Hello,
I have some experience of towing (mostly caravans) with 3 different Omega's. One 2.5 and a pair of 2.6's.
My initial response to your question is, I would think carefully.
The reasoning for this is the quoted rating is a combination of vehicle weight, power, gearing, brakes and the safety regulations in force at the time the assessment was made. Although looking at the 2.5 Vs 2.6 many of those parameters will be the same or very similar, not all are. It is confusing, but the published data is the published data. This is what would be referred to in the event of an incident.
My last point is nothing to do with the law, as such, but seems to me to be based on a degree of reasonable common sense. Here in the UK we have an organisation called the Caravan Club. In my opinion, they are exceedingly up their own arses in most respects. They recommend to not exceed 80% of the towing car mass in your choice of trailer (or caravan). Based on experience of towing various rigs, some of which did not conform to the Caravan Club recommendations, for stability and towing comfort I think they are right on this point. Of course, many people exceed this and have done so for many years. The curb weight of a typical Omega is around 1600Kg+-
1875 is a fair bit heavier than that. We have a phrase, the "tail wagging the dog"
Whatever you decide to do, good luck in your travels.
Graham.
In short. You can't.
Although where did you get that table from? The numbers are suspicious. GM deliberately doesn't include general towing weights in the Omega hand book on the basis that each trim affects it (ie sunroof/no sunroof), instead it refers you to the chassis plate for that particular vehicle.
On your chassis plate in the front door frame there's information. This tells you what you can tow with that chassis:
1. Manufacturer (Opel/Vauxhall/Cadillac/Chevrolet).
2. Type approval number.
3. VIN.
4. Permissible gross (max) VEHICLE weight.
5. Permissible gross (max) TRAIN (car plus trailer) weight.
6. Max front axle weight.
7. Max rear axle weight.
8. Paint/trim code and any local market info.
Basically you subtract 4. from 5. This gives you the maximum you can tow with that chassis.
Changing the gearbox and engine won't change the amount that that particular car can LEGALLY tow.
If you happen to be pulled over or get check weighed and it is a heavier trailer than the plate allows for then you are in trouble:
Potentially no insurance, unroadworthy vehicle, dangerous load, no licence (for the weight of the car plus trailer).
Also, if you ignore the maximum weights and have an accident, again your insurers won't pay, and it could cost you your house/property.