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Old 08-14-2007, 12:49 PM   #11
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Originally Posted by Erdrick View Post
I kind of figured that the dealer (wanting to boost mileage) pumped up the tires themselves. People are complaining about not getting the mileage that they were promised with hybrids, and this is just one easy way to increase peoples' FE, without them noticing anything different.
Ahhhh, yessss, that could definitely be it... Good thought.
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Old 08-14-2007, 10:29 PM   #12
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I wonder if you have taken a look at the owners manual yet, the owers manuals that I've been reading all say that if you are doing highway driving, or hauling alot of heavy loads that going over the door jam listed presure is recomended for safty and tire life, and the suspension is designed to absorb shocks, so I say go with a higher presure.
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Old 08-15-2007, 05:58 AM   #13
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Yeah, but those usually recommend a one or two psi bump, and not 10 or 20 like people here use.
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Old 08-15-2007, 07:48 AM   #14
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Before I came to this site I kept the tires on the back of my pickup fairly low 30-35psi, because with an empty bed the tires gripped better with less presure (less sliding/skidding).

Whenever I haul a load I bump up to 40-45 and if I'm hauling over capacity (I'm only a 1/2 ton) I'll bump up to 50ish. I really just judge based on how squished the tire looks (which is very subjective), but the reason for increasing psi with loads is to maintain the same contact patch and side wall deflection.

That is for a 5,000lb truck if weight were distributed evenly, so 1,250/tire and with tires at 40psi that means the contact patch has to be 31.25 square inches.

Increase with a load to 6,000lb and same distribution, 1,500/tire with tires at 40psi means contact patch is now 37.5 square inches and tires will look quite noticably 'squished', as if low on pressure. To maintain the same looking level of fill you'd need 48psi in this example.

The math doesn't matter, but the point is with bigger tires ('ballon'?) adding a significant load can make them look really low and I think that'd be more risk for a sidewall/bead blow out.

As for bumps, a lot of cars now come with overly stiff suspension with overly lower or lower than you'd expect, tire pressure. The reason for this is to soften the ride without compromising handling or longevity of the suspension too much. Increasing pressure will noticibly stiffen the suspension feel up and will transmit more bumps to the cabin, you'll feel more slight variations and things you didn't before. I can't see this hurting shocks too much as really only bottoming out or full extent up and down hurt them the most. Bushings I can see definately being worn, because they get worn the most during small aplitude modulations (like going over the seem joints on a bridge or something), I don't know that they'll last significantly less, but I'd think anytime they move they're being worn (because torquing of the bushing is occuring) and small back and forth torques are the best way to snap something that appears flexible in half (but yeah if you haven't guess I don't really know what I'm saying).

I'd say go for it, I really don't think higher psi tires can significantly affect suspension, they'll just give you a stiffer ride and let you take turns faster. Going over sidewall pressure does worry me though, about the high pressure blowouts mentioned above. I also do not know how to judge at what point I'm getting evenness of wear. I don't want the center of the tread of the tire to buldge more than the tread by the sidewall, etc.

My tires are rated at 44 and I tried 50 for a week but it really did worry me so now I'm at 46 and I doubt it's affecting much (since this is an increase from my normal 40, woo).
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Old 08-17-2007, 10:38 AM   #15
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i just started using FE techniques so i'm not the expert on this but i wanted to avoid a too stiff of a ride so I put in enough air to increase the psi to somewhere in the middle of the normal recommended and sidewall max psi.

I'm sure I can get more FE by max'ing it out but I also want to even out the treadwear and soften up the ride a bit.
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