overinflation and suspension
 

Most of the users on this site report that they run overinflated tires, or at least pump their tires up to the sidewall-listed max pressures. I myself am currently doing so, and have had absolutely no problems. I can take turns a bit faster, and my FE has definitely improved.

How though, is this kind practice on your suspension? While trying to convert my dad, he brought up a very valid argument. He said that having the tires too solid could transfer more vibration to the car's suspension, thus wearing out the suspension prematurely. In his case, since he carries very heavy loads (think close to max capacity in his Envoy XL), this problem could be exacerbated.

On a side note, he just purchased a Lexus RX400h for my mom, and it came from the dealer with 45 psi in the tires, EXACTLY what is listed on the sidewall as maximum allowable pressure. I mentioned this to him and he was a bit surprised.

He is letting the RX400h stay as his, but is also not budging on his own Envoy XL. I just want him to save as much fuel as he can, but I am not going to force him into it, and would rather present the issue to him with verifiable data and experience.

Is there anyone on the site that has experience with automobile suspension, and can definitively say whether or not my dad's concern is a valid one?

No experience on the suspension, but how often does he check the tires? Maybe the gs members should go around pumping up our friends tires without them knowing to help the unbelievers get better FE. :D:D

I can't imagine that the difference of tire pressure is really affecting the suspension much. But then again I don't haul anything in an Envoy.

My opinion is that the answer for this is a very touchy one. I'll say that all manufacturers design the suspension to maybe last only twice as long as the bumper2bumper warranty. And that the higher pressures in a vehicle not driven on nice roads will exhibit blatent signs of wear at-that-time.

But. Very Slightly worn suspension does not show driveability symptoms/noises besides lower fuel mileage, and where I am from, the repair shop will align my wore-out vehicle for years and years if-they-think I'm not going to pay them for parts replacement. The alignment is never satisfactory, and the fuel mileage never is what it was, which they find excuses for blah blah blah.

None of this is "definitively" speaking, but I "think" there would be more of a concern for sedans/coupes/hatchbacks over your familys SUV type vehicle.

GeekGuyAndy: He checks them at least once a month. We use one of those cheap pencil-type ones though, and I don't trust it very much. We have a nice compressor at our house, and I think it would make sense to just break down and get a nice air chuck WITH a gauge on it. That is how they all are in Japan anyways...

nortonpro: My dad lives and works in Michigan. He covers most of the Detroit, Lansing, Jackson and surrounding areas. He hauls heavy door frames, and as you know, the roads in Michigan are absolute CRAP. So, he does see very unfavorable driving conditions. This is one reason why I am not pushing him too hard. He has also worked on his own cars for many years, something that I can not claim to have done (yet). Oh, and his car is used 100% for work, as in, he doesn't drive it at all for personal use. If he is in it, he is using it to bring home the bacon. Speaking of which, this morning we had some really tasty bacon (the literal, not figurative type mind you!)

If the roads were in good shape around here, it wouldn't be nearly as worrisome to him. It is just that after driving on Michigan roads your whole life, you realize that they aren't exactly built to keep your car in good shape. Maybe it is just a ploy to get people to buy new cars more often...

I don't think the suspension will wear prematurely in any significant way, since it'll still get and take all the big bounces, which are what cause most wear. If you can feel an increase in bumpiness w/ pressure, your struts aren't absorbing it. Something I've wondered about is whether bushing wear rates increase significantly, since more smaller stuff getting through, however I don't think these would either, to the point of concern anyway. The most significant increase in risk imo is of a blow out/tire damage from deep pot holes/jagged edges.

as long as your suspention isn't warn out already I wouldn't worry about it, and if he is hauling heavy cargo then I would recomend that he fallows his owners manuals recomendation, and over inflate his tires.
what is going to cause problems are stiff suspention parts, or woren out supsention parts, as they are going to alow the rest of the vehicle to be affected by the shock of travling down the road.

Erdrick,

I bought a brand new 1995 Honda Civic VX in November 1995 and inflated every set of the 3 sets of tires (original and two sets of replacement Nokian NRT2) to the maximum sidewall pressure or greater. In the 12 years and 225,000 miles I owned that car, I never replaced a strut, spring or any other suspension or steering component; never had a bent wheel; never blew out a tire; never had uneven tire wear...in fact the tires wore more evenly than any other car I ever owned with normally inflated tires.

The car certainly had a stiff ride and bounced around on more bumpy roads, but it never bothered me. The benefit of substantial fuel savings outweighed the stiff ride.

Steve

I suspect that higher inflation may make bushings wear a little faster. So I need to figure out if I can change them myself...

On the Lexus, I bet that the 45 psi was something that the factory does, and that the dealer was supposed to lower the tires to the recommended pressure on the doorjambs.

Great info everyone.

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.

Fact is most later model cars with lower profile 14,15,16 and 17 inche tires have very little sidewall deflection. Pumping the tires up really doesn't hurt the ride quality over all much at all. Think about. A lot of sidewall deflection on such a low profile tire would be death to rims. Now a taller sidewall or as some liked to call them ballon tires. They do have deflection properties.

psy

Ahhhh, yessss, that could definitely be it... Good thought.

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.

Yeah, but those usually recommend a one or two psi bump, and not 10 or 20 like people here use.

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).

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.