Fish

iTrader: (26)

2KHarrier

You'll feel that 5% difference in the sidewall... 18's give this boat a harder ride to begin with, compared to the 17's. However, to answer the question, I have 45's on my car.

Johnhav430

I would go with 45's to keep the proper # of revs/mile. speedo etc. would be thrown off by keeping the width the same with a lower profile. If you do go lower profile you want to keep the circumference the same, meaning the tire would be wider. My BMW has 35's in the rear and 40's in the front and it's not really a problem...you just want imho the proper fitment...

Fish

iTrader: (26)

TriC

IMHO the difference in ride quality between 45 series tires and 40 series is not insignificant as the latter are notably harsher. The 45s on my LS skirt the edge of being unacceptable for a luxury car. Accordingly, there is no way I'd go with 40s, regardless of cost.

LS430inDE.

................................245/45/18........ 245/40/18
................................Current...............New..................Difference
Sidewall Height.........4.34''................ 3.86''................... -0.48''
Section Width............9.65"................ 9.65''........................ 0''
Tire Height...............26.68''............... 25.72''....................-0.96''
Tire Circum..............83.82''.................80.8''......................-3.02''
Rev. / Mile................755.91...............784.16 .................28.25

SIDE BY SIDE COMPARISON: Current Size 245/45R18.......New Size 245/40R18

If your speedometer reads 65 mph, you are going about 62.7 mph

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Posted above is info from my favorite tire site, discounttiredirect.com. Are you guys tired of me saying that yet?

I entered the original tire size and then the new tire size, and you can see the differences. The calculator can be found here... Tire size comparison calculator

As others have mentioned, I guess it all depends on what you're looking for/what your preferences are. Looking for lowest cost? Looking for lowest profile? (lol) Looking for harshest ride? Looking for loud tires? Looking for always wondering exactly what speed you're going because the speedo is not going to be accurate?

As you can tell, I'm not a big fan of changing the tire size. If I were to do anything, I'd personally buy wider tires if/when it was for my F150. Tires for the LS?....I'll always always always buy the 245/45/18. Even then, I'll look for an H rated tire instead of a V or a Z rated, etc. Personally, I'm looking for a great balance of smoothness with stability with least amount of road noise.

If price is your only consideration (as it seems like it is in your original post), keep in mind that the LS overall height will be lowered by an inch! I know there are some places that I've scraped my the underside of the front bumper, (which makes that TERRIBLE hard plastic scraping noise) when pulling into a parking spot! Do you encounter speed bumps, have a steep driveway, etc, etc, etc.

Sorry....had to edit original post because of the formatting.

PS....my preference would be the 245/45/18

warminwisc

Never heard a post like this but correct me if I am wrong U R running runflats which by all reviews do not help anything but having not to have a spare tire, but U have room specifically for a spare. Why? Not meaning to be anything but curious. If U are running runflats dropping down to any non runflat 40 or 45 that clears the calipers will be a better riding LS so its a couple miles speed difference adjust accordingly.

Another concern is if people questions the legitamacy of the miles on the speedo during resale but so it rides a little stiffer its a boat might be funner to drive but again no real reviews to compare to.

warminwisc

U drop down an inch it will handle better screw H's get V's

Johnhav430

imho the logic of runflats is flawed....yes you can drive 50 mph for 50 miles, but you also need to replace the tire after doing so, and shops are never supposed to plug a runflat (I was told it's because they have no way of being sure you did not drive on it flat). So to truly use them you would have to be kind of rich. My BMW came with RE050A runflats, and I plugged (not patched) 3/4, I wasn't rich enough to simply buy a new tire because I got a screw in them. But I did not replace them with runflats, and I don't have a spare either. When's the last time any of us actually mounted a spare on the road? On many roadways, troopers won't let you do it anyway. If I get a flat, tow me home with AAA Plus, and I'll either plug or grab a snow tire from my shed until I can replace...

At the end of the day I suppose we can do things the way our parents did. They just got bigger and lower tires without any regard to the size (Radial T/A's--as long as they fit and looked good, just do it). You can do that if you really want, the vehicle will not self destruct