I just bought an RX450h to replace my aged RX400h. I want to use the 18" wheels from the 400 on the 450 and vice versa. Will this work?

RX400H has 235/55/R18
RX450H has 235/55/R19

Will they work if I switch them over?

 

They will bolt right on and should be just fine. The 3rd gen 18 inch tire size is 235/60/18. So your old tires are .93 of an inch smaller. The 55 tires will have 716 revs per mile while the 60 tires will have 693 revs per mile.
50 mph will actually be 48.5 mph. So the speedometer will read about 2.5 miles per hour slower than actual speed.

https://tiresize.com/calculator/
https://www.clublexus.com/forums/tir...calculator.php

• Diameter difference between the 2 tire sizes:
• 0.93" (3.18%)

Most front wheel drive Toyota and Lexus vehicles wheels are interchangeable with the same 60.1 hub bore and wheel bolt spacing. The offset usually only varies a few degrees, not enough to make much difference. Many folks have put Highlander or other models wheels on their RX or used them for snow tire wheels.