All European cars have a maximum roof rack loading limit imposed on them by the manufacturer. Most cars are 75kg, some are 100kg, some larger vehicles/vans are as high as 150kg. You need to check your handbook.

I don't know about the trucks in the US, and I am not going to tell you that you cannot carry a 140kg boat on your roof. But I do want to give you enough information to make your own decision.

Remember the max roof rack loading is nothing to do with the strength of the roof or the rack its all about dynamic stability of your vehicle. i.e going around a corner at speed or more importantly under heavy braking. It is stupid to think that a vehicle with 74kg on the roof is safe and one with 76kg is not. But these limits are imposed for a reason. You just have to decide if 140kg on a 75kg rack is too much. If you were to drive everywhere calmly at 55mph perhaps it will be fine but under heavy braking from 70mph a 140kg is likely to rip the roof rack off its rails.

I am sure Wouter can provide an equation to prove/disprove this assumption