Bike fork

fork Fixes, Reviews & Guides

Embedded thumbnail for Review of BOS Deville Suspension Fork

Review of BOS Deville Suspension Fork

Timing is everything, and if you ride mountain bikes in the United States, your time is now. Bos Suspension, ridden to multiple world championships in downhill, cross-country, and even rally car...

Company: BOS
Type: Review
Embedded thumbnail for Properly Fit A Star Nut

Properly Fit A Star Nut

The star nut is pressed into the steerer tube and allows the fork and headset components to be pulled into place in the frame’s head tube. If you have a new fork, or have just cut down the steerer...

Part fork
Tools hammer
Type: Repair Tutorial
Embedded thumbnail for How to Route Brake Cable Hose on RockShox RS-1 Fork

How to Route Brake Cable Hose on RockShox RS-1 Fork

RS-1 Brake Hose Routing:

Proper brake hose routing on the RS-1 is important to make sure your hose is not rubbing on your wheel or tire, and to make sure the brake hose is not damaging the...

Company: DT Swiss
Type: Repair Tutorial
Embedded thumbnail for How to Install a Cane Creek Threadless Headset

How to Install a Cane Creek Threadless Headset

The headset is a small, yet critical component that is often overlooked. In this video you’ll see how to service, adjust, and install your thread less headset.

For this, you will need a...

Company: Cane Creek
Type: Repair Tutorial
Embedded thumbnail for DIY Straighten a Bicycle Fork

DIY Straighten a Bicycle Fork

A bent bicycle fork can happen in a number of ways - a bad wreck, a big bump, being backed over in the garage, etc. What's weird about these instances is that the bike can be bent in a split-...

Part fork
Company: Schwinn
Type: Repair Tutorial
Embedded thumbnail for Install and Mount Wired Cycling Computer

Install and Mount Wired Cycling Computer

We're going to go over how to install a basic wired bicycle computer. All you'll need is a third hand cable tightener and a pair of cutters. This particular computer users rubber...

Company: Bontrager
Type: Repair Tutorial
Embedded thumbnail for DIY Cut Bike Steer Tube and Tap Star Nut Down

DIY Cut Bike Steer Tube and Tap Star Nut Down

I'm going to be trimming down my steer tube. I actually just thought this up on how to tap the star nut down without using an actual star nut tool. What I'm going to do is...

Company: Cane Creek
Type: Repair Tutorial
Embedded thumbnail for How to Install a Star Nut in a Bicycle Fork

How to Install a Star Nut in a Bicycle Fork

I'm going to show you how to install a star nut into your bicycle fork.

Star Nut in Fork

In order to install the star nut straight into the...

Company: Park
Type: Repair Tutorial
Embedded thumbnail for How to Set Up Mountain Bike Suspension Fork

How to Set Up Mountain Bike Suspension Fork

Suspension on mountain bikes is a really important area, and with most suspension forks and rear shocks being air sprung, knowing exactly how to get the air into your fork and how much air should...

Type: Repair Tutorial
Embedded thumbnail for How to Install a Sealed Bearing Headset

How to Install a Sealed Bearing Headset

A headset is basically the piece that holds the fork to the frame of a bike, thereby allowing for steering. A sealed bearing headset normally has a plastic or rubber gasket to protect the insides...

Company: Cane Creek
Type: Repair Tutorial

The forks are two dropouts in the frame of the bike that hold the front tire, connected at the top by a crown. Above that, the steerer tube goes up through the headset and attaches to the handlebars enabling the rider to steer the bike. An axle (called a skewer) is threaded through the fork dropouts and the wheel, and clamps the two together.

Bike fork Fork location

Forks have many different profiles depending on the type of bike. Road bikes generally have narrow and rigid forks, while mountain bikes often have suspension. Forks with suspension create stable traction by keeping the bike in more frequent contact with the ground. They also help protect the bike from being damaged by providing a cushion while riding, which is why they're mostly used on the rugged terrain.

Fork travel

Forks come in many styles, and are a built-for-purpose component critical to performance in any riding conditions.

 

The most complex forks go on mountain bikes. Quality of each component of the fork (spring or dampening) effects the final price, and depending on company preference and suspension details, they can get quite pricey. Assorted parts such as o-rings and boots can be purchased online for pennies. Whole suspension forks come in under $60, but high quality forks will be greater than $200, with some special performance suspension going for more than $1,000.

Stoppie whut whut

Let's not leave out road cyclists. Road forks (often called 'rigid forks') from the finest manufacturers can sometimes be made of 100% carbon composite and alloys. On average they're around $350, but some nice performance models can exceed $1,300. The forks are an important part to the structure of the bike, with qualities like the rake that have a small margin of error to make the difference.

Road bike front wheel

To swap your forks, you will need these tools:

  • Crown Race Puller
  • Torque wrench
  • Tape measure
  • Repair stand
  • Hammer
  • Screwdriver
  • Allen wrenches 
  • Star nut setting tool
  • Hacksaw
  • Saw guide

Let's get started:

Removal

Put the bike securely on a repair stand.

Remove the front wheel and disconnect any brake lines

Remove the top cap on the headset and loosen the stem bolts.

The old steerer tube should slide out, but it is very important to maintain the order of the headset components. The old forks should be free and clear of the frame.

Crown race

Take the crown race from the old set of forks using the Crown Race Puller. It will need to be inserted on the new forks to give bearing to the headset when they are installed . Misuse of the crown race tool can damage the forks or the crown race itself.


Installation

Steerer tubes are manufactured long enough to fit any custom build imaginable. They are expected to be cut to the right length.

Marking the steerer

With the bike still on the stand, assemble the headset again by putting the new forks though the head tube. Put on the crown race, the spacers and the stem. With everything connected, mark with a pencil or sharpie where the excess steerer tube begins above the stem. The cut will be 4mm below this mark to make sure the steerer tube fits within the stem reasonably. Remove the forks and prepare to cut.

fork cut

Secure the forks on a workbench, and measure and make a new mark 4mm below the current line on steerer tube.

Properly cut tube

Using the hacksaw and sawguide, cut the forks 4mm lower than the mark made. File the rough edges after the cut for a professional finish.

With the forks now cut to fit your bike, the final piece is to install the star nut (on threadless headsets). This is what the top cap screws into to keep the forks from falling out the bottom. Secure the forks a repair stand. Park Tool makes a good installation tool, but for those of us on a budget, you can run a screwdriver through the center of the star nut, and lightly hammer it down into the steerer tube about an inch. There isn't a standard distance the star nut needs to be, just shallow enough for the the top screw to grab on to it.

Install the steerer tube through the headset, apply the spacers and the stem, and screw down the top cap to secure everything in place.

Replace the front wheel and the brake lines, and the job is complete. 

Install fork

Obviously the fork dropouts need to be deep and wide enough to accommodate the right wheel. The arms should have the right amount of rake for the frame. 

Rake

Bike forks are designed with something called rake. Basically the forks are curved forward to counteract the drag received while riding. This aids the bike in keeping sharp steering as the forks keep the wheel pushing ahead. It is measured as the inline difference between the center of the steerer tube, and the center of the skewer hole in the dropout.

Rake of the fork

Most road racing bikes have a rake offset of 40-45mm. Large wheels often require a larger rake offset.

Length
Fork length is measured from the bottom of the lower bearing race to the center of the dropout. Road racing forks are around 370mm in length.
 

Fork length

 
Width
Measured perpendicular to the forks at the dropout. Commonly referred to as spacing, road bikes usually have a width of 100mm while downhill and mountain bikes are wider. 

Fork Spacing

Steerer Tube dimensions

Steerer tubes can be different lengths to meet desired handlebar heights on both threaded and threadless headsets. They can't stand higher than the headset stack, and are therefore cut to the proper height upon installation. There are numerous adapter kits for smaller diameter steerer tubes fitting into different headsets. 

Steerer tube dimensions

A major aspect in mountain bike forks is the suspension. Telescopic, shock absorbing forks emerged in the early 90s, and technology has improved to today's space-age, ultra-sensitive suspensions systems we know and love. Suspension forks usually consist of a spring and a damper. The spring can be any mechanism (metal coil or even compressed air) that provides a varying level of stability to the fork. The damper could be a series of valves which oil passage is limited, providing the suspension with a softer bottom-end during high stress impacts. 

mountain bike forks

Some relevant suspension terms:

  1. Travel: the distance the axle moves
  2. Preload: initial tension on suspension springs before external loads are applied. Soft suspension has a less preload, and very rigid suspension has a high preload. 
  3. Rebound: refers to the speed at which the suspension returns to its initial state after an external shock. Rebound dampers vary the rebound speed, possibly causing the shock to return to normal more slowly.
  4. Sag: The resting height of the suspension with the rider included. This is taken into consideration for adjustment.
  5. Lockout: Toggle-like mechanism that bypasses suspension in desired situations that require a more rigid frame. Some lockout systems have a cancelation feature that activates under sudden unexpectedly high loads (like crashing) to protect the bike and rider.   
  6. Bob and squat: Phenomenon that occurs when the suspension responds to the pedaling of the rider, robbing some acceleration power.
  7. Pedal feedback: With the rear axle moving (and therefore changing the angle in relation to the bottom bracket), the chain is tightened and shortened. This is felt as torque that is opposite to pedaling when riding.
  8. Compression dampening: slowing down the rate of shock compression by forcing fluid (air or oil) through a valve. Resistance at the valve vary, and can sometimes be adjusted, therefore softening or hardening the ride. 
  9. Unsprung mass: Refers to the collective body of components unsupported by suspension. In the case of mountain bikes, this means only the wheels and other minimal parts below the shocks, but road cycles having no suspension system are nearly 100% unsprung mass. When the rider lifts from the seat, his/her knees provide shock absorption therefore rendering them sprung mass.