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Old 12-06-2014, 02:23 PM
 
Location: Estonia
1,707 posts, read 1,259,700 times
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If you run the tire sidewall max pressure, you tires will wear out unevenly, more in the middle, less on the edges. Results in 'good' mileage but poor traction.
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Old 12-06-2014, 07:39 PM
 
1,204 posts, read 4,095,856 times
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Unless I missed it in this thread, I haven't seen anyone mention the obvious fallacy with assumption that the max pressure on the tire sidewall should be the proper inflation pressure regardless of the car manufacturer's recommendation. Most cars use tires of a fairly common size...especially the more moderately priced cars that most people drive. I imagine a lot of those different cars have different manufacturer's recommendations....so why would you think a one-pressure-fits-all would be a good idea for all of them?

My MGB would drive you guys nuts....the factory recommendation is for the rear tires to have 4 pounds more than the fronts for proper handling. That's counter-intuitive considering that there is more weight on the front. Inflating the tires to the max would not only give the car a bone rattling ride, but would seriously alter the car's handling....
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Old 12-06-2014, 10:13 PM
 
1,690 posts, read 2,011,890 times
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Quote:
Originally Posted by JoeCartpath View Post
Unless I missed it in this thread, I haven't seen anyone mention the obvious fallacy with assumption that the max pressure on the tire sidewall should be the proper inflation pressure regardless of the car manufacturer's recommendation. Most cars use tires of a fairly common size...especially the more moderately priced cars that most people drive. I imagine a lot of those different cars have different manufacturer's recommendations....so why would you think a one-pressure-fits-all would be a good idea for all of them?

My MGB would drive you guys nuts....the factory recommendation is for the rear tires to have 4 pounds more than the fronts for proper handling. That's counter-intuitive
Not counter-intuitive to me. It is done to prevent oversteer.

This is not uncommon.

The original Corvair was, admittedly rear-heavy but called for 15 PSI front and 26 rear! If the tires were inflated equally one little twitch of the steering wheel at highway speed and you were lucky if the car did not spin out. (I owned a 1963 model briefly decades ago.) That these wild pressure recommendations were rarely observed is one reason the car got the reputation for losing control.

A very dramatic example of the fact that proper inflation pressure is determined by:

1--Tire size

2--Vehicle weight and weight distribution

3--Suspension design. Suspension design is one factor in "oversteer" or "understeer" which I discuss below. Too much of either one can be ameliorated through relative front/rear tire pressure adjustment.

Of course, the tire manufacturer is privy to #1 only. Assuming stock tire size or factory approved optional tire size, the vehicle manufacturer is privy to all three and hence qualified to put #s on a sticker on a door jamb or the glove box lid.

When the sidewall of a rear tire flexes under side load -- centrifugal force -- a car turns more than it is pointed to turn by the front wheel -- "oversteer." When front sidewalls flex under side load the car turns less than it is pointed -- "understeer." Oval track racers call "oversteer" a "push," understeer, "loose." Only a driver who spends weekends driving competitively on oval tracks is likely to be comfortable with "oversteer." With a little "understeer" you merely turn the steering wheel slightly more completely intuitively.

BTW, try to tell a stock car racer the more air in the tires the better the handling and he/she will probably be so contemptuous as not to even wish to talk to you.





Quote:
Originally Posted by JoeCartpath View Post
considering that there is more weight on the front. Inflating the tires to the max would not only give the car a bone rattling ride, but would seriously alter the car's handling....
Good post, Joe!

Don in Austin
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Old 12-06-2014, 10:57 PM
 
Location: Spots Wyoming
18,696 posts, read 35,420,950 times
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Quote:
Originally Posted by TrapperL View Post
Last time I checked, no car maker makes tires. The inflated pressure on the door is for the tires that it came with from the factory, not replacement tires. The guys will look at the tire makers max pressure to give you maximum fuel mileage. You should be thankful for that. I can just see my Bronco with 12.5 x 31 tires going down the road with 28 lbs of air.....until it's upside down in a ditch.......the tires take 50lbs.
The sticker in the door is for Manufacturer rated tires and is based on weight of the vehicle. So, if you replace with a load range D and it was recommended to be a load range C, then the numbers won't work. Same if you step up a size, or change to different sidewall ratings. But, if you put on what is recommended, the pressure is based on vehicle weight, Empty.
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Old 12-08-2014, 06:46 AM
 
138 posts, read 120,033 times
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Quote:
Originally Posted by wit-nit View Post
The tire information on those door posts are for the original tires the vehicle came with. If you've changed tires the pressure recommendation will probably be different and I would go by what the tire people say for the new tires for your area.
My original Michelins said 32 psi, my later version replacement Michelins say 35psi.
So what you're saying is if you buy a set of michelins that are a different model than the oem set of michelins the car came with you seek out a michelin rep in your area to find out what the pressure should be? Why not just put in what it says on the tire info sticker? It amazes me there's 6 pages on this. I'm a mechanic and i always fill the tires to what the tire info sticker says. I've never seen one of those stickers say the tire brand and model the car came with, just the size and recommended psi. If the car came with 225/60/16s and the recommended psi is 30 then there is absolutely no reason in the world not to fill the replacement tires of the same size whether they're goodyears, bridgestones or the cheapest chinese junk money can buy to 30psi. Now, as others on this thread have said, if there are other circumstances involved such as towing, beach driving, high performance driving, non-oem tire sizes, or just trying to squeeze every last mpg out of the car then it could take never-ending experimenting to find the optimal pressure and there are guys who devote a ton of time and research into this but for 95% of the cars out there running the stock oem tire size then the pressure on the tire info sticker is more than adequate.
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Old 12-08-2014, 03:51 PM
 
Location: Utah
4,968 posts, read 13,999,451 times
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Quote:
Originally Posted by vision33r View Post
In the winter time it's good to over inflate by 2-3 psi.
This is what I was told by my tire guy when I bought new tires last month. I wondered why they were inflated to 38 psi when my old tires were at 35. He said 38 was a good number for the winter. I also have a TPMS so I check my tire pressure twice a day...to/from work.
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Old 12-09-2014, 11:20 AM
 
Location: Huntsville
5,334 posts, read 3,594,211 times
Reputation: 6007
Quote:
Originally Posted by kmoran81 View Post
So what you're saying is if you buy a set of michelins that are a different model than the oem set of michelins the car came with you seek out a michelin rep in your area to find out what the pressure should be? Why not just put in what it says on the tire info sticker? It amazes me there's 6 pages on this. I'm a mechanic and i always fill the tires to what the tire info sticker says. I've never seen one of those stickers say the tire brand and model the car came with, just the size and recommended psi. If the car came with 225/60/16s and the recommended psi is 30 then there is absolutely no reason in the world not to fill the replacement tires of the same size whether they're goodyears, bridgestones or the cheapest chinese junk money can buy to 30psi. Now, as others on this thread have said, if there are other circumstances involved such as towing, beach driving, high performance driving, non-oem tire sizes, or just trying to squeeze every last mpg out of the car then it could take never-ending experimenting to find the optimal pressure and there are guys who devote a ton of time and research into this but for 95% of the cars out there running the stock oem tire size then the pressure on the tire info sticker is more than adequate.

If you buy a tire that is the same size but carries a different load rating, then yes you need to be aware of this and adjust accordingly. Brand does not matter. Load ratings do. The sticker is a vehicle manufacturer recommendation, not the tire manufacturer recommendation. It isn't the be-all end-all of tire pressure for your vehicle.
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Old 12-09-2014, 11:29 AM
 
4,429 posts, read 3,107,380 times
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Look at what the vehicle mfg recommends on door vs OEM tires that came with vehicle.

Those numbers will probably not match because one is recommended PSI while the other is MAX PSI.

I don't know about you but I'd go with recommended vs MAX
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