[Bob Allen]

The Tom and Ray column in this morning's Seattle Post-Intelligencer dealt with tire inflation. The writer noticed that the Jiffy Lube place where she takes her car has repeatedly "over inflated" the tires, to about two or three pounds under the maximum permissible pressure. She argued with the guys who insisted that this is better for the tires and is a Jiffy policy. The latter she confirmed by noticing the same practice at three different facilities. Her point is that she wanted the tires inflated to the recommended pressures listed on the inside of the driver's door.
Tom and Ray agreed with her. The maximum pressure, they say, is what the tire can hold as an absolute; to drive a car with this much, or nearly this much pressure in the tires is dangerous and will adversely affect both the wear of the tires and the handling of the car. Any increase in mileage is incidental to the increased danger from a poorly handling car.
Some of you are putting nearly the maximum pressure in your tires, which I believe is 44 psi for the OEM tires, in order to get better mileage. This might be a red herring, because what you may save in a few gallons of gas isn't worth the risk. Think of it this way: if your mileage goes up from 45 mpg to 47 mpg, you are saving only 0.1 gallon of gas per 100 miles while making your car less maneuverable.
I'm keeping my tires pretty close to the recommended pressure.

 

[melgish]

Great information. But why pay for all those extra air-bags if you're not going to increase your risk ...just a little

 

[AgentElrond]

In our case, 44/42 is below the tire stated max of 50 (2003) or 51 (2004); then again, my 2004 doesn't have "OEM" tires (came with Pirelli).

 

[Sanny]

Tires and Mileage - I know we've flogged this to death...

Amazing thing, really. I noticed on my last tank or two of gas (after having oil changed) that mileage was down 1 or 2 mpg. Really hot weather, so I thought maybe the tar on the road was hot and grabbing tires. Or high humidity. Or mood swings. But then it got cooler and mpg was still down. Hmmm.
:?:
Finally did what I should have done first - checked tire pressure. Yup - all over the map. One was 28, one was 36, and the other two were in between. Now all up to 38/36.

The amazing thing is not that I checked (although that was good), but that there is such a difference in mpg with tire pressure being off. Only because of the mpg display did I think to check. I wonder how often (mostly, probably) my tires were underinflated in my previous car.

Imagine that...

 

[Astrowoman]

Inquiring manatees want to know...

... if there is a correlation between "wandering wonders" and high levels of tire inflation.

 

[Sanny]

Inquiring manatees want to know...

... if there is a correlation between "wandering wonders" and high levels of tire inflation.

Tires of sig. different pressure will cause a pull. If front tire is really low on the left, the car will drag left. Think of it as the right tire is bigger because it has more air, or is dragging less cause it's less squashy. So, could be part of it. Ever have a flat while driving? hard to steer.

 

[Astrowoman]

Yesssssss... and how many of those who claim that they CAN'T (as opposed to, haven't chutzpah enough) drive through a tunnel at 70 mph with no hands have either high inflation or uneven inflation?

 

[Old n Bold]

Need to double check when a lub joint adjusts tire pressure. Took my PU in a month ago. Was told that they adjusted the pressure to what was listed on the door jam. The next day, I check the pressure. It had been sitting in the garage all night. The tires were cold. The pressure was about 3 lbs low all around.

Tires will almost certainly be hot or at least warm when you get to a lub joint. Pressure should be check with the tires absolutely cold--not hot nor even warm.

 

[DanD]

Wandering Inflators

Astrowoman has me wondering...

I just picked up a Toyota Certified 2002 Prius over July 4th weekend. The first owner only put 3009 miles on it before (for some reason) getting rid of it. My good luck. Been lusting after a Prius since they came out, but I drive cars until they DIE, and my 1990 Acura Integra just wouldn't give up.

Anyhow, I noticed 'wandering' behavior, and figured some of it was due to tire break-in, as has been discussed here. Also I had my (very good) mechanic check the alignment last week and he said it's dead-on according to the specs.

Last night I checked the tire pressures and all were about 5lb down from recommended levels! Hmmm. I think this is probably the old car dealer trick where every car on the lot is underinflated to make the ride softer, and thus 'more comfortable' during test drives by prospective buyers. Kind of disappointing to find this in a supposedly 'Certified' car.

I haven't driven the car since I corrected the pressure, but I will be on the road quite a bit tomorrow and will report back on the results. Hopefully my mileage will be a bit better too with the correct PSI.

The really interesting thing about the 'wandering' is that at least in my case it seems to be neutral - if I hold the wheel steady and fight the natural urge to correct every little deviance, the car will go straight ahead. You still feel it squirming back & forth (even without a noticable crosswind), but it doesn't really 'wander' off course, just 'wiggles' around a zero point.

I do a fair amount of highway driving at 80mph (required sometimes in Northern VA just to avoid getting run over), and it does seem worse as speed increases. But then so is the gas mileage :wink:

 

[romad]

Need to double check when a lub joint adjusts tire pressure. Took my PU in a month ago. Was told that they adjusted the pressure to what was listed on the door jam. The next day, I check the pressure. It had been sitting in the garage all night. The tires were cold. The pressure was about 3 lbs low all around.

Tires will almost certainly be hot or at least warm when you get to a lub joint. Pressure should be check with the tires absolutely cold--not hot nor even warm.

Which is why the Jiffy Lube policy

 

[GreyMud]

Yet another reason to not visit quick change places.

 

[Cully]

Ok so where do you really make the adjustment? Some sort of logic tells me to measure and adjust the tire pressure when the wheels are warm and been running for a while. Warm air expands right? So if I check and adjust the pressure to 42/40 or 44/42 when the tires are cold then when they warm up I will be leaning more towards the danger zone for pressure. On the other hand if I measure and adjust when the tires are warm then the pressure will drop a little when the car is parked and the last time I checked, it's almost impossible to swerve off the road when the car is parked in my garage. Of course you have to account for the season.

 

[melgish]

Fill them up cold, check them cold. The manufacturers (you know, the guys that stamped the words "Inflate to 44 psi max" on the tire) expect you to do it that way.

Seasonal changes can be handled just by checking frequently. Unless the temp swings from -40 to 100 between checks, everything will balance out and life will be grand.

 

[Hep]

Seasonal changes can be handled just by checking frequently. Unless the temp swings from -40 to 100 between checks, everything will balance out and life will be grand.

Yeah that was last week here.

Really in the winter we can go from -30 to +40 in a day. Not the weather that leads one to go out in the garage and check the tires, much less adjust the inflation. I will, once in a while, check to make sure there are still four tires and that none of them look flat. Then jump in and crank the heat.

 

[mrv]

like melgish said, measure when cold, inflate when cold. The max psi pressure stamped on the sidewall is marked "## psi max. cold" or something similar.

yes, you should check your tire pressures often. Minimally after each service (tires rotated but tech didn't readjust pressures for +2psi front bias, or tech decides to set them to some random psi all around). If there's been a dramatic change in temperatures since the last time you checked your pressures (say, last checked in winter and it's now summer), then your pressures could use some adjusting. My reading is 1psi for each 10^F (up/up or down/down). (My experience is winter services are the worst - car driven to dealer for service, it goes into their heated garage, they adjust the pressures (warm tires, warm garage), then when you check the pressure the next morning when cold - something like 10-15psi lower than I'd like...)

and it's also better to measure shaded tires (not in direct sunlight), but...

 

[DanD]

No more squirming

OK, I'm a convert. With correct tire pressure all around, the car no longer squirms or wanders on the road. Still way more sensitive than any car I've driven before, but I guess that's just the neutral suspension tuning. I will be checking the pressure weekly from now on. And while I don't neglect my cars, rarely before have they gotten more than a quarterly tire pressure check.

I suppose I'm beating a dead horse, but go check your tire pressure. yes, right now.

(no animals were harmed in the creation of this post)

 

[Thomme]

"Measure when cold, inflate when cold".

Yes, but how cold does cold have to be?
Hep checks it at -30 during a Minnesota winter.
I currently have to check it at 90-in-the-shade.

Everything's relative.

 

[Sanny]

You will have to drive to Hep's, and check it there, I think.

 

[Hep]

You will have to drive to Hep's, and check it there, I think.

Drive slow. 90 here today.

 

[Thomme]

You will have to drive to Hep's, and check it there, I think.

Sounds reasonable. I'm off.