Front suspension upgrade
Posted: Sun Aug 09, 2015 11:06 am
I've just finished the upgrade of my front suspension and love the results - so I share the details if anyone would like to replicate.
Management summary: YSS PD valves installed along with heavier viscosity fork oil and added 20 mm preload to stock front forks. It is a world of difference for roughly 100 USD and approx 2 hours of labour.
Note: Upon disassembly I have found that the free length of my fork spring is different from the details in the manual. My PCX 125 is a 2012 Euro model with eSP engine.
My measurements before the upgrade:
Total suspension travel: 92mm
Compressed lenght (60kg weight) 78mm
Static sag: 28mm
Loaden sag: 44mm
Free spring length: 292mm
After some research and doing my maths I decided to go gradually. I planned to change to heavier fork oil (factory 10w, changed to 20w) and install a Gold valve emulator cartridge equivalent YSS PD valve (I've ordered mine from http://www.brooksbarn.co.uk/YSS-238MM-P ... 1KYPC.aspx). I was considering to change to a heavier rate spring if that's needed as the next step.
If anyone really interested in how a motorcycle suspension works there is a very good detailed description at http://www.racetech.com/page/title/Emul ... hey%20Work.
I'll try to summarize some of it here.
A suspension's main task is to keep the vehicle's wheels surely on the road in any possible situation. It does a few things when rolling over obstacles. When it is forced to move, the amount of movement in reaction of a specific force is limited by the spring ratio (the strength of the spring), and the speed of the movement is controlled by the dampening of the fork.
Motorcycle forks are integrated units, where the damping and spring action is housed in the same enclosure. Damping is achieved by forcing a fluid through orifices. To simplify it imagine a piston what moves back and forth in a sealed container, against fluid flowing through holes made on the piston surface. The container is the fork leg, the piston is called the damping rod.
As fluids are non compressible, the viscosity of the fluid and the size of the holes will limit the speed of movement. We are usually talking about compression (when the suspension travels upwards) and rebound (when the suspension returns to it's normal length). The different damping for compression and rebound are achieved with different sized holes on the damping rod.
One can change to heavier fork oil resulting in more damping on both ways of travel. For spring action a progressive force is desirable - for damping it is not really beneficial. While more damping is generally the desired result for low speed movements, it can be very harsh when you hit a bump during braking. Therefore a degressive character is desired what cannot be achived with a simple damping rod setup.
To solve this I decided to go for the cartridge emulator setup, to overcome the limitations of the very basic design of the PCX forks.
The results are very good. By installing the cartidge with the original springs it provides about 20mm of preload resulting in less static sag, and enabling more usable suspension travel. The emulator provides stronger damping in normal conditions, and provides quick suspension action when a larger movement is needed. As described above I've bough an emulator manufactured by YSS.
I can recommend to anyone to use this setup - especially when upgrading the rear suspension.
Management summary: YSS PD valves installed along with heavier viscosity fork oil and added 20 mm preload to stock front forks. It is a world of difference for roughly 100 USD and approx 2 hours of labour.
Note: Upon disassembly I have found that the free length of my fork spring is different from the details in the manual. My PCX 125 is a 2012 Euro model with eSP engine.
My measurements before the upgrade:
Total suspension travel: 92mm
Compressed lenght (60kg weight) 78mm
Static sag: 28mm
Loaden sag: 44mm
Free spring length: 292mm
After some research and doing my maths I decided to go gradually. I planned to change to heavier fork oil (factory 10w, changed to 20w) and install a Gold valve emulator cartridge equivalent YSS PD valve (I've ordered mine from http://www.brooksbarn.co.uk/YSS-238MM-P ... 1KYPC.aspx). I was considering to change to a heavier rate spring if that's needed as the next step.
If anyone really interested in how a motorcycle suspension works there is a very good detailed description at http://www.racetech.com/page/title/Emul ... hey%20Work.
I'll try to summarize some of it here.
A suspension's main task is to keep the vehicle's wheels surely on the road in any possible situation. It does a few things when rolling over obstacles. When it is forced to move, the amount of movement in reaction of a specific force is limited by the spring ratio (the strength of the spring), and the speed of the movement is controlled by the dampening of the fork.
Motorcycle forks are integrated units, where the damping and spring action is housed in the same enclosure. Damping is achieved by forcing a fluid through orifices. To simplify it imagine a piston what moves back and forth in a sealed container, against fluid flowing through holes made on the piston surface. The container is the fork leg, the piston is called the damping rod.
As fluids are non compressible, the viscosity of the fluid and the size of the holes will limit the speed of movement. We are usually talking about compression (when the suspension travels upwards) and rebound (when the suspension returns to it's normal length). The different damping for compression and rebound are achieved with different sized holes on the damping rod.
One can change to heavier fork oil resulting in more damping on both ways of travel. For spring action a progressive force is desirable - for damping it is not really beneficial. While more damping is generally the desired result for low speed movements, it can be very harsh when you hit a bump during braking. Therefore a degressive character is desired what cannot be achived with a simple damping rod setup.
To solve this I decided to go for the cartridge emulator setup, to overcome the limitations of the very basic design of the PCX forks.
The results are very good. By installing the cartidge with the original springs it provides about 20mm of preload resulting in less static sag, and enabling more usable suspension travel. The emulator provides stronger damping in normal conditions, and provides quick suspension action when a larger movement is needed. As described above I've bough an emulator manufactured by YSS.
I can recommend to anyone to use this setup - especially when upgrading the rear suspension.