tech
Air Down
Basics
Anyone who has
been off-roading more than a few times understands the
reasons to "air-down". If you don't know why then read
on.
Airing Down
allows your vehicle's tires to conform and actually grip
rough off road surfaces while increasing the tire's contact
patch. The softer tires will also absorb bumps to make
your off road ride a bit more comfortable.
What's a "contact
patch"?
The tire contact patch is the actual surface of
the tire that meets the ground. This is
effectively the surface that provides the
traction to move the vehicle. Below is a
representation of the differences of the contact
patch relative to tire pressure. Vehicle
weight and tire stiffness will affect the patch.
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A common sound
before a trail run is the hissing of tires being deflated.
There are several quick deflator and auto deflator products
out there to help with the burden of airing down.
See QuickAir
Deflator from Sun Performance Review
See Oasis Off
Road Mfg. Automatic Tire Deflators Review
It is true that
you may loose a bit of ground clearance when aired down but
the benefits far outweigh the sacrifice. Perhaps a
good excuse for larger tires?
How low should you
go?
The following table can be
used as an initial basis for airing down your tires. Rim
width, tire construction, and weight distribution may
necessitate the need for adjustments. The pressures (psi)
in this table are applicable for most forms of four-wheeling
(up to 20 mph).
Tire
Size |
Gross
Vehicle Weight |
2000
lbs. |
3000
lbs. |
4000
lbs. |
5000
lbs. |
6000
lbs. |
7000
lbs. |
8000
lbs. |
215/75R15 |
11 |
13 |
15 |
N/R |
N/R |
N/R |
N/R |
235/75R15 |
10 |
12 |
14 |
16 |
N/R |
N/R |
N/R |
29x8.5R15 |
10.5 |
12.5 |
14.5 |
15.5 |
N/R |
N/R |
N/R |
30x9.5xR15 |
9 |
10 |
12 |
14 |
16 |
N/R |
N/R |
31x10.5R15 |
8 |
9 |
10 |
12 |
14 |
16 |
N/R |
32x11.5R15 |
7.5 |
8.5 |
9.5 |
11 |
13 |
15 |
18 |
33x9.5R15 |
9 |
10 |
12 |
14 |
16 |
N/R |
N/R |
33x12.5R15 |
7 |
8 |
9 |
10 |
12 |
14 |
16 |
35x12.5R15 |
6 |
7 |
8 |
9 |
10 |
12 |
14 |
36x14.5R15 |
5 |
6 |
7 |
8 |
9 |
10 |
12 |
38x15.5R15 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
225/75R16 |
11 |
13 |
15 |
N/R |
N/R |
N/R |
N/R |
245/75R16 |
10 |
12 |
14 |
16 |
N/R |
N/R |
N/R |
265/75R16 |
9 |
10 |
12 |
14 |
16 |
N/R |
N/R |
285/75R16 |
8 |
9 |
10 |
12 |
14 |
16 |
N/R |
295/75R16 |
7 |
8 |
9 |
10 |
12 |
14 |
16 |
N/R =
Not Recommended |
After a day on
the trail with your tires deflated it comes time to go home
and re-inflate. There are several ways to accomplish
this. See Air Up Basics.
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