OT: auto tire inflation specs?

[eddief]

So my oldish RAV4 has a fine set of Michelins on it. Love em. Costco inflates them to the spec printed on the car's door jam = 29. I took the car to a new indie repair place for an oil change the other day and he inflated the tires to 40 psi. Today I had Costco rotate, balance, and inflate and they insisted on 29.

Called indie guy today cuz I thought he might actually be a buffoon and not a good mechanic. He said he recommends tire inflation to near the max printed on the tire for better wear and better gas mileage.

What the hell?

[MattTuck]

Remember the Ford / Firestone problem?

The pressure recommended by car manufacturer is to enhance the handling, ride of the car. The tire manufacturer gives recommendations for the actual tire, not the over all vehicle.

Higher pressure will certainly lead to better mileage, and maybe better wear. But probably worse ride quality. It's like bike tires.

[Louis]

It's like bike tires.

In that case I'd go with around 95 psi front and 100 psi back.

[deechee]

40 seems way high, especially for a Toyota. From what I've seen Toyota tends to have high sidewalls (the 2nd number in the tire size, aspect ratio) to help soften the ride. The harder the tire, the harder the ride. More bouncy ride = bad braking too.

On the other hand, those spare donuts can go ultra hard. I have a mechanic friend who often picks up beaters and I've seen him drive them around with a bunch of mismatched donuts at 80-90psi haha

[eddief]

Tires have been known to lose up to 1psi (pounds per square inch) every month, so check all tires, including your spare, once a month (or before a long trip). It痴 easy. Here痴 how:

Purchase a trusted tire pressure gauge.
Check your tires 田old before you致e driven or at least three hours after you致e driven.
Insert tire pressure gauge into the valve stem on your tire. (If you are using a digital tire gauge like the one pictured, the gauge should begin reading the air pressure immediately. Refer to your air pressure gauge owners manual for correct usage instructions. If using a "pencil" style tire gauge, the gauge will 菟op out and show a measured number. When you hear a 菟ssst sound, that痴 air escaping the tire. The escaping air shouldn稚 affect pressure substantially, unless you hold down the air pressure gauge too long.)
Compare the measured psi to the psi found on the sticker inside the driver痴 door of your vehicle or in owner痴 manual. DO NOT compare to the psi on your tire痴 sidewall.
If your psi is above the number, let air out until it matches. If below, add air (or have a Michelin retailer help you) until it reaches the proper number.

[Ken Robb]

Any "expert" who thinks inflating all tires to almost the max on the tire sidewall without considering vehicle weight, load and driving conditions IS a buffoon.

[cp43]

Any "expert" who thinks inflating all tires to almost the max on the tire sidewall without considering vehicle weight, load and driving conditions IS a buffoon.

I'm with Ken on this one.

FWIW, the shop I go to always inflates to manufactures suggestion.

[David Kirk]

Any "expert" who thinks inflating all tires to almost the max on the tire sidewall without considering vehicle weight, load and driving conditions IS a buffoon.

+1

Unless you have the vehilce fully loaded to its max capacity then the guy is WAY off. The number on the door jamb is a very good place to start and if i were to deviate from it it would be only by a pound or two max......no way 11 psi.

dave

[AngryScientist]

He said he recommends tire inflation to near the max printed on the tire for better wear and better gas mileage.


IMO, being a "car guy" and a good mechanic means that a person has a good general understanding of how things work. getting the fundamentals and having a good problem solving aptitude. understanding why your car runs like crap with a bad o2 sensor as opposed to replacing it because an OBD code tells him to.

given the statement above, i dont think that this particular mechanic "gets it".

[Mark McM]

Is your indy car guy a hypermiler? No doubt some people who are most interested in maximizing fuel mileage are inflating their tires to their maximum. But people who are more interested in things like traction, handling, shock absorption, braking, and maximizing tire life will inflate their tires to the recommended value.*

*Note: Most owners manuals do recommend some deviations from the recommended value for situations like hot weather driving, or extended high speed driving, but usually no more than a few psi.

[zap]

any "expert" who thinks inflating all tires to almost the max on the tire sidewall without considering vehicle weight, load and driving conditions is a buffoon.

+5

[eddief]

for half a century...almost. Glad I was experienced enough to be suspicious. I was surprised to see 40 psi on the invoice and glad I called him back and let him explain his point of view. He's been in biz for a really long time, but I guess that does not mean he's good. Will probably look for another mechanic when or if the Rav ever needs work. 12 years old, 76K miles, nothing ever gone wrong.

[regularguy412]

My daughter is the proud owner of a 2013 Rav4 AWD. Coincidentally to the OP's post, I'm purchasing new Michelin Guardian tires for it tomorrow morning. Also coincidentally to the tire purchase, my daughter showed up at my doorstep yesterday morning with her little SUV and said, "Dad, I have a new light on my dashboard". So, OK, I head outside to check and it's the TPMS light. Tire Pressure Monitoring System-- as I have come to find out. Turns out, that if the pressure in any tire falls 2 lbs below whatever the 'set' pressure is (more on that in a moment), the the light comes on in the dash.

So I set about to check the pressures, and all were slightly low, around 28 lbs, but within one pound of each other. So I fire up the compressor and move all of them up to 32 lbs. Finally found the reset switch. It flashed 2 times and went out. All good, so I thot.

Got a text later that morning and she said that the light came on again, but then went out. I suppose that maybe I didn't get the replacement pressure up quite high enough, but with a bit of driving around and getting on up in the day, the air in the tires probably heated and expanded a little and raised the temporary effective pressure.

I've come all this way to say, that the guy who airs up the tires to 40 psi may just be doing it so the TPMS light won't come on,, even if there's not one on that vehicle.

Oh and about that 'set' point -- it may be that if you let the tire pressure get low enough,, like 20 lbs and re-set the light/set point, you may NEVER see that light on again,, unless you actually have a fully flat tire.

So tomorrow I'll ask my tire man what he thinks about this whole scenario.


Mike in AR:beer:

[Vinci]

40 psi is ridiculous. You are far more prone to losing traction with the tires that hard. You also stand to get some uneven tread wear.

Follow the recommendation on the door jamb for the indicated size. If you change your tire size, you may want to bump up or down a couple psi, but you'll never be near the max printed on the tire while cold.

BTW, it's important to measure tire pressure when the tires are cold. When they are warm (from driving) the pressures will be entirely different.

[Ken Robb]

Recommendations on door jamb/owners' manual are tested by the car maker for that vehicle. Max pressures on tire sidewalls are listed to keep people installing tires on whatever cars that may be inappropriate usages are just to keep the tires from failing but have nothing to do with providing good performance or ultimate safety.

[wallymann]

i drive a modern european sports sedan. doorsill spec is 32PSI cold, i run 40PSI as a matter of course. i prefer the firmer, more direct feel and ride. i assume i get slightly lower rolling resistance and resultant fuel savings...but i'm sure it's trivial.

around here in MI with these brutally beat-up roads, especially in winter/spring, more PSI actually is a good idea to protect the rim from damage by potholes/etc.

i've worked with tire engineers from bridgestone in the past, automobile tires have LOTS of margin designed into their structure.