The question is how accurate are those 50 cent pressure transducers?
Most likely more accurate than the 25 cent pressure gauges most of us have. I have found my Pressure Pro transducers are spot on and I can monitor the pressure changes as I am towing. The pressure always increases after 5 miles so I know the transducer is working. Then 100 miles or so I check pressures again. Gives me something to do during a long boring tow.
"Myth: “I don’t have to worry about checking my tire pressure because my tire pressure monitoring system (TPMS) does it for me.”
Real Deal: Actually, TPMSs are kind of like your slacker roommate who doesn’t get around to telling you the microwave oven’s busted until after you open your frozen lasagna dinner box. They’re not required to issue that warning ping until your tire pressure is 25 percent below the vehicle manufacturer’s recommendation. By then, you’re already well below the pressure required for safe driving. A TPMS isn’t designed as a friendly reminder – it’s a last-minute warning before imminent tire failure."
My '07 Buick TPMS actually tells me to the exact pound of air pressure which each individual tire has...at any time. It's a lot better than the average TPMS.
Every day when I start the engine...I push the button on the dash and check each tire's exact air pressure.
I find mine is extremely accurate...it always corresponds exactly to my mechanic's lever air pressure gauge....no matter whether it's 40 below or 95 above....weather we experience in the Canadian Prairies.
* This post was
edited 08/14/12 10:36am by Lessmore *
One technology measures changes in tire diameter (from not enough air) and use that as a proxy for air pressure.
A more expensive technology uses an actual pressure sensor, and is more accurate.
here are two kinds of TPMS employed in motor vehicles, indirect and direct. Indirect TPMS uses the speed sensors in the ABS (anti-lock braking system) to compare wheel rotation speeds to determine under-inflated conditions. An under-inflated tire has a slightly smaller diameter than correctly inflated tires, thus it rolls at a different rate from properly inflated tires when the vehicle is in motion. The system alerts the driver when it detects an under-inflation condition. However, it cannot generally detect tire deflation until the tire is at least 25 percent under-inflated.
Indirect TPMS is inexpensive and easy to install, but it is not as accurate as direct TPMS. What's more, the user has to reset the system every time the tires are changed, rotated, or re-inflated.
Direct TPMS employs pressure sensors installed on the wheel rims to provide independent, real-time air pressure measurements for each tire that can be transmitted to the vehicle instrument cluster to instantly inform the driver. Direct TPMS can also employ additional components, such as MCUs and RF devices to expand the system's capabilities. The optimal TPMS solution includes:
Sensors for measuring pressure and temperature inside the tire
Controller with time base for periodic measurements
Means to identify which tire is providing the data
Data output to the vehicle chassis
Command input for diagnostics and wake up
The Freescale direct tire pressure monitoring system
Freescale's MPXY8300 TPMS (see Figure 1) is the first of its kind to integrate a pressure sensor, an 8-bit MCU, an RF transmitter, and a two-axis (XZ) accelerometer all in one package.
Precise pressure measurements: The low-power, surface micromachined, capacitive pressure sensor's p-cell (pressure cell) measures pressure range from 100 to 800 kilopascale (kPA). 101.3 kPa is equal to one atmosphere pressure. The TPMS also offers high-pressure range p-cells for truck tires (100 to 1,400 kPa) and optional reduced accuracy calibration for lower cost applications. Freescale's capacitive surface Microelectromechanical Systems (MEMS) pressure sensing technology also offers significant power usage advantages over piezoresistive bulk MEMS. These include 0.14 µA supply current (3 V, 30 KHz) versus 600 to 10,000 µA and 0.9 nano-amp-second (nAs) minimum charge per reading versus 60 to 1,000 nAs for piezoresistive bulk MEMS.
OK... the specs:
X- and z-axis accelerometers
Pressure and temperature sensors ± 10 kPa pressure sensor acuracy (@ 100 - 800 kPa pressure range, 0 to 70ºC)
In other words, it is not bad accuracy wise at room temperature, but once it gets hot, the accuracy is less -- probably have a software correction based on the temp. sensor.
Myth: “I’m replacing only two tires, so they go on the front.”
Real Deal: Actually, it’s the rear tires that provide real stability, no matter if your vehicle is a front-, rear- or all-wheel drive. So here’s the scenario – You’ve got two good tires on the front and two near-bum tires on the back. It’s raining. The tires on the front will disburse the water beautifully. But the water will literally lift your two worn rear tires off the road. Now, you’re doing a reverse wheelie and don’t even know it. Okay, so it’s not quite that dramatic – yet. One slight wrong move and you’re flirting with a dangerous spinout. Trust us – if you can only buy two new tires, put them on the rear.
I disagree with this one. Not because the theory is wrong about handling - that part is correct. But if I am buying only two tires, it is because two have worn to the point of no value, and two are good enough to run for a while. I want to maximize the life of the remaining tires by equalizing the wear over all four. I'm putting the new tires wherever the rate of wear is highest, which is usually the steer tires on a RWD vehicle. If the two old tires are so bad that handling is a concern, I wouldn't continue running them on either axle.
I wish the TPMS would quit working on my F250. If the rears get below 70psi or the fronts below 60, the info center is taken over by bells and warnings. So I have to keep them aired up loaded or not. Paint stripes feel like bricks.
I've never bought just two tires unless it was for my Harley.
'10 F250 XLT CC SB 5.4L 5spdTS 3.73 89k miles
ex '95 Cummins,'98 12v Cummins,'01.5 Cummins,'03 Cummins; '05 Hemi
2017 Jayco 28RLS TT 32.5'. Reese HP Trunion.
I have bought two tires on several occaisions. Always because a road hazard made one tire unrepairable, with plenty of life left in the set. But I like to match tires on an axle, so bought two. My goal is to maximize the overall life of the mismatched set, so I'm going to want to use the old tires where they will wear the least, while the new ones catch up.