Let Me Tell You The Ins and Outs Of Suspension-corrected Forks

From Rookie’s Keyboard,

Hello, friends

It’s Sunday evening where I live. A perfect timing for a simple tutorial, a cold beverage in an aluminum can, and a new tutorial that will help you understand the cycling world a little better. 

Today’s topic is an enigma known as “Suspension-Corrected Fork“. 

It sounds complicated, but it’s as simple as 2+2.

First, we have to analyze how a suspension fork operates. 

When a suspension fork faces an obstacle or the rider shifts their weight onto the handlebars, the fork compresses and gets effectively shorter. 

After overcoming the obstacle, the fork returns to its original non-compressed length. 

In its short (compressed) position, the fork brings the handlebars closer to the ground and with them rider too. 

The geometry of frames designed for suspension forks must account for this shift. If it doesn’t, the rider will get too close to the ground when the fork is compressed and may fall over the handlebars. 

So, what is the required change? 

In simple words, the head tube (front of the bike) has to sit higher. In more complicated words, the head tube angle has to get slacker. 

The head tube angle is the angle between the head tube and the ground (or a line perpendicular to the ground passing through the front and rear axle). 

(It will all make sense in just a second. Hold on. Tik-Tok can wait.)

If we take a standard rigid fork (the type that you find on retro 26″ MTBs) and place it on a frame designed for a suspension fork, the head tube will get too close to the ground. The outcome will be a compromised geometry and an unpleasant (if not dangerous ride).

This is where suspension-corrected forks come to save the day. 

A suspension-corrected fork is longer than standard rigid models. As a result, it preserves the original head tube angle of the bike (when the fork wouldn’t be compressed) and the overall geometry. 

Calculating The Length of a Suspension-corrected Fork

At this point, many rookies will assume that the suspension-corrected fork has to match the length of the original suspension model. It’s logical, but the game isn’t so simple because of a little phenomenon known as fork sag.

Even when the fork isn’t facing an obstacle, and you aren’t leaning on it, it compresses ever so slightly. That movement is called sagging, and the distance is known as “sag”. 

To find a suspension-corrected fork of the perfect length, it’s necessary to know the sag too, and take it out of the fork’s length. 

Measuring The Sag Of A Fork (Ghetto Method)

It’s super easy to measure the sag of a fork. All you need is a single zip-tie. 

Step 1: Wrap the zip tie right above one of the fork’s seals as shown in the image below. 

Important: Don’t use the zip tie as it’s normally intended. Instead, slide it in reverse so that the teeth don’t catch. That way you will be able to easily remove it later. 

Step 2: Get on the bike and move your weight to the middle (above the bottom bracket). 

Don’t get too close to the handlebars as the shift will affect the measurement too much.

Step 3: Get off the bike and measure the distance between the zip tie and the seal. 

That’s the sag. Record that measurement as we will need it for the next step. 

Selecting a Suspension-corrected Fork of The Right Size

The length of a fork is the distance between the axle and the top of the crown. 

Some noobs (no offense) might mistake the crown for the arc. Don’t worry I was less educated than you when I started. 

The arc is the bridge between the two lower boots (lowers for short) and doesn’t move. Meanwhile, the crown connects the stanchions and sits higher.

When the fork compresses, the crown gets closer to the ground whereas the arc doesn’t move.

To learn what type of suspension-corrected fork to get, you need the following data:

  • The axle-to-crown (ATC) length of the original fork
  • The sag of the original fork

Subtract the sag from the ATC, and you will have the length of the correction fork you need to preserve the original geometry of your bicycle. 

Of course, it may be difficult to find a SC fork with the exact measurement. Some deviations are fine, but no more than 20mm. 

Also, you have to be aware of the repercussions. 

If you get a longer-than-needed SC fork, you will elevate the front end of the bike and make climbing more difficult. 

If the fork is too short, the head tube angle will get steeper (close to the ground), and you risk getting over the handlebars. Descents will be scarier and less efficient. 

A Note On Head Tubes

Don’t forget that the new fork has to be made for the original head tube. The part that you have to look for is the steerer.

Most suspension-corrected forks are designed for MTBs and come with a 1-1/8″ steerer. 

If you have a more modern frame, chances are that it has a tapered head tube. In other words, the top of the head tube is narrow and gets progressively wider. 

In that case, a standard 1-1/8″ fork won’t work unless you get an adapter (reducer) for the lower part of the head tube. Ideally, you will find a tapered SC fork. But to be honest, those are very rare, at least where I live. 

There you have it, friends. 

That’s all you need to know…

Oh, wait. I almost forgot. We also have to talk about the fork’s material. You have three options – steel, aluminum, and carbon. 

IMO, the best option is steel as it gives a smoother ride (unlike aluminum) and costs less than carbon. 

Aluminum is cheap and light but has no compliance and will do a number on your wrists…wouldn’t be my choice for a fork material. 

Carbon is compliant and light, but expensive and is as fragile as a chicken leg on impact. 

So, steel is real, once again. 

There you have it, friends. Another educational article for the rookies out there. 

Until next time,

– rookie






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