What happens? Ride will be rougher, traction reduced, MPG will improve, drifting will improve, car will be more fun to drive especially if it is a rental with a stick shift. GO GO GO.
This may be too much info, but here it is. The manufacturer's tire pressure recommendations are primarily for ride comfort and tire wear. If the tire pressure is too low, the tires will wear faster on the outside edges first. Too high of a pressure and the tires will wear down the middle of the tread first. There is a balance of support from the tire side walls and air pressure that keeps the tire tread flat on the road surface which encourages even wear across the entire width of the tread. Also, the more tread in contact with the road, you'll have better control over steering and braking and cornering. If you tend to run the car at heavier loads, higher pressures are needed.
The 40 psi is the maximum recommended COLD tire pressure specified by the tire manufacturer. Cold pressure is where the tire hasn't been run on the roadway. Running the tire causes the tire to heat up due to friction and also causes the tire pressure to increase by about 4 lbs. The 40 psi takes into consideration this 4 psi increase.
Heavier vehicles run tires with higher pressures due to the loads they carry. So the tires are rated for those heavier loads.
I like to run higher pressures, but 38 seems excessive, stick with 34. These people that insist on following the manual in this regard however have no idea. Most slightly older cars recommend pressures in the mid 20's, which is ridiculous when newer tires have a max rating of 44psi and gas was half the price 10 years ago.
The max pressure on the side of tires is not the makers "recommendation" but the highest pressure at which the tire is safe to use. Go with the CAR makers recommendation - usually on a sticker in driver door opening . . . . I sometimes add a couple pounds if the car is heavily loaded, but no more than that. As others say, handling can get tricky and center of tires will wear.
You're still under what? Have you actually put a gauge on those tires? If they are at the max, the doofus that put it up there needs a slap in the head. Before the first drive of the day, drop all the tires down to 35 or whatever is on the door jamb.
I remember the Firestone/Explorer fiasco. I'll still take chances with manufacturer's recommendations eventhough I think Ford was at fault with that one. After all, they spent millions of dollars of R&D to come to the conclusion they came up with. The problem were the tires. Firestone makes tires. Period. Nothing else. Ford chose to equipped their vehicles wioth those tires. Firestone makes many different tires and Ford chose those for the Explorer. It was in error, but most tire stores will tell you to go by the manufacturer's specs to determine correct tire pressure. I agree.
You will never notice a difference even if you go to the 40lbs max. these are just suggestions by the manufactures and have a built in safety factor, after all they don't know if the tire will be used on a truck or a hybred car so they use conservitave numbers
All you had to do was to use Google Search to get information from accredited automotive sources. Also with Google is an explanation of all of the data embossed on the sidewall of each tire. This data incudes the date of manufacture, year/month. Since auto and truck tire manufacturers have no idea on what type of vehicle and to what type of service they shall sustain, it is up to the vehicle manufacturer to make the determination as to the type of tire to be installed. The engineers that design the vehicle make choices based on certain tire specifications. I have a moderately performance car, a 2001 Audi TT FWD. The specs call for "high performance, A temp rated, top of the line tires. Yet, the car is hardly a Porsche as to handling. The recommendations as to pressure come from Audi not from the tire maker as I can install tires from any manufacturer. The car manual and somewhere in the chassis of the car there is the pressure recommended, cold tire, with often a slightly higher pressure for high driving or carrying close to max payload. Please use Google as to over inflation or under inflation of tires to see photos of the consequences. Tire must have flexibility to grip. They operate at about 180 to 200 degrees in temperature to produce desired results. You must use the auto maker recommended cold air pressures, not what is on the sidewall.
Bottom line, with a PSI any more than a pound or two over the recommended would unnecessarily make your ride more harsh and could potentially wear your tires unevenly or prematurely.
over inflation causes the center of the tire to wear much faster than the outer edges... u want to keep ur tires about the tire specs ask for, keep in mind temperature and many things can fluctuate it a lil.
I'm still under the tire manufacturer's recommended max psi. of 40 but the psi that my car recommends is 34 what if I go to 38?
Inflating above car maker's recommendation will give you more hydroplaning on wet surfaces (not a good thing), less traction (less rubber in contact with the road), rougher ride, accelerated suspension wear, shorter tire life. Some people claim they get better MPG due to lower rolling resistance. The lower tire life and accelerated suspension wear cost far more than any gas you might save.
Be careful. Increased tire pressure with standard wheel widths may make the tire wear in the center. Wish you had listed the year make and model so we could check the standard wheel width.
better gas mileage
less traction
tires will wear out the middle sooner than the outer edges
increased chance of a blowout --- especially in hot weather
stiffer / bumpier ride
The tyre will bulge slightly in the centre of the tread making it wear faster in the centre and wera out quicker overall
The tyre contact patch will not be the best for the weight of the car and so grip will be slightly reduced in dry conditions and much more reduced in wet conditions
They give a tyre pressure for a reason and that is going to be the best one for grip and wear so it makes no sense to alter it.
over inflation wears the center of the tire
under inflation wears the edges and is evident from sidewall scrubbing
It can cause premature tire wear and will not perform as rated to do so by the manufacturer.
The ride will be rougher, the handling will be worse, and your tires will wear out faster.
There is no "up" side to this.
Ian
please have a mechanic look at it
