Front suspension upgrade

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Oyabun
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Front suspension upgrade

Post by Oyabun »

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.
tomtomclub2005
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Re: Front suspension upgrade

Post by tomtomclub2005 »

Hi, It is really a pity you did'nt document your install with pics... How many holes did you had to drill on the fork rod?

Cheers,
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Re: Front suspension upgrade

Post by Oyabun »

Hi Tom
I've only done it overnight so had no chance document it. I have to say though I'm just setting up my new workshop and not really good in photodocumenting either especially when I see such great articles like Maddie's.
I'm still experimenting with fork oil viscosity so I'll change the oil once more. When I install the new rear suspension they will come out too and I'll be able to document it properly (I've already done the instructions part).
You don't have to drill new holes, just enlarge the existing ones.
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Re: Front suspension upgrade

Post by tomtomclub2005 »

Hi Oyabun

I was asking because i don't feel very confy dismantling the whole fork - your mod looks interesting, i have already installed harder springs and changed the oil to 15W but still it's all quite hard on the incredibly bad bumpy roads here in Brussels ( I have YSS offsets mounted too) what version of pcx do you have, the current one?
PS: i had made a tutorial for mounting YSS on current model PCX on the french forum, and changed the spings and oil in the front fork, so that is ok - I'm just weary to dismantle the whole fork and how to take out the rod without braking anything :)
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Re: Front suspension upgrade

Post by Oyabun »

If you already got to changing fork oil and feont springs then you can easily install the PD valves too.
The beauty us that it's not needed to dismantle the whole fork. You simply remove the allen bolt at the bottom of the fork while it is open and voila the damping rod will come out immediately. The rod only has fo come out to enlarge the compression bleed holes on them and they go back without further dismantle so seals, and sliders stay in their place. The emulator then intalled on top of the damping rod and held on it's place by the spring tension.
The issue with installing heavier oil without the emulator valves is that you get your forks reaction even harder. I mean it gets progressive - slighoy more damping on small bumps and very strong on sudden big ones. Which is not good. You actually want to have degressive damping action. Good damping on smaller movements, but you want to enable the fork to soak up large bumps more freely. That's what these emulators do. Rebound is controlled by the original damping rod and changed by oil viscosity while compression is co trolled by the emulator and can be adjusted with the spring r e and preload. Really ingenious.
I have kept my original springs and use the preload provided by the emulator valve. I've found this setup to be more useful on the similarly bumpy roads of Budapest than using a heavier rate spring - however I usually ride solo and my weight is only 75 kgs without gear.
My pcx is an eSP from 2012 as in my details - however as I understand it has the same suspension as the curent model. There has been a change of the spring used in the front fork with the eSP model change in 2012 with the free length of the spring changed from 27xmm to 29xmm. Mine is already the newer one.
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Re: Front suspension upgrade

Post by tomtomclub2005 »

Excellent, thanks a lot for info. I am really tempted - will search to get them.
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Re: Front suspension upgrade

Post by tomtomclub2005 »

I received my valves today however there are absolutely no instructions whatsoever with them. Oyabun can you help? did you receive my email?
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Re: Front suspension upgrade

Post by tomtomclub2005 »

So here is the first replication :D
Mounted this week-end, took me the best part of the afternoon.

Issues encountered:
  • Had to dremel a bit the top damping rod for the valves to sit flush so have one handy
    Missing Manual so unsure if the two turns have to counted as valves are shipped or not
    One bottom nut of the damping rod does not tighten to torque as it should so i have to redo it
In this un-optimized set-up, ( hard springs/15 Grade oil) the results are simply stunning for such a simple looking device - i am enjoying a new bike!
  • Way better confort, ( I wish my YSS could get the valves treatment too by now)
    Less braking sag,
    pcx feels livelier- reponds to directions change better, countersteering a breeze now as it should have been from the beginning
So this is how it feels to have a proper fork- My daily commute just got fun again as it should be
I wish to thank Oyabun for the support- i would have never launched myself without it!
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Re: Front suspension upgrade

Post by Oyabun »

Tbank you for the feedback. Good job, I have to say I had no issue with the damping rod fitment.
Good to hear that you like the result. If you don't mind I might go and post here (after correcting typo errors which I tend to make especially when typing on my tablet) the essence of the advice /lessons learnt I sent through email so anyone might attempt the install later can possibly benefit from them.
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Re: Front suspension upgrade

Post by tomtomclub2005 »

Sure, please do, This mod is the best 90 eur I've spent on the bike-

here is a pic of the valves sitting on the damping rod, bottom one has been Dremeled about 0.5 mm inner of top rod, the upper as is . Maybe it will not be the case for others. Just be warned it might happen and to have one ready if you install, i didn't like the idea of the valve not being flush.

My advice would be to check the fit before you proceed to enlarge the holes on the damping rods so you can do all the cleaning and deburring once , not twice as i had to do ;)
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Re: Front suspension upgrade

Post by tomtomclub2005 »

And for anyone attempting to install here are the instructions that i finally found on the net- mine came from ebay uk and they guys didn't bother to answer any of my mails requesting them, talk about bad customer service!
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Re: Front suspension upgrade

Post by RRocket »

I may have missed it...but how many ml (or cc) of oil did you put in each fork?
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Re: Front suspension upgrade

Post by tomtomclub2005 »

I've sticked with the stock amount 75mm from top of fork with fork tube fully compressed- from email exchanges with Oyabun stock for eSP is 122 ml +/- 2,5. Oyabun further tweaked for his valves and went 130 ml, increasing the fluid level to 72-70mm.
He might want to chime in and comment :)
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Re: Front suspension upgrade

Post by Oyabun »

Yup.
Depending on the year of manufacture it could be 118ml for bikes before 2013 model year and 122ml (+ -2.5ml for both) since 2013 as later models have a tad longer suspension travel. Both have fo be filled to 75mm from the top of the collapsed fork tube as per factory recommendation for stock forks.
I filled mine to 72mm as the valves add some height to the damping rod and I wanted to make absolutely sure that they never go starving for oil as it can cause cavitation (air bubbles developing in the fluid and collapsing and causing pitting on metal surfaces) and detoriation of operation on long term.
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Re: Front suspension upgrade

Post by tomtomclub2005 »

Update: I fixed torquing on the fork wich would'nt tighten down to it

I also fished and zeroed in the valves and then applied two turns (as per manual). Mine were about 4/5 turns and it was way too much of good thing: almost no drivers' sag, very little dive while braking, the bike felt a bit tilted on the back.

Fixed now-

Sorry no figures, Oyabun does it the right, scientific way- i have two kids home and very little time, not to mention i don't have a workshop and work outside so i'm stuck with empirical work.
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Re: Front suspension upgrade

Post by Oyabun »

LOL. Thanks for the praise. I can't help, I'm an engineer - so need some good theory to oroduce replicable results.

Good job. I hear what you say, two kids here too. I've tried child labour as it is (almost) free, but took me lot longer to finish consistently. ;-)

Enjoy the ride, keep the shiny side up.
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Re: Front suspension upgrade

Post by Mario »

Very interesting read!!

Is there also an front suspension upgrade solution for the Forza 300?
May the Forza be with you!!
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Re: Front suspension upgrade

Post by Oyabun »

Mario wrote:Very interesting read!!

Is there also an front suspension upgrade solution for the Forza 300?
Yup. Same thing can be done.
Am I right that the forza has 33mm front forks?
If yes, I even have an extra set of valves ( I have mistakenly ordered one size larger ones first) which I could send over to you.
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Re: Front suspension upgrade

Post by Oyabun »

Just checked. Forza 300 front fork seems to be 35mm router diameter. The valves I have should fit those perfect (they are the 26.5mm ones)
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Re: Front suspension upgrade

Post by Mario »

Oyabun you got my attention ;)

Found this info on a application list from YSS
They speak of "265 + spacer / 15W / 195 / 35C"

265 must be the diameter 26.5mm / spacer?
15W fork oil thickness (how much?)
195 (maybe ml ?)
35C (don't know)

You speak of enlarging holes (than there is now way back!!) is this also necessary for my Forza 300?

Is there a picture/video tutorial how to do this mod? (I never worked on front and rear suspensions)

I am also planning to buy the rear YSS Shock Absorbers (like the Öhlins Imagemore but way to expensive o_O ) , I think there must be some balance between the front and rear suspensions??

Image

Oyabun wrote:Just checked. Forza 300 front fork seems to be 35mm router diameter. The valves I have should fit those perfect (they are the 26.5mm ones)
May the Forza be with you!!
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