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Why Do Dirt Bikes Have Upside Down Forks?

Have you noticed those dirt bikes racing around on the tracks and trails while their forks are inverted? There is a clear reason:

Upside down front suspension forks on a dirt bike allow the front end to be stiffer. Riders using inverted forks are then able to have greater responsiveness in their steering and this leads to better cornering, as well as better handling in whoop sections. As a result, there is reduced stiction between the lower and upper halves of the fork.

There is a lot of engineering jargon and technical reasons why dirt bike riders choose to modify their dirt bikes like this, but Frontaer will try to keep things simple.

Fitting Dirt Bikes with Upside Down Forks

Having inverted forks has sound engineering principles, but do you really need it? Well, if you’re riding a dirt bike, then it really depends on your riding style. Most commonly you’ll find riders choosing to reverse their forks on their road motorcycles as opposed to dirt bikes.

If you’re the type that wants to win championships or take the lead in a recreational group ride, then you’re going to be pushing yourself behind the limits of your forks. This is when you’re going to move up from amateur to professional, and as a race bike, you’re going to want forks. The same can be said for adventure motorcycles who need to be stiffer in the front end to cater for the additional weight of camping gear and additional fuel.

The rigidity can far outweight the cost, but it still depends on your riding style and type of motorcycle, as well as your weight. For those who love to claim some airtime, the suspension lifecycle will be enhanced through inverting the forks in most cases.

To invert them, you can often get this done yourself or get a mechanic to go through the process. This will cost you $200 or if you do it yourself, 2 to 3 hours of your time on the weekend.

Disadvantages of Inverted Forks

While many sing the praises of inverted forks, and they certainly do have their advantages, there are some downsides too. This is why you won’t see them on most dirt bikes, despite the riders knowing of their upsides.

The disadvantages include:

  1. Challenging to Service. If you’re riding often and clocking up the miles, then you’ll be servicing your dirt bike just as often. The services on the fork seals will be challenging, especially as you won’t have a drain on your upside down fork. How are you going to release the oil? Certainly you’re going to need some assistance there and mechanics themselves have a tough time with this task.
  2. A Hazard to Braking Systems. When your fork seals let themselves go, then you can have a genuine issue on your hands. With upright forks, a leaking fork seal isn’t too hazardous and you can ride it out until you get back to the trail head or finish your race since gravity is on your side. With a USD fork, this is very much a case of gravity working against you. Given the location of the fork seal (directly above the front brake assembly), all that fluid is most likely going to end up on your front pads and tyre.
  3. The upfront cost. To transfer from upright to inverted front suspension forks requires time and patience, with some extra help if you’re not mechanically inclined. If you’re not happy with the handling or the dangers that it poses, then you’ll spend additional time reverting it back.

Now – don’t let us scare you here. Thousands of dirt bike riders would only get behind the handlebars if their forks were inverted already given the advantages.

Closing Thoughts

You really have to weigh up the cost. It’s very debatable among the dirt bike riding groups on Facebook, but one thing is for sure – they certainly do make your suspension a little tougher but aren’t without the risks.

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