If you are building a Knucklehead, Flathead or Panhead chopper, one of the first big decisions is the frame. For rigid Big Twins from the 1930s to the late 1950s, that usually comes down to two classic designs: the straightleg and the wishbone. They look different, they belong to different eras, and the right choice depends on your engine and the bike you want to end up with.
We have been building replica frames for these engines since 1982, and we get this question more than any other. Here is how we explain the difference.
The short answer
- Straightleg: straight front downtubes. Used for Knuckleheads from 1936 and Big Twin Flatheads from 1937, both through 1947, and again for Panheads from late 1954 to 1957.
- Wishbone: front downtubes that curve outward around the front of the engine. Used for Panheads from 1948 to early 1954.
Both are rigid frames (hardtails), with no rear suspension. The rear swingarm did not arrive on the Big Twins until after these years.
What is a straightleg frame?
A straightleg frame has two front downtubes that run in straight lines from the steering neck down to the bottom of the frame. It is a clean, lean and purposeful look, and for many builders it is the definitive pre-war and wartime chopper frame.
The straightleg is the original frame for the first Knuckleheads in 1936, and it carried the Knucklehead and Big Twin Flathead through to 1947, including the distinctive 1946 bullneck version. The straightleg design then returned for the Panhead from late 1954 through 1957.
Our straightleg frames come in several versions to match the original model years, with different rake angles:
- 1938–1940: 28° rake
- 1941–1945: 29° rake
- 1946 bullneck, 1947 and late 1954–1957 Panhead: 30° rake
What is a wishbone frame?
The wishbone frame gets its name from the shape of the front downtubes. Instead of running straight, they bow outward and curve around the front of the engine, a little like the wishbone of a bird. It is one of the most recognizable frame shapes in American motorcycle history.
1948 was the first year of the wishbone, and also the first year of the Panhead engine. The wishbone stayed in use through early 1954, which makes it the frame of choice for most early Panhead builds.
Our wishbone frames are available for 1948, 1949–1951, 1952–1953 and early 1954 Panheads, all with a 30° rake.
How to choose: four questions to ask
1. Which engine do you have?
This is the most important question. Frames were built around the engines of their era, so the model years of your engine will usually decide the frame for you. A Knucklehead or Big Twin Flathead points to a straightleg. An early Panhead (1948 to early 1954) points to a wishbone, while a late Panhead (late 1954 to 1957) points back to a straightleg.
2. Do you want a period-correct bike?
If you are restoring a bike, or building something that should look right for its year, match the frame to the engine's original model year. That is exactly why we build our frames in year-specific versions instead of one generic frame.
3. Which look do you want?
If the engine leaves you a choice, it comes down to style. The straightleg gives a tight, minimal and aggressive line that works perfectly for a stripped-down chopper or bobber. The wishbone has the softer, flowing curves of the late-forties and early-fifties bikes, and it frames the engine in a way that many builders love.
4. How do you want the bike to handle?
Rake affects how the bike steers. A steeper rake (a lower number, such as 28°) gives quicker, lighter steering. A more relaxed rake (such as 30°) gives a longer, more stable feel at speed. Every Edlund frame is built to the rake of its original model year, which is listed on each product page.
Brakes
All of our frames are available with a mechanical drum brake setup as standard, or with a hydraulic brake setup. Choose the option on the product page when you order.
Why an Edlund frame?
Every Edlund frame is built on castings poured in our own molds at a foundry in Vetlanda, Sweden, and handcrafted in our blacksmith shop — four generations of metalwork since 1935. You get the original look and geometry, without hunting for a tired original frame. Shipping is free worldwide.
Still not sure?
Send us a message at info@edlundframes.com with your engine and model year, and we will help you choose the right frame for your build.
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