ninjette.org - View Single Post - DIY- Replace fork seals, dust seals and fork oil

leed · February 13th, 2012, 09:03 PM

Sounds like things are working out for you!

I did want to touch base on what @Domagoj was saying.

Forks and rear Shocks (as well as shocks elsewhere) are relatively simple. They usually (sometimes gas) use some sort of oil (as you know) that travels between two volumes. In between the two volumes is a valve. This fluid system is a damper. Around that you usually have a coil-over or in our case a coil through, which is simply a spring.

Increasing the weight of the oil will increase the strength of the damper. What I mean by that is, the faster you push/pull, the faster it reacts. This is why RacerX tends to exhibit a harsher ride from the heavier (higher viscosity) oil. Changing oil alone will not stiffen the front end. For a heavier rider, you apply a constant force onto the bike (your weight). If your sag is too high, you want to increase your spring force.This is done through preload or respringing as you have delved into.

You do have to be careful, though. Ideally, there is a balance of both preload and damping force to where you will have ideal handling in the majority of road surfaces. The main purpose of the damper, as Damogoj was saying, is to reduce vibration of the system (up and down oscillation of the front end of the bike after a disturbance), not just the spring [minor nitpick!]. This is important when you hit surfaces that are repeatedly bumpy or you accelerate. It helps control the oscillations and prevents the system from getting unstable [see steering-damper for steering issues!].

TL;DR:

Higher viscosity oil makes the forks stiffer when hitting something fast and hard (IE: unexpected pot hole, or short small bumps at speed). It will not, however, prevent the rider from bottoming out when travelling over a speedbump at recommend speed.

Too high and you'll feel like you can feel every bump, too low and you'll feel like you're floating up and down a lot after/during bumps.

Springs and preload are what you need if the forks travel too much for your weight. Too high and you'll feel like you're sitting on a brick. Too low and you'll just feel like a low rider.

EDIT: I should note: Damper force is a function of velocity, where as spring force are simply a function of displacement.

February 13th, 2012, 09:03 PM	#70
leed ninjette.org sage Name: David Location: Loves Park, IL Join Date: Feb 2011 Motorcycle(s): Time will tell Posts: 969	Sounds like things are working out for you! I did want to touch base on what @Domagoj was saying. Forks and rear Shocks (as well as shocks elsewhere) are relatively simple. They usually (sometimes gas) use some sort of oil (as you know) that travels between two volumes. In between the two volumes is a valve. This fluid system is a damper. Around that you usually have a coil-over or in our case a coil through, which is simply a spring. Increasing the weight of the oil will increase the strength of the damper. What I mean by that is, the faster you push/pull, the faster it reacts. This is why RacerX tends to exhibit a harsher ride from the heavier (higher viscosity) oil. Changing oil alone will not stiffen the front end. For a heavier rider, you apply a constant force onto the bike (your weight). If your sag is too high, you want to increase your spring force.This is done through preload or respringing as you have delved into. You do have to be careful, though. Ideally, there is a balance of both preload and damping force to where you will have ideal handling in the majority of road surfaces. The main purpose of the damper, as Damogoj was saying, is to reduce vibration of the system (up and down oscillation of the front end of the bike after a disturbance), not just the spring [minor nitpick!]. This is important when you hit surfaces that are repeatedly bumpy or you accelerate. It helps control the oscillations and prevents the system from getting unstable [see steering-damper for steering issues!]. TL;DR: Higher viscosity oil makes the forks stiffer when hitting something fast and hard (IE: unexpected pot hole, or short small bumps at speed). It will not, however, prevent the rider from bottoming out when travelling over a speedbump at recommend speed. Too high and you'll feel like you can feel every bump, too low and you'll feel like you're floating up and down a lot after/during bumps. Springs and preload are what you need if the forks travel too much for your weight. Too high and you'll feel like you're sitting on a brick. Too low and you'll just feel like a low rider. EDIT: I should note: Damper force is a function of velocity, where as spring force are simply a function of displacement.