AgentUnkind

Ok, shoot me, but I tried searching and couldn't come up with an answer. Whats a good PSI to inflate your tires to for normal driving, day to day driving in the 7, Im using it as a DD right now until i can afford to fix the beater or get a new one. The tires on the 7 are Ventus Hankook HRII 245/40 ZR 18. So any info is appreciated.

Alex

rotorsownyou7

It should say on the side of the tire.

DamonB

No, that's the MAXIMUM pressure the tire can be safely run at.

The correct pressure will be listed on the sticker in the driver's door jamb. On just about every car I've ever been in I like the tires a few pounds higher than what's posted but that's just personal taste.

If the tire is non-stock in size and wider your pressure will still end up about the same as what's posted on the car unless you go really crazy with wheel width. The volume of air in the tire is what supports the car and a wider, lower profile tire still holds roughly the same amount as a narrower, higher profile tire.

Try 28 psi.

snub disphenoid

Yeah, I maintain 30psi at all corners. For autocross I jack it up to about 38psi front and 42psi rear.

rynberg

It's amazing that basic car care facts like tire pressure are not common knowledge....

For autocross I jack it up to about 38psi front and 42psi rear.

If those are cold pressures, that's a really, really bad idea.

FDjunkie

The 'correct' tire pressure (for any car) is a function of the tire's width and its aspect ratio, wheel width, offset, and diameter, plus the suspension type (and any changes like ride height), current alignment settings, position on vehicle (front vs rear, etc) intended use, driving style, and so on. For any meaningful suggestions you need to provide more of these details.

However, you might also consider just buying a tread-depth gauge and using it to regularly check tire wear. By recording the readings from each tire and comparing them over time you can make informed decisions on the ‘best’ tire pressure for your application.

Sgtblue

iTrader: (16)

FWIW, I'm running stock size BFG KDWs on pretty stiff coilovers. During warm weather and around town I run 28 psi. For me, this seems to be the optimum pressure for handling and comfort and I haven't noticed any abnormal or uneven wear.

DamonB

I think you're confused. Please explain to me:

How does wheel width effect tire pressure?

How does wheel offset effect tire pressure?

How does wheel diameter effect tire pressure?

How does suspension type effect tire pressure?

How does ride height effect tire pressure?



The volume of air inside the tire supports the weight of the vehicle. The greater the volume of air inside the tire the lower tire pressure you can run and still hold up the car. When going to much wider tires than stock the pressures do not automatically need to be dropped because most people add the wider tire to a larger diameter wheel, so the volume of air inside is actually about the same as it was before.

All you need to know to come up with tire pressure is tire size, weight of the vehicle and the weight distribution. Anything after that is small changes in pressure for ride quality or larger ones for harsh competition environments. Tire pressures are NEVER on the side of the tire, only the maximum safe pressure. The tire manufacturer has no idea what vehicle you're installing this tire on so he can't tell you what pressure to run. He can tell you that if you inflate the tire past what he recommends that you risk overstressing it's internal structure and overheating the tire possibly causing catastrophic failure. That's also why there are many different load rating of tire available. You wouldn't expect a tire from a Camaro to survive under a loaded full size pickup even if they are the same size. The truck's tires are rated for increased load.

9 times out of 10 the stock tire pressure setting will be in the ballpark unless you've done something nuts like add 4x4 mudders.

Some good reading from our sponser Tire Rack:

http://www.tirerack.com/tires/tirete...l/pressure.jsp

http://www.tirerack.com/tires/tirete...vs_dryperf.jsp

http://www.tirerack.com/tires/tirete...vs_wetperf.jsp

http://www.tirerack.com/tires/tirete...k_pressure.jsp

http://www.tirerack.com/tires/tirete...l/sidewall.jsp

http://www.tirerack.com/tires/tirete...eral/speed.jsp

FDjunkie

DamonB, I agree with everything you say. But my point was only all the items listed can and will affect how the tire interacts with the road, and therefor what tire pressure might be a good starting point. And since AgentUnkind had already stated that he has non-stock tires, it seemed reasoanble to ask about other changes. Such changes seem very common for many that post here.

For example, we've probably all seen cars with wide tires on narrow rims that have resulted in quickly wearing out of the center tread area, or forced the owner to use a lower tire pressure.

DamonB

Wide tires on a too narrow wheel is not an air pressure problem. It's a fundamental problem of mounting the tire to an improper wheel.

I still would like to hear examples of how ride height, wheel offset and suspension type effect tire pressure.

connor@tirerack

I have to agree with Damonb. A tire's width and its aspect ratio, wheel width, offset, and diameter, plus the suspension type (and any changes like ride height), current alignment settings have nothing do do with a tire's needed air pressure. However it is true that the position on vehicle (front vs rear, etc), intended use can factor into how the tires required air pressure. Most manufacturers require a different air pressure in the front and rear due to how wieght is distributed in the vehicle. If you are racing the vehicle then you would want to adjust your air pressure to suit the type of track you are driving on. When you are done on the track you should adjust the air pressure back to the recommended air pressure for the street.

Mazda's recommended cold PSI is listed below for your review.
1985 and prior RX7 -- 27 psi front and rear
1986 to 1995 -- 32 psi front and rear

I am not saying you have to run at these PSI listings. Most people tend to have preferences and run a little higher or lower as DamonB posted. This is simply what Mazda states they recommend you use in the tire for ride quality and handling reasons. Keep in mind that running a tire at lower than recommended air pressure can cause load capacity issues and can cause the tire to fail when driving. I would suggest that you run at a minimum of what Mazda recomends.

WorldPax

There's nothing wrong with that. Especially if you're bleeding them back down after every run as you should be.