Precharge a Shock Pump Video
Learn how to Precharge a Shock Pump for the most accurate adjustments.
We get a lot of clients looking to really dial in suspension. Here’s an often overlooked trick – how to precharge your shock pump.
It’s not difficult however it’s strangely controversial. Sometimes science has that affect I guess, the world isn’t flat either…
Transcript below video.
So, here’s the basic on why you precharge a pump. Volume change. PSI and Volume are related. When you increase volume, say, by adding the length of pump line, the PSI will drop.
Working to fine tune PSI in small increments this will create issues.
Example: you want to add 2 PSI to your rear shock. You attach the pump, without precharging it, and have a reading of 140psi. You add 2 psi going to 142 and take a rip. And it is worse. Well, as we show in the video the shock set at 150psi without precharging the pump shows 140psi. If you simply “added” 2 psi you’ve actually dropped the shock by 8psi, or over 5%.
Some manufacturers suggest a standard number of pumps to make up for this difference. While better than nothing this method doesn’t take into account air temperature, altitude, or psi differences.
Precharging the pump in basic steps
This really is a simple idea when you get your head wrapped around what you’re doing.
Before the schrader valve opens on the shock the gasket on your shock pump creates an air tight seal. You will feel some pressure on the threaded interface while your shock pump will read 0.
Pressurize the pump as close as possible to your shock’s setting. Continue threading the connection to open the schrader valve and the air pressures will equalize. Make your adjustments from this point.
Understanding your shock’s starting PSI will obviously make this process easier. If you’re not sure on the PSI, or at altitude or in dramatic temperatures you may need to guesstimate the first setup. You can do this through sag, or feel, etc to get a baseline PSI. From there precharging the pump will help you drastically.
How to Pre-Charge a MTB Pump
Install the pump to the valve. Just prior to valve opening the pump should make an airtight seal.
Pressurize the pump to the estimated amount in the air can. This means the gauge and pump length will now be approximately equal to the air can pressure. If you do not precharge the pump the additional volume from the gauge and hose line will decrease the pressure you read “in the shock” as you are actually now reading what’s “in the shock, and pump”.
Over 20k views – 90 thumbs up and 15 thumbs down… Always blows me away on the digital haters!
Thanks for the read – see you on the trails.