Most vehicles have a specified Tongue weight. I cant remember what my old 4runner was but my 95 pound rack with 4 bikes equalled about 250 pounds. This was within spec from what I remember. Google it would be my suggestion.
Its not the vehicle that has a tongue weight, but the hitch itself. Class I (anything 1 1/4") has a 200lb weight limit. Class II (most 2" hitches used for racks and light towing) have a ~300lb weight limit. Class III ~600lb. Not sure where the amount of torque put on the hitch is factored in as the weight shifts outwards (ie one bike vs 4 bikes). You can safely assume that any rack capable of carrying 4 bikes will be ~50lbs and then each bike will be ~30lbs.