Have any of you tried to upsize your tires on the 20” rim to put more sidewall between the rim and road to cushion the ride. I have the sorry Bridgestone eco tires and will need to replace them soon. Between the lower profile snd the tires, I’ve never found the ride to be a compliant as I’d like.

 

You must keep the same overall diameter, so the best way to increase sidewall is to move down to 19-18" wheel

 

I would try other tires —a set of Michelins perhaps—in the same size before going to different rims just to get more sidewall. Also, check tire pressures with a very good gauge, running a couple pounds too high can seem quite stiff with some tires.

 

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“Must” is false. Ther is room to upsize to a degree, I’m just wondering who has done it and what they upsized to. I’m going to upsize, I just haven’t figured out what size or brand tire.

 

Well when i was getting tires I did a decent amount of research, the 235 width tire is pretty garbage, its a weak size tire for a suv that weighs this much. Thats why its not compliant. Moving one side larger on the width tire will help out a LOT even if you leave the side wall the stock 50 profile as in 245/50/20. 235's are great for a little 4 door sedan that weighs a bit over 3,000lbs but not for a 4400lb suv, moving to a 245 width drastically improves the strength and load of the tire as 245's are a common truck tire size that are a bit more expensive but built stronger for "truck stuff". That said, truck tires are generally more loud so there is a trade off, but they last forever and also can easily handle more abuse. I was in a pinch and live in a slightly snowy climate so I went really wanted to try out the michelin crossclimate2's in 245/50/20. I had this very discussion with the "tire specialist" about moving up a size in width to get the higher load range/load index truck type tire in 245 but keeping the profile the same 50's as i believe it might rub if you up the profile when turning, but it seems there is plenty of room to go a bit wider. But the 245's were on back order and I just went with the oem size and to be honest its way better than the garbage ecopias. I was on the bars at 20k miles with the ecopias and the turning was very poor not to mention the wet/snow performance was nonexistent. The only pro the ecopia has is that they are quite as heck. My michelin's are a bit louder but definitely more compliant even at stock side wall size it comfortably eats potholes and cracks in the road.

So foot notes
235 width size tires are for small suvs and sedans
- the rx is a smaller suv but it doesnt weigh the same as a small suv...
245 width size tires you start getting into "tires for trucks"
-which can handle some weight

The only decent 235's are with a sidewall of 65 or higher, this is when the tire load range and load index increases to make a real difference. Such as tires on uhauls sprinter vans, otherwise known as cargo vans which can easily load 4000 pounds in the back. But I'm pretty dang sure a side wall of 65 wont fit in the rx's wheel well haha

Edit:
Sorry I was mistaken when i said the 235/50/20 was the oem 4th gen f sport wheel, its actually 235/55/20 when I looked at my tires today lol. Just look at the manufacture website to find what you would like, most 235's have a load index of 100-102 V or H which is only 1600-1800 pounds per wheel. When you get into the load rating of +105 which is roughly ~2100lbs there is a substantial jump in load or weight in can handle which really equates to the tire being able to handle turn in and handle the weight instead of the side wall flexing too much and rolling over which gives you the stupid mush feeling and horrible turn in.

Heres a helpful link if you would like to read up
https://www.tirerack.com/tires/tiret....jsp?techid=35
But just know if you do increase the load index/range to the "light truck" sized tires, you cannot go over 100mph, thats why all common trucks like rams, silverado's, tundra's, are all limited to ~102 mph. Its very very dangerous to exceed the mph rating which is doable in the lexus with enough room.

 

Sure, you can diameter upsize to whatever you would like but it wouldn't be recommended by most all experts (I'm not one, just a long time (old) car enthusiast). A number of vehicle technologies (speedo being a basic component, ABS, TC, etc.) are developed/tuned for a particular diameter of tire. When most people talk of "upsizing" they mean width - I've upsized tires (225-235-245-265...) on a number of my vehicles in the past (my BMW 325is, 135i, various Corvettes, Infiniti G35, and others going way back) but never bothered with a diameter tire change. Note, I have Michelins on my 2021 RX350 (20" wheels) and I'm very happy with the ride (first Lexus) - maybe because I'm more of a performance orientated individual, I prioritize handling/looks over cushy ride.

 

good points on several aspects. Thx.