TruTune "magic" spacers

24/12/23 10:08 Filed in: Gear

The progression in an air shock is a predictable process. Halve the air volume, double the pressure. The choice the manufacturer makes is what is the overall progression. Longer travel demands somewhat greater progression, as do higher speeds and bigger jumps. So a pro rider doing a pro enduro race needs more progression to make the fork behave as desired than does an amateur who rides slower.
One way to adjust this is through volume spacers inside the air chamber. Some shocks and most forks have these as regular options and may even include some in the package if you buy it aftermarket (whether your new bike includes any depends on the deal the bike brand does with the suspension brand). Back 15 years ago when these bits of plastic weren't offered by suspension brands, a mechanic could achieve the same thing with a lump of grease inside the air chamber somewhere out of the way.
The Fox brand ones for forks clip on to the underside of the air cap and each other. The RockShox brand ones for forks are threaded onto the air cap and each other. Same end result, slightly different method. For rear suspension, they are usually bands that run inside the air can around the hydraulic innards and therefore very specific to the model of shock in question.

But what if zero spacers is still too much progression? And with some of the forks on the market today that is a real issue for many riders. My Zeb wasn't giving me full travel when set at a reasonable sag, and felt way too soft if I lowered initial pressure enough to achieve near-full travel.
Enter the magic of TruTune negative spacers. They look like one massive spacer of either Fox or RockShox variety (I purchased both so I can compare them directly). The end of the spacer is a filter allowing air to enter (but not oil?). Inside is something special. As the pressure increases, the amount of air that is soaked up by the carbon inside also increases. This happens instantly and therefore lowers the progression of the fork. They produce a smaller and a larger version for people who want a little less or a lot less progression.
With a normal amount of sag on my Zeb I was also seeing full travel on the o-ring. Success.
My partner is a small woman and her new Fox 38 with a TruTune inside it also returned full travel when pushed hard but started with a good sag point around 20%. Most success.
While 100 pounds plus shipping is expensive, it is a minor expense compared to even a few thousand dollar new bike.

Michael Hanslip Coaching

If you want to go faster, you have to pedal harder

TruTune "magic" spacers