Planning to keep my current ride height on my Sportwagon so how much ride deterioration can be expected.
Also concerned with increased torque steer and wandering in truck ruts.
Currently running stock 215/50/17 Michelins.

Turning to your specific question, the main concern would be the clearance of a 235mm wide tire from the upper control arm (at the front pair) when the wheel is turned. Even when the OEM 215/50R17 tires are mounted, there is scant clearance; with a 235/40R18 tire, you should be concerned about rubbing. A lower offset wheel would increase clearance, but would alter the steering geometry (the steering axis would no longer meet the road at the midpoint of the tire width). As you note, you would also have an inch less of sidewall to flex at each wheel, so there is less spring action in the tire, giving a harsher ride and increasing the likelihood of edge lift under lateral stress. Also, the wider and shorter contact patch would be more prone than the OEM tire to being steered by irregularities in the road surface -- the obverse side of quicker steering response from inputs at the other end of the system.

Out of curiosity, why do you (your topic line) consider a 235/40R18 an "upgrade" from the 215/50R18 size?

Thanks for the response. As far as clearance it seems from searching these forums that there are many who have this tire without any rubbing problems.
It seems to depend on the particular brand.
I have a track on a set or RX8 18x8 wheels which I am considering. My main goal is to improve handling and steering response with the side benefit of improved ascetics from the 18 inch wheels. The car has only 20k so I will wait awhile on a shock upgrade until needed.


Wouldn't the shorter sidewall lead to better overall handling?

As with most things in life, there are trade-offs. The shorter, stiffer sidewall will give a more direct, "quick," feel to the steering. Too direct, too quick, and you edge into twitchy.

The wider, shorter front-to-back, contact patch on the pavement makes the tire less self-steering in the direction pointed and more responsive to turning input, whether that turning input comes from the steering wheel or from irregularities in the pavement.

The wider footprint gives a longer path for water trapped under the tread to go to be fully evacuated, so a wider tire is more prone to hydroplaning than a narrower one at any given speed.

A longer, more flexible sidewall provides more springiness and a softer ride, and less susceptibility to damage from road hazards, than a shorter, stiffer one does. In terms of cornering, a tire with a supple sidewall can be designed to "extend" the contact patch up the lower portion of the sidewall when the tire shape distorts under lateral load, while short, stiff sidewalls tend to provide more sudden transitions at the borderline where traction is lost, as the entire tread tends to stay flatter as it lifts off as a unit.

It is all a question of which side of the compromises you prefer.

I have 04 wagon- just got new wheels 17x8 48 mm offset (17x7-OEM) wraped with 225/50 R17 General Exclaim UHP-maximum wheel with for this tire is 8" so with tall side wall it's spread and hight still the same as a OEM 215/50 R17 but tire has wide contact patch. Ride softenes almost same but cornering and respond alot better then OEM combo. As clearance go-front almost stay the same-on the back I roll fenders just to be safe. May try next time 235/40 R17 will see how long this tires will last me. Load raiting affect how soft side wall going to be higher load most likely will give you stiffer fill.

Would you say I'd be better off with slightly stiffer springs and keep the stock wheel tire combination?
The Michelins have plenty of life left in them so there is no rush to replace them.

RB springs for wagon will not slam it down, but give you nice ride ..Invest in sway bars!!! This is hard to beat mode. First I installed rear Progress sway bar -lil difference but better then stock,then I got front RB bar- that changed everything !!! I think for wagon (havy back) Progress bar on the rear better then RB bar ( OEM wagon thiner then sedan bar -I guess wight difference ) Front swap is hard but I did it in 3 hours alone-second set ofhands will be a big plus in this install.

I just install 235/40/18 with RX-8 wheels, and honestly, it's a great upgrade. I have yoko es100, I don't have any rubbing issues.

I feel a huge difference in handling. I used to run stock 18'' with pirelli

It all depends on what your priorities are in the changes.

If the rear is riding low, then XAM's advice on springing and sway bars would be the place to start; worry about the wheels and tires later.

If you want to improve road handling, so that you can leave the Infiniti G37 coupes in the dust when they have to slow down for the curves, then a simple tire change, using your current OEM wheels, to Hankook Ventus V12 evo ($85/each in the 215/50R17 size at tires-easy dot com) or Vredestein Ultrac Sessanta ($140/each in the 225/45R17 size at performanceplustires dot com -- West Coast -- or slightly more at Euro-Tire -- East Coast, depending on shipping costs to your location) would give you far more bang for the buck than any other cash expenditure of the same order of magnitude.

posttosh,

CND just placed the Hankook Ventus in 2nd place in a tire test, and the price can't be beat.

Whats the estimated tread life?

SmokeU6s

After reading that exact article I went into my local Discount Tire Co. to check em out and the guy working there said you can expect 45000miles from them even though the warranty Discount Tire is 30000 (or somewhere around there). But he said it all is dependent on how you drive because he figured that the estimate he gave me is an underestimate because its what Hankook gives them which he figures is with mixed driving. He guesses that if you drive like a little old lady you'd easily make it to 60000 or if you are hard on them or use em for auto x or something you would of course get considerably less. After he told me that I walked out and was like DER! Doesn't take a genius to know that how you drive affects how your tires last.

hyperlite,

thanks for the update. Considering they are about $20/tire cheaper than the avids they look to be my next purchase.

I have not seen any recent Car and Driver test results, but that is consistent with a spate of recent tests by German enthusiast magazines. (BTW, there are several models of Ventus. The Hankook Ventus S1 evo that Tire Rack sells, for instance, is a very different tire than the Hankook Ventus V12 evo that has excelled in the German testing.)

The UTQG Treadwear rating of the Hankook Ventus V12 evo is 280. The OEM Michelin Pilot HX MXM4 tires have a UTQG Treadwear rating of 300; theoretically, then, the Hankooks would wear out in 14/15ths (fourteen-fifteenths) the number of miles compared to the Michelins. So, if you get 36,000 miles out of the Michelins, then -- theoretically -- you would get 33,600 miles on the Hankooks. (Due to granularity -- Treadwear ratings are in multiples of 20, so the difference between "280" and "300" could represent anywhere from 1 to 39 units -- and due to differences among manufacturers in interpreting the detailed mandatory procedures for the testing of Treadwear, the Treadwear numbers should not be parsed too finely.)

Just installed RX8 wheels with Potenza RE760 in the 235/40/18 size.
Handling is like night and day compared to the stock tires and wheels.
Will upload some oics soon.