Here ya go, I took the liberty of asking the Mazda folks what the deal is with it:

 

That's ok, I think I would just get annoyed at looking at the psi in all the tires. It would become one of those compulsive things you are always looking at to make sure the correct pressure was there... I am glad it's only an indicator light.

 

Anyone have any experience with this type of sensor? How low is a tire if the warning light comes on? Is it any different than looking at a tire and noticing that it's low?

I guess this just doesn't make sense to me since I check my tire pressure on a regular basis anyway.

 

I'm left wondering what criteria it uses for "low" pressure. Is it an absolute value, e.g. 20psi, or is it a differential from the average pressure of the others?

What I'm getting to is that some of us like to run a few extra pounds in our tires, to give sharper steering response in exchange for a slightly reduced ride quality. Obviously a differential detection method would be preferable in these circumstances.

 

My 1998 Plymouth Prowler has a low tire pressure sensor in all four tires. For the first few months I had the vehicle I was stopping and checking my tires every single day. It was the most aggravating thing I have ever done.

Finally I went to the dealership and complained about this problem and then it was brought to my attention that tire pressure monitors are not all that great. You see, rubber just like most other materials expand and contract with temperature changes. Of course I knew this just like I am sure you all do, but I never applied it. When tires have temperature changes (whether they be drastic or small) the rubber expands and contracts thus causing the pressure in the tire to change in small increments. My tire pressure monitor on the prowler was just that sensitive. (What was plymouth thinking?) Hopefully the pressure monitor on the RX-8 will not be as sensitive. I actually had an electronics guru unhook the pressure monitor on my prowler because I really got tired of the bright yellow LOW TIRE WARNING constantly flashing on my dashboard.

Introduction: I have been watching and reading this forum for way long but have never actually logged in until tonight. I pre-ordered my RX-8 in Jan. and since have been counting the days until I receive it. For the longest time it was a huge toss-up between the 350Z and the RX-8 (which I am sure you are all tired of hearing). Anyway, from what I have learned through this wonderful website the RX-8 wins hands down. From this point in time I am just hoping I will still say that in June when I am driving my shiny new Titanium Gray RX-8 Six Speed off the lot at Royal Mazda in Metairie, LA (USA). I am just as excited as you all are and I hope this car meets your expectations as well as mine! Thanks for having such a wonderful and informative website!!!!!


LARRY

 

Welcome to the Forum!!! Hope you enjoy your RX-8 when it gets here.

 

Welcome to the forum. I am not to concerned about the tire sensor, I do hope it is not that sensitive. I have a compressor in the garage so I can fill up whenever needed

 

Well assuming the "standard" pressure recommendation of about 32-34 psi cold, I'd hope the sensor wouldn't go off until about 26psi cold or something like that. It would be annoying and possibly dangerous if the sensor kept "crying wolf"

 

What a lot of cars are doing for tire pressure checks is a differential thing, where they use the ABS sensors to see if one tire is rotating at a different speed than the others. If it is, it's usually because it's low. Obviously there's some algorithms to figure this out and not trip just when going around a corner, etc. GM uses this a lot on some pretty mainstream cars, and I think it's relatively inexpensive since you can leverage the existing ABS sensors. A true individual pressure check, like Corvettes have, is much more expensive.

Sometimes the ABS method can be thrown off. I had a rental car with this feature and parked on hot, sorta soft pavement. When I drove off, it tripped the sensor since a wheel had chunks of road tar stuck in it, making it out of balance until they came out (and after I pulled over to check the tires, of course).

 

Here's how the SmarTire system works:

Sensors in all four wheels monitor PSI (+-1) and temp (+-5). As tires heat up normal PSI increases and the monitor uses a graph to take this into account. You set a cold (65 degree) PSI (let's say 35 PSI), a warning range (let's say +- 5 PSI) and an alarm range (let's say +- 10 PSI).

As you drive you can see current PSI and temp for each tire and how much over or under the "ideal" PSI that is. If it's 85 degrees out then the tire should be 37 PSI and if it falls to 32 PSI the warning sounds. If it goes below 27 PSI the alarm sounds.

I have this installed in my BMW and it's a great system. Prior to getting it I had two rear flats where I could not tell the tire was flat from ride quality alone. Since installing it I've gotten two low pressure alarms that saved me from driving on dangerously low pressures. Great stuff and not annoying at all to check tire pressure every now and then to see where it's at. The RX-8 probably won't have this advanced a system but it'd be nice if it did.
________
STEWING

 

sounds cool.

But if you get aftermarket rims and tires wont it be thrown off?

 

Good question. I don't think so though, as there shouldn't be anything on the rim itself, just a gauge to measure pressure.. but who knows..

Though with 18s... I don't see much need to change out

 

I will definitely get winter rims/tires as I'm sure others will..

 

The RX-8 is probably using a differential system as descibed above. That's why it can't tell you which tire is low on pressure.

That being the case, it won't be a problem with aftermarket rims (bigger or smaller) as long as you get 4 of the same :p

 

i hate the tire sensors. i've yet to see one that's accurate enough to beleive. I'll just take out the bulb that lights the warning and walk around my car befroe i get in it

 

I agree! I'd rather them do away with the sensor and throw in something more useful, like, umm, say, a 6-disc CD changer?!?

 

they can't, it's the law.

 

It's the law where exactly?? Not where I live...

 

It's not a law in Missouri. Actually, I have never owned a car with tire pressure sensors.

 

i'm sorry it's not the law yet. federal law requires them starting in november.

quick search of the net led me to this article first:

Friday, May 31, 2002


Automakers given a choice under tire pressure monitoring rule




WASHINGTON (AP) -- Automakers may install one of two types of tire pressure monitors under a compromise between government vehicle safety experts and the White House.

The agreement announced Thursday will require that vehicles built after November 2003 have a dashboard warning to alert drivers when their tires are underinflated.

Auto manufacturers applauded the decision for providing flexibility. Safety advocates said the rule is insufficient to protect consumers and was made to save automakers money.

Some automakers already sell tire pressure monitoring systems, but they are not required by law. Congress ordered the monitors as part of strengthened tire safety laws passed in 2000 in response to the recall of millions of Firestone tires.

The tires were linked to at least 271 deaths and thousands of accidents, many of which occurred after the tread separated from the tire. Underinflation may have been a factor in some of the accidents.

The National Highway Traffic Safety Administration first proposed a rule that would have required "direct" monitors in each wheel that would alert drivers to low pressure.

At the urging of the automotive industry, the Bush administration asked the agency to change the rule to allow a less expensive "indirect" system that would work off the antilock braking system. Such a system would measure the rotation of all four tires and alert the driver if the rotation of one was markedly different.

Unlike the direct system, this option would not identify the specific tire that was underinflated. It would not alert drivers if the tires lost air at the same rate.

The compromise will allow vehicle manufacturers to use either type for three years. NHTSA will study each system and write a final rule for the monitors installed in vehicles built after November 2006.

Public Citizen President Joan Claybrook said the consumer advocacy group will file a lawsuit in an attempt to block the government from allowing both options. Claybrook, a former NHTSA administrator, said the indirect systems don't work well enough to meet the requirement of the law.

"We think this is a fraud on the consumer," she said. "This is just gross interference of the White House on behalf of the auto industry."

NHTSA estimates the indirect system costs up to $21.13 for vehicles that already have antilock brakes, compared to at least $65.84 for the direct system.

The rule requires that each automaker have a monitoring system in 10 percent of vehicles built during the first year of the initial phase, 35 percent built during the second year and 65 percent made during the third year.

The direct system will warn drivers when a tire drops 25 percent below the manufacturer's recommended inflation rate. The indirect system will alert drivers when there is a 30 percent drop.

The Rubber Manufacturers Association, an organization that represents tire makers, said the rule is insufficient. The group says the rule could lead some drivers to believe they are safe when the tire pressure is too low.

The association said NHTSA should have required a system that warns motorists when tire inflation pressure is unable to support a vehicle that is fully loaded.

"By the time it reaches that 30 percent level, the tire might already be below the level where it can carry that load," said spokesman Dan Zielinski.

A NHTSA study found that a quarter of cars and a third of light trucks are driven with at least one tire substantially underinflated.

NHTSA says pressure monitors would increase fuel economy and reduce wear on the tires. The agency also said there would be fewer crashes due to tire blowouts, immobilized vehicles or poor vehicle handling from pressure loss and hydroplaning.

On the Net:

National Highway Traffic Safety Administration: http://www.nhtsa.dot.gov

 

anything that makes a car safer im all for but i can't wait to break this law :D

I think i'll go rip the tags off all my mattresses right now too!!!