Correct air pressure for 2000 Honda Civic tires?

The door panel reads 30psi. I just got two new tires from a mechanic who seemed pretty knowledgeable and he filled up the front tires to
40psi and the back to 35psi. Why did he do that when the door panel says 30?
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Joe wrote:

He obviously was a 'lot' less knowledgeable than he let on eh.
The BS artists that figure if you can't dazzle em with brilliance, baffle em with BS are in real trouble because of the internet.
Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's - Gone to the rust pile... Canadian Off Road Trips Photos: Non members can still view! Jan/06 http://www.imagestation.com/album/pictures.html?id !15147590 (More Off Road album links at bottom of the view page)
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I suppose when customers drive out with higher pressures, this results in fewer comebacks than when they leave with lower pressures. Few people check their tires on a regular basis, so...
He probably overinflated to seat the beads, then dropped it down a bit after. Lower the pressure yourself (cold!) back to 30. You may find your tires spec at about 45psi max pressure, so that brief visit to 40 did no damage.
Say, do your new tires vibrate at around 55-60 mph? Just asking.
--
Tegger


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Tegger wrote:

Most tires say on the sidewall what pressure is allowed to seat the beads and I've never seen any that don't allow at least 40 PSI for that purpose. Most then spec 32-25 PSI max pressure, with a few spec'd at 41. So the initial 40 PSI makes perfect sense, and I'm guessing he backed it down to 35 as that was the max running pressure on the sidewall. You would be correct to drop it down a little more based on the door placard.
nate
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He's not.

WIdepsread ignorant misconception that the pressure on the side of the tire is a recommendation. Weight of vehicle, spring rates, center of gravity, propensity to oversteer/understeer, roll center, front/rear weight bias etc. etc. are all factors that affect optimum tire pressureas much as the tire itself. Thus the "PLACARD ON VEHICLE" that the writing on the tire tells you to reference. Unfortunately, most lube franchise and tire store employees are not capable of reading that far. There is also a widespread ignorant belief that since the perils of underinflation are well known it follows that the more air the better.
I would trust Honda's chassis engineers long before some Firestone dude and so should you.
Don www.donsautomotive.com
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Here's the reason for my question - I went on a trip not to long ago and checked my tires before leaving and they were at 32psi (I had recently had a mechanic perform an oil change). I lowered the psi to 30 as it said on the door panel and had a blowout on the road. I'm wondering if that blowout was due to underinflation.
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From underinflation by only TWO psi? I very much doubt it.
More likely the tire had undergone long-term severe underinflation (like 10psi) or suffered a sudden large gash due to road debris.
--
Tegger


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Joe wrote:

Nope, More like you hit a chunk of junk in the road or a curb causing it to blow. Doesn't take much sometimes.
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Joe wrote:

Not unless you had a leak. However on a road trip I probably would have fudged the pressure up a little bit, because a) you generally are heavily loaded on a road trip b) you're also likely to be traveling on a freeway at high speed and c) higher pressure gives somewhat better fuel economy, but at the expense of ride and possibly handling - all of which would indicate bumping the pressure up a little.
nate
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Don wrote:

Yes. well its seems there also seems to be a widespread misconception that a person asking questions on Usenet is always providing accurate factual information. For all anyone one can tell from reading the question asked, the poster may have picked the car up from the shop drove it 10 miles home on a hot day and then checked the tire pressure.
-jim

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would that make that much of a difference in Psi if it was a hot day? For the record the car had been sitting in my garage (on a hot day) for about 6 hours when I checked the pressure.
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On hot days, the air pressure in tires does expand, but you shouldn't bleed off any air pressure.I remember an article I read in an auto magazine over thirty years ago that some auto manufacturers reccomend a lower than optimal air pressure for a softer ride.I checked the air pressure in the tires of my 1978 Dodge van before I went to the food store this afternoon.I keep about 40 psi in the tires regarless of what the manufacturer says and what it says on the tires. cuhulin
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the place card on the door panel is for the original tire the model came with :banghead: if underinflated you can cause mageby riding on the side wall if over inflated you can cause a air pocket in the rubber itself and increase in you chances of a flat
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Joe wrote:

Because he knows more about tire pressure than the engineers who designed your car.
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The pressure marked on the sidewalls is a maximum, usually needed to reach the maximum load capacity of the tire (which is also marked on the sidewall) but not necessarily where the best handling is found with more-normal loads. That, as you surmised, varies from car to car and is found on a door panel or in the owner's manual or some other place specific to the car.
See for instance http://www.tirerack.com/tires/tiretech/techpage.jsp?techid 7&currentpage=1
Racers and advanced sports car enthusiasts might "chalk" tires or use pyrometers to fine-tune the best tire pressure for what they are doing, or will bias it in a certain direction to get a specific cornering result; but regular folks doing ordinary driving, and who haven't made suspension mods or major changes in the size and type of tire, will probably find the best advice on the door panel.
If you're going to err, it's better to be a bit overinflated (within the sidewall rating) than grossly underinflated. But why err when you can be right? Remember to take the readings "cold" (i.e., before doing much driving) and to re-check every few weeks or before a long trip, whichever comes first -- tires lose air over time, and sometimes just one of them will do it faster.
Cheers, --Joe
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