The tunnels themselves can be full size (which is good for reduction of boundary layer effects) but the models are typically 60%. There do exist some 50% models

The tunnels themselves can be full size (which is good for reduction of boundary layer effects) but the models are typically 60%. There do exist some 50% models for cost reasons, but the correlation is worse and there are problems like the pirelli-supplied model tyres (amongst many other things) tend to be a bit crap.