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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.
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....
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
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....
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.
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.
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.
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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Quote:
Originally Posted by TrapperL
Okay arm chair generals, here's one for you. My older Supercrew came factory with P255/70/17 tires. The max air per the tires was 35 lbs. For those tires, that's what I ran in them but that's not the point. My wife just bought a new Fusion. Tire size P255/70/17..........sound familiar? Yep, both P rated car tires in the exact same size and NONE made by Ford. The Fusion tires per FORD is 51 lbs. The exact same size tires but a tremendous difference in the air pressures. The 51 lb recommend by Ford is also the max air pressure on the tire. It has to do with the fuel mileage package on the car which is great at 45 mpg hiway. So tire size is irrelevant as to the pressure you should use. When the wife's car needs tires again, we may not necessarily buy the exact brand and that new tire may have a 35 or 40lb max air limit. According to some of you, I'd have to run Fords recommended 51lbs in a tire only max rated at 35 or 41lbs. It won't happen at my house. We just aren't that stupid here.
I can only assume none of you remember the Explorer and Firestone issue. Ford recommended far too low of air pressure and tires were blowing up from the added heat which deteriorates the carcass. Firestone had issued a warning to Ford but Ford didn't want give up the cushy ride. Handling was horrible obviously and tire life was short. I personally don't care what you run in your tires, you can run them flat for all I care. But if you want the best fuel mileage and the best handling for your car/truck, read the max air level on the side of tire and consider that as the air pressure you need. You'll also note, on the side of the tire it reads XXlbs COLD. That means the tire is expected to take on more air pressure as it heats up or driving on hot asphalt. Normally any tire has a built in 10lb safety margin for any expansion. If you don't want to follow that, then pull yer big boy panties up and run whatever you want.
Re: Wife's Ford Fusion.
I just checked on tirepressure.com and the highest recommended cold tire pressure on any Fusion, model year 2013 or earlier, is 35psi. Low end of range, 32psi. Normal car pressures. I'd love to see it in writing, anywhere, that "Ford recommended" 51psi in any vehicle they ever made aside from Econoline vans, Broncos, and Excursions.
It's not "Ford recommended 51 pounds"... That 51psi is 99.999999999999% likely to be the Max. Cold Pressure(those words exactly required by law) stamped on the tire sidewall. Not what Ford or Mercury recommended in Fusions or Milans from those model years.
Last edited by TheGrandK-Man; 05-13-2020 at 06:32 PM..
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As far as the O.P. issue is concerned - overinflation of tires by discount oil places, etc - there is one silver lining:
I have my own tire pressure gauge, a Longacre Digital model with adjustment down to one-fifth PSI, or kPa if you really want to dial in precise pressure. So early next morning, I go out with the gauge, and bleed off the overinflation down to precisely the vehicle-recommended pressure, or one PSI over at each corner.
Car drives, handles, and rides like a dream, steering reaction and reaction to bumps is the same side to side, all predictable.
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