Changes in rake and length from stock dimensions and geometry can diminish suspension action commensurate with the amount of change. In the glide design and to a lesser extent in the springer, your frame rake angle and front end length dictates how well the "suspension" part of the design works. The triple combination of triangular design, TIG welded, chrome-moly tubing and proper mating of the parts before they are welded together add up to benefits a glide or springer cannot matchĪn additional benefit of the girder design is that the length of the forks and the rake in the forks or frame does not determine how well a girder works - the pivot points still pivot, and the spring compresses and rebounds as it should. Chrome moly is best welded using TIG (also known as heli-arc) for proper joining of the parts We use 4130 chrome-moly, seamless tubing on the round girder because chrome-moly is one of the toughest metals available for this kind of job, it is normally used in making airframes or race car chassis. The triangle is then divided into two smaller triangles with the addition of the cross member at the bend of the rear leg. A long triangle is then formed from the axle hole to the triple trees. The triangle in the Durfee Girder is incorporated into the design by using two legs, with the rear one bent.
It has been proven that the triangle is one of the strongest structures for support as can be evidenced by looking at almost any bridge, rail road trestle or skyscraper frame. The Durfee Girder like all true girders gets a lot of its strength from its triangular design. Many others besides Indian used the girder design, in fact a lot of the other American and most of the European motorcycle manufacturers of that period used girders in their production motorcycles. Imagine extreme heat, no roads, blowing dust and sand, hills, valleys and craters that could swallow a tank and you start to get the picture of how rugged these front ends were and how good they can be today with advances in materials and processes unknown 70 years ago. Army while out chasing Rommell and gang in the Sahara Desert during World War II. The Durfee Girder is actually based on the girders used on the Indian motorcycles of the 1930's and 40's which were a good design, being rugged enough to be used by the U.S. This may or may not be true because if designed properly, a Girder offers some benefits that a Glide or Springer can't - yet gives outstanding performance and great looks, which is what most bike builders seek in the first place. The glide is currently the most popular, to the point of being boring and is sometimes thought to be the best performer of the three. These three are the most commonly used by custom bike builders, because they are proven designs offering good looks and performance for road handling. When selecting a custom front end for your next project, there are three main styles to choose from, the Glide or Hydraulic, the Springer, and the Girder. Most people think that a girder front end is for looks only, and does not help in making the bike handle. For more info, visit our disclaimer page.Ĭopyright 2014-2022 may not know much about them, so figured I'd add a copy/paste from the old Durfee site about "Why a Girder". This site participates in several affiliate programs.
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Related Articles: Motorcycle Frames and Suspensions Wide Glide Conversion How To Polish Aluminum Motorcycle Parts Motorcycle Quotes and Sayings Properly designed and constructed, they will handle as good, if not better, than any other motorcycle front end. Pound for pound, they will deflect less than other types of front suspensions. Girder front forks were used on motorcycles for many years. Generally, average trail length on a motorcycle front end is between 3-1/2 to 6 inches. Too much or too little makes a bike hard to control. The importance of trail is often overlooked. Trail is measured in inches, and should always be a positive number. Rake is measured in degrees, which means the larger the angle, the further out the front wheel will be.įront-end trail is the distance between a vertical line from the center of the front wheel's steering axis, to where the tire makes contact with the ground.
The angle of front-end rake is formed between the frame's neck and a vertical line. In 1948, a Vincent Black Lightning (Black Shadow racer) with a "Girdraulic" front end set a new world record of 150.313 mph at Bonneville Salt Flats.
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