SilverLady

I think I also read that the altimeter uses the air pressure inside the cabin, which of course would make it way off with the windows closed. It does know when it is up in the mountains (it gave much higher numbers in the Catskills, for instance), but let's say that I wouldn't want to fly a plane using it .

Jasp - those milage numbers do sound low for I95, although if some of that is passing Philly during rush hour that is another story. You might want to do the hassle of recording milage vs actual gallons at fill up and get a true number.

Some of the good milage I have gotten has even been during ascent, so I doubt that is the problem.

I bought the RX partially to have a better milage vehicle, but that has been a bust. The RX averages maybe a couple of miles per gallon better (based on its trip computer). From what I could tell the hybrid RX400H only does one or two mpg better than the regular RX350, so that is no panacea either.

The G Man

My sister just bought a RX350, the mileage is not much better than the GX. I guess all those luxury items and the sound insulation don't do much for gas mileage.

loflin

FYI, related to comments on Lexus altimeter works "just" on barometric pressure...

ALL altimeters work on barometric pressure. Just the more precise ones, are much more expensive. Also, to be accurate (i.e. for airplanes) they need to be calibrated each time (or at least once a day) to a known altitude.

Now a days with the GPS satellites, if you get grab enough satellites you can get an elevation, but again the accuracy depends on the number of sats.

Not sure whether the Lexus alti works on inside or outside air, but it really is a myth that car cabins can be "pressurized" like an airplane cabin. They can't, even with windows up, and A/C on re-circ, there is still an outside air flow.

This should not be confused with the pressure you may feel when you crack a window at high speed, that pressure differential is due to the venturi effect of the outside airflow around the car, causing a pressure differential.

The G Man

So what you are saying is that each time you want to use the altimeter, you need to calibrate it to the current barometric pressure by setting it to a known altitute.

CVsIS250

There still has to be some type of figure used to calculate miles left. You can't use D=R/T without know the actual fuel consumption of the vehicle. You are sure the statistics weren't changed to reflect?

CV

The G Man

The mileage left is based on the MPG reading of the trip computer.

loflin

Yes, for "real" altimeter's. I don't think ours works that way, never really tried.

If you've every flown in a small plane and could see the cockpit, that's one of the pilot checkoffs. Every airport (large or small) has a known and published altitude. Pilot dials in the known altitude while sitting on the ground. Then they are good to go.

I'm not familar with the latest airplane technology, perhaps now they use radar or something along with topo maps. But I'm sure there is still an altimeter in there.

yaro1

Yes, that is correct. Try it! Or, if you just want to see how high you are climbing, set it to 0 when you start, and then whatever it reads is approximately how high (or low) you have gone from your initial altitude.

I can't comment on it's usefulness, but it sure is interesting to know how high some of those mountains in PA are when driving around.

Obviously, the easiest way to set it is to be at sea level (at a beach) and set it to 0. Otherwise, check some map data to find the altitude of your house, and just set it from there whenever you want.

The G Man

Here is a stupid question. Let just say I calibrate the zero at sea level, what happens if I travel long distance to another region where the base barometric pressure is diff. ie: if I travel from a low pressure zone to a high pressure zone. The gauge will no longer be accurate, correct?

JASP615

so how do you reset this? I thought that GPS would set this?

Sami

The G Man

You can adjust it by pushing the up and down arrow.

loflin

Not a stupid question.

Sames applies if you stay in the same place, and a front comes thru (or leaves).

I haven't looked into how much variation weather can affect vs the change due to actual altitude. So I don't know if significant.

However, in a car, what do you do with the altitude information anway, not much, just interesting. And if it's 500 feet off, does that have any significant impact to anything we are doing. Not really, in my opinion.

I consider the altitude readout is just a "freebie" as they had to include a air presssure sensor as part of the engine control package. Interesting to glance at, occasionally.

ADVocate

For the Distance Estimation, and the Fuel AVG calculation, you can simply reset the computer for the AVG calculations (I believe you hold down the set button for a few seconds or something like that). That will zero out all the values and it will simply start over on its' calculations.

As for the Altimeter, it is the barometric type. You CANNOT set it accurately. Nor, will it ever give you an accurate reading. It relies on Atmospheric pressure that not only changes with Altitude, but weather as well. So if you set it up at sea level, and you have a storm on your journey upwards, it will rarely give you an accurate reading at all. But, it is a good "guess-timate".