The Serial 1 SWITCH/MTN features an adjustable suspension fork from SR Suntour. The Zeron 35 Boost offers many adjustment options to customize the fork’s performance to match your terrain and riding style. One of the most important settings is setting proper preload. In this article we’ll briefly discuss how to set preload on your new Serial 1 ebike.
Identifying a couple of key definitions will help us better understand the topic: preload and sag.
Preload is the amount of pressure on the fork’s spring, in this case compressed air, when the fork is in its fully-extended position. Preload is adjustable to allow for proper sag under varying rider weights. The lower the preload setting, the lower force needed to compress the suspension. If your fork preload is set to 70 psi, for example, a force greater than 70 psi will be required to begin to move the suspension.
Sag is the measure of how much the fork compresses when the rider is sitting on the bike, or standing in their riding position. SR Suntour recommends sag of 20%-25% of total travel. The Zeron fork provides 130mm of travel. To calculate sage we’ll take 20% x 130mm = 26mm, which is our desired amount of sag. The amount of ‘air’ or ‘preload’ will be adjusted until we reach the recommended sag setting. There is a recommended air pressure guide on the left leg of the Zeron fork.
For a rider of 65-75 kg, the recommended starting pressure is 60 psi-70 psi. The following table shows some recommended pressure settings.
This is a good place to begin setting sag, though we can more accurately determine the correct sag through the following steps:
- Have the rider sit on the bike with their riding gear on (clothing, helmet, and any packs).
- Have a second person stand at the front of the bike, stradling the front wheel. They should hold the handlebar to steady the bike vertically.
- Have the rider get on the bike and stand as if riding the bike. Compress the suspension fork a couple of times by pushing down on the handlebars from this position. Have the rider stand up in a position similar to how they would ride through rough terrain.
- Once the rider is still, push the rubber o-ring down on the fork legs to the bottom of the stanchion.
- Carefully get off the bike without upsetting the fork.
- The o-ring will now show a distance from which the ‘sag’ measurement is determined. The distance from the o-ring to the extended portion of the fork is our sag measurement. Measure the distance from the o-ring to the extended portion of the fork and compare that to the target of 20% or 26mm..
- If the distance is greater than the desired sag, increase pressure with a shock pump and repeat the process. If the distance results in a lesser amount than the desired sag, use a shock pump and reduce the air pressure and repeat the process.
There is some variation in setting proper sag based on personal preference, terrain, and riding style. A setting of 20%-25% is recommended but if you find that your riding results in very little of the suspension travel being used, adjustments will need to be made. If you find that you frequently ‘bottom out’ or use all of the available travel in a quick and sudden way, causing a loss of control, adjustments will need to be made. Before your ride, push the rubber o-ring down to the bottom of the fork stanchion and use that as a gauge to determine if proper travel is being attained during each ride.
With a little preliminary work, you’ll get the desired result of suspension that performs in a way that maximizes safety, control and performance allowing you to Enjoy Every Ride.