KNOWLEDGE FROM THE FORT - HANDLEBAR TUBE DIAMETER
KNOWLEDGE FROM THE FORT — BLOG #4
HANDLEBAR TUBE DIAMETER: FITMENT, PROPORTION AND DESIGN
When choosing a set of custom motorcycle handlebars, tube diameter is often thought of purely as a styling decision.
Thicker tubing gives a heavier, more substantial appearance. Smaller diameter tubing can produce a cleaner, lighter look. But when we design and manufacture a set of handlebars at Fortress Motorcycle, diameter is about considerably more than appearance.
Before deciding how thick the main sections of the bars should be, we first have to consider how those handlebars are going to fit the motorcycle.
The lower clamping diameter, riser width, grip and control sections, throttle system and front-end clearance can all affect the final design.
And these specifications aren't necessarily the same from one Harley-Davidson to another or for other makes and models too — or even between different generations of the same model.
LOWER CLAMPING DIAMETER
Harley-Davidson has used several different handlebar clamping diameters across its model range over the years.
Two of the most common are 1" and 1¼", while some of the smaller Street models use 7/8" diameter bars. There are also exceptions, such as the Milwaukee-Eight Fat Bob, which uses a substantially larger 1½" clamping diameter.
This means that knowing someone owns a Harley-Davidson — or even knowing that it's a Softail — isn't necessarily enough information for us to manufacture the correct bars.
The exact model and year matter.
It's something we've spent a considerable amount of time researching and compiling at Fortress Motorcycle. When you're manufacturing handlebars for different motorcycles and generations, these relatively small dimensional differences become extremely important.
RISER WIDTH CAN CHANGE TOO
Clamp diameter is only one part of the lower handlebar specification.
The total riser width can also vary between models and generations.
For example, older Softail Fat Boys used a total riser width of approximately 5", whereas the newer Milwaukee-Eight Fat Boy uses approximately 6".
Sportster 883 models can be around 5" or 5¼", depending on the particular setup.
The same thing can be seen with the Softail Breakout. Earlier models used approximately 5", while newer models from around 2018 use approximately 5¼".
These differences might not sound enormous on paper, but when you're fabricating a set of handlebars specifically for a motorcycle, a quarter of an inch matters.
This is also why we've built up our own fitment information over the years rather than assuming that one set of dimensions applies to every Harley.
THE GRIP AND CONTROL SECTIONS
There is one dimension that remains relatively consistent across many of the motorcycles we build handlebars for.
The grip and control sections are generally 1" diameter.
That remains the case even when the main body of the handlebar is considerably larger.
A set of Fortress bars might therefore have a 2", 2½" or even larger main tube diameter, while transitioning to the correct 1" sections required for the motorcycle's grips and controls.
However, even the 1" control area isn't necessarily identical between motorcycles.
The required length of the grip and control sections can vary between models, and the throttle system also has to be taken into consideration.
A conventional cable-operated throttle and an electronic throttle-by-wire system don't necessarily require the same arrangement.
So although the grip diameter may remain 1", we still need to establish exactly what motorcycle the handlebars are being manufactured for.
LOWER SECTION POSITIONING AND CLEARANCE
There's another consideration that isn't immediately obvious when looking at a finished set of handlebars.
Sometimes the lower section of the bars cannot simply be positioned where it would normally appear most logical.
The motorcycle's upper fork assembly can dictate where that section needs to sit.
A good example is the Harley-Davidson Sportster Forty-Eight (XL48).
The position of the top fork nuts has to be considered when designing the lower section. Depending on the handlebar design, the lower tube may require offset positioning to provide the necessary clearance.
This means we're considering several things simultaneously:
Clamp diameter, riser width, lower-section position and front-end clearance.
They all have to work together.
It's another reason why a custom handlebar isn't simply a piece of tube bent into a particular shape.
THEN WE CAN TALK ABOUT THE MAIN TUBE DIAMETER
Once the critical fitment areas have been established, things become considerably more interesting from a design point of view.
The main body of the handlebars doesn't have to remain the same diameter as the clamping or grip sections.
Depending on the handlebar design and motorcycle, at Fortress we can work with main tube diameters including:
1¼" — 1½" — 1¾" — 2" — 2¼" — 2½" — and even 3".
This is where diameter becomes a major part of the overall appearance of the motorcycle.
Going from a conventional diameter to a 2" bar doesn't simply make the handlebar look slightly thicker. It can completely change the visual weight of the front end.
Move into 2¼" or 2½" tubing, and the bars become an even more dominant part of the motorcycle's design.
And on the right build, 3" diameter tubing can look incredible — particularly on large muscle-style custom motorcycles where the proportions of the bike can carry something that substantial.
BIGGER ISN'T ALWAYS BETTER
That doesn't mean we'd simply recommend the biggest tubing possible.
Proportion matters.
The diameter needs to complement the motorcycle rather than overwhelm it.
A diameter that looks perfectly at home on a large custom, Fat Boy or heavyweight cruiser could look completely out of proportion on a smaller motorcycle.
Likewise, tubing that's visually right for a lighter bike may look undersized when fitted to a large custom build.
We consider the bars as part of the complete motorcycle:
The front end. The tank. The forks. The overall stance. The rise. The width. The pullback. And the particular style of handlebar being manufactured.
All of those elements influence how the finished bars will look.
DIAMETER IS ONLY ONE PART OF THE GEOMETRY
This is also why our previous Knowledge From The Fort articles have looked separately at rise height, pullback and total handlebar widths.
None of these dimensions exists in isolation.
You can have the right rise but the wrong pullback.
You can have the right pullback but the wrong width.
And you can choose an impressive tube diameter, but if the proportions or fitment are wrong, the finished handlebar still won't be right for the motorcycle.
A well-designed set of custom handlebars is the result of all of these dimensions working together.
EVERY MOTORCYCLE IS DIFFERENT
Over the years we've accumulated a considerable amount of information about the different motorcycles we manufacture handlebars for.
That's important because manufacturers change specifications.
A newer version of a motorcycle doesn't necessarily use the same clamping diameter, riser width or front-end arrangement as the model that came before it.
That's why, when ordering custom handlebars from Fortress Motorcycle, we ask for the exact make, model and year of the motorcycle.
From there we can establish the important fitment requirements before working with the customer on the part they really want to see:
the design.
Whether that's a relatively traditional diameter or a huge set of 2½" or 3" muscle-style bars, the principle remains the same.
GET THE FITMENT RIGHT. GET THE PROPORTIONS RIGHT. THEN BUILD SOMETHING DIFFERENT.
Handcrafted. Personal specification. Built different. Built Fortress.