High air pressure vs lower air pressure in tires.

[aquariuscsm]

I read on a forum one time where someone posted that lowering your tire pressure a bit will give you a smoother ride. Then someone else chimed in and said raising the pressure a bit will increase gas mileage.

Any pros/cons to doing either one? I always just keep mine around the 30 psi mark like the tires say.

Just a bit of curiosity I guess.

 

[Quattro Pete]

That's basically true. Start with the mfg recommended PSI and go from there, a few PSI up or down. If you increase it and the ride doesn't suffer much, keep it there. You'll get slightly better mpg. But never go above the max PSI listed on the sidewall.

 

[VeeDubb]

I agree with Pete. I'll just add that in some vehicles, like Toyota siennas, running 5psi over manufacturer recommended will substantially increase tread life. Not sure whether Toyota got it wrong or what by recommending 35psi in such a heavy vehicle. But seems many sienna owners who run 35psi have tires that are shot by about 20k.

 

[XS650]

It's unusual that going down in pressure from mfrs recommended pressure is a good thing. Tire wear increases, handling decreases, noise increases all for a slight improvement in straight line ride.

 

[Quattro Pete]

XS650, I would agree with that for the most part. Although there are some exceptions. For example, in my car, the manufacturer recommends 33 PSI front and 41 PSI rear. I tend to keep the rear PSI lower (about 35-36) in order for the car to not be too tail-happy.

 

[aquariuscsm]

Originally Posted By: Quattro Pete
XS650, I would agree with that for the most part. Although there are some exceptions. For example, in my car, the manufacturer recommends 33 PSI front and 41 PSI rear. I tend to keep the rear PSI lower (about 35-36) in order for the car to not be too tail-happy.


Same with my car. I`ve experimented a bit with air pressure,and if I have it at the recommended psi (32),the rear tires spin too easy,either at 1st gear starts or 1st to 2nd gear shifts. Lowering it a bit really smooths things out,especially the ride. Haven`t had any negative effects..........I`ve had the same rear tires for about 3 years/30k miles and the tread still looks new.

 

[XS650]

Quattro Pete, that's why I weasel worded it. I have one car that the door jamb sticker says 36 front 45 rear.

 

[Quattro Pete]

Originally Posted By: XS650
Quattro Pete, that's why I weasel worded it.

Gotcha.

 

[CrazyMike]

In the summer I run 38/36psi in the Van to hep with the weight and handing (oem is 35/35), in the winter to keep the tread pliabe I run lower than oem with the Nokians. Perfect wear and traction.

My truck, no way I's run 55/70psi like Ford recommends, only if loaded right up.

Keep in mind guys what your tire says for max psi, you may have a rating of 35/35 on your door and your tires are only rated for 35psi max. I wouldn't recommend exceeding the max on the tire.

 

[CruzNlife1]

Originally Posted By: CrazyMike
In the summer I run 38/36psi in the Van to hep with the weight and handing (oem is 35/35), in the winter to keep the tread pliabe I run lower than oem with the Nokians. Perfect wear and traction.

My truck, no way I's run 55/70psi like Ford recommends, only if loaded right up.

Keep in mind guys what your tire says for max psi, you may have a rating of 35/35 on your door and your tires are only rated for 35psi max. I wouldn't recommend exceeding the max on the tire.


It depends on the load range of the tire. Some of the 250's and 350's run upwards of 60+ psi at all corners. I've got an 01 tacoma. Stock dunlops say max PSI on sidewall is 41 psi. Doorjamb says 28 Front 32 Rear. They tell you more in the rear because they assume you'll be towing or have something in the bed. I run 32 at all 4 corners since I rarely have anything back that. For about 2 years I was lifted and on 33" load range D Tires. Max PSI on the sidewall was 65 or so psi. I had to run them at 52 even on my little tacoma just to maintain tirepatch (at 35 psi I was wearing the outsides of the tires and they just flat out looked low) If the manf. is saying such high psi it's because of the stock tires they use. I used to work tires, ALOT of different vehicles at different pressure requirements front and back. People make the mistake of going by the max on the sidewall, thats not what the manufaturer suggests. You want to run the highest psi you can while maintaining a full, even footprint (you can do this with chalk in the street) and while staying in the limits of the tire itself. 32 gives me an even footprint, less rolling resistance and a smooth quiet ride...

 

[CrazyMike]

Originally Posted By: CruzNlife1
Originally Posted By: CrazyMike
In the summer I run 38/36psi in the Van to hep with the weight and handing (oem is 35/35), in the winter to keep the tread pliabe I run lower than oem with the Nokians. Perfect wear and traction.

My truck, no way I's run 55/70psi like Ford recommends, only if loaded right up.

Keep in mind guys what your tire says for max psi, you may have a rating of 35/35 on your door and your tires are only rated for 35psi max. I wouldn't recommend exceeding the max on the tire.


It depends on the load range of the tire. Some of the 250's and 350's run upwards of 60+ psi at all corners. I've got an 01 tacoma. Stock dunlops say max PSI on sidewall is 41 psi. Doorjamb says 28 Front 32 Rear. They tell you more in the rear because they assume you'll be towing or have something in the bed. I run 32 at all 4 corners since I rarely have anything back that. For about 2 years I was lifted and on 33" load range D Tires. Max PSI on the sidewall was 65 or so psi. I had to run them at 52 even on my little tacoma just to maintain tirepatch (at 35 psi I was wearing the outsides of the tires and they just flat out looked low) If the manf. is saying such high psi it's because of the stock tires they use. I used to work tires, ALOT of different vehicles at different pressure requirements front and back. People make the mistake of going by the max on the sidewall, thats not what the manufaturer suggests. You want to run the highest psi you can while maintaining a full, even footprint (you can do this with chalk in the street) and while staying in the limits of the tire itself. 32 gives me an even footprint, less rolling resistance and a smooth quiet ride...


I agree with all that, cheers eh!

Mike.

 

[rpn453]

Mazda recommends 32 psi all around on my 3. 32 psi provides good handling, but the center of the tread wore more than the edges at that pressure and wheel hop is a problem. 28 psi practically eliminates the wheel hop, but I can feel the sidewalls deflecting too much under hard cornering at that pressure. So 30 psi is my compromise.

Like QP said, start with what's recommended and adjust from there to get it the way you want.

 

[wantin150]

CruzNLife1,

And why would you suppose that the vehicle mfg would recommend different tires pressures front and rear? Maybe to balance out a suspension/handling issue to reduce the amount of oversteer (which is almost always more difficult to control than understeer)? My old Tacoma recommended 29/29 so I would hazard a guess that a difference in front to rear pressures isn't necessarily a load issue, but a handling one.

 

[occupant]

I prefer to go with 80% of maximum or the placard pressures, whichever is higher. On my tow truck, this means 80% of 125 (100) or the placarded pressure of 100. Works for me. On my wife's car, it's 80% of 45 (36) or the placarded pressure of 32, so I go with 36.

 

[Colt45ws]

On my car I found that 40 front 30 rear gave a good looking wear pattern. I believe the placard recommends 35/35. I did bump the rear to 35 when I had it loaded up for my drive back to Washington.

 

[lasmacgod]

An extra 5 psi above placard recommendation, so long as the tire's max psi isn't exceeded, will reduce chances of hydroplaning while maintaining good tire wear and handling. The water pushes up on the center of the tread, reducing tread contact by leaving only the outer edges of the tires in contact with the road. The increased pressure reduces the chances of the water lifting the center of the tread, thus reducing the chance of hydroplaning.

 

[CrazyMike]

Originally Posted By: lasmacgod
An extra 5 psi above placard recommendation, so long as the tire's max psi isn't exceeded, will reduce chances of hydroplaning while maintaining good tire wear and handling. The water pushes up on the center of the tread, reducing tread contact by leaving only the outer edges of the tires in contact with the road. The increased pressure reduces the chances of the water lifting the center of the tread, thus reducing the chance of hydroplaning.


This may work for a heavier vehicle, say a mini-van with soft sidewall Uniroyals or Michelins, or a Town Car, but for a light car, a Camry or Focus, that's the last thing you want to do. That placard psi is at max payload, if you're not running there you're over inflated and your tires aren't providing maximum traction..

 

[CapriRacer]

Originally Posted By: CrazyMike
Originally Posted By: lasmacgod
An extra 5 psi above placard recommendation, so long as the tire's max psi isn't exceeded, will reduce chances of hydroplaning while maintaining good tire wear and handling. The water pushes up on the center of the tread, reducing tread contact by leaving only the outer edges of the tires in contact with the road. The increased pressure reduces the chances of the water lifting the center of the tread, thus reducing the chance of hydroplaning.


This may work for a heavier vehicle, say a mini-van with soft sidewall Uniroyals or Michelins, or a Town Car, but for a light car, a Camry or Focus, that's the last thing you want to do. That placard psi is at max payload, if you're not running there you're over inflated and your tires aren't providing maximum traction..



Uh....not exactly.

My experience is that even for small vehicles, the specified inflation pressure is all over the lot - maybe not as bad as SUV's, but certainly not very consistent. It all depends on how much load carrying capacity the tires has (how big it is) compared to the weight of the vehicle.

AND

Regarding the +5 psi recommendation - even if it results in more than the max as specified on the sidewall, it's still OK. Dry traction differences are hardly noticeable and wet traction, especially hydroplaning, are generally improved.

 

[XS650]

Originally Posted By: CapriRacer

Regarding the +5 psi recommendation - even if it results in more than the max as specified on the sidewall, it's still OK. Dry traction differences are hardly noticeable and wet traction, especially hydroplaning, are generally improved.


CR do you have a source for that?

I don't doubt you at all. I also don't hesitate to do it myself when conditions all for it but would like to have another source for the Doubting Thomases.

I'm particularly interested in the P-metric 35 psi sidewall pressure not being an absolute max number.

 

[CrazyMike]

Quote:


Uh....not exactly.

My experience is that even for small vehicles, the specified inflation pressure is all over the lot - maybe not as bad as SUV's, but certainly not very consistent. It all depends on how much load carrying capacity the tires has (how big it is) compared to the weight of the vehicle.


I agree, but what did I say differs from this or conflicts, nothing from what I can tell.

Quote:

AND

Regarding the +5 psi recommendation - even if it results in more than the max as specified on the sidewall, it's still OK.


I would never recommend this to anyone, nor call it ok. It might tolerate psi beyond it' max rating, but the tire isn't designed for it. I won't bother commenting on the horrible ride over-inflating provides, or the accelerated center wear, find me a tire shop or a manufacturer rep that will say go ahead. Liability is the key. No decent tire shop will over-inflate for you, and if something tragic happens, guess where liability lies.


Quote:
Dry traction differences are hardly noticeable and wet traction, especially hydroplaning, are generally improved.


Dry or wet, your threshold limit for traction is reduced if you're running excessive psi. If you've improved resistance to hydroplaning you've raised the outer edges, now you can maintain faster speeds before losing contact, but braking and cornering is compromised. How is this a good thing.

You can't tell me a Toyota Echo, an Avalon, or a Honda Accord or Civic has better handling qualities and traction with excessive psi, let alone it improving in the wet.