The Ultimate Truth About Lugged and Unicrown Forks

from Rookie’s keyboard

Hello, friends

Today, I am going to teach you everything you need to know about lugged and unicrown forks – the topic may sound complicated, but it’s not. 

Let’s go

Lugged Fork(LF)

Lugged forks have legs pressed into a steel sleeve (lug) and secured via brazing.

Brazing is a metal-joining process during which two metal pieces are “glued” to each other by melting a metal rod over the connection points.

The filler material is brass or silver because they have a lower melting temperature than steel.

During brazing the base material (in this case the fork’s tubes) is never heated to melting temperatures. As a result, there’s less chance of compromising the integrity of the materials.

Unicrown Forks(UF)

The legs of unicrown forks are TIG-welded to another tube. The term “unicrown” is used because the crown isn’t an independent piece. It’s formed by the fork’s legs and middle element.

A Unicrown Fork

The Advantages of LFs

  • “Hot” Vintage Design

Lugged forks are elegant and give a classy vintage look to a bike. Hence retro bike appreciators often put great pride into their lugged components.

  • Repairs

Brazed frames and forks are much easier to repair because the builder can heat the joint to melt the brass and take out the affected tube.

The Disadvantages of LFs

  • Pre-determined Width

The crown of LFs predetermines the distance between the fork’s blades. Therefore, the fork’s clearance is fully dependent on the available lug. 

If the builder wants to make a fork for wider tires, a new lug will have to be purchased or fabricated.

  • Steerer Tubes Are Built Only For Road Bikes

The lugs are usually made for thin steerer tubes designed for steel road bikes.

Good luck building a lugged MTB fork with an oversized steerer tube by relying on stock lugs.

  • Slow Production

LFs are slower to produce because:

  1. A lug is needed.
  2. Brazing is slower than welding.
  • Low Supply

The low demand for lugged forks and the slow production process naturally results in limited supply. 

Most lugged forks available today come from old-school bikes. A modern lugged fork can still be found, but there aren’t many to choose from.

  • Aluminum Can’t be Brazed

Aluminum forks cannot be brazed for the following reasons:

  1. The filler brazing rod has a higher melting point than aluminum. The long exposure to heat will irreparably damage the aluminum tubes.

2. Some filler rods melt at lower temperatures so that aluminum can be brazed, but they don’t provide enough strength to build a strong fork.

Consequently, lugged forks are limited to steel only.

The Advantages of UFs

  • Simplicity

A unicrown fork is made of three tubes – a super simple design.

  • Variety

UFs allow the production of forks for wheels of all widths without having to purchase a special lug.

The extra width can be achieved by using longer tubes and bending them at a larger angle.

  • Steerer Tubes Of All Sizes

Since no lugs are pre-determining the thickness of the tubes, the builder can easily make forks using slim or oversized steerer tubes.

  • Many Models To Choose From

The fast manufacturing process and the quick customization make unicrown forks the default choice for scaling bike businesses. Thus, you have many models to choose from.

The Disadvantages of UFs

  • Generic Appearance

Unicrown forks are seen on some of the cheapest bikes out there and often lack style.


For two forks to be interchangeable, they have to satisfy the following requirements:

  • Matching steerer tube length
  • Matching steerer tube thickness
  • Approximately the same blade length

If the criteria aren’t met, the following problems will occur:

a. You won’t be able to secure the fork to the headtube.

b. The fork won’t accept the wheel or will create massive changes to the geometry of the bike.

If the new fork is designed for smaller wheels, the original bike wheel won’t fit.

If the new fork is built for bigger wheels, it will accept the smaller wheel, but the combo will greatly alter the geometry of the bike.

If the bike uses rim brakes, the brake pads won’t align with the new position of the rim, and the bike will lose its front brake.

Even if all of the criteria above are met, there’s one more problem that you might face when going from a unicrown to a lugged fork or vice versa.

If you look at the crown area of a unicrown fork, you will see that the distance between the crown race and the bottom of the steerer tube is greater than that of a lugged fork. This distance is known as stack height.

The extra stack height of unicrown forks lifts the front end. If a unicrown fork is replaced by a lugged one, the front end of the bike will drop by as much as 20mm.

This will result in the following changes to the bike’s geometry:

  • Steeper head tube angle

The head tube angle (HTA) of a bike is the angle formed by the headtube and the ground.

The greater the fork’s stack height, the slacker the head tube angle becomes. Conversely, if the fork’s stack height is reduced, the angle gets steeper.

  • Lower Bottom Bracket

The shorter stack height of a lugged fork will lower the bottom bracket too. A lower bottom bracket increases the bike’s stability but greatly diminishes the bike’s clearance.

Different Fork Rake?

A switch from one type of fork to another could result in a different fork rake.

The term fork rake refers to the hub’s offset from the steering axis.

The term trail refers to the tire patch behind the extended steering axis.

A shorter rake (offset) brings the axle closer to the steering axis and thus increases the bike’s trail.

Conversely, a long rake (offset) pushes the axle further away from the steering axis and decreases the bike’s trail.

The decreased trail will “sharpen” the bike’s cornering but also make it more unstable when moving in a straight line.

Honestly, in most cases, it’s best to avoid replacing a lugged fork with a unicrown one and vice versa to prevent incompatibility issues and unpleasant changes to the bike’s geometry.


The strength of a fork is not decided by the assembly method.

The parameters determining the strength of a fork are:

  • Design
  • Material
  • Tube Thickness
  • Production quality

Thus, it’s not possible to conclude which one is stronger.

What I would choose?

Lugged forks are cool, but not cool enough for me to slave to them. If they don’t fit the bill, I’d happily use a unicrown model as I do. 

IMO, unless you’re going after a certain road bike look, then a unicrown model will save you money while also giving you more options to choose from.

Until next time

– Rookie






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