This appears to be a bit of a head scratcher to me. Two fairly similar vehicles with the same drive train and yet, the towing capacity is radically different.
2024 NX450h+ is 2000 lbs
2024 RX450h+ is 3500 lbs
Both have the identical 4 cyl A25A engine and eCVT transmission and have the same rated HP. The RX is roughly 9 inches longer and ONLY 325 lbs heavier than the NX. It does not really seem that there would be such a great difference in towing capacity between these two vehicles. I mean...the towing capacity of the RX is almost double that of the NX. Am I missing something here?

 

I won't pretend to know all the differences between the NX and RX platforms. While they obviously share a good bit, there are also many other things that might go into determining tow ratings of the tow vehicle: tires, brakes, suspension, oil coolers, coolant system sizing, gearing, unibody construction, etc., etc.

 

Is there a towing package available for the RX450h+? My read of the manual is that the vehicle has no Lexus recommended towing capability without a towing package, and I have not been able to find a towing package for the RX450h+.

Ive not read the manual for the NX450h+, so I dont know if the same is true.

 

There's no indication of a towing package on the Monroney sticker for my RX450h+. On the NX450h+ however, the Monroney does indicate that there is one included. I've yet to determine exactly what this towing package entails. Some say a transmission or engine oil cooler and a larger capacity radiator but, I cannot really verify this. The list price shows $160 and that pretty much covers the suggested retail cost of the converter (Toyota part PT725-48232). This is installed at the forward part of the cargo area, at the right side under the floor area. After mounting, it simply plugs into the harness. A pigtail (about $21 from Curt) from the right rear bumper area is also needed to connect to the 4-way trailer plug on the trailer itself. So far, I have not been able to find any heavy duty radiator lsted as an option for the RX models but, that is mainly because the Lexus parts online database is not up to date. There is nothing shown for newer models and when I enter my VIN, it shows....Not found! It appears that most Canadian bound RX models come standard with a tow package. from what I have read on this site.

 

If I go to the build option on Lexus.com, I can select a tow package for the RX350, 350h, and 500h, but the 450h+ does not have that option, but it does have the option for a tow hitch that includes a harness.

 

IDK the vehicle, but the drivetrain is not the biggest component in determining towing ability.

Biggest determinant is chassis rigidity and braking ability. 200hp and 200 ft/lbs will easily two 5k lbs, if the rest of the vehicle is up to it. Compare those aspects. Also, US tow ratings are massively out of line with foreign ones; different rules apply. Exact same vehicle can be 5k lbs in the US, 7,500k lbs the entire rest of the world (early 100 LC was this way, I know).

 

I put RX500h brakes on my NX. It surely stops better when towing ~2000lbs than my old oem brakes, I’ve heard of places to get towing recertification over seas.

 

eTrailer shows 3 different manufacturers of hitches for the 5th-gen RX, all with a 3500lb tow rating:

https://www.etrailer.com/hitch-2023_...isibleProducts

 

it comes down to chassis and suspension design (rigidity).
this is a similar conversation had regarding the RX vs the Highlander.

essentially the more soft, carlike the ride, the less capable the towing ability.
crossovers can 'get it done' occasionally but they just aren't designed to take the stress like a rigid, body on frame/unibody truck (IE Lexus GX).
these are basically cars. they are not the heavy duty SUV's that defined earlier eras.

think about it another way: the NX is rated up to 125mph but just because it 'can' doesn't mean it wouldn't be quite hard on the car to use it in that way.

my first hand 2 cents, having my RX set up for my jet ski, is towing anything over +/- 1000 lbs on the RX is going to be stressful in a way most Lexus owners would find unacceptable.

 

FWIW, Lexus UK publishes the same towing "capability" for all RX versions, so that suggests to rigidity argument behind the advertized capability, rather the drivetrain being the reason (since drivetrains are widely different in nature between the 350H, 500H and 450H+):

https://media.lexus.co.uk/wp-content...-Tech-Spec.pdf