerable. This is the type of shoe that an individual might get in an extra tight size. One to one and a half sizes too small is good for sport climbing...and for those who engage in bouldering, they are among the only ones that should consider wearing shoes that are two sizes too small...
--Jason D. Martin