How to Choose a Motorcycle Frame Builder: Geometry, Welds and Paperwork

Choose a motorcycle frame builder who will agree the geometry with you in numbers before cutting any tube, can explain the material and welding method, and can show you finished frames on bikes that are being ridden. They should also hand over the paperwork your state needs to register the bike. The frame links the steering head to the swingarm and carries the engine and rider, so it decides how the bike handles and how safe it is.

This guide is part of our custom motorcycle building hub. If the frame is one part of a bigger project, start with how to find a custom motorcycle builder.

Key takeaways- Decide first whether you need a modified stock frame, an off-the-shelf aftermarket frame or a one-off build.- Agree rake, trail and wheelbase in writing. These numbers shape handling.- Ask what the frame is made of and how it is welded.- Keep the receipt or bill of sale for the frame. In California, a bike built from parts can't be registered without receipts for major parts, including the frame.

Do you need a frame builder at all?

There are three ways to get a custom frame, and each one calls for a different kind of shop.

By Wikipedia's definition, a chopper frame has always been cut and welded at some point. A hardtail is simply a frame with no rear suspension. If you are still choosing a style, see custom build design ideas.

What the frame has to do

A frame's main job is to keep the steering head and the swingarm pivot rigidly connected, so the bike handles predictably. It also carries the engine, the rider, any passenger, the fuel tank and the battery. Ask any builder which layout they propose, whether a cradle frame, a trellis or something else, and why.

Geometry: the conversation to have first

Frame geometry comes down to four measurements: wheelbase, steering axis angle, fork offset and trail. Together they have a major influence on how a bike handles. On motorcycles the steering axis angle is called rake, and it is measured from the vertical. Trail is the distance on the ground between the front tire's contact point and the point where the steering axis meets the road.

Choppers get their stretched look from changed steering angles and longer forks. That look comes with handling trade-offs. A good frame builder should talk you through them before you commit, not after.

Ask for:

1. The planned rake, trail, wheelbase and fork length, in writing.
2. How those numbers suit your riding, whether that's short city hops, highway miles or shows.
3. Any legal limits where you'll register the bike. Wikipedia, for example, quotes North Dakota rules that set rake between 20 and 45 degrees and trail between 2 and 14 inches (5 to 36 cm). Check your own state's rules with the DMV.

Materials and welding

Steel tubing is still the common choice, though frames are also made from aluminium, titanium, magnesium and carbon fibre. No single material or design suits every bike. Ask the builder why they chose the material for your frame.

• Chromoly (4130-type) steel has an excellent strength-to-weight ratio and is stronger than plain 1020 steel. Wikipedia notes that it isn't easily welded and that it calls for heat treatment to avoid cracking. Ask how the builder handles that.
• TIG welding gives the welder more control and can produce stronger, higher-quality welds. It is also harder to master and slower than other methods. Ask which process they use on the main joints, and why.
• The jig. Ask how the frame is held straight while it is welded and how it is checked for alignment afterward.

How to judge a frame builder's work

Photos show finish, not alignment. Ask to see frames in person, ideally on bikes that have covered real miles.

• Welds: even and consistent along each joint, with no grinding hiding the work.
• Motor mounts and tabs: they should look planned, with brackets for the engine, transmission, oil tank and wiring rather than add-ons.
• Straightness: ask how they check alignment and whether you can see the record.
• Owners: talk to two or three customers about how their bikes ride after the first few thousand miles.

For a structured side-by-side, use how to compare custom motorcycle builders and their work.

Paperwork and registration

If your bike is built from parts, the frame's paperwork is part of registering it. California's rules are a useful example. A motorcycle built entirely from parts, even Harley-Davidson parts, can't be registered as a Harley-Davidson. It must be registered as a specially constructed vehicle. The application needs bills of sale or receipts for the major parts, including the frame. It must also list materials and labor costs. The California DMV manual on specially constructed vehicles gives the full list.

Before you order, ask the builder exactly which documents come with the frame. Then check with your own DMV that those documents are enough. For the whole registration process, see how a custom motorcycle build comes together.

Questions to ask before you order

If the engine is being built at the same time, put your frame builder and your engine builder in touch early. See how to choose a motorcycle engine builder.

Red flags

• The builder won't give geometry numbers, or says the bike "will handle fine".
• No finished frames or riding owners you can check.
• No written estimate or warranty.
• No receipt or bill of sale for the frame, which can stall registration.
• Vague answers about material, welding process or how alignment is checked.

Gear that suits the bike

A stripped-back custom deserves gear made for it. Leather Collection motorcycle vests come in snap-front, zip-front, side-lace and summer styles, mostly in cowhide, and every vest has a custom size option. You can also upload your own design for a printed lining, such as a club logo or a sketch of the bike.

Related guides

• To find frame builders near you, use the same approach as finding a local custom motorcycle builder.

FAQ

Is it cheaper to build a bike from a frame?

We have not found sourced figures that settle this in general. Cost depends on the frame, the engine, how much fabrication and paint is needed, and the paperwork. Ask for an itemized written estimate. In California, the registration application for a bike built from parts must also record materials and labor costs.

How do you make your own motorcycle frame?

You need a geometry plan, a jig to hold the tubes straight, and welding skill to match the material. TIG welding offers the most control but is hard to master, and chromoly brings its own welding demands. You can also pay a frame builder for the frame and do the rest yourself. Either way, keep receipts for every major part so you can register the bike.