Tire Inflation FAQ

[midnightfxgt]

Hey Guys,

There have been many questions with regards to Summer/Winter wheel and tire setups, and their tire pressures lately. Hopefully this can end a lot of the repetitive threads, and shed some light on the subject.

1. What should my tire pressure be set to?

A. Your tire pressure should be set to the specifications listed on your door placard, or in your owner's manual. This is reinforced by recommendations from top tire manufacturers, such as Goodyear: http://www.goodyear.eu/home_en/tire-advice/faq/tire-inflation.jsp

Every vehicle model is different. Weight, handling characteristics etc all come into play. Lots of research and design is taken into consideration when a manufacturer makes a recommendation.

2. What should my Winter/Summer tires be set to?

A. Same as above. Manufacturers specifications are the best bet for most drivers.

3. What is MAX Pressure, and should I inflate to that?

A. Max pressure is the maximum pressure that the tire can hold. Should the Max Pressure read 50PSI, and you decide to fill the tire to this pressure, you can run into issues once the tire warms up. During the normal operation of a tire, the air inside will heat up.

4. When should I inflate my tires?

A. Tires should be inflated when "cold". This means when the car has been driven less than a mile, or has sat for longer than one hour.

5. Can I run more/less air in my tires?

A. Yes. You can run whatever pressure you would like. Many experienced drivers prefer to inflate/deflate tires 1-2PSI from the Manufacturer recommended specs. Lower pressure generally means more traction, while higher pressure can be slightly beneficial to fuel mileage. For example, I run an extremely small sidewall (25series on a Mazda3), and inflate my tires to 34PSI to help prevent damage from potholes to my rims.

6. Can I inflate as high as possible for better mileage?

A. Some people have recommended very high (40-50PSI) pressures to obtain the best fuel mileage. While fuel mileage may go up, the increased mileage would not be very large. When inflating this high you can also loose out on traction, prematurely wear tires, and void your tire's warranty. For Example, Hankook's Warranty: http://www.hankooktire.ca/Serv/Warranty.aspx?pageNum=3&subNum=2&ChildNum=1



NOTE: While inflating tires drastically over/under the manufacturer's recommendations has been done many times, and will be said by some to be superior, a good general rule of thumb is: If you have to ask about tire pressure, your best to stick with tire and auto manufacturer's recommendations. They are there for a reason.

-John

[midnightfxgt]

If anyone has tire inflation questions, they could post them here, and I can update the FAQ as needed :)

I am trying to be as unbiased and factual as possible.

[pwdunmore]

Sticky? might end a lot repeated tire questions threads

[cwp_sedan]

Sticky? might end a lot repeated tire questions threads

Already done!

[JHX 1138]

I've got a tire inflation question. To check tire pressure at home on my Mz3 I bought a Michelin digital tire pressure gauge from Crappy Tire. $15, on sale from $30.
But the damn thing won't lock onto the valve of my tires! I can usually get a reading from my FR tire after 5-6 attempts but I remember spending 5 minutes trying to get a read from my FL tire but I couldn't. Meanwhile the gas station air pump has no problems locking onto the valve and filling it up with air. BUT the air pump at PetroCan is from the 1950's since it uses a "stem" gauge and it's impossible to figure out where "32" is since the markings are rubbed out!

Are all the CT gauges crappy like that or are any of them good?

I feel like I need a good home tire pressure gauge because all the gas stations REMOVED the nice digital air pumps they used to have 1-2 years ago...

[Hyperion]

You get what you pay for, but my $5 gift basket one is working awesomely.
You probably aren't pressing straight down and hard enough.

[peterm15]

I've got a tire inflation question. To check tire pressure at home on my Mz3 I bought a Michelin digital tire pressure gauge from Crappy Tire. $15, on sale from $30.
But the damn thing won't lock onto the valve of my tires! I can usually get a reading from my FR tire after 5-6 attempts but I remember spending 5 minutes trying to get a read from my FL tire but I couldn't. Meanwhile the gas station air pump has no problems locking onto the valve and filling it up with air. BUT the air pump at PetroCan is from the 1950's since it uses a "stem" gauge and it's impossible to figure out where "32" is since the markings are rubbed out!

Are all the CT gauges crappy like that or are any of them good?

I feel like I need a good home tire pressure gauge because all the gas stations REMOVED the nice digital air pumps they used to have 1-2 years ago...

There is rubber on the top of the gauge. The part that connects to the valve stem. Tear it off. Its only for looks.

[aris]

Nice write up John

[JHX 1138]

There is rubber on the top of the gauge. The part that connects to the valve stem. Tear it off. Its only for looks.

nope...

i actually had an Accutire gauge i bought 5 years ago for the acura, that always worked well, but i gave it to a friend. CT doesn't seem to sell that brand anymore.
and yes i do push pretty hard on the stem, lol

[trulankan]

I've got a tire inflation question. To check tire pressure at home on my Mz3 I bought a Michelin digital tire pressure gauge from Crappy Tire. $15, on sale from $30.
But the damn thing won't lock onto the valve of my tires! I can usually get a reading from my FR tire after 5-6 attempts but I remember spending 5 minutes trying to get a read from my FL tire but I couldn't. Meanwhile the gas station air pump has no problems locking onto the valve and filling it up with air. BUT the air pump at PetroCan is from the 1950's since it uses a "stem" gauge and it's impossible to figure out where "32" is since the markings are rubbed out!

Are all the CT gauges crappy like that or are any of them good?

I feel like I need a good home tire pressure gauge because all the gas stations REMOVED the nice digital air pumps they used to have 1-2 years ago...

the one I got is branded "Slime" and it seems to work well once it is locked in. Only thing I've noticed is the reading differs from what my digital air compressors says by about 1-2 PSI

[midnightfxgt]

Yeah, pressure gauges can vary a pound or two. I like to try a couple of diff digital ones and see if they are close to eachother.

[Olestra]

I've got a tire inflation question. To check tire pressure at home on my Mz3 I bought a Michelin digital tire pressure gauge from Crappy Tire. $15, on sale from $30.
But the damn thing won't lock onto the valve of my tires! I can usually get a reading from my FR tire after 5-6 attempts but I remember spending 5 minutes trying to get a read from my FL tire but I couldn't. Meanwhile the gas station air pump has no problems locking onto the valve and filling it up with air. BUT the air pump at PetroCan is from the 1950's since it uses a "stem" gauge and it's impossible to figure out where "32" is since the markings are rubbed out!

Are all the CT gauges crappy like that or are any of them good?

I feel like I need a good home tire pressure gauge because all the gas stations REMOVED the nice digital air pumps they used to have 1-2 years ago...

I would not trust those gas station tire gauges. Who knows if they are calibrated and how people treat them.
I'm sure people just throw the end of the hose on the ground after use which may knock the gauge out of calibration.

For gauges, I've tried digital before and returned it immediately. I couldn't read the screen in -20 weather.
Can't beat those $10 mechanical pencil gauges. Those are the only ones I trust.

[Gen1GT]

Old thread, but I thought I’d contribute. Often times “tuners” will plus size their wheel/tire package. We often think jumping from a 225 or 235 tire from our stock 205 tire will result in a larger contact patch, but this isn’t the case. Tire construction plays a small part, but contact patch is entirely dictated by vehicle weight and tire pressure. We can use the following formula to calculate contact patch:

Area = Weight / Pressure

Using an example, let’s say your vehicle weighs 3000 lbs, and your tires are at 32 PSI

Area (in²) = 3000 lbs / 32 psi
Area = 94 in²

Divide that by 4 tires, and each tire has 23.5 square inches of contact area. The size of your tire makes no difference. Each tire will require 23.5 in² to hold your vehicle off the ground, and it doesn’t matter if you have 195/70/15’s, or 235/35/18’s.

Consider that the plackard on your door with the tire pressure recommendation is for fuel economy just as much as handling. Most manufacturers would not sacrifice the poor ride that results from 35 PSI if they could get away with 30 PSI. If you want a larger contact patch, try experimenting with tire pressure. You may actually see improved handling with LOWER tire pressure. There could be a compromise with steering sharpness, and this is entirely dependent on tire quality. A high quality tire could have sharper handling at 30 PSI than a budget tire can at 40 PSI. Also, high performance tires can handle the heat generated from running 30 PSI instead of 35 PSI, so often when you plus size a tire, you’re putting on better tires anyway. Lower pressure means more sidewall deflection, but a good tire can handle the heat.

But don’t get caught in the false dichotomy between tire pressure and handling. F1 cars run less than 25 PSI in their tires, and they have tall-ass sidewalls to boot. Also consider drag cars who run 10 PSI or less. This is to get a ginourmous contact patch. They handle like ass, but tonnes of grip.

[midnightfxgt]

Tire width is a factor. 110%

[Kiyomi]

Old thread, but I thought I’d contribute. Often times “tuners” will plus size their wheel/tire package. We often think jumping from a 225 or 235 tire from our stock 205 tire will result in a larger contact patch, but this isn’t the case. Tire construction plays a small part, but contact patch is entirely dictated by vehicle weight and tire pressure. We can use the following formula to calculate contact patch:

Area = Weight / Pressure

Using an example, let’s say your vehicle weighs 3000 lbs, and your tires are at 32 PSI

Area (in²) = 3000 lbs / 32 psi
Area = 94 in²

Divide that by 4 tires, and each tire has 23.5 square inches of contact area. The size of your tire makes no difference. Each tire will require 23.5 in² to hold your vehicle off the ground, and it doesn’t matter if you have 195/70/15’s, or 235/35/18’s.

Consider that the plackard on your door with the tire pressure recommendation is for fuel economy just as much as handling. Most manufacturers would not sacrifice the poor ride that results from 35 PSI if they could get away with 30 PSI. If you want a larger contact patch, try experimenting with tire pressure. You may actually see improved handling with LOWER tire pressure. There could be a compromise with steering sharpness, and this is entirely dependent on tire quality. A high quality tire could have sharper handling at 30 PSI than a budget tire can at 40 PSI. Also, high performance tires can handle the heat generated from running 30 PSI instead of 35 PSI, so often when you plus size a tire, you’re putting on better tires anyway. Lower pressure means more sidewall deflection, but a good tire can handle the heat.

But don’t get caught in the false dichotomy between tire pressure and handling. F1 cars run less than 25 PSI in their tires, and they have tall-ass sidewalls to boot. Also consider drag cars who run 10 PSI or less. This is to get a ginourmous contact patch. They handle like ass, but tonnes of grip.

tire width matters. so does the compound of the tire, just as much as proper tire pressure. your saying that a tire width 195 vs a 235 with the same pressure will have the same handling? go try that out at the track and get back to me on that. well actually, that wouldnt be a good representation because you would be faster with the wider tire due to added braking ability and stability even with the added drag. more like test the g's on corners. have you seen how wide and big drag cars run and their compound. how fn wide are those tires? like 400+.. same for the f1 cars, they have so much downforce they dont need to go wider with the slicks they have, not because of tire pressure.... you even said that sidewall matters, that is part of the size of a tire.

your calculation is for a static situation where no cornering is happening. now what happens when you turn. most of that weight and pressure goes to the outside wheels. a 195 vs a 235 will not provide the same traction in a corner just because they are inflated the same. by your reasoning, going to extremes, a 275 tire will corner the same as a 205 and a cars corner speed will not be affected if the tire pressure is the same. if that were true, you would want to run the smallest tire possible to save weight and reduce rotational mass.

[midnightfxgt]

By your "theory"... double the load on a tire would create double the contact patch. Thats just wrong.

Think of a Mazda3 on a 275, and on a donut, both inflated to 32PSI. The contact patch is nowhere near the same.


http://www.enginebasics.com/Chassis%20Tuning/Tire%20Contact%20Patch.html

[Destarah]

Given that this is a sticky thread, I though it prudent to necro it and back up Gen1GT ... fact is he is correct, the area of the contact patch does not change just because the tire gets wider. The contact patch gets wider, but it gets shorter at the same time (front to back as it were). The link to carbibles.com in the "Wheel/Tire FAQ - update" sticky goes into great detail. Please check it out if you still are skeptical.

Dan

[Destarah]

Sorry, I should have included a link to the reference I made ... here it is tyre_bible_pg3 (http://www.carbibles.com/tyre_bible_pg3.html)