Oddly, ever since I have put on my 18" rims... I have been noticing lower mpg... I use to get around 350 miles with a full tank.. but now it is around 290... so I was wondering if the tires pressure was the reason... so all of you with 18" rims.. what it the correct psi for 18" rims..???

BTW.. I'm running 235/40/18..

 

It should say on the tire. The rims dont have much to do with it.

 

Well... what I meant was that using 18" rims and tires setup might cause the loss of mileage per gallon... compare to using 16" stocks

Of course, the tires says 50 PSI for maximum pressure.. but I'm not suppose to fill it up to 50 PSI ..right??

 

yes,you're right - you should check any documentation or with the people who sold you the tires as to which tire pressure(s) would be appropriate for you Maxima's weight and weight bias.

Your new wheel/tire combination may be considerably heavier than stock. Basically, 1 pound of rotating unsprung weight (wheels/tires/brake rotors, etc) equals 8 pounds or so at (legal) highway speeds. So if each tire is, say, 2.5lbs heavier and each wheel is 2.5lbs heavier, at highway speeds your car "thinks" that its weight has gone up by 320lbs, or more that 10% heavier than stock. You can expect your gas mileage to suffer at highway speeds as a result. Even in stop-and-go traffic gas mileage will suffer, because your engine has to work harder to get that extra mass on the ends of your axles moving.

All this extra weight will have a negative effect your brakes, too.

A little research goes a long way...

Sorry to be the bearer of bad news.

Mark

 

My gas mileage stayed the same when I put on my 18's. Even with stock tires, tire pressure is extremely important when it comes to gas mileage, performance and comfort. Even a 10% deviation in tires pressure (4-5 psi) can result in greater fuel consumption.

But, to answer your questions, I keep mine 235/40 18's at the same as the recommened tire pressure as the stock rims as indicated in your manual. Optimal tire pressure is determined by the manufacturer by taking into consideration the weight, speed, handling etc. of your car and should not change when you upgrade your tires. Remember, even though the volume of air might change in a container, the psi should remain the same.

Call tirerack.com @ 1-888-541-1777 and they'll tell you the same.