Heh Heh Heh...
On this subject, my thought has always been along the line of thinking as T-Al, that an underinflated tire would have a lower effective radius, hence would require more revolutions for the same distance travelled.
Then I saw the "circumference" argument from SteveL and Haha.
To borrow from a Web link included below, let's call TAl+ERD50+myself+others the "radialist" camp, and SteveL+Haha+Samclem+others the "circumferencialist" camp.
I discovered that what I always take for granted has been challenged. And yet, it is not so easy to dismiss the "circumferencialist". To do so, their argument about "traction" must be addressed, but I got to admit I do not have an answer offhand. I can see the point that if the steel belt circumference is
not very compressible, and if the tire
does not slip, how do you satisfy the circumferencialist camp?
The best way to settle this is to go out and do some measurements yourself. However, I am afraid measuring the distance travelled with a few tire revolutions may not be decisive enough, due to the small errors required.
Heh Heh Heh...
The inquisitive mind just got to know who is right. Sooo, I searched the Web. This is fun. What an ER'ed guy do all day?
Heh Heh Heh...
Found several patents and engineering conference papers on applications of the "radialist" principle for mandated TPMS (Tire Pressure Monitoring System). Basically they compare the rpms from each wheel to determine if a tire has been underinflated, or use GPS for accurate determination of distance travelled.
http://ddl.stanford.edu/files/NLSlipAVEC2002.pdf
http://ieeexplore.ieee.org/Xplore/login.jspurl=/iel5/10947/34462/01644529.pdf?arnumber=1644529
http://www.embedded-control-europe.com/pdf/ecemay04p20.pdf
Method for monitoring tire pressure variation of automobile tire and system for realizing the same - Patent 7395177
Soo, the academia and industry are in the radialist camp.
Heh Heh Heh..
Also found several forums whose members were also inquisitive on this very same question.
The most relevant info came from this guy, who has done what all of us would have done. He tapped into the wheel revolution sensors of his Prius ABS (Antilock Brake), and looked at the signals on an oscilloscope carried in his car (Obviously an EE like myself). He looked at the signals with both wheels at 43 psi, then with one deflated to 35psi.
His conclusion: Radialists win!
Quote:
"But that difference between 43 and 35 psi, still quite tolerable from a safety standpoint, created a significantly measureable delta in wheel speed."
I don't profess to know how the tire gets deformed so as to deceive the circumferencialists, but the real world is what it is.
Heh Heh Heh...
Details are at
http://www.techno-fandom.org/~hobbit/cars/tpms/pts.txt
The next question is: How to explain the "circumference" enigma