I test drove a 2004 LS430 (Modern Luxury) with 17" tires and a 2005 LS430 (Modern Luxury) with 18" tires and noticed a difference in the ride. The 17" tires do have a better ride (softer). Is it my imagination, or does everyone concur?

 

were they both the same tires?

 

No it is not your imagination, the 17" are smaller and have more rubber to absorb the bumps better. The 18" have lower profile & are a tad bigger so you will get less "floating" feel when driving. The 18" will have a firm or stiffer ride than the 17" wheels.

 

Tee,

That was precisely my thought...but was hoping the LS430 could somehow "compensate" for that difference.

 

Sorry physics playing it's role on this one.

 

Generally, a smaller wheel / taller tire sidewall will ride softer than a larger wheel / shorter tire sidewall. However, higher tire pressure, performance or runflat tires with a stiffer sidewall, and some stiff high-mileage tread compounds can all make for a coarser ride.

 

It has nothing to do with the diameter of the tire.. it has to do with the sidewall series..

aka XXX/45/XX, XXX/55/XX, thicker sidewalls (55 series) are cushier.. 35's are super low profile and not very comfy.

 

I also test drove a 05 or 06 (cant remember) when I was looking at cars that had the "Sport" option and 18s on it. I was excited about checking it out but it ended up being disappointing to me. Not much difference in handling at all. Really did not like the harsher ride compared to the standard model with 17s.

 

You could achieve the softer ride by putting bigger sidewalled tires on the 18's..

it just won't look very good.

 

And your speedometer will be slow compared to your actual speed.

 

All three numbers in the tire size determine the diameter. The second number is the multiplier (for the first number) for sidewall height. For a 245/45R18's, the sidewall will have a height of 245*.45=110.25mm/25.4=4.34 inches. So the overall tire diameter will be 2*sidewall height+wheel diameter = 2*4.34+18=26.68". A 225/55R17 tire will have a sidewall height of 225*.55=123.75mm or 4.87 inches*2+17 or overall diameter of 26.74". This means the tires for 17" wheels will have 13.5mm or 0.53 inches more rubber between the wheel and the road. Tire diameters will actually slightly vary (by like 0.2") since the same size tire from different makers can vary a few rotations per mile (one reason not to mix tire brands), so you might be able to choose 18's that are slightly larger than another brand.

FWIW, my local dealer (only 1 lexus dealer in town) had 3 LS's, all with 18's: one modern luxury, one custom luxury, and one ultra. I drove the modern and ultra about 20 miles each, including a rough section of road near my house. Both the normal and air suspensions felt similar (except the air suspension seems to float a tad more) in terms of how much I could feel the roughness and seams in the road. IMHO, the air suspension doens't buy one much. I got the ultra for the rear A/C, plus it was in the best condition by far. If my air suspension goes south after 100K mi, I'll replace it with the modern luxury or sport suspension.

 

I drive an 06 LS430UL with 18's and test drove an 05 LS430UL with 17's for someone else and noticed a distinct difference in that the 17's ride had more float like Tee said.

 

FWIW, my plans, regardless of whether the car I buy has 17" or 18" factory wheels, is to use 17" wheels for winter tires and 18" wheels for summer tires.

 

When we purchased our LS 430, there were not any "Sport" packages available locally, but all the So. Cal. cars seemed to have 18s vs 17s. I'm not unhappy with the fairly soft springs on the standard suspension operating with the 18s, but I did install the "Sport" rear roll bar (roughly $120 for the bar and bushings) and that did cut down on some of the understeer.

A bit of research indicates that the "Sport" package consisted of the increased dia rear roll bar, stiffer springs and stiffer shocks. I think the stiffer springs were also sold in some markets as the "rough road" option.

 

I don't know bout 18's but I have a set of 17" wheels that I use in the summer and a set of '02 16" wheel/tires that I use in winter and I prefer the 16's ride (not quite as harsh) over the 17's. But I like the look of the 17's better.