17 July 2006
SETI League
PriUPS Project


A Soon-To-Be-Missed Opportunity

It is universally recognized that "proper tire inflation" is critical to achieving good gas mileage and vehicular safety.  Exhortations to this effect appear in government publications and the assorted documents that come with your car and its tires.  In case you forget the actual tire pressure you should be using, you can even find the recommended values inscribed on a label on the doorpost of your vehicle.  Accordingly, we all carefully check our tire pressure frequently and adjust it to optimum.  I do this, for example, every time I refill my lava lamp.

OK, so we almost never check our tire pressure.  Even I, something of a mileage fanatic, occasionally do a walkaround and look at all four tires.  If none is noticeably low, I forget about them for a couple of weeks.  "Noticeably low" would probably mean that the tire pressure was deficient by over 20%.  So much for good mileage!   I doubt that you are any more assiduous than I am.  And even if you are, your crappy manual tire pressure gauge is notoriously inaccurate.  Try to get the same reading on successive measurements and see if you don't agree.

Tire and auto manufacturers together decide what the optimum pressure is for each vehicle and tire combination.  Typically the pressure is given as a range, e.g., 30-32psi, or pounds per square inch.  In percentage terms, this is a fairly wide range, which means that proper inflation isn't something that requires a precision manometer or standards lab to achieve.  If you read the newsgroups devoted to various vehicle subjects, you will frequently find discussion threads where people are arguing that overinflating tires will increase mileage.  I don't know if they are correct; I tend to believe that the manufacturers know what they are doing and that their recommendations are sound.  What does happen with incorrect inflation?

  • Extremely low:  You have a flat tire!

  • Very low:  The tire is visibly deformed (partially flat) and will overheat very badly as soon as you start driving.

  • Somewhat low:  The tire will overheat and energy will be lost to this, resulting in worse mileage.  It will also cause uneven wear and reduce the life of the tire.

  • Normal:  Even wear, expected gas mileage, no overheating.

  • Somewhat high:  Uneven wear resulting in reduced lifetime and harsh ride.  Possibly slightly improved mileage.

  • Very high:  Although this applies more to truck tires, there is a lot of stored energy in the compressed air.  The tire can literally explode with potentially lethal effect.

In other words, it's a good idea to have properly inflated tires.  And it's a good idea to check your tire inflation, even though you and I are too lazy to do so.

Which brings me to the "missed opportunity" in the title.  As an example of your government in action, there has been legislation that requires automobiles to provide an indication of "low tire pressure."  This has been an optional feature on many vehicles for a long time; it will now be required.  But unfortunately, the "indication," as is often the case, will be in the form of an "idiot light," which is the colloquial designation for a simple indication that "something is wrong" rather than any useful diagnostic.  Incomprehensibly, simple readouts of quantities in common units seem to be beyond the imagination of vehicle designers.  Thus, in many vehicles, we have an "oil" light and a "temperature" light, but their illumination gives no further information, much as the bizarre "check engine" light serves no useful purpose.

I personally would like to see a big panel of readouts for all of a vehicle's important functions, much as appears on an aircraft panel.  However, I'm not sure that the expense would be warranted or that any significant number of drivers would be hypnotized by, for example, the EGT (exhaust gas temperature).  However, in this age where almost every car has some sort of digital display, how much effort would it be to actually display the tire pressure, using a calibrated bar graph with a green "normal" region?  The sensors in the tire surely would be capable of transmitting the pressure to, say, the nearest pound, which is roughly 3% the normal reading.  3% is not rocket science!  The bar graph would show the tire pressure for each tire sequentially, or, if the car's display is large enough, for all at once.  How much would this cost?  Possibly nothing!  If each sensor already specifies which tire it's associated with, and transmits the pressure number for the car computer to qualify as "OK" or "TOO LOW," then all one would need is to send its information to the display.  If the sensors are less "sophisticated" then they would need to be upgraded.  By not requiring at least that the sensors be capable of providing this information, our brave new legislation is accomplishing far less than it otherwise might, and an opportunity to remedy the problem will be years in the future.

I would cast my vote for the upgrade, even if it's part of an extra-cost package.  By actually having an accessible display of tire pressure, I could:

  • Carefully inflate the tires to the maximum of the "normal" range.

  • Note if and when one or more is getting near the bottom of the normal range.

  • Note if any tire seems to be losing pressure unusually fast, which would point to a possible safety problem.

  • Note which tire is problematic, instead of having to investigate them all when the idiot light comes on.

Do I need to mention, Mr. Government, and Messrs. Auto Manufacturers, that this kind of information would also be helpful in keeping our country's gas consumption lower, while encouraging car owners to keep their vehicles better maintained?  Not to mention placing any blame for suddenly reduced mileage on tire inflation rather than creating the assumption there's something wrong with the car?

For me and others of my ilk, it would also be entertaining:  I like numerical instrument displays that give me things to contemplate and calculate while I'm driving.  And, of course, it would mean I have to refill my lava lamp much less frequently.  

Richard Factor