The main route to the "smoothest and quietest ride possible" is to use the OEM standard size wheels and tires - 225/60-16 tires on 16" wheels.
Here is what Lexus says about using 17" wheels and 225/55HR17 tires that were optional on the 2002 LS430:
"Optional 17 x 7.5-in wheels with 225/55HR17 tires are expected to experience greater tire wear than the standard equipment tires, 225/60HR16. Tire life may be substantially less than 15,000 miles, depending on driving conditions. Your riding comfort may decrease and road noise may increase during driving. Please consider all this when selecting an LS 430 equipped with this option."
The 255 section tires you currently have on your car put a lot more rubber on the road which makes your car find a lot more road imperfections.
Jim - Lexus LS driver from 1990 to 2014 - Now driving a 2014 Toyota Sienna Limited with all packages and options
the lexus quote is based on their factory tires. there are numerous other tires available that will last much longer than the factory oe tires in 17".
255 60 17 is a weird size. definitley shouldn't be on the car as it is much too tall.
a wider tire will be louder than a narrower tire. i'd get the factory spec size 225 55 17. that will quiet the noise down.
have you inspected your current tires for wear? if they are wearing unevenly, that will cause noise too.
36psi is about right... too low pressure will increase the chances of bending a wheel on a pothole or other road hazard.
if you're not a brand snob, one of the best stock size quiet tires for an ls430 is a kumho solus. i've installed many of those on people's cars and they ride and handle as well as a michelin and usualy take less weight to balance. oh yeah, they cost half as much too.
Dodge Ram cummins turbo diesel, 5 speed, 344 HP, 788lb.ft. 18/21mpg, shooting for 1000 lb. ft. on stock turbo.
Kawasaki Ninja ZX-12R 1200cc's, 190 hp of pure evil on 2 wheels.
95 Jeep Cherokee BDS/hybrid 5" lift, 32x11.5 BFG mt's, welded rear diff, long arms, etc. trail beater.
Try the Michelin Energy MXV4 Plus or the Primacy MXV4 which is better than the Energy MXV4 - the Energy is more of a low rolling resistance tire while the Primacy has better treadlife and better wet behavior.
The negative of over-inflating a tire (which is what you are doing by going to 35 vs. 30) is that the tire will bulge, however slightly, in the middle, causing the car to ride on more of the middle of the tire, vs. evenly on the whole tire. This causes two things - much faster wear on the middle of the tire, causing it to wear out faster, and potentially unstable handling, as there is less tire on the road, allowing it to slide easier etc. 32 is the max that I would go to, if I was looking for a stiffer ride.
i can vouch for the mxv4. The black jade has michelins and consistently get 25-26 mpg at 70-80 with a medium foot almost 30 with a light foot and 60mph. My white 93 cant get better than 23 no matter how slow or light i touch the throttle. the 93 has bf goodrich touring ta's from sam's club. T- rated. Michelins are V rated. Both cars are identical. New Spark plugs and wires and air filters. The only difference is the white 93 has no engine undercover. hmmm i wonder what kinda difference it makes.
95 LS400 Diamond White Pearl 114k
94 LS400 Opal White 161k
94 LS400 Dark Jade 225k
93 LS400 Diamond White Pearl 287k
I personally had good experience with the Falken FK-452.
on a stock rim: 225/45/17
they are ZR rated, takes a heavy load. thread wear is 300 alittle on the soft side so it will wear down faster but pretty sticky.
Smooth ride. thick enough to absorb a lot of the road noise. drops the car a touch. Well, compare to your 60 series it will drop it alot!
pic for ref: (mild 2"drop on suspension the tires did the rest)