A Dummies Guide to Bike Fork Sizes and Types

Bike forks have changed many times, so we are left with different sizes and types. And if you are new to mountain biking, all of these differences can be hard to know and understand.

So, in this article, we’ll tell you all about these fork types and sizes and where you can expect to see them.

What is a Bike Fork?

Let’s start right at the beginning and explain what a bicycle fork is. Bicycle forks are what hold the front wheel on the bike. The forks are separate from the bike’s frame as far as moving parts go. 

Forks have a huge amount of purpose on a bike, and although they might look like a fairly basic part, they serve many purposes.

What is the Purpose of the Fork?

Forks on bikes are not just there to hold a wheel, and you can completely change the way a bike rides but swapping out the forks for different types and styles. 

So what is the purpose of a Fork;

Steering Axis

The First thing a fork has to do is give the rider the capability to steer the bike. Forks connect to the bike through the headset. The headset is a set of bearings that can spin the fork left and right freely, giving it the ability to change direction.

Suspension

Forks are also vital for giving us suspension, especially on mountain bikes. Suspensions increase comfort and allow you to go off-road without killing your butt and back. That’s because they make going over lumpy terrain easier and much more comfortable for the rider. 

Geometry

You can have aggressive racing bikes or comfortable endurance bikes. The forks play a huge part in the bike’s geometry and the feeling it will give you when riding.

Ability

Forks can give a bike better ability. For example, suspension forks mean the terrain can be rougher, and the bike will be able to handle it. 

Forks with a longer rake that sit the front wheel further forward have the ability to make the bike longer and improve rider control. Forks with a shorter rake can make a bike feel more agile.

What are the different types of fork models?

Before we go into sizes, it’s important to speak about the two main types of forks, Rigid and Suspension.

Rigid

Rigid forks are forks that are stuck in one single position. A good example of a rigid fork is on a road bike. You can use it to steer, but it can’t move in any other way. These forks are lightweight, stiff, and very agile.

Suspension

Suspension forks are what you will typically see on a mountain bike. They have the ability not just to steer but can also shorten and lengthen vertically. The right spring and dampener give the bike a better ability to roll over bumps and lighten the load off your hands.

What are forks made of?

You’ll find bike forks in three different materials, and each of them gives the bike some very different abilities when it comes to riding.

Carbon Fiber

Carbon fiber is an excellent material, and it is by far the lightest and stiffest material you can buy when it comes to bike components. 

It is the most common material on rigid forks, and you will see many bikes completely built from carbon fiber. The best rigid road forks are carbon fiber.

Steel

Steel forks are fairly heavy and very strong. They have an amazing ability to be flexible enough to soak up the road’s vibrations. You will see many of these forks on touring and gravel bikes.

Aluminum

Then you have aluminum which is nearly as stiff as carbon, but it is heavier and very cheap to produce. You will see these forks on entry-level budget bikes.

A lot of things go into making suspension forks. You have metal tubing, Springs, rubber gaskets, foam inserts, and oil. They are very complex and are full of amazing components.

What are the Different Fork Sizes?

Typically on bikes, you will see a few different sizes of forks. You get different sizes on types of bikes. On-road bikes, you will get 700c, 650c, and even 650b. 

These refer to the size of wheels they fit and the type of tires. An easier way to understand this is to come away from the French measurement and go to the mountain bike sizing of traditional inches.

29″

The 29″ fork is currently the largest fork on the market and fits wheels that are 29″. Wheels this big are excellent at rolling over obstacles. They are also very efficient at high speeds, and you have many tire choices.

27.5″

27.5″ forks suit 27.5″ wheels, and this size is a little smaller than the 29″. They can work around objects more easily and are much more agile than larger wheels as they are smaller. They are excellent at acceleration and for very technical short courses are amazing.

26″

The 26″ wheels are the smallest on this list apart from children’s sizes. They were a very common size 20 years ago and the standard size most mountain bikes would use. 

They are now not so common, but we must mention them as you will see this size on some downhill bikes. Being even smaller than the 27.5″ wheels, they are extremely agile and quick to accelerate.

Headset Sizes 

When thinking about fork sizes, you also have to think about headset bearings sizes because unless you have the right size, the fork won’t work. 

There are many sizes, such as 1″ straight, 1 1/8, and many more. There’s also a tapered steerer, which is the design on the tubing and is very common on modern forks. You will have to ensure if you ever change the fork, whatever you take out will have to match the headset type.

Brakes

Another thing worth thinking about is brakes. On old bikes, you would either have disc or rim brakes. Typically on most modern mountain bikes, you have disc brakes. 

You’re going to want to ensure that you are not using a very old fork with rim brakes and go for disc instead, as this is how many bikes are. Modern forks have disc brake mounts for your brake caliper to rear on.

Suspension Travel

When looking at a new pair of forks, sometimes the first thing you want to know is about the travel. The travel is the amount that the suspension fork can move vertically. Depending on what kind of mountain biking you might be doing, you might need more or less.

XC Mountain Biking 

When riding XC, you will want a 100-130mm travel on your forks. This is because XC, or Cross Country as many call it, isn’t super technical and doesn’t require a huge amount of travel. It’s about lighter and faster forks.

All Mountain – Trails

Then you have All Mountain and Trail bike forks. On all-mountain and trail bikes, you’re going to want a bit more capability than XC, so you want the fork travel to be about 150mm. This ensures you can do jumps and get over those tougher obstacles.

Enduro

Enduro racing and riding are very demanding on the forks as you’re going to be getting air often, and it’s going to need to be able to dampen out a very demanding course. The travel on enduro forks is as much as 180mm.

Downhill

Downhill courses are the most demanding courses you can get for off-road riding, and you need an incredible amount of capability. Downhill mountain bike forks can go all the way to 200mm+. 

How Does a Mountain Bike Suspension Fork Work

Mountain bike fork works differently from what many people think, and typically the most common type uses a coil spring. 

When you look at a set of forks, most people assume that forks have a spring on each side and oil dampens the movement, but you couldn’t be more wrong.

When you look at a bike fork, there are two main chambers. On one side, you have a spring, and on the other, you have a damper. The spring takes the impact and rebounds back to the original position when you go over a bump. 

This alone would make cycling very difficult, and it would be very tough to control, so we require a way to dampen this process, and that comes from the other chamber, which has air inside it. The whole system is completely lubricated with oil as it works.

The beauty of this setup is that it is very light and efficient, but you can also adjust the way the suspension works. You can lock the spring if required, for example, if you are riding on a road, and you can also adjust the amount of dampening that the fork does.

Unique Types of Suspension

In this article, we are speaking about different types of suspension, and although we have given the basic types and sizes, it’s vital to speak about some of the unique types of suspension forks on the market. 

The Lefty

Cannondale released a fork called the lefty. This is an incredible fork, and unlike your typical suspension, where you have twin fork legs, you have only a chamber on one side. 

This does make the suspension lighter and much stiffer but does come with challenges such as needing certain wheels to ensure it can work properly. 

Trust Message

The Trust message is a multi-link fork that looks nothing like a traditional fork and works uniquely. What makes it amazing is it is very light with its full carbon chassis and has a very short axle to crown.

Lauf Forks

Lauf makes forks mainly for light XC bikes and Gravel bikes, and they are full carbon forks with a carbon fiber blade system for suspension. It doesn’t offer much travel, but it is incredibly light and looks insane.

How Do You Choose a Fork for your Mountain Bike?

What’s your budget?

Forks are not cheap, and you can find yourself spending a lot of money on a set. So the first thing to think about is how much you want to spend.

What riding will you be doing?

Then it would help if you thought about the riding that you’re going to be doing. If you plan on XC, a light fork with minimal travel will be fine. You will need something a little more off-road-ready if you’re doing downhill.

Will it fit?

Then you will need to check if it’s going to fit. You need to check the wheel’s size that you plan to put into them. You also need to check the headset size to ensure it will fit into your frame and fork. Lastly, you need to ensure the wheel axle matches your bike and wheels.

Is it a reputable brand?

It’s important to think about brands as well. You want to go for a good brand. Not only because you get assurance that you have support channels to go down if you have any issues, but you also can easily get spares if they release newer models or change the design later in time.

Geometry

Also, thinking about fork offsets, head angle, and stack height will help you get the right bike fork. Asking a bike fitter for help is an excellent way to look at bike frames and forks. 

Conclusion

When it comes to forks, it can be very challenging as there are so many on the market and quite a few different sizes and types. Spending time doing your research and making sure you get it right the first time will go a long way and be well worth doing.

 FAQ’s

What’s a Threaded Headset?

A threaded headset is a very old fork that you used to have to screw bolts on the steerer tubes. It’s old school, and unless you’re really into classic bikes, you won’t see them often.

Does Rider Weight matter with Forks

Only when it comes to the adjustment phase will it matter. You might need a little more dampening or maybe even a little less. 

What do you class as Expensive Forks?

Good forks are not cheap. A high-end set of downhill forks can be $2000 or more. Try not to spend more than a brand new bike when you think about a fork upgrade.

Is less travel a lighter weight fork?

Typically the lighter the fork, the less travel. Big downhill forks are very heavy, but it does work when going downhill.

Photo of author
Written By Robbie Ferri
My name is Robbie Ferri, I’m an Ultra Endurance cyclist from the UK. I have been lucky enough to have cycled all over the world. With some amazing world record attempts, bikepacking races, and many miles under my belt I couldn’t think of anywhere I’d rather be than on my bike.

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