this post was submitted on 18 Jul 2024
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Mechanic Advice

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The age old tire pressure question (lemmy.world)
submitted 1 month ago* (last edited 1 month ago) by venusaur@lemmy.world to c/mechanicadvice@lemmy.world
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2001 Infiniti QX4

Placard on car says 26 psi cold

Tires say 32-49

Rear tire is set to 27 cold

Does this look under-inflated? What’s the lowest I should go?

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[–] RestrictedAccount@lemmy.world 15 points 1 month ago (1 children)

I would 1)go with the vehicle placard as the default and and limit driving until I 2)call a reputable dealership

I think it was the Ford Explorer that required lower tire pressure because the vehicle was a rollover threat at normal inflation pressures. But people were worried that the tires would blow out if under inflated. There were a ton of lawsuits.

They did a 60 minutes piece about Jeeps on this too.

It was a mess.

[–] venusaur@lemmy.world 3 points 1 month ago

Damn. I feel like 26 is pretty low. Some old threads about R50’s said they had a TSB raising it to 30 so that’s where I’m at now. Dealership said follow placard but the car is so old they don’t know or care

[–] Successful_Try543 11 points 1 month ago* (last edited 1 month ago) (2 children)

If there is a minimum required pressure written onto the tire, I'd go with that one. A little more than the pressure required for the car doesn't hurt.

[–] lemming741@lemmy.world 9 points 1 month ago (1 children)

They may have originally specd lower pressure for ride comfort. I agree with using the tire's minimum.

https://en.m.wikipedia.org/wiki/Firestone_and_Ford_tire_controversy

[–] Zwiebel -1 points 1 month ago (3 children)

Why is everyone recommending the minimum here? I've always heard to go a smidge above the maximum for the fuel savings

[–] ColeSloth@discuss.tchncs.de 14 points 1 month ago

It gives you a fairly small gain in fuel mileage, but comes with several downsides.

For one, it's harder on your suspension system and gives you a rougher ride. This will wear out your struts faster, which is kind of expensive.

Next, it lowers the footprint of the tire with the ground. This means that you have decreased road grip and it will take longer to stop in an emergency.

Lastly, it means your tires won't last as long. The tread will wear uneven and it may cause tires that should last you 50,000 miles to only last 35,000, for instance. A rather large waste of money due to how expensive tires are, now.

[–] Annoyed_Crabby@monyet.cc 14 points 1 month ago (1 children)

If by maximum you mean the pressure recommendation by the car manufacturer, then yeah it will help with fuel saving. If by maximum you mean the pressure provided by the tyre manufacturer, please don't do that lol. Jumping from 26psi to 32psi isn't much, but jumping from 26psi to 49psi is way too much especially for car with only 1 passenger, it's gonna wear the middle of the tyre without the weight pressing down to give it an even wear. The money you save here will be used to replace the tyre earlier than it should. Will also cause terrible braking.

[–] glarf@lemmy.world 3 points 1 month ago

Yep I have to second, you lose a ton of safety when overinflating tires like that due to the tire not gripping the road as it would if correctly inflated. Not a trade off I'd make with my life.

[–] Hubi 4 points 1 month ago* (last edited 1 month ago)

Because on OPs car the recommended tire pressure is lower than the minimum recommended by the tire manufacturer. Increasing it even further may affect ride quality. In most scenarios your approach is correct.

[–] venusaur@lemmy.world 3 points 1 month ago

Thanks!

[–] zer0hour@lemmy.world 4 points 1 month ago (2 children)

would you be able to post a pic where it says the minimum psi on the tire? I work with tires and wheels and I have yet to see a tire with a range of psi like what you're describing and I'm curious to see.

I would set the pressure to what is listed on the placard.

usually with an 8 ply passenger tire, you shouldn't go below 20 psi.

[–] zer0hour@lemmy.world 3 points 1 month ago

oh also, the tire in the pic doesn't look under inflated to me, but looks can be deceiving

[–] venusaur@lemmy.world 2 points 1 month ago (1 children)

I’ll try to post a pic tomorrow. Just saw this on the Nokia website:

We recommend using the vehicle manufacturer’s suggested tire pressure for all season tires

Not sure what the numbers on the tire are for then.

[–] zer0hour@lemmy.world 2 points 1 month ago (1 children)

they're for the technicians mostly. basically safe maximum levels to get the tire installed on the wheel and other safety information. sometimes you really have to inflate them when installing to get the tire to seat properly

[–] venusaur@lemmy.world 1 points 1 month ago

Got it. Thanks!

[–] Hubi 3 points 1 month ago (1 children)

I agree with the other poster. You should go with the minimum on the tire because it's the manufacturer's specification. You don't necessarily see that a tire is underinflated but there can still be too much stress on the sidewall.

[–] venusaur@lemmy.world 3 points 1 month ago

Thanks. I’m compromising at 30psi

[–] Death_Equity@lemmy.world 2 points 1 month ago (2 children)

The placard on the driver's door frame is what you use.

The tire itself has no relevant information for a driver, only for an installer at a shop mounting the tire.

[–] thisbenzingring@lemmy.sdf.org 9 points 1 month ago (1 children)

*as long as the tire is the same size as suggested by the manufacture

[–] Death_Equity@lemmy.world 6 points 1 month ago

Even if you have a different size than is OE. You only disregard the psi, that is based on gross vehicle weight, if you know what you are doing.

It doesn't matter if you have 265/70r16 and go to a 275/50r20, you still use the same pressure because your car still has the same GVWR.

[–] venusaur@lemmy.world 1 points 1 month ago (1 children)

Thanks. What does the installer use the info for?

[–] Death_Equity@lemmy.world 2 points 1 month ago (1 children)

Practically, nothing. The pressure on the sidewalk is what the manufacturer says will seat the tire on rim, but reality dictates you add pressure until the tire pops into place. That may be 40psi, but I have had to use over 100psi to get a tire to pop in place if that is what it needed and the tire lube wasn't enough and you correct to manufacturers' spec once the beat seats.

[–] venusaur@lemmy.world 1 points 1 month ago

Interesting. Thanks!

[–] Nomecks@lemmy.ca 1 points 1 month ago* (last edited 1 month ago) (1 children)

The placard is useless if the tires aren't the factory type. Don't inflate tires to less than minimum pressure if you don't know that they're the right tires for the vehicle.

[–] venusaur@lemmy.world 1 points 1 month ago (1 children)

Thanks. They’re the right size but what other factors do I need to account for when matching a tire?

[–] Nomecks@lemmy.ca 1 points 1 month ago* (last edited 1 month ago) (1 children)

Load rating is a big one. Speed rating and number of plies can affect it too

[–] venusaur@lemmy.world 1 points 1 month ago

Thanks I’ll check those. These seem to be pretty heavy duty tires