Yes, how much psi do I need in the 18" wheels? Right now there is 30, but should it be higher???

Thanks!

 

Your owner's manual covers this. 30PSI seems way too low. The 17" wheels take from 38-41PSI depending on conditions.

 

30 PSI is not "way too low", just a bit lower than recommended. Keep them in the mid-30's and you'll be fine. Tune up or down depending on ride and handling preferences.

 

Again, 30PSI is way too low. 8PSI lower than the lowest recommended pressure for the 18" wheels per the MINI owners manual.

If you are running at >100MPH or running the MINI loaded weight wise, than the pressure should be 41PSI by the manual.

By running 8PSI below the recommended pressure you run the risk of a blowout. Read you MINI owner's manual. It starts on page 88 in my manual.

 

Have you checked the manufacturers web site for their guidelines ? What does the info tag on the door post say ?

 

LOL, a blowout? Come on man, be reasonable here; running 30 PSI is not going to cause a blowout. Top Fuel dragsters run ~4 PSI in their huge flexible slicks and they go over 330 MPH. The owners manual, while very helpful, is hardly the be-all end-all of automotive knowledge.

 

[quote=Cooptime;2159323]How much air pressure in 18' tires??? quote]

Those are mighty big tires. They might rub.
I'd go with 34 psi for the smaller 18" ones.

 

Ryephile - Do not miss inform the masses based on your personal opinion.

Top fuel dragsters tires and Mini Cooper tires are not comparable.

Underinflated tires and overloaded vehicles are the leading causes of tire failure.

The above two statements are undisputed.

Refer to your printed label(s) inside your driver’s side door frame or owner’s manual for tire pressure information.

If you have anymore questions, refer to www.safercar.gov

 

If you look at the sticker on the drivers side door jam of the car it states 33. . .

 

For the 18" wheel you need to check and see what the spped rating is on the tire. V is 33 and 38. W is 38 and 41.

 

You need to back down and recognize how idiotic your statements are. My personal opinion happens to coincide with the factory recommendations, as you just wrote:

You only need to run high pressures if you plan on breaking the law and speeding. Surely someone like you that follows strict procedure and rules wouldn't do such a thing?

30 PSI is not grossly underinflated as you would prefer people believe as you spread your fear tactics. An Explorer running 30 PSI is not going to spontaneously combust in a violent pile of underinflated stupidity. Running less than 25 PSI, that might be up for actual debate, and 20 PSI is generally going to be regarded as too low.

The world is not black and white. Get a grip and try to understand that we're not all running our cars with 8 people in them with our tires at 22 PSI driving at 150 MPH. Obviously that would be ill advised.

 

Haha...thanks! Yeah, I wanted really big rims haha.

The reason I couldn't check the door is that the car came with 16"-ers. So, therefore it only suggests for that size. I bought the 18" later.

 

Thanks guys!

I'll check the manual. I only asked b/c my car came with 16s and I got some 18s. The sticker in the door was for the 16s, so I wasnt sure. I didnt think to check the manual. I'll get right to it.

 

Again, just your opinion.

 

I agree with Rye in this debate. I run 31 PSI front and 33 PSI rear on the track for traction purposes. On the street I generally run 1-2 PSI higher because the tires don't get quite as hot. The owners manual isn't about performance, handling, or anything else, it's about 99% of the drivers out there that drive at 70 mph in the slow lane. It should also be noted that the tire pressures recommended in the owners manual apply to OEM Runflats, not to EVERY SINGLE TIRE MADE.

It's common practice on the track to fiddle around with tire pressure to get the back end to rotate around corners better.

On the track if you pump your tires up to 41 PSI cold expect them to top 50 PSI by the time they warm up. That's exceeding most manufacturers recommended maximum tire pressure (Which you should NEVER even get close to... And REALLY the only way you're going to see a blow out in a tire with good thread).

Here's an example of what various pressures do to the tire:



The tire on the left is GROSSLY under-inflated. Under 20 PSI total pressure. Notice the tire has minimal tread contact with the ground do to inadequate pressure. A tire in this state could potentially unbead from the rim, causing a sudden loss in pressure and/or traction. Steering feel will be sloppy, with very mushy turn-in.

The tire in the middle is GROSSLY over-inflated. Over 42 PSI total pressure. Notice the tire's sides aren't even touching the ground because the tire is ballooned out with the pressure. A tire in this state is prone to blowouts from heavy jars (Potholes) and will handle horribly because the sidewall isn't actually contacting the ground. Picture your car on the road, and rather than the tire keeping the car upright, the car will roll on an arc during turns (Ever seen a motorcycle tire? it's shaped like that for a reason, car's don't need to lean into turns though ).

The tire on the far right is perfectly inflated. Between 29 and 36 PSI total pressure. Notice the sidewalls are in contact with the ground, the center of the tire is in contact with the ground, the sides aren't bulging out. This is optimum for safety and handling, and will be most resistant to uneven road surfaces, etc.

Where you set your tire pressure is largely a function of what you're using your car for. If all you do is drive on the freeway, and couldn't care less about a bit of extra traction. Say you drive in the rain a lot, and your car never really sees twisty roads. Your tire pressure should probably be around 34-36 psi.

If you enjoy twisty roads and think you want to push the car a little more around the corners, set your pressure to 32 front and 34 rear.

If you don't think 2-4 psi of pressure makes a difference ask anyone who races. 1-2 PSI of tire pressure in the front or back can mean the difference between coming in first and coming in 5th.

If you don't know what you're talking about, please just don't comment...there's enough grossly inaccurate information floating around these forums. We don't need people thinking their car is going to spontaneously combust because they're running 2 PSI lower pressure than people doing 140 MPH on a track pulling 1.2 g's are .

Happy motoring, hope this helps.

 

An increase in tire pressure, due to temperature changes, will not be seen in a nitrogen filled tire.

If you are running a lower tire pressure they will heat up faster. That is what typically causes a blowout at freeway speeds.

Also, running a lower tire pressure will adversely affect your fuel economy.

 

My door sticker (2003) lists 11 different tires (5 different sizes) with a
table showing which pressures for which tires under different loads.
Except for the tiny spare, the pressure recommendations are
remarkably similar for the regular street tires across the range.

 

Do you run two tire valves? Last I checked even at ambient air pressure (1 atmosphere, 0 psi of inflation) there is still oxygen in the air. The only way to do what race teams do with nitrogen is to have a purge valve open while filling the tire with nitrogen. The Costco BS doesn't do anything, it's a sales gimmick, nothing more. The only real benefit of using pure nitrogen is the fact that it's a "Dry, Inert" gas. Water vapor in normal air (Which is 78% nitrogen last I checked) causes that air to expand, which in turn, raises pressure. The systems that places like Costco use cannot ensure that water vapor won't get into the tire, because they're not designed with that in mind. This is something that race teams spend millions on to shave off 1/4 of a second, and has no actual bearing on the street.

And yes, lower pressures will cause higher temperatures, because the whole tire is touching the road now! What a concept. I've personally gotten my street tires up to 180 degrees + on the track, on R-Compounds they've seen 230-250. If you're seeing those kinds of temperatures on the street I must be missing something, because even at speeds far in excess of the legal limit the tires rarely get above 130. It's hard cornering and braking (Working the tire at it's limits of adhesion), not sustained speed that cause tires to heat up. Heat is directly proportionate to friction. There's a LOT less friction rolling down the highway at 100 MPH than there is taking a corner at 30.

As for gas milage, this isn't about gas milage, but of course pumping tire pressures up is going to increase gas milage, look at the diagram, at 40 PSI only about 60% of your tire is actually in contact with the ground, i'd say that reduces rolling resistance just a bit. At 60 PSI it would be even less! Lets run that in our cars!

Tires blow out because the tread is worn down to the cords and people are too idiotic to replace them, or because they're so overinflated that they exceed the tire manufacturers recommended maximum inflation specifications, and catastrophically fail when someone hits an uneven road surface (exceeds maximum design limits for pressure on the tire's sidewalls, which are made out of nylon in most cases).

Look up the leading causes of tire blowouts. According to the NHTSA the majority of tire failures are first caused by inadequate tread (Driving your tire when the steel belt is exposed and you're not actually driving on any rubber) or drivers hitting a curb or other irregularity in the road that puts an undue amount of stress on the tire.

As I said, unless you actually have something factual (Based in science rather than speculation), don't post, all you're doing is confusing people and stirring up unneeded drama. Your total contribution to this thread has been based on anecdotal data you read in the owners manual (Which probably recommends tire pressures to promote more even tire wear, and doesn't have a thing to do with safety) and media hype. There is no actual scientific basis for any of the claims you've made. Running 30 PSI of pressure isn't going to do anything other than make the car handle better.

 

Again, just stick to the actual facts versus your opinions. That is what misleads people. www.safercar.gov

 

Threads merged.

 

Almost every example on there refers to high profile SUV or light truck tires rated at R or S (106 or 112 MPH) . Not low profile performance tires (Does anyone have tires rated at less than H on their car (130 MPH)? Most of our cars are at least V Speed rated (149 MPH). Mine are rated to W - 168 MPH ).

I'm most certainly using actual facts. I don't know how much more extreme of a load tires can take, I race my freakin car. One lap around the track and my tires see more heat and load than an entire week in your car on the street. There simply isn't any basis in fact that running tires 2 PSI lower than is typically recommended (For handling and traction purposes) would have any averse effect on tire durability.

If you're telling me that by running tire pressures at 30 PSI it's placing so much load on the tire that it's going to fail from going over temperature (75 mph on the freeway at 32 PSI is somehow equal to 149 MPH at 36 PSI? Please...) you're simply wrong. At 41 PSI cold inflation, if you drove even close to aggressive you'd be exceeding the maximum inflation pressures for almost every tire out there, not to mention you'd only have about 50% of the tire's surface in contact with the road at 48-50 PSI.

I'd much rather have my tires running a little on the warm side and lose 1-2 mpg than have my car go out of control at 90 MPH because I don't have enough tread in contact with the road . Have you ever been going 150 MPH and turned your steering wheel to find that nothing happens? It's pretty scary .

There are enough forces working against cars at speed (Lack of downforce?) I don't need to make my steering any lighter by creating a bubble of air between the surface of the road and my tires.

 

Not true - nitrogen expands with temperature exactly like any other gas. Regular old "air" is 80% nitrogen anyway, so even if nitrogen didn't expand with temperature, the difference from replacing that last 20% with nitrogen wouldn't be that great anyway.

There *is* a theoretical advantage to using "dry" gas (nitrogen or otherwise) to fill your tires, because the water vapour in regular moist air will flash to steam and increase your tire pressure beyond the normal thermal increase if the tire gets hot enough.

For a street-driven car, it's a non-issue, because the temperature *inside the tire* would have to get up to about ~300 °F for the water vapour to turn into steam.

 

False, unless you've decided to discard the laws of physics

True, however [as rustyboy155 accurately states] at highway speeds and cornering forces you will not reach temperatures anywhere near what us experienced racers see on the roadcourse. Your statement is only applicable to grossly under-inflated tires, which is not 30 PSI as you would like to scare people into believing. You obviously lack experience in tire extremes and have little physical understanding how tires get heated up in performance driving.

You are definitely misleading everyone out there driving run-on-flat tires. They are engineered to be run at 0 PSI at highway speeds for long periods of time, despite what their recommended guidelines are.

Again, only if your tires are grossly underinflated. We're not talking 30 PSI, or even 28. Grossly underinflated, as rustyboy155 accurately depicts, is about under 20 PSI. Obviously this will depend on tire compound and construction.

Final Thoughts: You clearly have your head in the sand regarding this topic and are unwilling to entertain more experienced persons here. You obviously haven't driven your cars hard enough, and then measured your tire pressures, to understand the huge difference between cold and hot pressures. When we offer basic pressure advice it's assumed to be cold pressure. When we're talking race pressures it's assumed to be hot pressures.