The Basics of Upgrading the Fork on Your Mountain Bike (Check Before You Buy!) [Video]

Words by: Liam Woods

When choosing a new fork, it can be complicated figuring out what fork fits your bike. In this blog, we’ll go over the key things to keep in mind when making mountain bike upgrades with a new fork. There are tons of options (including fitment options) to consider so that you can be sure the fork fits your bike. As you read further, we’ll go over the more common questions and discuss the more modern products (roughly ‘09 and newer). There are millions of bicycles out there in the world -- and all sorts of exceptions to “common” -- so please keep that in mind.  

Fork Type and Travel

There are lots of bike front forks out there -- literally hundreds. You’ll not only want to get one that fits your bike but is also intended for your style of bike. This can almost always be determined by the travel of the fork. If you’ve got 80-100mm travel, odds are you’ve got an XC bike or general light trail bike; 120mm-140mm, you’ve got a modern-day trail bike; 150-170mm, it’s probably a modern-day enduro bike; and 200mm, you’ve most likely got a downhill bike.

You always want to keep the same fork travel that your bike is made for. When frames are engineered they are designed specifically around a certain travel fork. If your bike is meant for a 100mm travel fork, stick with 100mm and you’ll be happy.

If you desperately want to get a new fork with more or less travel, we NEVER suggest you go more than 20mm away from what the bike was designed around. If you do that, you are taking a major risk of disrupting the structural integrity of the frame and fork. You will also totally mess up the handling characteristics of your bike.

Steerer Tube Size

-Most common steerer tubes these days are tapered, which is 1.5’’ at the bottom and tapers to a 1-⅛’’ at the top. This is most common on newer bikes (2009+), but it is very rare or non-existent on older bikes. Older bikes often have a straight steerer, which is just straight 1-⅛’’ all the way. Certain older bikes might have a threaded straight steerer,  but that is extremely rare.

-You need to be sure you get the right size steerer tube because certain frames only fit certain steerer tubes. If you are planning to keep your existing headset, those are only designed for a certain size as well.

-Keep in mind there are some other weird steerer tubes out there. Cannondale and Giant are two bike brands that have made some super confusing and proprietary steerer tubes for their bikes only. If you’ve got one of those… you may be in for a struggle.

Wheel Size

-This seems obvious but as there are three wheel sizes these days (26’’, 27.5’’ and 29’’), it makes a big difference. So know your wheel size because bike front forks are specific to wheel size.  

-To add a bit more complexity, you’ve got Fat bikes and Plus bikes that use one of the three common wheel sizes, but need a different fork because of the super wide tires. If you’re in this boat, you’ve got to figure out what you’ve got and get a fork with the same spec. Eg. 27.5+, 29+, Fat Bike specific, etc. 

Offset

-This is only important for 29’’ wheeled bikes. Offset is how far the front hub sits out in front of the imaginary line that runs through the steering axis. All forks just come in the offset they come in, however, many forks made specifically for a 29’’ wheel are offered in two offset types. Standard and 51mm offset. The majority of modern-day 29’r frames are engineered around a 51mm offset fork as the 51mm offset simply works better with the 29’’ wheel. In some cases, there is a 29’r frame that is designed around a traditional offset, but that is rare and becoming more and more uncommon.

-If you have a 26’’ wheel or a 27.5’’ wheel, don’t worry about this at all. If you have a 29’r then you need to make sure what fork offset your frame is intended to use, very likely and most common it will be designed for a 51mm offset.I'm not going to explain what fork offset does as that is a whole topic on its own, one which we explained in our video on Fork Offset Explained.

-If you want to geek out more on fork offset, PinkBike wrote a great article you can read here.    

Axle

-You’ll want to get a fork with an axle that fits your front hub. Although 15x100  axles are very common, there are plenty of other “common” ones these days like the 15x110mm Boost axle, or the 20mm axle which is and always has been only 110mm wide, or the quick release axle also called QR or 9mm. Keep in mind a 15mm axle can also be called QR15, this means the 15mm axle has a quick release lever as shown in the pic below. Some 15mm and some 20mm axles have a QR feature and are often called QR15 or QR20 but that simply refers to the way you install/remove the axle from the fork. When you just hear "QR axle" with no reference to 15 or 20 then that means 9mm quick release style and not a thru axle. The 9mm QR axle is not a thru axle so the fork does not come with an axle and looks like the RockShox fork image shown below. 9mm QR is more old school and/or cheaper style. And of course, don’t forget the ever confusing Fat Bike axles... but that is a whole other topic. 

-Another confusing thing: The Predictive Steering hub. So far this is only available for RockShox RS1 forks, and if you have an RS1 fork you can only use the Predictive Steering hub. At the moment no other forks but the RS1 use this style axle/hub.  

-Know your hub, know your axle and get a fork that matches. Or you can opt to buy a new front wheel/hub/axle conversion kit if that option is available.

Brake Mount

-There are two mounting types (on modern-day MTB’s made for disc brakes), post mount and I.S. mount. Post mount is where you only have two bolts that mount the brake caliper to the fork, and they thread directly into the fork. The I.S. style mount always needs an adapter, two bolts go through two holes on the fork and thread into an adapter, then two bolts come straight down from the brake and thread into that adapter. Post mount style is more common on 2010+ bikes, and I.S. is more common on older bikes. But there are always exceptions.

-The 160 post mount is the most common on 2009+ bikes/forks. This means you can mount disc brakes directly to the fork, no adapter is needed and it will be spaced for a 160mm rotor. However, some forks like the Fox 36 series use a 180mm post mount. Newer Fox 40’s use a 200mm post mount, where the old ones used a super confusing I.S. mount that worked with a 160mm I.S. adapter but was spaced for a 203mm rotor.

-If you’ve got an older bike or entry level mountain bike you might have V-brakes. These mounts work and look entirely different than disc brakes. There is only one type of V-brake mount for mountain bike forks. So if you’ve got V-brakes and intend to keep them, you will need a fork with V-brake mounts.

-Brake adapters deserve an entire blog post of their own. (Or a dictionary-sized book!) The topic is seeming to get less complicated as time goes on but is still one of those things where lots of forks used different sizes and styles of mounts over the years.  

Air vs. Coil??:

Air VS Coil, the debate that still goes on everyday. When you are looking to upgrade your suspension fork, it's likely you will be looking at an Air fork. They are more adjustable, feel smoother most of the time, and normally they are the upgrade option. If you currently have a lower end coil fork, an air fork will make a huge improvement. Now, there are a few coil forks coming back to life in the mid-high end range, like MRP Ribbon Coil, CaneCreek Helm Coil, and the new Marzocchi Z1 Coil fork, are new coil options if you want a set it and forget it fork. If you are also looking to maybe turn your mid-high end fork into a coil fork, you can look at Push Industries ACS-3 coil insert kit. 

How Much Should You Spend?:

The last thing to consider is how much do you want to spend? This is hard to answer as it depends on your budget, riding amount, style, as well as what bike you are putting it on.

If you are upgrading a bike that is more than 10 years old, it's likely that you might want to think about even making those upgrades. For a little bit more money, you can often get a more modern mountain bike that has newer standards and geometry.

If you have a bike that is only a few years old, it's very likely you can make some upgrades that will work for your bike and might be future proof as well if you wanted to upgrade other parts as well. It also depends what you are looking for in your fork upgrade. Do you want a better feel, more travel, more adjustments, or lighter weight? Those are all things you should consider when looking at new forks.

Generally, the more money you spend you get better performance, in trail and XC forks you get a lighter weight fork and a better feel, on trail/enduro forks you normally get better performance, stiffer chassis, and more adjustments.

So are you the type of rider that needs any of those things? Then you might want to look at the upper midrange to high end forks. If you just want something that feels a bit better than you can probably look around the entry level - mid range type of forks. 

Beyond all these little things, you’ve got loads of options as far as features you want on your fork: lockout, compression, rebound, air or coil spring, etc. These require their own blog posts as well. All in all, this stuff can be more than a bit confusing…

Final Thoughts:

Wow, that is a lot of information to digest and think about. Upgrading your fork can get you some major performance improvement but it’s important to understand the right model for your bike. Also consider things like your bike's age, and how much it's worth to you. Then look at Wheel Size, Axle Type, Steerer Tube Type, Travel amount, Brake Mount type, and fork offset. With so much to consider, it's a great option to contact our customer service team, the experts at Worldwide Cyclery are here to help you get the correct fork on your bike, maybe give you some options to choose from and get you the best fork for your bike. 

This article was written / authored by Liam Woods. Liam has been in the bicycle industry for over 10 years as a racer, professional mechanic, service manager and as of late, media and content creator. Liam has ridden thousands of different bikes, ridden countless components, tested endless MTB apparel of all kinds and written reviews on it all. He's a key piece to the Worldwide Cyclery "All Things MTB" content creation puzzle. He also makes consistent appearances on the Worldwide Cyclery YouTube channel and Instagram.