HIT MTB Air Fork Piston Upgrade - Fox 36 Float NA2 2018+

FAQ

HOW CAN ACTIVATED CARBON POSSIBLY INCREASE THE EFFECTIVE AIR VOLUME?
It may seem counterintuitive, but adsorption is how this happens. As the fork or shock is compressed, some air adheres to the surface of the carbon. The air adhered to the carbon can have much higher density, and so reduces the pressure in the rest of the gas (compared to a chamber without any activated carbon). You can find out more on our Technology page.

IS IT THE SAME AS OTHER PISTON UPGRADES ON THE MARKET?
The HIT piston contains activated carbon. As well as providing increased effective volume, it also reduces the speed sensitivity inherent to an air suspension. The result is much greater compliance than simply increasing air volume, helping to provide a lot better small bump sensitivity and a more predictable feel.  

IS THE ACTIVATED CARBON AFFECTED BY MOISTURE?
The effect is influenced by moisture, as water vapour competes with air in attaching itself to the carbon surface. In the sealed fork chamber, the amount of moisture is not sufficient to influence the effect or degrade performance over time. Provided the piston is stored in dry conditions when out of the fork the performance will not be affected. Even after exposure to high humidity, the difference in performance is small as the surface area available for the air molecules at high pressure is still very high.

DOES THE CARBON RELEASE POWDER OR DUST INTO THE FORK?
We use a fine filter that we have selected out of many, having subjected it to shakers, test riding and dyno testing to ensure that there was no build-up of powder over time. We also apply a coating to the carbon to minimise powder production and allow a tight pack of granules in our products, reducing internal movement.

IS THE EFFECT DEPENDENT ON TEMPERATURE AND PRESSURE?
The effective increase in volume is temperature dependent, with around 5-10% variation between 0 and 40C. This is a small difference In terms of total fork volume, and so does not cause a dramatic change in feeling. The air pressure in the fork is slightly more sensitive to temperature than a regular air spring - the reason for this is that the carbon stores air in its pores which can be released by heating (and vice-versa trapped by cooling). The net effect in the fork depends on the amount of material, so we have found the right balance based on our test riding. The effect is also dependent on charge pressure, with higher pressure resulting in a smaller (but still stiffness reducing) effect. The pressures at which the activated carbon is no longer effective are much higher than those found in MTB air suspensions, including shock absorbers.

IS THE ACTIVATED CARBON AFFECTED BY SUSPENSION OIL AND GREASE?
When activated carbon is used in filters, substances accumulate and saturate the carbon as contaminated air or water flows through, and so over time the filters become less effective and need to be replaced. In the sealed environment of the fork, the only contaminants that can affect the behaviour are suspension oil and grease, and they do not continuously flow through the material and the degradation in performance is much lower.

Based on our lab tests, our products stops adding effective volume when they are half full of suspension oil (by volume). Typically, the total amount of oil inside the air chamber for a service is around 3ml which is a lot less than the volume of carbon we use. Our HIT piston is purposely designed and tested to avoid contamination with oil and grease. We do however recommend not using excessive oil or grease in order to minimise any performance changes over time.

Delivery

For spare parts, if they are in stock we will send them out the same day if we receive the order before midday (except weekends). If we receive the order after midday, we will do our best to despatch them same day, but it may be the following working day. Orders placed after 3pm on Friday will be despatched on the following Monday. We normally send spare parts by Royal Mail post (see below or our 'Shipping' page for cost/delivery times).

Forks, shocks and large/heavy orders go by courier. UK deliveries are with DPD Local, for overseas customers it's DPD, FedEx or DHL.  In all cases these are fully tracked services and you'll need to sign for the delivery - please provide a suitable address with extra instructions if necessary.

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