How To Measure For Springer Forks
In order to build a set
of Springer Forks that will properly fit your particular frame configuration we
need a few measurements. Please don't just guess at these dimensions. They are
all critical to the proper design and fabrication of the forks and/or component
parts that we will be custom making per your specifications. We want you to have
a perfect fit when everything is installed on the bike.
To begin with you need to have the bike level, preferably on blocks under the front of the frame with the rear wheel still touching the ground. Then use shim blocks to set the height of the lower rails, at the front of the frame, to the 'ride height' you want to have when your weight is on the bike and it's actually going down the road. Most people like to have the front of the rails about one-inch higher than the rear when the bike is under load but some people like it higher so just mock the frame up and gives us the dimension labeled 'FH' on the diagram.
When you set the lower
rail height it also changes you rake angle from whatever the 'stock' value
was since the frame makers set rake when the frame is in the jig. You can use
one of the cheap plastic 'angle-finders' sold at most home-supply type
stores like Home Depot to find this angle. For the vast majority of frames this
angle will be somewhere between 33 and 47-degrees. This angle corresponds to the
angle labeled 'RA' on the diagram.
The next measurement
needed is labeled as 'NH' on the diagram. This is the neck height measured
from the lowermost rear edge of the lower bearing cup to the ground.
Needless to say that
imaginary measurement line needs to be perpendicular to the ground and not
skewed at some angle.
Next we need to know the
height of the front axle from the ground line. Tire/wheel combinations vary
depending upon the actual tire and wheel you own so don't just assume that
some catalog specification will match what you actually plan on running. This
distance is labeled 'AH' on the diagram.
The next thing needed is what we call the 'neck-length' (NL). Basically this is just the distance between the outside surfaces of the upper and lower dust shields. The diagram below is a sketch of a typical neck assembly.
This distance can vary
considerably from one bike to the next so take some time to get this as close as
you possibly can. Different bikes will come fitted with different styles of
bearing preload nuts and locking washers. We will supply a new set with the
forks but the proper fitment of the trees may still need to be adjusted slightly
using shim washers especially if you change bearings. Quite often there is a
significant amount of space between the upper bearing preload nut and the actual
bottom of the upper tree and this is normal
Most Springer manufacturers set this 'neck length' at 8-inches as it's become a de-facto Harley standard so if you can't get an accurate measurement from your bike this is dimension that we will use and it will work with about 95% of all stock Harley frames and aftermarket frames made to use a standard Harley steering stem.
Also note whether you'll
be needing an older Sportster stem (7/8") or a Big Twin stem (1").
Lastly we need to know
the diameter of the axle you're going to be using to match your wheel
bearings. The most common sizes are 5/8 and 3/4".
Send us the measurements
you've taken and we'll get back to you with a confirmation as to the length
of forks needed for your particular bike.
If it turns out that
there might be some issues with 'trail' on your project we'll also give
you some suggestions about alternative Springer design possibilities like raked
trees or dropped rockers to improve the proposed handling characteristics.
(Note that using 'Dropped' rockers to bring trail back into a 'normal' range will change the length of the fork legs needed for a particular bike significantly so you can't install such rockers on an existing set of forks).
You can email with questions: email@example.com
or call 214-734-0200
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