I am wondering whether reducing the weight of the tow vehicle can increase its towing capacity? Here's why I want to know and why I think it should.
Ignore mfr approval for flat towing and transmission lubrication (I have investigated that). I want to know whether I have the capacity to flat tow my 2019 Miata (manual) behind my 2017 Lexus RX 350. My RX is 2WD and does not have the towing package. Mfr's rated towing capacity is 2,000 lbs (3,500 w/ towing pkg).
The RX weighs 4,222 empty and GVWR is 5,665. Max payload is 1,444, which checks. The Miata weighs 2340 and would be empty except for a braking system, base plate, wiring and half a tow bar, say 2440 lbs. 2,440 lbs would appear to exceed the RX' 2,000 lb towing limit, however...
I am under the impression that a vehicle is approved to tow its rated towing capacity (2,000 lbs here) when it is at its GVWR assuming no other limit is exceeded. Is that right?
If so, my RX is approved to tow 2,000 lbs when it weighs 5,665 lbs (its GVWR). Yet if towing capacity remains constant, it is not allowed to tow one more pound even it loses 1,000 lbs of people and cargo and weighs 4,665 lbs. Why couldn't I tow another 1,000 lbs if the car weighs 1,000 lbs less?
Handling and braking can't account for the 2,000 lb restriction remaining in place, because the towing capacity can be raised by 1,500 lbs by adding the towing package which does not modify any handling or braking components. They just increase heat dissipation and electrical supply (trans cooler, engine oil cooler and bigger radiator, fan and alternator).
So if the RX has the trans and engine oil cooling capacity to move 7,665 lbs when 5,665 lbs is in the tow vehicle and 2,000 lbs is being towed, why could it not move 7,665 lbs without modification if the tow vehicle weighs 4,665 and the towed vehicle weighs 3,000 lbs. The cooling and electrical loads on the RX are not increased a bit by moving 1,000 lbs back 20 feet. (The Miata would be equipped with brakes and would weigh well under 3,000 lbs).
FYI, I normally tow below the speed limit, day time only, watch my gauges, change fluids with synthetics when recommended or sooner, and drive gently. I find no indication on the Internet that the RX has transmission problems.
Your thoughts, please, and thank you for your help!
Bob