The comparison between straight and curved forks requires an explanation of a few basic terms describing the geometry of a bicycle:
1. Fork rake (offset)
The fork offset also known as fork rake is the perpendicular distance between the steering axis and the front axle (the center of the front wheel).
In the graph below, the fork offset is in blue.
“Trail” is the horizontal distance between the front wheel’s point of contact with the ground and the section where the steering axis intersects the ground.
In the image below, the trail is presented in blue.
What are Curved Forks?
Curved forks have a noticeable curve near the middle of the blades (sometimes lower than that).
The image above shows a curved, steel fork taken from a retro mountain bike. Notice that there isn’t a curve at the crown. It’s all in the legs.
Since curved forks are always rigid, they’re mostly seen on commuters, retro MTBs, gravel, and road bikes.
What Are Straight Forks?
As the name suggests, straight forks have straight blades/legs.
It would be incorrect to say that straight forks are completely straight, however, because the legs and the crown connect at an angle.
The image above shows a straight blade fork that can accommodate both V-brakes and disc brakes. Note that the fork itself isn’t straight.
Purely straight forks are found primarily on BMX bicycles. However, BMX forks have an offset too. The difference is that it’s achieved through the dropouts welded to the front of the fork’s legs.
The Impact of Curved and Straight Forks On a Bike’s Geometry
If the offset, the trail, and the axle to crown measurement of a straight and a curved fork designed for the same type of bicycle are equal, then the geometry of the machine wouldn’t change regardless of which model is used.
FAQ: How can a curved and straight fork have the same offset?
The offset of straight blade forks is achieved by offsetting the legs at the crown whereas the offset of a curved fork comes from the bent blades.
Even though the two types of forks have a different design, they can produce the same wheelbase (the distance between the front and rear axle.)
The image above shows a curved fork and straight one with the same offset. Notice that the dropouts coincide.
However, if the parameters of the two forks are not the same, then the geometry of the bicycle and subsequently its handling would be altered.
For instance, if the new fork has more trail, the bicycle may feel more stable but its responsiveness would suffer due to the increased contact with the ground. Conversely, if the new fork has less trail, the steering of the bicycle will become faster.
Also, a fork with a greater offset will effectively lengthen the wheelbase of the bicycle and push the front axle further away from the rider. The result would be more stability but also loss of steering agility.
If the offset of the fork is reduced, then the front axle would be closer to the rider, and the speed of the steering input will go up. This change will affect the stability of the bicycle, however.
The Advantages of a Curved Fork
Versatility for Frame Builders
Curved forks allow builders to use one type of fork for multiple frame geometries because the offset comes from the curve and can, therefore, be added later.
A frame-builder can keep a certain amount of non-bent forks and bend them according to the frame geometry and the desired wheelbase.
Curved forks are often considered as more compliant thanks to their shape and extra length. The curvature acts as a spring and negates some of the road vibrations. Conversely, straight blade forks tend to be stiffer horizontally.
Since the absorption properties of curved forks reduce some of the stress on the wrist and elbow joints, some touring cyclists prefer curved forks over straight blades ones.
Having said that, a curved fork isn’t more compliant than a straight blade one by default. You also have to take into consideration the material.
For example, if the straight fork is made out of carbon fiber, it can be just as compliant as a curved fork made out of steel.
Moreover, the size of the tires is of great importance too. A bike may have a curved steel fork and yet offer a harsh ride due to its thin high-pressure tires.
Note: Some people disagree with the notion that a curved fork is more compliant than a straight one because most of the deflection happens at the crown and head tube area regardless of the legs shape.
Nonetheless, some riders report a noticeable difference between a curved and straight fork in terms of compliance.
Curved forks are more traditional and offer a style appealing to people who like classic bicycle lines.
If you’re after a vintage look, curved forks could help you achieve that image.
The Disadvantages of Curved Forks
Extra weight (potentially)
Curved forks are longer than the straight blade ones. Therefore, they also have the potential to be heavier. However, the final weight depends on the used material and the design of the fork. In some circumstances, a straight blade fork will be heavier than a curved one.
More complex manufacturing
The bending of a curved fork’s blades adds an entire step to the manufacturing process. Also, the production of a raked fork requires more material.
The longer production sequence and the extra resources make the production of curved forks questionable from a financial standpoint.
Fewer options if you want disc brakes
Many curved forks are designed for some sort of rim brakes. This limits your options if you want to have both – a curved fork and a disc brake.
Nonetheless, there are still a sufficient amount of curved models (e.g., Surly Long Haul Trucker fork) that have mounts for disc brakes.
Note: When a curved fork uses disc brakes it tends to be stiffer because its legs have to be stronger than normal to handle the torque created during braking. Without that extra reinforcement, the leg to which the disc mount is attached may bend and break catastrophically.
If you’re looking for the most compliant curved fork, it may be worth it to explore non-disc brake options.
The Advantages of a Straight Fork
Straight carbon forks are easier to produce
Carbon straight blade forks are easier and more lucrative to produce thanks to the simpler shape.
On the other hand, curved carbon forks are more complex and riskier to make because carbon can get “wrinkles” when molding it into a curve.
(Wrinkles compromise the integrity of carbon components and increase the possibility of a crack.)
Wrinkle prevention requires a more complex production system and more intensive quality control. Subsequently, most carbon forks have straight blades due to the simplified production process and lower costs.
The shortest distance between two points is a straight line. Hence why a straight blade fork requires less material. This peculiarity creates an opportunity to have a lighter fork.
Shorter production process
Since straight blade forks don’t have to be bend, the manufacturing process is shorter – a trait that makes straight blade forks more lucrative.
More models with disc brakes
Disc brakes are more common on straight blade forks.
Straight blade forks look more modern and some people consider their aesthetics a better match for aluminum and carbon frames. This is a subjective point, of course.
The Disadvantages of Straight Blade Forks
Harsher ride (potentially)
Straight blade forks are shorter and tend to be stiffer. Therefore, at least, in isolation, they should offer a harsher ride.
But as already mentioned, the bicycle’s geometry, the tires, and the materials of the components determine the overall riding experience.
A bike with a straight blade fork may end up feeling more compliant than one with a curved fork thanks to additional cushioning provided by the rest of the parts.
Limited post-production adjustments
The offset of a straight blade fork comes from the crown. Therefore, all adjustments have to be made during the production process.
Some people consider straight blade forks highly unaesthetic and responsible for the soulless look of modern bicycles together with the slopped down tube.
When Did Straight Blade Forks Originate?
The rise of the straight fork is often attributed to Ernesto Colnago – an Italian entrepreneur, inventor, and founder of the bicycle manufacturing company Colnago.
According to the story, Ferrari engineers asked Colnago why he was putting curved forks on his bicycles. The only possible answer was tradition.
After testing, the team concluded that a straight blade fork offers sharper performance, better absorption, and is also kinder to the headset. This collaboration gave birth to the Precisa fork. You can read more here.
However, some people don’t agree with those findings. During the 80s and 90s, some producers of mountain bikes were claiming the exact opposite, namely that a curved fork is more compliant and absorbs the road better.
Frequently Asked Questions
What would happen if I replace a curved forked with a straight blade one (or vice versa)?
If the new fork has a different axle to crown length and offset, the handling of the bike will change noticeably. Also, the stress on the head tube could increase.
To avoid similar complications, the new fork would have to have the same axle to crown length and offset. Otherwise, the geometry of the bicycle would be compromised.
What’s best – a straight blade or a curved fork?
Ultimately, the material, the production quality and the parameters of the fork (offset, trail) determine most of its performance qualities.
Whether it’s curved or straight is of lesser importance. Most people would have a hard time noticing a difference between a curved and straight blade fork if both of them have similar characteristics.
More often than not, the choice is driven by the search for specific aesthetics. Straight blade forks look more futuristic and “racier” whereas the curved ones are more elegant.