PSI in Kumho tire
- Thread starter SlamminRIde
- Start date
Hey, if you drive like a granny (defeating the purpose of a fun car like the P5), and don't at all care about being prepared for the inevitable (accident avoidance), use the door psi.
As with everything, there's trickle-down. Just because you are not a power lifter doesn't mean you shouldn't use powerlifting techniques to increase progress in the gym; just because you aren't a marathon runner or sprinter doesn't mean you shouldn't train like one for fitness; and just because you never push the limits in your car, doesn't mean you shouldn't be prepared to. Take notes from people who do those things, and benefit from their experience. Don't take my word for it; ask a racer/autox'er.
You assume the auto maker knows best. You're right, they know best for 1) their own pockets, and 2) their intended target demographic. I sold VW's for a while, and here's what sells: "ooo, see how solid the door *sounds* when it closes?"; "yeah, hit that divot in the road faster, see, I bet your piece of crap has a lot more rattles and sqeaks, you NEED this car". Mazda specs a tire pressure in those lines: soft, quiet, comfortable, but still safe-ish in a majority of conditions. This equals sales.
If auto makers were about ultimate safety and performance, there'd be no aftermarket. Fact is, *we* CAN make our cars handle better than Mazda; we're not saddled with marketing and bean-counter issues. So go up the pressure and throw a fat rear sway on there!
As with everything, there's trickle-down. Just because you are not a power lifter doesn't mean you shouldn't use powerlifting techniques to increase progress in the gym; just because you aren't a marathon runner or sprinter doesn't mean you shouldn't train like one for fitness; and just because you never push the limits in your car, doesn't mean you shouldn't be prepared to. Take notes from people who do those things, and benefit from their experience. Don't take my word for it; ask a racer/autox'er.
You assume the auto maker knows best. You're right, they know best for 1) their own pockets, and 2) their intended target demographic. I sold VW's for a while, and here's what sells: "ooo, see how solid the door *sounds* when it closes?"; "yeah, hit that divot in the road faster, see, I bet your piece of crap has a lot more rattles and sqeaks, you NEED this car". Mazda specs a tire pressure in those lines: soft, quiet, comfortable, but still safe-ish in a majority of conditions. This equals sales.
If auto makers were about ultimate safety and performance, there'd be no aftermarket. Fact is, *we* CAN make our cars handle better than Mazda; we're not saddled with marketing and bean-counter issues. So go up the pressure and throw a fat rear sway on there!
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jaguarMKIX
Member
Actually what the tire manufacturer has on the sidewall is the max pressure that the tire can be safely operated at. For example, when seating the bead on a tire you may have to go above this pressure. Having a high psi in your tires can not decrease gas mileage, due to the fact that there is less of the tire touching the ground (rolling resistance) and the diameter of the tire is larger creating a larger circumference (less revolutions per distance traveled).
If the size and type of tire did not dictate what tire pressure to use when why do different tire manufacturers have different maximum pressures? Not all tires are created equally. I do not think you know what you are talking about since you disagree with yourself. You say that tire size (volume) and amount of air does not matter but then say volume and amount are directly related to pressure.
At a fixed temperature, increasing the amount of air in a fixed volume increases the pressure. With a greater volume, a larger amount of air is needed to reach the same pressure. You can look at Boyle's law to see this.
Sometimes car manufacturers are wrong. Remember Ford/Firestone? Ford lowered the tire pressure in the tires to 26psi from firestones recommended 35psi (not the same as the max psi) and the effect of that was the increased friction between the tire and the road as well as in the tire. The heat separated the tread from the base plies and boom. Mazda determines the pressure with NVH in mind, which may or may not be best for performance, mileage or wear. Usually, selling a car (and saving money) is the priority of a car company so they may lower pressure (like Ford) so the vehicle feels more comfortable to the customer.
In reference to your larger tire footprint is better for winter traction. That is wrong in the case of snow unless you are planning to have your car float on the snow. Narrower tires allow the tire to easier displace the snow and reach the road below (where there is more friction). In the case of ice, it is better to have a wider tire but you should not be driving on sheets of ice anyway.
Where did you back your information up? All that you did was provide a link to the tirerack, where they discuss the disadvantages of under inflating and over inflating.
What is this nonsense about 34psi not being 34psi? 34psi is always 34psi above atm at sea level. Weather does cause differences in the density of the air so you should check your tire pressures often, but when you check it and it says 34psi that means it is 34psi. Keeping the tire at the optimum psi will increase tire life but that does not mean what the car manufacturer says is the optimum psi. Different tires have different construction (plies, rubber etc.) Tire manufacturers do not know the weight of your car but car manufacturers do not know what tires you use. A tire with less plies will have a lower max operating psi. That same tire will distort with more or less pressure. A tire with a higher amount of plies will distort less with more or less pressure and will have a higher operating psi. Car manufacturers base those pressures (just like everything else in a car) on NVH b/c people like their vehicles smooth quiet and vibration free. (Look at the protgs poorly designed engine mounts). In addition, you can see NVH taking the highest priority in trucks, they used to have solid front axles and now they have weaker independent axles. Leaf springs used in front and in the back and they were short and full size throughout, now the leaf springs are only in the back (sometimes trucks dont even have them) are long and tapered (easier to bend). This is b/c more people are buying trucks just to drive to home depot once a year while using it the rest of the time to pick up their kids from soccer practice.
Ultimately, it is up to you to decide what pressure to run in your tires.
I am a racer and have done auto cross several times. My one uncle owns a race team with three vintage triumph TR-4s and one TR-5, which I drove quite often as the registered driver for events. He's 60 years old and we restored the cars ourselfs. My other uncle owned a very good auto repair service station for over 40 years, and my father use to drag race on a semi-pro level. So please do not tell me I do not know what I am talking about.
I agree that a high performance tire does a stiffer side wall and much better construction there for you can run a slightly higher tire pressure in those tires for track and let's call it spirited driving. A cheap all condition tire will "roll" more and is not made for aggressive driving because of the softer side wall and more comfort designed tread patter, but by over inflating a cheap tire to compensate for the lack of built in performance you are decreasing the foot print of the tire and there in decreasing the performance that tire is capable of.
When im at the track we are always checking and changing our tire pressure thru out the day depending on conditions to get optimal feel and results for the way I drive the car. Every car is a slight bit different and every person drives there car slighty differently. About once a month I check my tire pressure on on my cars when there cold in the morning and set the tire preasure to the recommended psi +/- 1psi for error. In the winter I will usually put in about 2+ psi cause I know the tires and air won't be heating up that much when it's 20 degrees out side and the summer I leave it where Mazda recommends unless I know I'm going to be driving the car harder.
Let's just say this and be done with it. The sticker recommondations are a good place to start and will work for most people in most conditions. If you drive a bit more spirited then increase your pressure as you wish. Do not exceed the Max tire pressure that it on your current tires. That max will change from tire to tire because some tires are better constructed then others. If you have a cheapo set of all seasons don't expect to drive like a friggin master track star, get a better set of tires that are designed for those conditons. If you drive in the winter get a set of winter tires they make a huge difference, Follow the same guidlines as above. Generally speaking a narrower tire IS what you want for drive IN SNOW. 2-3" of fresh snow a narrower tire will "cut thru the snow better and get down to the pavement to provide better traction. It's a snow plow effect, a wide snow tire is like taking the width of a snow plow and trying to shovel with it, a human would not be able to that, a narrower snow tire is like a regular shovel, much easyier to move the snow out of the way. Now that was for driving IN SNOW, if you drive ON SNOW, like we often had in wisconsin where I lived until last year the story can be a little different. When there is very heavy snow fall and you are driving on top of the snow there is no way your tires will get down to the actuall pavement so a lower tire preasure will widen your tire foot print slightly as long as you are driving at slower speeds as you should be in such conditons. Now, if you do find your self stuck, one trick that I learned is to let almost all the air out of tire so that it get's really wide and flat, then slowly, VERY VERY SLOWLY drive out of the hole your in, you do not want to spin the tires in this situation as it will pack the snow and make it even slicker. Once your unstuck reinflate your tires and be on your way again.
Now, everyone may not agree with me on this and argue up and down about it. All I know is that it has worked several times in the past for me including recently in late december here in portland area when we got something like 15-17" in a two week period.
Take it or leave it that's up to you. Just drive smart, and have fun out there.(drive)
P.S. I'm really not trying to piss people of here. Just telling it like I see it. And like anything in this world, consider all sides, form your own opinion, and be respectfull to others. Then do what YOU want to do with the information out there.
Love and peace to all Mazda Zoomers out there, I'm out.
no one's pissed, it's all good. 
some noob may just find this enlightening. one question, ride92: if you understand how tire pressures affect performance on the track, as obviously you do, whyever would you step off the track and follow the door jam recommendation? that makes absolutely no sense.
some noob may just find this enlightening. one question, ride92: if you understand how tire pressures affect performance on the track, as obviously you do, whyever would you step off the track and follow the door jam recommendation? that makes absolutely no sense.31 psi front/rear here on 215/40R17 Kumho Ecsta SPTs (not that the size matters). The tires are rated for a maximum pressure of 50 psi but I won't ever be anywhere near that. I have found that 31 psi is the perfect balance for handling and acceleration. Any higher and the fronts will spin too easily and the rear wants to kick out. Any lower and the sidewall becomes too soft and there's excessive body roll. Just remember, when all you guys are having fun bumping up your tire pressures into the 40 psi range you're significantly reducing the contact width of the tire. Think of it this way, do you see top-fuel drag racers with tires about to burst or tires barely inflated? Also, you will find that a tires handling ability is more a function of the rim it's mounted on and the "stickiness" of the tire itself.
See, that's cool. ^ You found an ideal pressure for your car/tire/needs, and have specific reasoning for your choice.
No. I mean it's possible with some tires, but when the max PSI is 51, and I'm at 40, and I'm experiencing even wear....I am not reducing the contact patch one bit. My Impreza had camber plates and bolts, struts and springs, and the huge sway bars and end links. I had Falken 451's on there with 38 front/42 rear, with max negative camber up front (talk about reducing contact patch, if only while going straight!) and -1.5 rear, and driving 15 miles of canyon to go to work daily I was still experiencing shoulder wear on the tires.
They go in a straight line. Throw a curve in the drag strip, and you'd see them madly pumping up tire pressure.
10lbs below max tire pressure is no where near 'about to burst'. The recommended door pressure is, however, near 'about to slide off the rim'.
Rim? Not really. Stickiness? Hell yes. Nearly any car can pull a g with Hoosiers. :lol:
I use the door jam recommendations as just that, recommendations. I drive completely different on the track then on the street so I run my tires different. I don't have the time nor the obsession to be checking tire preasure every couple of hours to ensure Optimal performance for temp and duration of drive ahead. I just set my tires, currently at about 32psi all around and seems good enough for my daily 13mile commute. When I go to the track I change it, but that's a different story out there.
Just because you ran your tires a certain way on your Impreza doesn't mean it's right. Fine, so top fuel drag cars aren't a good example, but how about F1 cars, they go around curves, right? Let's see, what kind of tire pressure do they use? Well every source I've checked has said 15 psi! Sure they are lighter than typical passenger cars but the same principle applies. Our cars are only ~2800 lbs so they don't need tire pressures in the 40 psi range to operate at peak performance. More pressure != better handling. Also, model air as an ideal gas, P=rho*R*T. How much do you think the temperature of the air increases while driving? Therefore, how much does the pressure increase. The ONLY reasons for running such high tire pressures I can think of are to increase gas mileage (less contact area, and therefore friction) or if you are hauling heavy loads.No. I mean it's possible with some tires, but when the max PSI is 51, and I'm at 40, and I'm experiencing even wear....I am not reducing the contact patch one bit. My Impreza had camber plates and bolts, struts and springs, and the huge sway bars and end links. I had Falken 451's on there with 38 front/42 rear, with max negative camber up front (talk about reducing contact patch, if only while going straight!) and -1.5 rear, and driving 15 miles of canyon to go to work daily I was still experiencing shoulder wear on the tires.
They go in a straight line. Throw a curve in the drag strip, and you'd see them madly pumping up tire pressure.
10lbs below max tire pressure is no where near 'about to burst'. The recommended door pressure is, however, near 'about to slide off the rim'.
Let's just consider this argument beat to death and leave it as-is. Most of us think one way, and you think the other. So be it.
thecrash91
Member
- :
- 2003.5 Mazdaspeed Protege
temperature in fact DOES affect air density. if you have a tire with 32 psi that you just filled in 80 degree weather, and take it into a meat fridge at 20 degrees the tire will seem to be filled with less air and the psi will decrease, because the air becomes more dense. you cannot beat physics buddy, it is explained here
http://en.wikipedia.org/wiki/Ideal_gas_law
http://en.wikipedia.org/wiki/Density_of_air#Effects_of_temperature_and_pressure
if you do not understand the equation on the second link then dont even attempt to challenge physics again. people honestly need to educate themselves before opening their yapp.
Larger volume tires can use far less pressure.
Up to a point, yes, it does. Too high, and you will diminish handling.
If you drive 'spiritedly', you are under 'heavy loads', exceeding the capacity of the door recommendation.
It just blows my mind that someone (not you specifically) would admit that pressures need to be tweaked by the lap on the track, with pressures no where near the door recommendation, then step off the track as if into some alternate universe in which different rules of physics apply, and use the door recommendation.
jaguarMKIX
Member
Actually, I am an engineering student, and I do not need Wikipedia to tell me that temperature has an effect on the energy of air molecules. In fact, I said in my first post that temperature has an effect.
What you said was, "whats 34 psi in colorado is NOT 34 psi in california."
That is what you posted and what I commented on.
34psi is always 34psi. psi is a measurement of pressure, just like torr, pascals, at and bar. You need less moles of air to fill that same tire up in California if the temperature is higher. If you want 248207Pa of pressure in your tires when the temperature is 273.15K (32F) outside and the "tire" or what have you, has a volume of 1 cubic meter you need 109.3 moles of gas. If the temperature is 308.15K (95F) outside then you need 96.9 moles of gas. Therefore, you need less moles of gas in California if the temperature is higher. That is without taking into account water vapor and condensation.
That second equation was a joke, try deriving the Schrdinger equation for a single particle in three dimensions.
thecrash91
Member
- :
- 2003.5 Mazdaspeed Protege
ok, i dont think you understood what i was saying then, i meant if you filled a tire in california to 34psi and took it to colorado it would change. thats what i meant. i see why it could be mistaken
