I just picked up my 2017 RX350 F Sport 3 last week (Silver atomic, black interior) and have a few questions.

The first is with the accuracy of the tire sensors. When i first picked up the car, they weren't working - the sales person said that they had just put on the winter tire/rim set (20 inches) and I'd need to drive it for a while that night for them to register. I forgot to check the tire sensors in the menu at the time. I remembered to check them over the last few days and usually check them 15 to 20 minutes after driving for a while am finding that the psi's are usually different on all 4 tires and noticed the following:

1. The two front side tires's psi are never the same (driver side always at least 2 psi higher and sometimes 3 (the usual difference is that the front driver side is always at least 1 or 2 psi higher than than the front passenger side)
2. sometime the psi on the two driver side tires are the same and the don't match the psi on the passenger side tires
3. at times none of the tires psi match - difference of a total of 3 psi among all 4 tires
4. the recommended psi for the 20 inch size tires on the side of the door is listed at 33, but the psi on the tires usually around 36 to 33, but have been as high as 37 and as low as 32

How accurate is the psi listed on the tire sensor system that shows up in the front display? Should i be concerned about the differences in the two fronts and at times the two rears, or the driver side in general being higher than the passenger side? My old 2010 Ultra premium just gave a warning when there was an issue with tire pressure, but didn't actually list the tire pressure so am unfamiliar with how it works now and how much attention to pay to differences.

 

check pressures cold and adjust as needed.

 

Not sure how you can stabilize all four to the same psi as there's always some fluctuation. No need to be concerned though that one or another differs. I believe a warning light is only triggered if any one of the tires falls below 30 psi. I try to keep mine around 35.

 

The first thing that you need to do is to use a good tire pressure gauge to check to make sure that all 4 tires are inflated to the proper pressure and to the same pressure. It doesn't sound like you have done that. The time to do that is when the tires are cold (when the car has not been driven for at least an hour). It is not unusual for a dealer/shop to be less than careful about making sure that they have inflated the tires to the proper pressures.

After you have confirmed that all of the tires do have the proper pressure, the time to use the car's tire pressure monitoring system is when you first start the car, not after you have driven for 15 or 20 minutes. The only meaningful readings are for cold tire pressure. After you have started driving and the tires have warmed up, tire pressure readings are typically 2-4 psi higher than cold tire pressure.

Once you do start driving, it is not unusual for pressure readings to change from one moment to the next or for one tire to have readings that are a pound or two different from the readings for another tire because, depending on driving circumstances, one tire could be warming up more than another tire.

Also, after doing a tire rotation, switching wheels, etc., you are supposed to re-initialize the tire pressure monitoring system. I don't have an RX. So, I don't know the location of the button that is used to do that on an RX, but, in your manual, you should find the location of the button and instructions for how to do this. If this is not done, the readings for the system might not match up correctly with the right tires.

 

kss, do as JS suggests, but I would expand on it:
You don't mention if you ever manually checked the tire pressure. You need a good quality gauge and a small air compressor(or a gas station close by). When tires are cold, either first thing in the morning or a couple of hours after driving, check and adjust each tire up or down. That's the only way to be sure of what you got. Then see what the TPMS system says. It's normal for the pressure to go up as you drive and the tires heat up, but they all should stay within a pound or two, depending on say, if the sun is shining on one side of the car etc.
For what it's worth, I've always set my pressure about 3 pounds or so above what the label says on the door jamb. I find I get longer tire life and somewhat better handling without making the ride harsh.

ps...in the time it took me to type this, I see lesz jumped in with more good stuff!

 

I found the tire pressure sensors are useless in Canadian Winters. I parked at my work place in the morning and when I came back about 7 hours later to go home, the tire pressure sensor warning was on. That's cause at -35 C windchill in Calgary that day the sensor malfunctioned. Lexus told me just drive around and it will go away and they were right. It is annoying to have it here in Calgary. When temperature drops, two things could happen; the sensor may detect less pressure due to air being so cold inside the tire hence lowering the pressure reading OR the sensor could malfunction (that was my case, it was frozen).

Oh well, you can't have nice things in Canadian winter.

 

Tires lose about 1 psi for every 10 degrees F drop in temperature. If your tire pressure monitor is giving a warning when you first start the car and if the warning light goes off after some driving, it means that your tires are under inflated. The only meaningful readings are ones that are taken when the tires are cold before driving. In your case, driving may warm the tires enough to turn off the warning light, but they are likely still under inflated because the warning light turns off when the pressure gets within something like 5-7 psi of what the recommended pressure is.

In the northern US, I typically will have to add about 5 psi or more in the winter. In Canada, I'm sure that even more air needs to be added to be at the proper inflation level, and, if you are not adding a good amount of air in the winter, you are driving with under inflated tires, which makes the tires less safe, and it also increases tire wear and reduces fuel economy.

 

So should I increase the air/PSI in winter? What do you think is the best? 32 PSI or higher?

 

Many have commented to check and set the pressure when tires are COLD, regardless of what the outside temp is. I go with 35 psi - you make prefer a bit less for a softer ride.

 

You should, regardless of what the outside temperatures are, try to keep your tires as close as possible to 33 psi or whatever is recommended on the plate or sticker that is on the driver's side door jamb. As mikemu said, what is critical is to check and set the tire pressure when the tires are cold, which means when it hasn't been driven for at least an hour or more. Any check of pressure, either done manually with a gauge or with the car's pressure monitoring system, is meaningless once the car has been driven for a while and the tires have warmed up.

To maintain proper pressures, you should be adding air in the winter and letting air out during the summer. Typically, I will check and adjust tire pressure at least 4 times per year. I'll add some air in the fall when the temperatures start to drop. Then, I'll add more air when winter temperatures really set it. At the end of the winter, I'll have to let out some air, and I will let more air out when we approach the warmest temperatures for the summer.

 

Check the pressure with a good instrument and write it down, start the car and drive for about 5 min to give the computer time to register and adjust then compare the pressure you took with what's showing in the cluster. Per my Lexus dealer when you start the car you won't get the proper readings immediately and you'll see a pressure difference of about 1-2 psi as it is almost impossible to fill exactly each tire the same. One piece of advice is to fill the tire with nitrogen which has bigger molecules and is therefore less prone to seepage. Also at the beginning of winter over inflate the tires by approx 5psi that ought to see you through the winter with all its fluctuations.

 

I'm super picky about tire pressures and rotation. I have my own air compressor, torque wrenches (for rotation) and several excellent tire gauges. I've found that the Tire Pressure Warning System readouts are around 2 psi higher that the actual tire readings all around when tires are cold in my garage.

 

There is far from universal agreement about whether there is anything to be gained by having the tires filled with nitrogen.

First, regular air already has 78% nitrogen, and, after a nitrogen tire fill, the amount of nitrogen in the tires only goes up to about 92%. So, in essence, when you do a nitrogen fill, you are replacing about 1/2 of the oxygen in the tires with nitrogen.

Also, once you do a nitrogen fill, you can no longer use a compressor at home or at a gas station to add "air" when the pressure is low because, as soon as you start adding regular air, you are negating any alleged benefits of the nitrogen fill. Thus, whenever you need to increase the pressure, you have to go to the car dealer or a tire shop that has the equipment needed to do a nitrogen fill.

For those reasons, many feel that nitrogen fills are nothing more than hype and a way for dealers to have another dealer add-on that they can add to the price of the car and one that is pure profit for the dealer.


That is interesting.

I am also quite obsessive about having my tires inflated to the proper tire pressures. I've now had 2 Lexus vehicles with the tire pressure monitoring system, and, on both of those vehicles, the tire pressure monitoring systems have consistently yielded readings that are about 1 psi lower than the readings that I get when I manually check the pressure with a high quality gauge.

In any case, I still consider the TPMS to be a valuable tool because, once I know how its readings compare to actual pressure, it allows me quickly to look at its readings and to know the actual pressure by adding 1 psi to the system's reading, and I don't have to walk around the car and manually check the pressure in all 4 tires.

 

thanks everyone for the information and advice. I took into the dealer today and a tech checked the pressures. He said they are within limits, but one was a couple of PSI under. He also said to check the pressures cold and recommended around 35 psi for winter use. When i picked up the car, the sensors weren't reading and the sales guy said to drive it for a while and than check, so I had thought i should be checking the readings after driving for 15 or 20 minutes. That's probably why the readings were as high as 37 psi, when on the low end they were 33 psi.

He did say the readings were accurate, but would vary if you measured with external gauges and that there is even variance among the pump/gauges they have in their shop. We reset the tires after he added some air, but the tire sensors didn't show any readings until a few hours later.

 

I too thought so and never used it for the reasons you mentioned, this RX came with nitrogen, but I must confess that I haven't had any seepage or loss of pressure in 1 yr.
I think the jury is still out and it may indeed be a marketing gimmick, but if all else fails it may worth a shot.