A motorcycle’s frame or chassis is the main support structure of the machine. The engine along with many other components of the bike are all mounted onto this metal skeleton. The majority of motorcycle frames are made of steel or aluminum. But some high-end and racing motorcycles feature titanium, magnesium, or carbon fiber frames. Regarding their design, the most popular motorcycle frame types are backbone, cradle, and trellis/perimeter.
If you want to find out more about motorcycle frames, you are in the right place.
We at PowerSportsGuide have compiled the basics of this key part into this post!
What is the Frame of a Motorcycle?
Although frameless motorcycles have already been invented, almost every stock motorcycle comes with a metal frame.
What is the frame of a motorcycle? In a nutshell, it’s a metal base on which the entire vehicle is built. The frame not only houses the engine, but also provides connection points for the rear suspension, handlebar, fairings, footpegs, seat, and many other smaller parts of the bike. This means the frame on a motorcycle does the same job as the backbone in our body.
It’s also good to know that front forks are typically not considered part of the frame.
Officially, the frame of a motorcycle is its metal frame completely stripped without any bearings, forks, or other additions.
What Types of Motorcycle Frames are There?
The different types of motorcycle frames have various names, which are often referred in their design. The seven main types of motorcycle frames are as follows:
- Backbone or Spine
- Double-cradle or duplex
- Monocoque and pressed
Let’s get down to the nitty-gritty and talk about each one in detail!
1. What is the Backbone Motorcycle Frame?
A backbone motorcycle frame features a pretty simple design. As its name suggests, this type of frame acts as a backbone on which the other components are directly connected. On these bikes, the engine basically hangs off the frame. This is why backbone motorcycle frames are also referred to as spine frames.
Thanks to their simplicity backbone frames are easy and cheap to manufacture. Because of this, they are commonly used in entry-level motorcycles.
Unfortunately, this type of frame is weaker and offers less rigidity than other frame designs. This means that backbone frames can only handle less powerful engines.
2. What is Diamond Motorcycle Frame?
Diamond motorcycle frames feature a diamond shape, which is where the name comes from. It’s a lesser-known fact that the earliest motorcycles featured this frame design! This is because the earliest motorcycles were actually bicycles equipped with very small engines. That’s why diamond frames are closely related to bicycle frames.
This type of frame was commonly used on early Indian motorcycles.
3. What is a Single-Cradle Motorcycle Frame?
Single-cradle motorcycle frames also feature a single down-tube frame. This design is actually a special type of diamond frame; hence, these terms are often used interchangeably. But the main difference between diamond and single-cradle motorcycle frames is that in the latter the engine is mounted closer to the ground.
This means in a diamond frame the engine sits higher, which results in a higher center of gravity.
Just picture a bicycle with an engine in place of the water bottle!
But if you bend the pipe where the bottle sits and move this point towards the ground, you virtually get a single-cradle frame.
This new shape offers more space for the engine, which is already closer to the ground.
Since the engine is virtually placed in a loop, these frames are often called single-loop motorcycle frames as well.
4. What is a Double-Cradle Frame on a Motorcycle?
Unlike their single brothers, double-cradle motorcycle frames feature two down-tube frames. This doubled tubing provides a more rigid structure and better support for the engine. Double-cradle frames are stronger, more durable, and can handle more powerful engines. This construction is also known as a duplex or double-loop frame.
We also have to mention half-duplex motorcycle frames as well. These frames feature a unique design, as they are actually a combination of a double and a single-cradle frame.
These frames are often used on cruiser motorcycles, which can feature a “soft tail” (with a rear suspension) or a “hard tail” (without a suspension).
5. What is a Perimeter Frame on a Motorcycle?
It’s safe to say that most high-performance and racing motorcycles today feature a perimeter frame. These frames have two huge beams that directly link the swingarm and the steering head. There is a great deal of distance between the two beams in order to enclose the engine. To keep the weight of these large beams low, perimeter frames are usually made of aluminum.
Perimeter frames were originally developed for racing purposes, but today they are commonly used in many high-performance street motorcycles as well.
6. What is a Trellis Frame on a Motorcycle?
It’s safe to say that trellis frames are very much like perimeter frames. But instead of the two large aluminum beams, these frames are built of many short pipes. These little pipes are welded together to form a rigid structure. A well-designed trellis frame can be lighter and even more rigid than many perimeter frames!
They are also easier to manufacture as the process doesn’t require special machinery. On top of that, trellis frames look really cool, so they are typically part of the design, especially on naked bikes.
Trellis frames are used in Ducatis as well as many KTM bikes.
7. What is a Monocoque Motorcycle Frame?
Monocoque motorcycle frames work in the same way as a car chassis. This means they are actually one piece of metal, which provides outstanding strength and rigidity. Monocoque frames are expensive and hard to manufacture, which is why they are mainly only used in racing bikes.
If the structure is designed with additional supporting elements, it would be considered a semi-monocoque frame.
What Are Motorcycle Frames Made of?
Besides the shape, the material the frame is made of is no less important. The most commonly used motorcycle frame materials are as follows:
- Composite (mainly carbon fiber)
It’s safe to say that the majority of motorcycle frames are still made of aluminum or steel. The latter is cheaper, but aluminum is lighter.
To get the best of both worlds, more and more motorcycles come with hybrid frames that feature both steel and aluminum parts.
A few high-end bikes feature special frames that are made of titanium, magnesium, or carbon fiber.
Which Type of Steel is Used for Motorcycle Frames?
One of the most commonly used types of steel for manufacturing motorcycle frames is carbon steel or “mild steel.” The main advantage of these frames is that they can be more easily repaired if bent. On the other hand, this material is quite heavy. Besides carbon steel, many motorcycle frames are made of alloy steels like chrome moly. These frames are lighter but harder to fix as they are prone to cracking when they bend.
Which Type of Aluminum is Used in Motorcycle Frames?
It’s hard to tell what type of aluminum is exactly used in motorcycle frames, as they are typically custom alloys. And for obvious reasons manufacturers want to keep this a secret! However, there are rumors that some of the most common types of aluminum used in motorcycle frames are most likely the 7xxx and the 6xxx series.
How Heavy is a Motorcycle Frame?
Despite their large dimensions, these metal frames are quite lightweight. As a rule of thumb, a motorcycle frame weighs about 17-80 pounds depending on the size, design, and material. You can find the lightest motorcycle frames in dirt bikes as they only weigh about 17-25 pounds. The perimeter frames of sportbikes weigh 25-30 pounds, while cruiser’s double-cradle frames weigh about 50-80 pounds.
(These numbers are just ballpark figures, as the weight of a motorcycle frame always depends on several factors!)
The lightest perimeter frames can be found in high-end BMW sportbikes. These lightweight motorcycle frames are made of carbon fiber and weigh as little as 17 pounds, which is about 11 pounds lighter than a regular steel frame.
For example, the frame of the vintage Honda SL350 K1 weighs only 28 pounds, while the 2004 Suzuki GSX-R 1000 perimeter frame weighs about 25 pounds.
The heaviest motorcycle frames are arguably the huge monocoque box frames, which can reach or even exceed 100 pounds.
This seems like a lot, but don’t forget that these frames also contain the fuel tank and other parts of the bike.
FAQs About Motorcycle Frames
As a takeaway, we’ve compiled some frequently asked questions about motorcycle frames!
What is the Chassis of a Motorcycle?
The chassis of the motorcycle is actually its frame, so these terms are often used interchangeably. The chassis of a motorcycle is the main supporting structure of the machine. The other components like the suspensions, wheels, engine, seat, gas tank, are all mounted onto this framework. The chassis ensures the motorcycle’s stability, strength, and proper handling.
Where is the Chassis Number on a Motorbike?
The chassis number on a motorcycle is typically stamped on the right side of the tubing or the headstock tube. The latter is the short tube on the front of the frame directly above the front forks. A motorcycle’s chassis number is often referred as the VIN (Vehicle Identification Number).
What is a Twin-Spar Frame?
Twin-beam or twin-spar frames are just synonyms of perimeter motorcycle frames. The term “twin” refers to the two large beams that are the main components of these frames. These beams enclose the engine and directly connect the headstock tube with the pivot points of the swingarm.
What is a Deltabox Motorcycle Frame?
The Deltabox frame is one of the most well-known perimeter motorcycle frame series designed by Yamaha. This frame gets its name from its shape and design (Delta=triangle symbol in the Greek alphabet). According to Yamaha, the Deltabox frame offers excellent torsion rigidity and a well-balanced structure, which results in superb stability and responsive steering.
Do Frameless Motorcycles Exist?
Surprisingly, frameless motorcycles do exist! However, they are pretty rare and used primarily for racing purposes. The main idea behind the frameless design is to reduce weight and manufacturing costs.
On frameless motorcycles, the rear swingarm is attached directly to the engine, which takes over the role of a classic frame.
One of the most well-known frameless bikes was the Britten V1000, which was built for racing purposes in the ‘90s.
When it comes to the newest bikes, one of the most well-known semi-frameless motorcycles is the Ducati Panigale.
We can’t say that this bike is completely frameless, as its front forks and engine are still connected to a small aluminum box (which is often considered to be a monocoque frame). Simply put, this box and the engine itself act as the frame of the machine.
Just like on real frameless bikes, on the Panigale the rear suspension is directly attached to the engine.
How are Motorcycle Frames Made?
Today, the majority of motorcycle frames are manufactured by special machinery. Depending on their design and material, frames can be welded or fully machined.
However, a small series of custom motorcycle frames are still being made by hand welding and by using pipe benders.
Here’s a great video on how custom motorcycle frames are being made:
What Types of Tubing is Used for Motorcycle Frames?
Generally speaking, three different types of tubes are used for manufacturing motorcycle frames:
- ERW (Electric Resistance Welded)
- DOM (Drawn Over Mandrel)
- Chrome Moly (Chromium-molybdenum alloy steel)
ERW is considered to be the most basic tubing for motorcycle frames, while DOM tubes are significantly stronger. The latter is often used for manufacturing chopper frames.
The best of these three types of tubing is arguably Chrome Moly or “chromoly” tubes, which are made of a more complex alloy. Thanks to the additional elements this material is stronger than ERW and DOM tubes.
Which Frame is Best for Motorcycle?
Many riders say that the best motorcycle frames are perimeter and trellis frames. They can handle high performance, offer excellent rigidity and directly connect to the forks and the swingarm. That’s why they are commonly used in high-performance motorcycles. On the other hand, they are hard to manufacture, very expensive, and don’t fit the design of many types of bike. Because of this, the best frames for cheaper motorcycles are still backbone and cradle frames!