Hi Catigale!
Without getting into a total thread rehash, i think daves numbers on tow ratings underscore the fact that the "tow rating numbers" are more marketing tools than engineering analyses.
LOL! – Yeah – on a whim the marketing guys moved the tow rating from 2000 to 5100 pounds!
That doesn’t make sense, and if it doesn’t make sense, then it’s not true.
The source of discordance among manufacture’s ratings is that they each choose a different set of test and measurement standards that show their own vehicles to be the best. The engineering and measurements are still done, they have to be; to suggest otherwise is folly.
To change a vehicle’s tow rating engineers can simply change such parameters as the grade, the grade length, the ambient temperature, the brake fade requirements, the acceleration, the axel ratio, FEA data, the level of structural deflection, engine temp rise …
The criteria being measured certainly are many and complex, but they are being standardized by SAE J2807, which is presently being adopted by some (ultimately all) manufacturers, so very soon you will be able to compare the ratings directly between them.
A google search should give you an outline of SAE J2807. Or if you pm me I can send you (or anyone else who’s interested) a summary version of it, which I got as a member of the engineering community, that might not be available online.
Best regards! Brian.