Twisted Choppers Shows Us How
Article By: Twisted Choppers – twistedchoppers.com
Originally Published In The March 2015 Issue Of Cycle Source Magazine
So you want to ditch the stock hydraulic front end for a custom springer. The first thing you need to know how to do is take measurements for your new built to order piece of hardware. This is one of the most important pieces of the puzzle to get right for many reasons. You want to be sure that the front end is the correct length so that your ride is nice and level. It’s also important for the front end to work with the front wheel, tire and the frame. Taking accurate measurements not only ensures that the front end will be the correct length, but that the frame geometry is correct as well. Frame geometry is an important factor when changing front ends. Simply having a frontend that is the correct length to provide a level stance is not good enough. Rake and trail must be taken into consideration to ensure that your bike performs as good as it looks. For this reason, Twisted Choppers requires you, our customer, to provide specific measurements upon ordering your custom springer.
As shown above, there are 6 key dimensions that need to be measured. All measurements should be done with the cycle standing upright with the front wheel straight or with the frame supported at the correct ride height. It is also necessary to make sure the measurements are taken on a consistent flat surface. A square or plumb bob should be used when taking all of these measurements to ensure that they are accurate, if a measurement is taken out of square it will be longer as a result and will affect the overall calculation. The first measurement is the radius of the front wheel and tire. The distance from the ground straight up to the center of the axle is the (A) distance. The best way to measure this is to make sure the tire is properly inflated and the wheel is completely vertical when looking at it from the front or back. Set one leg of the square on the ground and align the second leg to the center of the axle. Measure straight up along the square from the ground to axle center and you have the Wheel Radius (A).
The next two dimensions are the Upper Neck Height (B) and Lower Neck Height (C). Again these measurements should be taken using the same technique as the first. It is important to note that if your frame requires neck cups for the bearings these will need to be installed prior to measuring. When looking at the frame from a side profile, measure from the ground to the CENTER of the neck cups (top for B and bottom for C). The most critical of these two dimensions is the Lower Neck Height (C) as the bottom triple tree of the springer is fixed and cannot be moved.
The fourth dimension is the Neck Rake Angle (D). In the US this measurement is included angle between the frame neck and plumb (true vertical). It is important to physically measure rake, even if you “know” what your frame or bike’s rake is (or is supposed to be). Wheel size, tire manufacturers, tire wear, and the way you have your bike mocked up can all have an effect on the actual measured rake of a motorcycle. There are a few ways to take this measurement, the cheapest and easiest way it to buy an $8 angle finder from a hardware store and set it on the front of the frame neck. Note that this measurement will typically be between 28° and 40°, if your measurement is something outside of this range you either have a super raked out chopper frame or you are reading the wrong angle (meaning you measured from the horizontal and not the vertical).
The fifth dimension is the Frame Ride Height (E). This measurement is easiest explained as the distance from the ground to the bottom of the lower frame rails on a rigid frame. If your bike has rear suspension, ride height can be measured either with or without a rider. This measurement is not of particular importance for determining correct springer configuration, but is a useful check dimension if something doesn’t seem correct in the others.
The sixth dimension is the length of the neck (F). It is important to note that if your frame requires neck cups for the bearings these will need to be installed prior to measuring. This measurement is not of particular importance for determining correct springer configuration, but is a useful check dimension if something doesn’t seem correct in the others.
Using the six measurements described above, the team at Twisted Choppers calculates the correct springer front end length for your application and verifies the trail calculation to ensure a properly handling motorcycle. Twisted Choppers offers different rocker arm configurations to allow the custom springer to be assembled with correct geometry for your application. As always we are here to help and happy to answer any questions you may have. Twisted Choppers 27085 S Tallgrass Ave, Sioux Falls, SD 57108 www.twistedchoppers.com firstname.lastname@example.org P: 605.498.0105 TF: 888.507.7233 F: 605.368.9990
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