there is a difference but it's not huge by any measure imho. and also keep in mind the 19" summer tires are more expensive

 

Yes, the 19" has 1" more diameter, and in turn, the F Sport 9" rear rims have another 1" width for greater added "unsprung" weight.
This unsprung weight increases the momentum imparted onto the body structure for a slightly less comfortable ride.
For the smoothest ride, the unsprung mass of the wheels and tires must be as light as possible, while the sprung mass of the body on the suspension must be as heavy as possible.
A light unsprung mass will also help the rear wheel/tires track bumpy corners.

 

There's a tradeoff with offset tires in the rear because you're going to a shorter sidewall, so there is potential weight savings in the tires themselves at all corners. The benefit is a larger contact patch under the drive wheels which helps during weight transfer under acceleration. Interesting topic.

Anyone care to weigh tires and wheels for the debate? No?

 

the ride has more to do with the lower profile tires than unsprung weight. some 19" forged wheels are considerably lighter than cast 17" or 18" wheels, but they still ride harsher.

 

Not only do the tires affect the ride more, but the air pressures used affect the ride even more so again.
Thus the OP should always be encouraged to check tire pressures before test driving.

 

most definitely. tire choice and tire pressure make huge difference. choose the wrong tire and it's stiff like hell. between 33psi and 38psi it's noticeable difference

 

+1 also came from a TL. Love the ride with the 18" MXM4's on. Personally I prefer the GS Luxury to the F Sport or the LS460. It seems like the perfect balance for comfort and performance.

 

I hope some will find below info useful. I have driven:
2013 Luxury:
. Stock 18 Dunlops: I thought they were good. I give them an 8.
. Replacement 18 Yokohama: It was hard to compare since the Dunlops alread had 30K+ on them (if I remember correctly). The replacement tires were OK at the beginning and as I put more miles on they got better. I give them a number around 8.

2015 F Sports:
. Stock 19 Dunlops: It was a disappointment coming from a luxury model. I can not believe why Lexus even put them on the GS. I give them a 6-7 (my passing grade is 75% ) I don't care if these are made for high performance. The tires are so loud and noisy. They don't quite fit GS (grand touring sedan as Lexus calls it)
. Stock 19 Bridgestones: Significantly better than Dunlops but still noisy compared to both 18s I had before. They got better after a few hundreds miles. I give them a 7-8.
. Michellin 19 PSS: What a difference! Dealership pumped the puppies to 38-39psi but the ride was still so much better than all above tires. I give them 9. I would give them a 10 if they came with wall that provides extra protection for the wheels as found in other tires. Not best looking tires but definitely most comfortable.

 

Appreciate the info. As soon as I have the car (Luxury) I plan to swap the factory tires with Turanza Serenity Plus. I heard they are the quietest tires out there.

 

I dunno, they rate behind the Pirelli Cinturato P7 Plus in that regard.

I'm getting ready to replace the stock Bridgestones on the LS and I'm looking at both those tires, I think I'm going to go with the Pirellis.

 

The Bridgestone Turanza Serenity Plus are very light on the power steering, and very quiet too, and apparently less rolling resistance for superior economy too, and very long tread life too.
However, I find that the ride is lumpier and thumpier; in other words, not the best for ride comfort...

 

Interesting. So you don't hear the road as much as you "feel" it.

 

What's wrong with the stock rubber on the LS? LS is supposed to be the ultimate quiet machine.

Where did you see the Turanza vs Cinturanto comparo?

 

The stock rubber is really crappy, Bridgestone Turanza EL42. 240 treadwear, hard and loud. The LS still rides great and is super quiet, but I know it will be even better on better tires. Terrible of Lexus to put such inferior tires on the LS.

Here are the test results from TireRack, they directly compared the Pirelli Cinturato P7 Plus, the Bridgestone Turanza Serenity, the Continental PureContact, and the Michelin Premier. The Pirellis won in ride and noise.

http://www.tirerack.com/tires/tests/...y.jsp?ttid=188

 

Haha, as a test car they used the noisiest luxury sedan out there, the 3 Series. I wonder if it's by design or that's what they had laying around.