5. The center of the mark should hit the tire at the bulge, 3”-4” off the ground (see Figure F or
I). This may be changed by adding or removing Chain Wheel Spacers between the arm and
the Chain Wheel. These Chain Wheel Spacers are 3/8” thick. If the vehicle is an empty truck
that will normally be hauling a lot of weight (i.e. over-the-road hauler, dump truck, or fire
pumper) you will want to try to keep this measurement 3 ½”-4” off the ground because of the
squash in the tires when the vehicle is loaded. For vehicles with 16” tires, this measurement
will need to be between 2 ¾”-3” because the bulge sits lower. The Chain Wheel needs to hit
at the bulge of the tire. NOTE: if you are mounting the chains on a bare chassis this
measurement needs to be 4”-4 ½” off the ground because the weight of the body will drop
the height of the Insta-Chains slightly.
6. Now check to see if the wheel mark is at the centerline of the tire, this is very critical to
ensure the proper throw of the chains. The truck must be on the ground to ensure proper
measurement.There are two methods for accurately finding the centerline:
a. Take a plumb line and hang it from each side of the tire rim. With a piece of chalk,
make a small mark on the tire where the plumb line hits the sidewall. Measure the
distance between these two marks (R in Figure I). Divide this measurement in half
and measure this distance in from one of the plumb line marks (R/2 in Figure I).
Make a small chalk mark at this point. This is the centerline of the tire and axle. For
example, an 11R-22.5 tire has an outside rim measurement of 23 ½”; half of this is
11 ¾”. This means that the centerline is 11 3/4” from one side of the rim.
Now draw vertical line on the tire. The center of the Chain Wheel mark must be lined
up with the centerline of the tire. It may be up to ¼” behind the centerline but NEVER
in front of the centerline.
b. Use a Digital Level placed inside the rim. Place the level on the ground and zero it
out. Then place the level inside the rim and find the center of the tire, this will be the
centerline of the tire/ axle. Hang a plumb line down to make a mark at the bulge of
the tire.
If you have a Universal Mounting Bracket you can adjust the unit so that it hits on centerline
by loosening the two Mounting Tube Flange Bolts and push the unit forward or backward so that
the Chain Wheel hits the center of the tire.
If you have a fixed Mounting Bracket or a 3 Coupling Nut Style bracket, you can try adjusting
this in the two mounting holes where the Chain Unit attaches to the Mounting Bracket.
7. Each chain strand has 10 links of chain for trucks with 19.5 tires and larger. If the strands
drag on the ground in the disengaged position, you may cut 1 link off each strand. DO NOT
REMOVE MORE THAN 2 LINKS OF CHAIN. On vehicles with 16” tires you only have 8
links of chain, DO NOT REMOVE LINKS. There must be a minimum of 9 links (8 links for
16” tires) for the Insta-Chains to work effectively. If they are still dragging on the ground or
are close enough to the ground to cause undue wear, Insta-Chain sells a Chain Tray to
raise the chains off of the ground.
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