With mountain bike technology becoming more advanced year by year, we find that we are always searching for the next best thing to help us go faster and ride farther. Whether it be more efficient drivetrains or faster tires, there is always something we can buy to upgrade our bikes and our rides. Sometimes it feels like its hard to keep up, especially when it comes to your wallet! |
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If you ride in any type of rough terrain you will realize how important it is to have the proper suspension components on your bike and also how important it is to have them adjusted correctly to get the best possible performance out of these parts.
Many people opt for custom tunes from places such as PUSH Industries to get the most that they can out of their forks and shocks while others might start replacing internal parts such as dampers or adding tokens. Regardless of your method, there is always room for improvement when it comes to suspension tuning.
One component you can use to improve the performance of your fork is called the Runt from Diaz Suspension Design in Durango, Colorado. The Runt is a drop in air cartridge that offers you two air chambers to help fine tune your fork's damping and overall performance. It is designed to improve the initial, mid, and the end stroke of your fork's travel giving you a more linear stroke like a coil fork would have.
The Runt slides into the upper leg of your fork under your air cap where your tokens\spacers would go if you used any. After installing the Runt you will have a low (main) and high (small) air chamber which you will adjust according to your weight and riding style.
When the low air chamber's pressure equalizes the high chamber's pressure, the floating piston begins to move, allowing for a linear pressure curve. The image below shows the cycle of the fork piston with the Runt installed.
But rather than going too much into the science behind the runt we would now like to talk about its performance. We did a test run with a Fox 36 fork with a PUSH tune without the Runt on a fast trail that had some rough hardpack as well as loose rocky sections. We used Strava to time the run and then installed the Runt and did the run once again without purposely trying to go faster than normal. The first round yielded a 25 second increase in time for a 4 minute run. Then we made some adjustments and ran it again and took off another 10 seconds. Of course there are always other variables to account for but overall it was quite a noticeable improvement.
The Runt is very sensitive to pressure changes adding or removing only a few PSI will make a sizeable difference in how your fork performs. It's a good idea to do the same run over again after making any changes to see how it feels. They have an initial setup formula where you take your original fork PSI, drop it by 5-10 PSI and that's what you set the low chamber pressure at. Then you will double that number for your high chamber pressure. So if you normally run 70 PSI you can start by filling your low chamber to 60 PSI and your high chamber to 120 PSI. Just be sure to fill your high chamber first. Diaz Suspension also says you should try and keep the 2:1 ratio when making changes and also make your changes in 2-5 PSI increments.
Depending on your fork model, there is also the option to change out the shims to increase the performance even more. This will require a bit more work and you will have to take apart your fork to use them so if you are not comfortable with that then you might want to think about having someone do the work for you.
Overall, the Runt made a nice improvement in all types of riding conditions but seems to perform better at higher speeds which is what you normally find with forks in general. If you are creeping over big rocks then you are going to feel it no matter what fork you have. And for only $200 it's definitely worth trying because its not going to break the bank for most people.
The Runt is only available for certain forks made during certain years and here is the current breakdown.
- Fox 36 - 2018-Current
- Marzocchi Bomber Z1
- RockShox Lyrik or Yari (Solo Air and Debonair)
- RockShox Pike or Revelation (BOOST 110mm, Solo Air and Debonair)
- RockShox Pike (NON-BOOST 100mm, Solo Air)
- FOX 34
- FOX Step-Cast 34
- FOX Rhythm 34
- Marzocchi Z2 Bomber
