Advantage of 18" Tires?

[Kevinc5a]

What is the advantage of the 18" tires on the Premium Plus?

 

[ImInPA]

With a lower sidewall and wider footprint, it could be argued that larger wheels could contribute to better steering. Of course this also depends on a number of other things. All things being equal, larger wheels are heavier, which, reduces acceleration and increases inertia. Heavier wheels also are slower to resond to suspension inputs and require specific tuning to compensate (Vs smaller wheels). Cosmetically, I personally think larger wheels are better looking (assuming a pleasing spoke pattern in the first place) because they better fill the wheel arch. Truth be told, there are no real advantages to 18" rims over say 17" rims and there are disadvantages.

Because tires for an 18" wheel are generally more expensive than for smaller rim sizes, there is a huge advantage to the tire manufacturers.

 

[Mark_888]

The advantage (other than cosmetic, which each person can decide for themselves) is that an 18" tire has a lower aspect ratio (P235/50R18) than the 17" tire (P225/55R17) for the same car (where both tires have about the same overall diameter). The aspect ratio (50 vs. 55 in this case) is the ratio of the height of the tire (from wheel to road) to the tread width.

Since both tires have the same overall diameter, a tire that has a lower aspect ratio has a little bit wider tread (235 mm vs. 225 mm), and the height of the tire (from wheel to road) is a little shorter and therefore stiffer, both of which improves handling and braking.

The disadvantage is that a lower aspect ratio is that the ride is a little harsher, and gas mileage is not quite as good due to more friction between the tire and road due to the wider tread width (although the difference in gas mileage may be small between these two sizes on the Genesis).

 

[CanukV6]

What is the advantage of the 18" tires on the Premium Plus?

So Hyundai can justify the price difference
(and all the other stuff mentioned above).

 

[Kevinc5a]

Has anyone contended that the reported suspension problems may be related to tire size?

 

[ImInPA]

Has anyone contended that the reported suspension problems may be related to tire size?

I have not read anything about that here. I am sure that wheel weight and the weight of the suspension components were all part of Hyundai's setup. I am not even sure that I would say the Genesis has a "suspension problem." Some find the suspension far to bouncy (some even sense this to the extreme), some find it far too soft, and many, if not most, find the suspension just fine. In my personal test drives, I found the the suspension in the Genesis to be very good. There were a few bumps that it could have absobed better, but, I personally found nothing objectionable in the Genesis suspension.

 

[Mark_888]

Has anyone contended that the reported suspension problems may be related to tire size?

They are not related. A 50 series tire is not all that harsh.

I have a V6 with the 55 series tires (17" wheels), and have definitely noticed the suspension problems. The suspension issue is not really that ride is harsh (although it is firm), it is that the rear springs/shocks are too bouncy under certain road conditions as if there is a resonance frequency problem. Seems less noticeable in warm weather or after accumulating some mileage (I suspect it is the warm weather and the problem will return this winter on my V6).

 

[CanukV6]

I have the stock 18" wheels/tires for summer and a set of 17" winter wheels/tires for the snow season. I would say that the ride was slightly better on the winter set-up probably due to the higher profile tires and softer tread and/or sidewalls.

Mark brings up an interesting point though regarding the warmer weather and higher odometer mileage. When I got my car in late October 2008 it was already getting cold and I did definitely notice the harsh ride on the stock wheels/tires. I still had the problem with the winter set but not quite as bad. When I swapped back to the 18's again this Spring, I was expecting the ride to get worse again but I haven't noticed it as much so far. Maybe I just haven't hit that bad road surface combination yet that causes the problem, but maybe the warmer weather and mileage (I now have 24k km or 15k miles on the car) have 'softened' things up a little.

I have always believed the problem was with the shocks, not neccessarily the springs and warmer weather might have some influence on them. It could certainly explain why some people - maybe in warmer regions - haven't seen the problem at all.