photo: Leah Barber

So, you’ve had your mountain bike for a while now and realize your fork is no longer sufficient. You’ve probably reached this conclusion in one of two ways. Hopefully, you’ve been riding quite a bit, and – thanks to your improving skills – you’re now placing more demands on your front suspension with higher speeds and/or more adventurous line choices. Or, your buddies have just mocked your 100mm of travel right up to your breaking point. Either way, the pressure to go long is real.

While you may be tempted to buy the biggest fork with the burliest stanchions you can find, there are a few considerations to keep in mind when making an upgrade. Be sure to read this entire article to stay safe and avoid any surprises.

Travel trade-offs

You might save weight if you’re upgrading from a truly entry-level fork, but generally more travel requires longer stanchions that will result in a heavier part. As forks get longer, stanchions also increase in diameter to prevent the fork from flexing like a wet noodle.

They call this a Fox 34 because it has 34mm (diameter) stanchions. Also, the Kashima coating matches the fall colors in North Carolina’s DuPont State Forest quite nicely.

Fox Suspension Float Performance Elite LV Rear Shock 2018
$152.99    Chain Reaction Cycles (US & Canada)   AD 

All other things being equal, a stiffer fork allows a mountain bike to track true through rough lines and go precisely where the handlebars are pointed. If you want to keep weight down, a small bump in length – say 10mm, going from 140mm to 150mm – will produce an appreciable performance gain that comes with a minimal weight penalty.

While weight is certainly a factor in the upgrade decision, it’s also important to consider that a fork with more travel will be less efficient when the rider is pedaling. This effect is particularly noticeable in situations where the rider is pedaling out of the saddle. Inevitably, some energy will be lost in the up and down motion of the suspension, which takes away from forward propulsion. For racers, this compromise must be considered carefully.

Geometry changes

Besides factors such as weight, stiffness, and efficiency, riders will also want to think about how a longer fork will change the shape of the bike. As the fork gets longer, it raises handlebars up and slackens the head tube angle. As a rough estimate, each 20mm of travel added will correlate to a one-degree difference in the head tube angle.

Instead of the stock 150mm fork, I opted for a 160mm Pike on this Giant Trance Advanced frame build.

RockShox Pike RCT3 Dual Position Air 160 Fork - 27.5in - 2017
$789.95    Backcountry.com   AD 

Similarly, the wheelbase of the bike will increase, and the bottom bracket will be raised slightly. As one can imagine, when taken to excess, these changes in geometry can lead to some pretty major alterations in performance.


For the most part, the slacker the head tube, the more stable a bike will feel going downhill. A longer wheelbase has the same effect. All good, right? Well, everything has a downside. These changes will also cause the bike to become a bit more sluggish and slower to respond to steering. Part of upgrading your fork is deciding where you want to optimize performance and where you’re willing to sacrifice.

In general, bikes will happily accept forks that are up to 20mm larger than their designers intended. Feel free to go beyond that if you must, but be prepared for a bike that the manufacturer didn’t really intend to create. That doesn’t mean it will suck, but it’s just something to be aware of.

Look before you leap

Pivot Mach 4 Fox 34 Fork Front Suspension

photo: Leah Barber

Fox Suspension 36 Float Factory HSC LSC Forks - 29" 160mm 51mm
$509.98    Wiggle US   AD 

Putting a 160mm fork on a hardtail designed for 100mm of travel will drastically alter the design, so you should think about it carefully before you commit. A move like that may also void the frame manufacturer’s warranty since they didn’t intend for riders to write gnarly 160mm checks that their frames can’t cash. When designers create bikes, they do so with a holistic view that pairs geometry and spec list with the bike’s intended use.

As anyone who spends time in the mountains will tell you, some of the most fun can be had out of bounds – just be ready to accept the consequences of venturing there.

# Comments

  • rajflyboy

    They say you CAN’T over fork a bike

    I tend to agree with this from my experiences

    • Jason Brendlinger

      Not sure how that can be accurate. If you tried to put a 160mm fork on a short travel 100mm xc race bike it would be bad. 1st it would handle like garbage with extreme angles etc. Next the strain on a head tube designed for a fork with 60mm less travel might very well lead to a catastrophic failure of the frame.

      Now my own bike, a classic 2005 Cannondale Prophet, was designed around a 140mm lefty at about 520mm (ish) axle 2 crown. The bike has a max spec of 530mm a2c. Beyond that it could cause issues. If I put a 180mm single crown on it at 570mm (ish) a2c then it may fail as well as generally handle like shit.

      So it is very possible to over fork a bike. Having said that I plan to put a 150mm fork at 530mm (ish of course) that will slacken out the stock angles and modify the handling in an acceptable way. There’s room to play there within reason.

      Respect frame specs and limits and have fun.

    • dogboywonder

      Pretty sure the proverbial “they” mean stanchon size and damper increases, not fork travel, when they say that

  • Brian Gerow

    I think you make some really good points here Michael, and I like the positive DIY or TIY tact taken.
    Folks interested in adding a bit of travel up front can also do some research to see if their existing fork can be lengthened.
    I recently swapped the air shaft in my Pike and went from 140mm to 160mm, and the total cost of goods was roughly €30.

    • mongwolf

      Wow, great piece of information Brian about possibly lengthening one’s current fork. Thanks. That may come in handy someday.

  • Noggus

    I was lucky enough to be able to change the air tube (?) in my fork to get more travel out of it. Then I added tokens and lowered the air pressure. Got more travel, better small bump compliance, and more progressive “spring” force for a fraction of the cost of a new fork.

    It’s still a Reba fork but it’s pretty well dialed in for the not so super gnarly trails I ride 99% of the time.

  • mongwolf

    Hey Michael nice piece. Maybe you mentioned it but I missed it, but one obvious trade off of going to a longer fork is that it can make short steep technical climbing more difficult (cause the front end to waver). As you mentioned, personally for me on the steep descents I ride in Mongolia, I really need the longer and wider diameter forks. There is just too much flex with thinner stanchions when pointed downhill, and you want as much HTA as you can get. It pretty much requires 160mm minimum and 36″. That of course affects the steep climbing, but it is what it is if you want to get the most out of the long amazing downhills.

  • Revnick

    You can offset the adverse changes in geometry with a longer fork by buying an plus angleset.
    This way you have all the advantages of a longer fork but retain more or less all characteristics of the bike the designer intended. It will not be exact but it will come close.
    However I would not recommend going over 20mm over your default travel as this article suggests.
    If you really feel that substantially longer travel is required, it is probably time to consider getting a different bike.

  • Andres Franco

    I got a Trel Fuel Ex 9.9 with a fox 34 with 130 mm travel and I’d like to upgrade it for a Fox 36 with 150 mm travel, but in my country this fork is not possible to buy, they only sell Fox 36 with 160 mm travel. Are these 30 mm more too much for the bike?

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