Harsh Ride Quality on 20 inch tires

[danldale]

Has anyone tried a smaller rim and tire size to improve the ride quality? I want to know the cons before I buy 17 inch rims and tires.

[Zeus253]

Best ride and performance would be to maintain as much sidewall as factory. For example instead of 65 series (second number on tires) try 50-55 but rim size needs to match that number in terms of overall height. When put together, the new rime plus the sidewall height would equal the same total height of factory height. A very small amount wider will definitely help for traction especially side action / cornering. This is my opinion based on my experience. The less sidewall the worse the ride in rough roads like city pot holes. (Full disclosure to check on safety first then look cool second. Follow all applicable regulations in your area)

[danldale]

Thanks Zuess253. So you are not recommending reducing the rim size but rather the sidewall and keeping the 20 inch factory rims? As long as the new rims match the new tires I should see a reduction in the harsh ride? Seattle streets are terrible.

[RX400h]

According to tirerack.com, you can go as small as 18-inch wheels and tires. 
235/65/18
instead of what you have: 235/55/20

Wheels for 2019 Lexus RX 450h F Sport (tirerack.com) 18-inch wheels

Tire Search Results (tirerack.com)   18-inch tires

You may want to call them and verify that the 18-inch wheels will clear the brake calipers.

The larger the tire's aspect ratio, the softer the ride, so the 18-inch tires and wheels, with a 65 aspect ratio will be softer-riding than your existing 55 aspect ratio 20-inch tires.

The 18-inch tires will be .71-inch smaller in diameter which make your speed reading look a bit higher than it is.

If you have any questions, give Tirerack a call at 1-888-541-1777

• 888-541-1777

[Zeus253]

Yes, and "RX400h" has a really great answer. .71 difference I believe (almost 95%) that speedometer only off less than 2 MPH from reality.

[Zeus253]

For example, on my Vette having 40 and 45 series tires with huge rims; absolutely mandatory to have intensely upgraded shock and suspension to match. Otherwise driving would be more torture than enjoyable.

[RX400h]

Yes, Dan's 450H F-Sport does have an upgraded suspension, I believe, but the larger aspect ratio of 18-inch tires will certainly make a difference on rough surfaces.

[danldale]

Thanks a bunch for the replies! I placed an order for black 18” rims with 235/65/18 Michelin Cross Climate II tires. I will post a review when I get these on the road. 

[danldale]

Costco came with an early install of the new 18” Velux Black rims and Michelin CrossClimate2. A much improved ride! Road bumps are greatly attenuated. It’s not a Bentley glide to be sure, but those OEM 20” wheels really transmitted the bumps where as the 18” absorbed those very same bumps. I call this a success. Thanks for all the advice!

[Dansforest]

I just bought a 2018 4 months ago, going through the same thing. Wondering if your ride quality really changed that much better? If not, I may dump the car, kinda sick of all the bumps.