Fork air gap

[bartonmd]

Flipper,

A suggestion, your weight at 70kg is on the light side for a 0.9 spring and this may be where you are running into a problem. I use a 1.0 spring and I weigh 110 kg.

With a too heavy spring, the suspension will feel too stiff and under damped with the lighter oil. I would suggest a .85 or even a .8 spring with the 142 mm air gap and 5w oil. I think you will be more pleased with the result.

You state that the roads there are a bit rough and it is more compliance you seek rather than less to help cope with this.

Get the spring rate right, set the sag and then work on fine tuning the damping with fork oil. I think you'll find a much better ride and traction as a result.

+1... I hadn't thought about the springs being too strong for him... Makes sense though...

Mike

[pug]

Flipper,

A suggestion, your weight at 70kg is on the light side for a 0.9 spring and this may be where you are running into a problem. I use a 1.0 spring and I weigh 110 kg.

With a too heavy spring, the suspension will feel too stiff and under damped with the lighter oil. I would suggest a .85 or even a .8 spring with the 142 mm air gap and 5w oil. I think you will be more pleased with the result.

You state that the roads there are a bit rough and it is more compliance you seek rather than less to help cope with this.

Get the spring rate right, set the sag and then work on fine tuning the damping with fork oil. I think you'll find a much better ride and traction as a result.

i believe exactly the opposite.

The first springs I used were WP's rated at about 0.9 kg/mm (do not remember exactly) and the differences were marginal, i.e. no bottoming resistance, front end very nervous in panic stops. And all this before dropping the front (now the tr. clamp is 5mm lower) , shimming the rear (now its 4 mm ) and installing the 18kg/mm sprung WP shock at the rear.

To my view the biggest drawback of the front is that it is undersprung, not overdamped.

Now I use Hyperpro springs and I am on the other side of the moon.

Yes I would like them to be a little softer but for as long as I am able, I prefer the aching arms over unstability.

Of course as I said previously all these findings are subjective and at the end is all about personal preferences and riding conditions (and habits).

[arcticflipper]

So I think what I'm trying and a lot of other guys are saying is that this is more of a personal preference thing.

There are a lot of options out there, and you will have to find the right setup for you. Whether it be a 5W fork oil and 3mm front drop, or a 10W oil and a OEM setup, you still need to do a bit of testing and decide for yourself which option works better for you.

There are various factors involved in this, and various opinions with regards to what works best for each person.

I will agree that a lighter weight oil does make the forks more reactive, quicker and does help a lot more on higher speeds. I did notice this when I had the 5W oil with 150mm air gap.

But the front felt a bit spongy to me, and a bit twitchy in and out of corners. I got the feeling that you needed to drive with a lot more precision than what I was driving with.

The 10W does make the front a lot harder, stiffer but I found it to be more stable in corners.

I suggest that you investigate this, get as much info as you can from as many sources as you can, Like was mentioned, several people on this forum uses and likes the 5W oil, some even use 2.5W, but then there is still also people that uses 7.5W and 10W oil. It is all a personal preference in my opinion.

The info that I gave was not too try and influence anyone or even try and point that someone's choice in oil is wrong, but only to possible help other viewers with regards to understanding a little bit more about forks and oils and that at the end of the day, I don't think there is a completely 100% right answer or a completely 100% wrong answer. It all comes down to your personal preference, what works best for you.

Even though I've tried to make it a little bit easier by doing the test, I think I might have just confused people even more, I did not expect the changes to be so significant between the oils, springs, valves etc.

So conclusion: IMO ask everyone why the use the oil they use, and if possible, test ride their bikes to get a feel for the setup, and then decide whether it works for you or not. This will give you a good basis to start from. I did unfortunately not have that oppertunity, thus I had to test it for myself.

Very wise words from Bartonmd: "Use whatever you want" It is you who will have to ride the bike, so make sure the setup suites your requirements.

[bartonmd]

I'll just add one thing: Did you try the factory reccomended air gap with the 5W oil?? Changing air gaps will change the fork action about as much as changing the oil itself...

Mike

[arcticflipper]

No, only thought of it as I was pouting the 10W oil in, I know, stupid I should've tried that first, before going to 10W..... :oops:

[HERBXX]

Just to add to the mix the visocusity of oil is not he same across brands. 7.5 in one brand may be thicker then 10 for another brand. It might be a good idea to stick with oine brand when making changes so that at least your sure your actually going thicker or thiner.

http://www.activeboard.com/forum.spark?for...7043&topicPage=

[pug]

Just to add to the mix the visocusity of oil is not he same across brands.  7.5 in one brand may be thicker then 10 for another brand.  It might be a good idea to stick with oine brand when making changes so that at least your sure your actually going thicker or thiner.    

http://www.activeboard.com/forum.spark?for...7043&topicPage=

True, check the links I posted previously in the first page. :!:

[pug]

Just to add to the mix the visocusity of oil is not he same across brands.  7.5 in one brand may be thicker then 10 for another brand.  It might be a good idea to stick with oine brand when making changes so that at least your sure your actually going thicker or thiner.    

http://www.activeboard.com/forum.spark?for...7043&topicPage=

Ok, I checked you link . WOW.

I admitt, is better than mine.

[arcticflipper]

Someone please explain what I'm looking at.

What does all the numbers mean?

I'm waiting for a comparison on the same info given by this sheet from putoline. I used the Putoline oil range in all the tests I did, and will also change to 7.5 putoline fork oil for the next test. HPX7.5

Name: HPX

> Tips & Tricks

Category: Front Fork Oil

Definition:

HPX Suspension Fluids have been developed in conjunction with high quality suspension manufacturers to meet the demands of today's sophisticated suspension systems. Highly refined synthetic based additives ensure a smooth and progressive suspension action for both cartridge and upside down systems.

Composition: Synthetic

Specification: Available viscosity grades SAE 2.5/ 5/7.5/10/15 & 20

Application:

Recommended for normal- and high performance road use.

Can be used in conventional- as well as up side down front forks

I have asked them to send me the same info as was posted on the above chart, to be able to compare the oils.

[HERBXX]

You are looking at the the real Viscosity of various suspension oils. The lower the number the thicker the oil. (the Viscosity index) columns. For example Silkolene Pro RSF(7.5) is 322 not much thiner then some of the 10w oils. It just tries to show how various fluids compare to each other .(look at the difference of all the oils of a given weight) . There is also stuff about temperature in the chart to that I don't really understand

[shovelstrokeed]

Flipper,

I think you are barking up the wrong tree here. I will refer again back to my post suggesting that you are working from a wrong base line with too stiff a spring.

The following is not based on any personal preference but simple mechanics and fluidics. Maybe not so simple really but sound experience based on years and years of suspension tuning on my own and other's motorcycles plus a bunch of advise from some of the top suspension tuners around.

The internal workings of the fork, primarily the damping system, are dependant on three things to work properly. Displacement (how far the forks compress or extend). Velocity (How quickly the displacement changes) and finally viscosity of the oil passing through the various ports in the damping system.

With too heavy a fork spring, you will not get the displacement nor the velocity needed to make the valving and porting in the damping system work properly. Air gap has little to no effect until the forks start to approach the limits of their travel and then it's effect is that of an additional linear rate spring applied to the metal sprngs in the fork. In other words, if you are not, in your riding, coming close to bottoming your forks on the largest of bumps, you are probably not sprung correctly. In effect, a too stiff a spring is negating the effectivness of the damping system.

The order of adjustment/modification has always been and always will be, spring rate, sag, damping. It appears to me, and this is opinion, that you are approachiing this from the wrong direction. The .9 spring at your 70kg weight would only be suitable for track riding and then on only the smoothest of tracks. To try to use it on bumpy streets is, again, my opinion, an exercise in frustration. In any case, you cannot compensate this with damping. A little bit less on the air gap can help with a too light spring but won't get the job done in the opposite case.

[arcticflipper]

Thanks, for all the info, slowly starting, well hoping that I'm starting to understand the suspension story a little bit better.

I will change the oil out to a 7.5W, just to test and see, and then the forks will go in for valving and professional setup - K-tech setup.

After this, I think I should then understand what the differences would be between the various setups and options.

[blackhawkxx]

A little bit less on the air gap can help with a too light spring but won't get the job done in the opposite case.

So me being 225 lbs. with stock springs could reduce the air gap to help my front end?

[shovelstrokeed]

Blackhawk,

Reducing the air gap won't help much for general riding as it is the spring rate which determines those motions I described when trying to explain to Flipper how the forks work. What it will do is make the overall spring rate a bit higher as the forks approach the limit of their compression travel. Actually, the spring rate won't get higher, that's slightly misleading, as the spring rate for the air gap is determined by the height of the column of gas left in the forks. The air gap is contributiing all through the stroke of the fork it is just that it doesn't become a significant factor until the fork approaches full compression.

Without all the yapping, a smaller air gap will help reduce bottoming but, at 225 lbs, which is more or less what I weigh, is gonna require a 1.0kg/mm spring or even a bit higher.

[blackhawkxx]

Thank you.