what is the correct pressure for 255/30 ZR 21 tyres on a 21 inch breyton rims?

Answer 1

It should be on the tire itself

Answer 2

First point:
You should be very proud of yourself that you even care about this! Far too many people don't understand the benefits and liabilities of incorrect tire pressure. Nice work!

Second point:
Do NOT inflate your tires to what is listed on the sidewall! That number is the maximum pressure to which you should inflate the tire while seating the bead, not the one that is most appropriate for your vehicle.

Third point:
JasonP makes a good point about over- and under- inflation, and using the wear of the tire to judge where you need to be. However, there are two main criteria that the T&RA (Tire & Rim Association) use to specify the minimum inflation pressure for a given size.
1) Load
To calculate the correct minimum pressure, you need to figure out what the maximum load will be for one corner of your vehicle. This can be done a multitude of ways, but the easiest (albeit most conservative) is to use the GAWR (Gross Axle Weight Rating) for each axle and divide by two. You can find this information on the sticker on the driver's door jamb.
2) Speed
This one is pretty easy. What is the max speed you expect to drive? (be honest.....if you sometimes hit 90 on the highway, use 90. An under-inflated tire can overheat and fail. [Ford Explorer/Firestone, anyone?])

Using these two pieces of information, anyone with access to a recent T&RA handbook can give you what the minimum acceptable pressure is. (Call around to a few good tire shops... they should have that information. If not, try calling The Tire Rack.) After you find the minimum acceptable pressure, you can use the "wear method" to determine how much more you should add for your particular circumstance.

Since a 30-series 21" rim is not standard fitment for any current production vehicle, you should also check to see if the tire is "Extra Load" rated. This means that less air pressure is needed for the same load/speed combination. Some tire manufacturers (especially the good ones) add this rating so that you don't have to pump up your tires to 45psi just to be safe!

I hope this helps!

Answer 3

The sidewall pressure reading is the maximum tire pressure for seating the bead when mounting. Not for driving. Personally I run around 32 psi, and then when I do an oil change and tire rotation I physically check the tire for irregular wear due to tire inflation. If the center is more worn out the tire is over inflated, if the side lugs are more worn the tire is under inflated. I then check and adjust the tire pressure. I do have to warn you that you do need to check your tire pressure when the tire is cold or run less than 5 miles. When a tire is under inflated it will build up more heat and effectively raise the pressure in the tire, in a sense giving a false reading. There is a precise balance and sometimes its hard to find. But when you do your tires will last longer and have better grip all around.

Answer 4

Read the sidewall of the tire fro the manufacturers recommended inflation pressure. It is required to be there by federal law.

Answer 5

Check specifications in the car's owners manual. If these are aftermarket rims, check tires' sidewalls for manufactures recommendations. OR, go back to where you purchases these rims/tires and ask them.

Answer 6

The short answer is whatever your car specifies is what you should use. When you open your door there should be a sticker that tells you or you can look in your owners manual. Don't use the number on the tire.

Answer 7

Exactly 32 lbs