But on the door it says 32 for all 4. My car will be 32 or 31 while running. when it sits, 30 on all 4. So i should give it more air?

 

A few things about nitrogen here:

First, nitrogen is already about 78% of the regular air you breathe every day; a tire inflated with nitrogen will probably never be more than about 93-95% nitrogen because no one is going to perform the number of fill/purge cycles necessary to get rid of all of the (21%) oxygen that's in regular air. All in all, the nitrogen percentage of a "nitrogen-filled tire" is really not that different than an "air-filled" one.

Second, nitrogen (which - surprise! - is also a gas!) expands and contracts with temperature just like regular air, although a tiny bit less. But at the above-calculated, best-case 17% difference, the reduction in pressure change with temperature is negligible.

The above said, there are two good, yet small, reasons to use nitrogen: First, nitrogen molecules are slightly larger than oxygen (yet slightly lighter, interestingly), so they escape ("permeate") through the rubber of the tire about 30% slower than oxygen, so a little less leakage over time. Second, nitrogen is a "dry gas" (it cannot "hold moisture" like "regular air" does), so it can help reduce corrosion of the tire's steel components (bead, sidewall reinforcement and belts). Do note that oxygen and water also permeate into the tire from outside, so the above benefit is not absolute, or even that large. Also note that many compressed [regular] air systems have moisture traps, which also help reduce issues caused by water.

Overall, inflating tires with nitrogen won't hurt them and may provide some minimal benefits. The bottom line: if you go someplace that provides free nitrogen, go for it. But I wouldn't pay for it. Rather than paying for nitrogen you are better off just buying a good tire pressure gauge and then checking and adjusting your tire pressures regularly.

 

That 32PSI reading on the door is cold inflation pressure. It is normal for the pressure to rise as you drive, that is taken into account by the engineers when they determine the cold inflation pressure. You should never go below that pressure but many people like to set their tires slightly above the cold inflation pressure. This can give a firmer ride and possibly slightly better fuel mileage.

 

I bought steel wheels and winter tires 225/65/17 and I have 18 originals. In the manual the 17 are suppose to be at 35 psi. Should I set it to 35 as per the manual?

 

I have the same winter setup. I didn't know the pressure were different for the 17" vs 18" tires. I would use the recommendation in the manual of 35 psi for the 17" tires. Good find.

 

Sorry to bring up an old thread. Anyone here running 255/45/20? My tyre shop recommends 34psi on it but I feel it's a little too low.

 

My NX came with 255/60/18 Michelins....the same brand of tires I've been running for over 40 years.

I have the tires inflated to 37psi cold because I like the handling at a higher pressure. Sure, the ride is firmer, but it's an F-Sport. I suppose I could have gotten a big, lumbering luxury car if I'd wanted a "luxury" ride.

In another thread I mentioned my wife has a Q3 (and I've been using her car for a number of NX comparisons)....she ran her Michelins at 42psi cold for a year, but recently dropped to 37 without an appreciably difference in handling....

Neither of us really care that much about gas/petrol mileage numbers other than being aware of them.

 

I just noticed that after latest maintenance Lexus inflated my tires to this pressure(55 psi):

No wonder my car feels like a train after its last maintenance. It is written on the tires that max pressure is 51. Why did they inflated it to 55psi?

 

There is HUGE monetary benefit to inflate tires with nitrogen, but it is to a dealer, not you.

 

I just checked this while working on my wife's nx.. For about a week I was wondering why the ride was so harsh, Turns out every tire was filled to about 42-44psi. WAY too much in my opinion!
Checked the door and sure enough it's 32psi. I dropped all tires to 32psi and will be taking it out tomorrow to see how it handles. It has to be better than what it was. As far as gas mileage. I'm not really concerned with it anymore because this thing sucks with mpg so dropping it to have a better ride quality than to save 2mpg is worth it in my opinion. I might up it to 35psi in the tires but 42 coming from the dealer to me seems like something that they should have "checked" before selling.
I'll report back on updated ride quality.

-Nigel

 

 

I picked my wife up from the airport yesterday and she commented on how the ride seemed smoother with the NX. Told her that the tires were filled to 40+ psi and that was causing it to be harsher than what it needed to be. I also noticed the lack of bumps and harshness. SMH at the dealer for filling them up that high... bunch of dummies. I will continue to ride with them at 32psi as that was a much better ride.

-Nigel

 

 

I do 32 or 33 psi and I always tell the dealership not to adjust as they always over inflate them if they do. You can feel the difference immediately.