Where to find an accurate tire pressure gauge???

I feel compelled to explain something about accuracy on guages here.

Suppose I have a guage that has a scale from 0psi to 50psi that is

4% innacurate.

Suppose you have a guage with a scale that goes from 0psi to

120psi that is 2% innacurate.

We both measure our car tires at 35psi. Which one of us has a more accurate reading?

Answer: _I_ do. The reason: With my guage the max deviation it will have is + or - 2psi

With your guage the deviation it will have is + or - 2.5psi. At

35psi, your actual pressure could be anywhere from 32.5psi to 37.5psi. By contrast, with me at 35 psi my actual pressure could be anywhere from 33psi to 37psi

This should tell you that trying to get a one-size-fits-all tire guage isn't the way to get high accuracy.

But wait, there's more!

Suppose I have a tire guage that is 100% accurate.

Lets say I used this accurate tire guage to measure my tires on a cold day after I had been driving for a while. Ambient air temp is about 50 degrees and tire air temp is about 80 degrees.

A week later the weather has changed and it's now sunny and hot. Air temp is about 80 degrees and after a while of driving on the road, tire temp has gone up to 130 degrees.

Guess what - that hot weather has just pushed the tire PSI up by

5 psi.

Ted

OK, perhaps I should "wephase my question." Where can I buy two accurate gauges, one for lower passenger car tire pressures, and one for higher bicycle tire pressures?

Every door jamb tells you the cold tire and hot tire pressures.

Consumer Reports found that most of the digital readout guages were accurate. That has been my experience.

Richard.

Oh boy. Here we go with the Consumer Reports garbage, again.

Larry Behold Beware Believe

The one I bought at Radio Shack has a unreplacable battery but seems very accurate and consistant and resets in a few seconds. You throw it away when the battery goes bad. It uses a lithium battery. I have lithium batteries on a shelf for over 10 years and they are still good so I am not too worried about the battery aging and i cannot imagine it uses much juice. I've had the gauage about 6 years now.

Well consider the source of the Condemner Retards quote!

Now, now, a tire guage is just the sort of basic, simple consumer item that they are actually qualified to test!

Ted

Yes, but this newsgroup is blessed with thought police who want to put a halt to any discussion that includes objective reports concerning a Consumer Reports test result.

Richard.

If you take the tire pressure for your tires off the door jamb you are cutting their life down.

The best pressure is to fill the tires up to about 5psi under the max pressure stamped in the tire sidewall, then take them out for a good run, get them up to operating temp, then stop and bleed any extra air off to get the psi right at max pressure.

You will get the best gas mileage, the best handling, and the longest tire life this way. You will NOT get the most plush ride. But, automakers have been saving money on car suspensions for ages by lowering the tire pressure instead of more expensive shocks and a better suspension.

Ted

Ted Mittelstaedt wrote: >The best pressure is to fill the tires up to about 5psi under the >max pressure stamped in the tire sidewall, then take them out >for a good run, get them up to operating temp, then stop and >bleed any extra air off to get the psi right at max pressure.

What a load of bull sh*t.

Yes, the max pressure on the tire is a cold inflation pressure and the temperature rise during use has already been accounted for. I tend to run at or near max pressure also. You get a slightly rougher ride, although with radials it isn't that noticeable and I get better tire life and fuel economy.

Now you can rail about the ills of running a pressure higher than the manufacturers specify.... :-)

Matt

That is BS also.

Run at max and your tires will wear out faster, although just the center of the tread. Ride will be considerably rougher and mileage increase will be minimal.

If you want a good increase in mileage, slow down a couple of miles per hour.

It used to be that the edges used to wear first in the fronts so adding a few extra pounds made sense. These days, at least with the Chryslers I've owned, the front and rears wear incredibly evenly. On my 94 LHS I never had the car aligned once. On my 99 300M the car was aligned once when the front struts had to be replaced because a giant pothole snuck up on me.

A classic sign of under inflation.

NO! Don't do this Ted (or anyone else.)

This pressure has been determined by the manufacturer based on many factors (least of which is tire life, and most of which is your safety.) A car is dynamic and can change weight and load ratios very quickly. Not to mention the dynamic loads imposed on it from the normal stress of acceleration, braking and road hazards. Tire pressure is not a constant, it rises due to heat and shoots through the roof when you hit a pothole. There are many, many factors taken into consideration by a manufacturer concerning the final recommended air pressure.

A tire is an extremely complex and dynamic part and the inflation pressures chosen represent the best compromise under the best and worst conditions (when you will need the all of the stability you can get.) Operate the tire in an over-inflation mode and lose a great deal of friction and stability. (And in-truth, you will SHORTEN the tire life, not prolong it. This of-course is even more pronounced for under-inflated tires.)

Operate the vehicle exactly like the manufacturer intended it to be, follow the instructions of the engineers, NOT the advice of the parts counter.

To recommend that tire be over-inflated is simply very bad advice and shows ignorance all that's involved.

Who knows more; the combined talent of the engineering department of a major automotive manufacturer or the mechanic who decides he know better?

Nope.

Nope, actually my tires wear much more evenly when inflated to the max PSI. I've done this for 20+ years now and never had tires wear out first in the center. I ran a set of Michelins on a Jeep Comanche for

90,000 miles ... and this was on a 4x4! The tires were rotated every 10,000 miles and wore out very evenly. Friends and family members who run the lower pressures recommended by the car makers never match my tire life.

Sorry, but that isn't my experience. Both of my Chrysler minivans like

35 PSI just fine and my K1500 likes 50 PSI just fine, except I do lower the rears to 40 PSI when the truck is empty.

I drive 55 already and can't stand to go any slower. And higher tire pressure will give better fuel mileage at even a slower speed. :-)

Matt

Yes, the pressure given by the vehicle manufacturer is a COMPROMISE that tries to be all things to all people and all conditions, but isn't optimal for any one condition. Since I know how I drive, I adjust the pressure to optimise the parameters of interest to me, which are tire life and fuel economy. I'm willing to sacrifice ride quality to achieve that and ride quality is the primary reason for the lower pressures the car makers recommend. As long as you don't exceed the max pressure listed on the sidewall by the tire maker, you aren't compromising safety or shortening tire life - you likely increase life as you run at lower tire temps at the higher pressure. Modern belted radials do not wear out in the center at the max pressure listed on the sidewall, at least not in the vehicles I've owned in the last 20 years (all on the heavy side though, such as minvans and full-size pickups). Maybe this isn't true for a Neon or Echo, but I have no experience with such light cars.

Matt

Which goes along with what Art was saying. There was a time in the earlier days of radial tires that the recommended air pressures were a lot lower than they are today (typically 24 to 26 psi IIRC). I distinctly remember a point in time when the recommendations suddenly were for higher pressures (28 to 30 psi) - probably about the time that wear patterns became more even acorss the tread. Art is correct that radial tires on the front used to wear out on the edges, and I have no doubt that that was in the days of the lower pressure recommendations.

Also, trends have been to wider treads which, for a given air pressure tends to lower the pressure requirements, i.e., tends to move the wear away from the edges and more towards the center.

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my adddress with the letter 'x')

Oh man! That would very much depend on the particular engineering department and the particular mechanic - I wouldn't paint either "group" with a super broad brush. We've all seen some pretty blatant examples of crappy engineering that passed thru the review of the "high performance work team" of engineers. As well as very good engineereing...as well as mechanics who understand very well where the engineers went wrong...as well as mechanics who don't have much understanding at all of what a good design is or isn't.

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my adddress with the letter 'x')