The math:

• 19": wheel = 9.5" radius 21" wheel = 10.5" radius
• 235/60R 19: 235 x 0.6 / 25.4 (mm/in) = 5.55" of sidewall 235/50R21: 235 x 0.5 / 25.4 (mm/in) = 4.63" of sidewall
• 19" tire total radius = 9.5 + 5.55 = 15.05" (30.1" diameter) 21" tire total radius = 10.5 + 4.63 = 15.13" (30.26" diameter)

As @nowlen noted, with the 19" you pick up almost 1" of sidewall (better cushioning), while the overall tire radius/diameter is almost the same as for the 21" setup (so odometer/speedometer will be accurate), and as @Urlik noted the car will be at the same height as with the 21" (only 0.08" difference - car height uses the radius of the tire). Odometer and speedometer are typically based on wheel rotations - the 19" and 21" should measure within a half percent of each other - driving 200 miles with the 19" setup would register as 201 miles.

 

I’m not as exacting as all of you are here…but I will say that I trust my visual acuity. On the sales lot here in Palm Springs, there are several 19” RXs directly next to RXs with the 21” tire. Seems to me that the 21”s tires puts the vehicle higher off the ground. I’ll take a photo soon. Separately, Tire Rack reviews rate the Michelin 19” quite a bit stronger than the Bridgestone 21”s. That said, despite the tires, a more perfect vehicle than the RX450h+ would be difficult to identify. Not to mention, I’m at 76 mpg now, since taking ownership. ✅

 

I had posted something then saw it was for the Gen 4 throwing the placeholder in while I went back. Cruising the web though it appears that Gen 5s are all 8.1". I suspect you're seeing an optical illusion due to the different wheel sizes.

 

That's consistent with my prior post, where I show 19" radius of 15.05" vs. 21" radius of 15.13", a difference of 0.08" (and the roof height of the 19" tire vehicle will also be 0.08" less).

That small a difference is essentially noise, though there's certainly nothing wrong with people preferring the looks of the 21".

 

AKA: My mind is made up, don't confuse me with the facts.