Fork springs

[foxbass]

Just changed the fork oil yesterday, to 15wt. Got really fed up with the amount of dive on braking and in the potholes of London roads. As I took the springs out they appear to be dual rate springs very similar to pics I've seen on Hyperpro's web site.
Mine is an 08 S2. Are these springs a model update or could the previous owner have already changed them? I was considering a change but maybe don't need to now.
Also has anyone an opinion on oil weight in conjunction with the amount used and what happens if one deviates from the recommended amount - I think its around 460ml each leg.
I weigh around 175 in full kit and have a regular pillion. Many of the roads I ride are complete rubbish with plenty of speed humps.

 

[greg]

they sound like the standard progressive rate springs that come with the bike

 

[nivag]

I put linear ohlins springs in mine. Oh just seen you've seen this http://www.600riders.com/forum/fz6-performance-mods-section/46348-suspension-upgrade.html lol

It's defo a improvement though I did the springs and heavier oil at the same time, I weigh 12stone.
Thinking back I'd like to see how much the oil change would of made before doing the springs but was feeling flush at the time

 

[foxbass]

I did some groping around on the net and googled suspension setup and found a site that helped a lot:
http://www.moto-racing.co.uk/Guides/motorcycleSuspensionSetup

The article leads one by the hand real easy so I tried the tutorial on measuring static sag and rider sag and noted the author's recommendations for normal riding.

Even with our basic suspension design I found that my bike falls within those nominal parameters. Except that I had already changed the oil to 15wt. To get the rear sag to fall about right I had to back off preload 2 notches but decided to go back up one as I ride 2 up a lot. I also keep a couple of psi extra in each tire as its tiresome to keep adjusting for her.

The only slight issue seems to be that of rebound which according to the site should be a little slower - it was well under a second. That may be irrelevant on real world roads however so I'm not disappointed.

I know the rear shock isn't up to much but it seems Yamaha didn't get things too far wrong on average with what is after all a quite basic machine and not a track day rocket. :thumbup:

I would recommend that before condemming your bike's bouncy bits you try the setup for yourself for peace of mind. Then go stick some R6 forks on if thats your desire!

Each to....

 

[foxbass]

Oh yeah, one thing I'm experimenting with is the oil level. When the new oil went in, with the forks compressed under the bike's weight, I topped right up to the washer then weighted the rear to let the forks extend before putting the stock spacer tube back and screwing the caps on.

I am of course much happier with the front with heavier oil and I'm quite light (under 12 stone), so......

Thing is I'm not sure what the effect is of upping the level a little over the recommended.
Ideas? Opinions?

Do tell.

 

[YZF73]

Oh yeah, one thing I'm experimenting with is the oil level. When the new oil went in, with the forks compressed under the bike's weight, I topped right up to the washer then weighted the rear to let the forks extend before putting the stock spacer tube back and screwing the caps on.

I am of course much happier with the front with heavier oil and I'm quite light (under 12 stone), so......

Thing is I'm not sure what the effect is of upping the level a little over the recommended.
Ideas? Opinions?

Do tell.

I was in exactly your position around a year ago, since then I've done plenty of research and have tuned the suspension on my FZ6 with the knowledge I‘ve gained, so I hope I can offer you some advice/guidance.

To answer your immediate question (switches into engineer mode :thumbup, the air trapped within the top of the fork can be considered a form of progressive spring, changing the size of the air gap allows you to adjust the progressiveness of this 'air spring', this mainly influences fork action within the bottom third of the suspensions travel.

The smaller the air gap, the more each unit of air trapped within the fork is compressed per unit of suspension travel, hence a smaller air gap will provide an air spring of greater rate increase per unit of travel than that of a larger air gap.

Basically, this can be used to optimise the amount of travel used, effectively providing a progressive bump stop toward the end of travel, however FZ6's from '07 onwards have a hydraulic bottom out fitted (not sure about the '04-'06 models), so this is not overly important as the hydraulic bottom out prevents you from getting anywhere near actual mechanical bottom.

I'm currently using a 115mm air gap, this is mostly to try and provide some assistance to the quite lacking low speed compression damping of the FZ6's forks. I'll spare you the full explination just for now as it's quite lengthy, however I'm more than happy to explain if you would like. As a general rule, your maximum decrease in air gap should be around the 20mm mark.


Dave Moss of Catalyst Reaction has made many videos on the various areas of motorcycle suspension tuning, I strongly recommend that you spend time watching them when you can (they're a little lengthy...), here's a few to get you started:


[ame="http://www.youtube.com/watch?v=mK3flKxf41U"]Motorcycle Suspension - Setting Sag - YouTube[/ame]

Dave Moss Insprung: Setting Sag, Dave Moss and Dave Williams talk about properly setting sag on a motorcycle. OnTheThrottle on USTREAM. Racing

Dave Moss Unsprung- Fork Springs, Did you know there are such things as linear and progressive springs? Do you know what is in your bike? Do you know how t...


The rest of the videos from that series are also available on that UStream channel, and segments of his series 'two clicks out' are available on YouTube, just shout and I can post you some more links. :ban:

Hope this helps you out, if there's anything else you think I might be able to help with please ask away. :rockon:


Yamahaboyz

 

[foxbass]

Thats brilliant! Thanks for that insight. I had no idea there was a slight upgrade to the later models.

If you just clarify tho, when you say 115mm air gap, what datum are you using to determine that? I am assuming its from the oil surface to the top of the tube? Do you take the measurement with caps off and forks fully extended/unloaded as in front wheel off the ground? Or with the spacers out and forks collapsed?

 

[foxbass]

The other thing I forgot to ask was did you measure your air gap with springs in or out?

 

[greg]

edit: ignore me

 

[YZF73]

Thats brilliant! Thanks for that insight. I had no idea there was a slight upgrade to the later models.

If you just clarify tho, when you say 115mm air gap, what datum are you using to determine that? I am assuming its from the oil surface to the top of the tube? Do you take the measurement with caps off and forks fully extended/unloaded as in front wheel off the ground? Or with the spacers out and forks collapsed?

Sorry, just to clarify there may have been an upgrade to the '07 onwards models, haven't had the chance to delve inside an '04-'06 model fork just yet...

Measuring air gap should be done with the forks removed from the bike and positioned as upright as you can by eye (best to have a friend help with holding the fork), all the internals removed (this includes: the fork cap, the washers at each end of the preload spacer, the preload spacer itself and the spring), fork collapsed completely to mechanical bottom (make sure you achieve this, the hydraulic bottom is quite strong), measuring from the oil level to the top of the fork tube (where the fork cap seats).

Couple of additional notes to go along with this, if you've just changed the fork oil, with a fair amount of oil in the fork, stroke it multiple times from top out to mechanical bottom to ensure that you bleed all the air from the fork, otherwise your level measurement won't be accurate. If you happen to overfill the fork slightly when adjusting the level, dipping the rule into the oil can be a relatively quick and easy way of removing small amounts of oil. :ban:


Hope this helps :thumbup:,

Yamahaboyz

 

[FinalImpact]

Yama - you are spot on with the measuring oil level. Question: if both of you measured the sag of the factory parts what numbers did you end up and how much do each of you weigh?

As much as changing the oil should help the rebound, it won't do much for the compression. So when you find you need more control it may be wise to install emulators or change forks.

Also it is the opinion of many including myself that these seem to ride better with linear rate springs.


I swapped fork but here is a little info for reference. A 2004 R6 was the donor bike with 3400 miles on it. The rates for the front are:

Stock FZ6 dual rate of:
Spring rate K1: __________7.40 N/mm (42.25 lb/in) (0.75 kgf/mm)
Spring rate K2: __________11.80 N/mm (67.38 lb/in) (1.20 kgf/mm)

R6 - which actaully ends up riding VERY NICE! Control is so much better!
Spring rate K1: ___________8.3 N/mm (0.83 kg/mm, 46.49 lb/in)


The sag on my 08 with 8k miles and me at 188lbs w/out gear:
Front sag = 43mm (compresses 1.7" from me sitting on it)
Rear sag = 29mm (compresses 1.1" from me sitting on it)

R6 forks installed:
Front sag = 31mm and adjustable +/-20mm
Rear sag 29mm

Several articles say that 25 to 35mm is good for the street while racing applications head closer to 20 to 25mm.

 

[YZF73]

Yama - you are spot on with the measuring oil level. Question: if both of you measured the sag of the factory parts what numbers did you end up and how much do each of you weigh?

From what I remember I was getting around 42mm, I weigh around 158lb + roughly 14lb worth of gear.

As much as changing the oil should help the rebound, it won't do much for the compression. So when you find you need more control it may be wise to install emulators or change forks.

This is exactly the problem I encountered, with the compression damping orifices having been made large to reduce high speed compression harshness, the low speed compression damping is almost non-existent. This is why I'm running a relatively low air gap to try and provide some assistance (I'm also running 35mm sag to try and provide a little additional travel).

I would agree that emulators are probably the best solution if you stick with the standard fork, I've actually been looking into this recently, and am very keen on them.

Also it is the opinion of many including myself that these seem to ride better with linear rate springs.

I agree completely, the main reason I changed springs was for this very reason. I found the original springs were too soft in the top, low rate segment of travel, then very harsh in the bottom, high rate segment (The fast rebound damping due to the stock 0wt fork oil probably wasn't helping either). Basically, it felt both excessively soft and wollowy (not sure this is actually a word?) during normal riding/braking, and excessively harsh over bumps.


I swapped fork but here is a little info for reference. A 2004 R6 was the donor bike with 3400 miles on it. The rates for the front are:

Stock FZ6 dual rate of:
Spring rate K1: __________7.40 N/mm (42.25 lb/in) (0.75 kgf/mm)
Spring rate K2: __________11.80 N/mm (67.38 lb/in) (1.20 kgf/mm)

R6 - which actaully ends up riding VERY NICE! Control is so much better!
Spring rate K1: ___________8.3 N/mm (0.83 kg/mm, 46.49 lb/in)


The sag on my 08 with 8k miles and me at 188lbs w/out gear:
Front sag = 43mm (compresses 1.7" from me sitting on it)
Rear sag = 29mm (compresses 1.1" from me sitting on it)

R6 forks installed:
Front sag = 31mm and adjustable +/-20mm
Rear sag 29mm

Several articles say that 25 to 35mm is good for the street while racing applications head closer to 20 to 25mm.

There's definitely some discrepancy between sources, I generally consider 40mm front, 35 rear to be the general road setup, 35 front, 30 rear for a typical track setup (my setup), and 30 front, 25 rear for racing applications, however this is up for debate.

Yamahaboyz

 

[foxbass]

Just rescued the grubby bit of paper I wrote the measurements on from the garage...

As stated earlier, I took my datum from the recommendations of a website (quoted above).
They look like this:

Static sag: Fr 25 - 30 mm Rr 5 - 10 mm

My actual: Fr 30, Rr 5

Rider sag (that is, combined): Fr 35 - 48 mm Rr 30 - 40 mm

My actual: Fr 45, Rr 30

This looks like Yamaha have designed an ok set-up but for the fact that I had already changed the oil for 15wt. (Which I know is only the damping factor)
From this result I tried backing off the rear preload one click as I leave it high to cope with a regular pillion. A slight improvement.
Also realised that I had waaay too much oil in (front felt too solid) and made with the turkey baster to lower it to the suggested 115 mm. I'd had it 30 mm higher!

Within the constraints of the bike's design I would say the effort was worthwhile. The front seems more in sync with the back with a less choppy ride (bucking bronco feel over rough ground).

As this is my first big bike I obviously have no other experience to compare with, but on balance I'm currently happy.

Anyone had experience with raising/lowering the oil level?