Shock oil

[GoLefty!!]

[ 

 

Give me the oil brands and I will find the correct ration in centistokes. this SAE nonsense really should not be used for Hydraulic oils

 

Please do: 

Fox owners need 7.5W. We can get 5W' date= 10W and 15W. So can you work out the ratio for 5W and 15W to = 7.5W. Mamapara and I would be very grateful.

 

This said there are a number of source on the web that disagree with your non-linear statement.

[/quote]

 

 

Fox Fork Oils are made by Torco. The 10W is Torco RSF Medium with  a blue instead of purple die.

kinematic viscosity is 9.57cSt at 100 degrees C and 32 at 40C.

 

The 5W is Torco RSF Light (usually purple but died Blue for Fox) and it's characteristics is 4.7cSt at 100C and  14.57cST at 40.

 

to blend a 7.5W or middle of the road product it would have to have a Kinematic Viscoity at 40C of 7.1cST @ 100C ; 23.285cSt at 40C.

 

Funny that Maxima Racing fluid medium, 7wt is 7.30 and 22 respectively....

(note not 7.5wt)

 

using the Log formula for lube oil blending I calculate that a 59% to 41%  ratio of 10wt to 5wt is required to achieve the desired 7cSt suspension oil if two oils of similar hydrocarbon composition is used.

at 50/50 (i.e. Linear blending)  the kinematic viscosity will be 6.6cSt. Since it is clear that fox use the SAE classification as a correlation to teh high temp ISO viscosity classification this oil would be a 6wt, not the 7.5wt required.

 

Hope this helps.

[GoLefty!!]

I re-ran the numbesr using the viscosities at 100C and the blend ratio would be 67/33 10w/5w to achieve 7.5wt

 

so depending on what operating temperature you have to cater for the blend ration will vary from 61/39 to 67/33.

 

Interestingly, I tried to find data for Torco 15wt all i could find was RFF 15 wt which is not synthetic and has similar viscosity properties to the 10wt product (Fox 10Wt). The blend ratio for this to the 5w is 60/40, not much different.

 

If they are using the same supplier as Rock Shox

 

The reason for this discrepancy is due to the different viscosity index of the two base oils (medium and light).

 

Hence, viscosity of lube oils does not blend linearly.

 

MTB fork oil can get very hot,....... however lets be pragmatic. For a weekend warrior the oil is probably going to operate closer to 40C so blend to the higher viscosity ranges at 40C and you'll be there.

 

this is for Fox Oil specifically. I will have run a model for each brand of oil since ones 10wt and another 5wt have similar viscosity properties!! This is why I can't fathom why the dickens they use these stupid SAE wt numbers for suspension fluid which is essentially a simple hydraulic fluid.

 

DO NOT USE GEARBOX OIL!! Thes have Viscosity Index improvers (VI) that can affect seals, cause them to swell excessively and fail. I say can because not all VI improvers affect neoprene and nitrile seals used in MTB suspension forks.

Some engine oils that are used as gearbox oils are ok but to keep it simple, use only hydraulic fluids for suspension.

 

GoLefty!!2009-05-23 02:46:34

[GoLefty!!]

bump

[GTRacing]

I' doing my float r, and need to get oil and a service kit, were eould be the best place in joburg?

[GoLefty!!]

suggest you try a motorcycle store.

 

YOu need to get some Torco RSF medium suspension fluid.

 

or you could pay more for the OEM FOX suspension fluid from your LBS

 

 

[Johan Bornman]

Lefty, you make some valid points.  Firstly, it is an absolute nonsense story that oils affect the seals used in forks. There are generally two (sometimes three) types of seals in  bicycle suspension forks and they're all made from a material that's impervious to any of the oils we use in there. Warnings by manufacuters are there only to cause FUD* and get you to buy the branded product from them.

 

There used to be dire warnings about lithium-based grease as well. Same story, lithium in grease is inert wrt seals.

 

Fork oil blending and custom fork tuning is something that's going to become fashion in MTB circles very soon. I've already seen this in the UK and the US. In South Africa at least one company is already doing this on the motorbike scene, where track days racing standard road motorbikes at race tracks are becoming popular. These bikes don't have the amount of adjustment you find on a top-end MTB fork and they make up for it by fiddling with the oil viscosity (weight or WT in fork oil parlance) in order to alter the damping behaviour of the fork.

 

I don't see whey cyclists would bother with all this. They simply turn a dial and you effectively have another Wt of oil in there.

 

As you say, 5Wt oil is simply a bit thinner than the same manufacturer's 10Wt oil but perhaps the same as another's 10 Wt.

 

Bothering to request data sheets from the manufacturers and then attempting to blend the stuff like fine wine, is not worth it. If the fork manual says you should have 7.5Wt in there and you only have 7 and 10 on hand, squirt a thumbsuck amount of 10 into the container and fill up to the mark with 7. It'll make you feel better even if logarithmic blending scares you.

 

Far more important is to service your fork regularly. Dirt-related stiction is thus eliminated and your fork will perform better, even with a grossly different oil from spec. And like Vanrini said, fresh oil sometimes brings back your lockout.

 

But mark my words, oil blending is coming our way. Not because it is needed but because...

 

Now for a blatant plug for my next fork service workshop:

Saturday 19 June at 14:00.

First person to book was Jules, come meet Jules, he's a nutter, he has a single-speed MTB.

 

 

 

 

[GoLefty!!]

oil "tuning" is already used by Fox hence they are so insistent that we use their oil. That way you  kno you are buying an oil that the damping circuit was tuned to perform with.

 

But Oil blending without log.log blending rules is a hit and miss affair.

When experimenting its best to work with the ISO viscosity. This weight nonsense needs to stop.

[knersis]

Hi Lefty, check out the chart on this lnk

http://www.pvdwiki.com/index.php?title=Suspension_Fluid

 

It rates all the different mtb shock oils (Fox, Rockshox, Manitou,etc and motorcycle oils (Bel Ray / Motul).

[GoLefty!!]

Thanks Knersis, this chart explains the situation very clearly. Copy it to your desk top and keep it.

 

The lubrication properties are imporrtant for obvious reasons hence most suspension units use a light oil so that a when the seal moves over the oil a hydrodynamic situation occurs, sort of like a waterski over water. So thats not an issue for suspension (unless you go too viscous). I do not recommend higher than ISO 32-34 in Mountain bikes. there simply is not enough weight behind the valving to mae it work effectively and youwill risk shim damage, even failure. I have seen this in FOX, RS, Manitou and in a Headshok DL70 suspensions.

 

The big deal is suspension feel which is efectively compression and damping rates. Oil affects this quite remarkably and it;s not jus the ISO viscosity to scutinise. We must also know the Viscosity index (VI). This determines how the oil behaves with a change in temperature.

 

Bodge mixing is fine if you have the time to experiment with many different  kinds of oils but this is very time consuming and expensive. And it can also affect the VI of the oil adversely.

 

I always say that for suspension tuning, first start with whats provided, i.e. the tuning facilities provided on the fork. Sometimes these adjustments are internal but they are easier to use and produce a more consistent result than changing oils all the time. Johan seems to agree.

 

Once you have a oil that provides the damping feel you want, marry it!!!

 

In My Lefty Terralogic I use Torco RSF medium. Its similar to Fox Suspension Oil 5wt.

 

For forks like RockSHox, Manitou Marzocchi, first try to establish exactly which oil they are using. then match it up to the chart provided on Peter Verdones website. Then select a more viscous or less viscous oil based on ISO numbers.

YOu only need to remember the SAE weight for purposes of over the counter purchasing.

 

the other trick to remember is too stick to either a mineral or synthetic. The two are miscible (except for mineral + PAG) but they affect the blend in strange manners.

 

Generally (and I mean very very very generally), when you mix a synthetic (PAO, XHVI) with a HVI (high viscosity index), the final blend will tend to behave more like the mineral oil than the synthetic which affects the log.log blending rule. You will even more lost now....

 

I suggest keep it simple and play around with off the shelf oils before blending.

 

The blend I provided for the Fox fluid is ok though. I catered for the base oils.

 

Happy playing!

[Johan Bornman]

 

cut cut cut cut

 

 

I do not recommend higher than ISO 32-34 in Mountain bikes. there simply is not enough weight behind the valving to mae it work effectively and youwill risk shim damage' date=' even failure. I have seen this in FOX, RS, Manitou and in a Headshok DL70 suspensions.

 

cut cut cut

 

 [/quote']

 

I find this discussion very interesting.

 

But Lefty, I don't understand how heavy oil could damage a shim. After all, it is a one-way valve and the only scenario I can see is that it won't close properly due to the stickyness of the thick oil. Are you referring to sliding inertia valves that won't open in thick oil and then putting all the force of a heavy bump on the shim from the closed side?

 

 

[BrendonMyb]

Holy mother, that is a lot of info to try digest yet alone try to fathom as im not good at all the algorithms that you have posted.

 

Here i was thinking it was going to be pretty easy to get my forks serviced & luckily rock shox suggest i only use 5wt & 15wt to run around the seals however im not going to buy 2 different oils just for the sake of lubing the seals. They will get the same treatment as what goes into the fork itself 5wt

 

Wish i could just get smaller qty of the oil as the motorcycle store i spoke to only sell it in 1Ltr QTY's. Oh well i guess it will last quite a couple more services then.

 

how is it that you are so knowledgeable about oils golefty?. generally thats not a thing that interests a whole lot of people.

 

btw i find this very interesting topic as well even though i dont understand some of the things you speak about but thats for me to go research not so...

BumpNgrind2009-05-27 03:49:05

[Johan Bornman]

Holy mother' date=' that is a lot of info to try digest yet alone try to fathom as im not good at all the algorithms that you have posted.

 

Here i was thinking it was going to be pretty easy to get my forks serviced & luckily rock shox suggest i only use 5wt & 15wt to run around the seals however im not going to buy 2 different oils just for the sake of lubing the seals. They will get the same treatment as what goes into the fork itself 5wt

 

Wish i could just get smaller qty of the oil as the motorcycle store i spoke to only sell it in 1Ltr QTY's. Oh well i guess it will last quite a couple more services then.

 

how is it that you are so knowledgeable about oils golefty?. generally thats not a thing that interests a whole lot of people.

 

btw i find this very interesting topic as well even though i dont understand some of the things you speak about but thats for me to go research not so...

[/quote']

 

By the looks of things, Lefty works in The Cartel's labs (Sasol) or perhaps at one of the oil companies, they're all based in Cape Town, aren't they? C'mon, let the cat out the bag.

 

As for you wanting to buy only one type of oil for your Rox. There won't be a problem, since the 15wt you want to substitute with 5wt is for the splash bath and is intended to lubricate the bushings and upper seal. Fox has an identical bushing design and uses 7wt there. As Lefty pointed out, the figure itself is pretty arbritrary in anyway.

 

An option could be to share amongst yourselves. There are quite a few Capie DIY fork service guys. They all recently participated in the Fork Service Workshop thread. You'll recognise the Western Cape guys by their front teeth. Make contact and swap recipies and share quantities of oil.

 

 

 

 

 

 

[Ox_Wagon]

I have some 5w motorcycle fork oil if someone want some.

Used about 50 ml on a fork I tryed to save.

 

 

[Jules]

 

Now for a blatant plug for my next fork service workshop:

 

Saturday 19 June at 14:00.

 

First person to book was Jules' date=' come meet Jules, he's a nutter, he has a single-speed MTB.

 

?

 

?

 

?

 

?

[/quote']

 

 

 

Johan, I may be a nutter, but I'm smart enough to know that you mean Saturday 20th of June . Start a separate post for the workshop, it'll reach more eyeballs that way.

[GoLefty!!]

But Lefty, I don't understand how heavy oil could damage a shim. After all, it is a one-way valve and the only scenario I can see is that it won't close properly due to the stickyness of the thick oil. Are you referring to sliding inertia valves that won't open in thick oil and then putting all the force of a heavy bump on the shim from the closed side?

 

Oil can damage a shim in the following ways.

Too thick for the shim stack and it creates to high a pressure on the shim surface since the oil will not flow through the bleed ports as quickly.

I believe the shim are being bent back and forth, the material work hardens and the fail.

 

Too thin and it can cavitate as the oil heats up. I've seen eviddence of pitting on some shims, suggesting cavititation is occuring. This couild happen in any fork actually, depending on the condition of the oil.

 

 

 

 

 

How do I know so much about oils...

 

The short answer is education and experience.

[BrendonMyb]

Well let me tell you this is an education of note for me & it will definately help put the puzzle pieces together when i pull the fork apart on Saturday.

 

This is probaly old news but i had no idea that the oil actually heats up to those type of temps. I purely under the impression that its there for lubrication ( which it is ) but without tempratures coming into the equation.

 

In other words lower viscosity oils will under perform from the get go if your ambient temprature is high for instance in summer & technically perform better with a lower ambient temp in winter

 

sho this is very interesting !!

BumpNgrind2009-05-27 06:08:01