Aftermarket
Accessories, Part III: Tired of Your Tires?
Or, One Thing Leads to Another!
by Bill
Burke
 In
the last two articles about accessories, I talked about
having the proper recovery equipment and winches. There are
several different ways to go from here--tires, suspensions,
lockers, body lifts, body protection and interior
refinements et al. Things like CB radios, first aid kits,
fire extinguishers, gas cans, spare tires, tools and spare
parts also have their place in the accessory
line-up.
The most common
improvement seen as an aftermarket accessory is the tire.
Right off the showroom floor, we see that the average tire
installed on the vehicle by the manufacturer is usually a
"P" (passenger) rated tire. Yes they usually put a passenger
car rated tire on your 4WD rig. Understand that the most
amount of driving for any SUV is on the pavement and the
manufacturers aim toward that end with the initial setup of
the vehicle, hence the very large aftermarket accessory
availability. Not all SUV's come with "P" rated tires;
however, some have the "LT" (light truck)
designation.
Changing the tires on your
rig means a significant investment, especially if you want
to go up to a bigger size. It can open a Pandora's box!
Usually, though, adding more ground clearance is the reason
to go to bigger tires, as is gaining better traction. Most
tires on stock vehicles are in the 29" range diameter. On
any trail, you will usually see rig tires in the range of
31" up 35" in diameter. There are bigger tire shod vehicles
out there, but I will stay in the realm of the average 4WD
owner. I will not get into tread design or tire make except
to say that I like an aggressive tread pattern. I have found
them to be good on all terrains, even sand if aired down
enough. It also depends where you spend most of the time
4-wheeling. But, that's another article!
And here is where one
thing leads to another! With bigger tires comes suspension
and gearing related modifications. These affect steering
geometry, power transference from the transmission/transfer
case and driveline angles. Depending on the stock ring and
pinion ratio and the overall final drive ratio that is
already installed, you may be able to get away with going up
a size or two from the stock tire, unless it is already an
option type tire that is in the 31" diameter
range.
To put those 33's or 35's
on, you must modify the suspension and maybe do some body
lifting or fender trimming. You will also have to change the
gear ratio in the axles--the ring and pinion. And while you
are in there, you might as well install those air lockers
you wanted. You can see that, indeed, changing your tires
does open up many possibilities.
Can the wheel bearings,
drive train, axle housing, engine and even the brakes
handle/stop the added mass of bigger tires and wheels? That
poor little 4 cylinder barely gets over Eisenhower tunnel as
it is. Add another couple hundred pounds and it's struggle
city. Now you are thinking about a V-8 conversion! If the
tires and axles are done right, usually the drive train and
power train will handle the extra weight just fine, unless
you have an older rig with lots of miles that has been
ridden hard and put away wet too many times.
You bought that new SUV
and you just got the IRS refund check! It's time for new
tires. You've also been talking to your friends who want to
spend your money real bad. They say that ARB lockers are the
cat's meow. Of course, since you are going to put bigger
tires on, you have to change the ring and pinion and add a
suspension lift. And since you are messing with the
suspension, you might as well do a shackle reverse kit and a
body lift to keep the tires from hitting the fender wells
now that you have all that articulation. STOP! Does it never
end? Well, not really! What about the highway performance
and street ability? Will they be compromised? If you (or the
shop you choose) do a clean and proper installation, then
the vehicle will handle really well on and off highway! So,
you see, it is not as easy as just going out and buying a
new set of tires.
You've picked out a set of
tires and, depending on the size, you must install a
suspension, or you just want to improve the handling
characteristics. Adding a couple of inches lift to your rig
is not out of the realm of possibility. Lifting a rig over 3
or 4 inches gets complicated and must been done with the
proper equipment and engineering, whether or not you are
doing a leaf, coil, independent or mixture. Driveline angle
is the biggest concern and steering geometry the second
biggest. Make sure the caster angle is corrected on the
front end. This helps the steering tires return to
center.
Some lift kits include a
transmission/transfer case "drop" kit to lessen the angle on
the driveline. Otherwise, you will be going through u-joints
prematurely. Some lift kits are not really good suspension
systems. They just lift the vehicle up and don't afford any
better articulation. A good suspension will allow the tires
to flow over the terrain with lots of flexibility. Downward
wheel travel is the key to articulation. It is great that
the tires come up into the fenderwells and the axle bump
stops work, but the real key to suspension travel is how far
down it goes.
Flexibility is another
important aspect of the suspension. When one wheel goes
down, the other wheel (on the most common solid axle set up)
moves up, and the springs must flex and twist to allow for
the added drop rate of the other side. Some suspensions,
like the independent front end style, will allow one wheel
to move independently of the other, hence the name! The
steering is affected by all this movement and must be
strengthened also with a stabilizer, support brackets as
needed, and possibly a steering gear box support.
The shock absorbers or
suspension dampers, must be changed as well. Usually a good
suspension will come as a kit--springs, shocks (dampers),
steering damper (stabilizer), bushings and hardware. A
reputable company will have a matched kit for your specific
vehicle and the type lift you are looking for. Don't cut
yourself short by just trying to get by with one item of the
kit. Save those pennies and get the kit all at
once.
There are also protection
plates for the spring pads, depending on what type
suspension and shock mounts. These plates will keep rocks
from shearing off the heads of any bolts, holding the shocks
or springs in place. Stronger mounting shackles are
available that will hold the springs in place (leaf springs)
better and in proper alignment during all that flexing and
springing taking place on the trail.
A good set of skid plates
or, underbody protection, are a must if you are going to do
any rougher 4-wheeling than dirt roads to the trail head or
fishing spot! Protection for the gas tank,
transmission/transfer case, differentials and or the front
end are a consideration. There are aftermarket protective
bars that will save the side rocker panels and fender
corners. Some 4-wheeling gurus will even cut off the ends of
the bumpers to allow the tires to climb easier over
obstacles instead of having the bumper hit the
rocks.
Tires, suspensions, axle
gears, lockers, nerf bars and skid plates each have a book
full of information alone. I have tried to inform you about
the things needed to upgrade if you really want to go to a
much larger size tire than the stock application. As I said
earlier, to just go up a size or two from the tire that came
with your rig would be alright, as long as that tire was not
already an option or add on. You can usually stay with the
stock rims if they are between 71Ú2 and 8 inches wide. They
will hold a 31/10.50 X15 size tire.
I have mounted a set of
33/12.50 X15 tires on an 8 inch rim. I like the fact that
the sidewalls bulge out and help protect the rims. Usually
when the tire fits the rim flush, the rims get scuffed. On
some trails, rocks or tree roots will catch the rim and bend
it up, releasing air. So, it is alright to have a tire bulge
on the rim somewhat. Don't let the tire store sell you rims
when you may not need them. An experienced tire dealer will
listen to you and know what you are getting at.
Now that you know that
upgrading tires can open a Pandora's box, I hope you have
fun using them. It might not take doing all that
modification to the suspension, etc. if you just want to get
a new set of tires that are a little more aggressive. These
can afford you many miles of off-highway pleasure without
all the "extras" that extensive modification
requires.
©Bill Burke’s 4-Wheeling America LLC
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Bill
Burke's 4-Wheeling America LLC
