This week on the Tuesday Tune we're delving into suspension fluids to discuss some of the demands placed on them and how the manufacturers develop the properties that are necessary to meet these demands. Since we at
Vorsprung Suspension aren't chemists, we invited Alex Marangoni, Canada Research Chair, Professor of Soft Material Sciences at the University of Guelph and the scientist behind
Whistler Performance Lubricants to explain a few things to us:
1. What the major demands on suspension fluids typically involve
2. What base oil types are used and their properties
3. Some of the compromises involved in oil design
4. How oil properties change with temperature and over time
From the workshop's point of view for servicing, we consider three main factors in the most relevant priority order when selecting an oil for a given application:
1. Viscosity - how thick the oil is, and its resistance to flow through shear
2. Viscosity Index - the thermal stability of the oil and ability to minimise changes in viscosity as temperature changes
3. Lubricity - its ability to reduce friction.
Each of these factors has to be considered in terms of its relevance to the oil's application. For example, fork splash bath lubricant needs to lubricate first and foremost, and forks in general are more sensitive to stiction than rear shocks as the rear shock has the leverage of the suspension linkage to help overcome its friction. Conversely, rear shocks see more heat than forks, so thermal stability becomes a bigger concern.
Following those three primary considerations are secondary considerations, in no particular order:
1. Oil durability - oil breakdown through thermal and shear stress occurs over time.
2. Environmental concerns (side note - WPL's oils are biodegradable and non-toxic... but they taste terrible and eating or cooking with them is still generally not recommended)
3. Price
4. Anti-foaming characteristics (for open bath/emulsion dampers only)
5. Other factors affecting performance such as adhesive additives ("tackifiers") that can drag oil past seals
So, here it comes....if the absolute difference in HIldebrand solubility parameter between the polymer (elastomer) and the solvent (suspension oil) is greater than 2, then they are compatible. This is based on experience and testing.
Now, which elastomer you say. Let's assume that all seals are made of NBR (Nitrile butadiene rubber under trade names such as Nipol, Krynac and Europrene), there is NO PROBLEM AT ALL since this elastomer has a solubility parameter of greater than 20, while WPL oils have a solubility parameter of about 15-17. So, we are all good. Having said this, let's pay tribute to mineral oils and PAOs which have Hildebrand Solubility paramters around ~10.
However, this analysis will depend on the type of polymer that you use....natural rubber (NR), styrene-butadiene rubber (SBR), epoxidized natural rubber (ENR), ethylene propylene diene monomer (M-class) (EPDM). You could just look up the value of the respective polymers and judge by yourself (all in interenet). But I think most manufacturers are using nitrile rubber, so, we can pretty much be cool about the whole thing. If we are talking about natural rubber....then we may have problems.
Does this help?
Next question would be what is made of what in a fork?
Orings are most likely NBR as you mention. Bushings seems to be made of PTFE. Dust seals from SKF (or Fox, RS and racing Bro) are made of NBR.
PTFE has a Hildebrand parameter of 6.2 which is then close to mineral oils and PAOs. But maybe 6.2 to 10 is enough? And maybe these 2 are not so common in suspension fluids?
What about the other components of the suspension oil like detergents, tackifier, VI improver, lubricants, etc...? Would they have similar Hildebrand parameters as NBR or PTFE?
It sounds like as long as I use fork oil in the right place (damper oil in the damper with the appropriate viscosity and lubrication oil in the lower legs) I can use any brands I have available.
Of the 1.4 billion gallons of lubricant oils used in the U.S. every year, 40% is lost due to evaporation or spillage into ground and waterways. That is way too much for me.....you even wonder where does the "properly" disposed oil go to?
So, here it comes....if the absolute difference in HIldebrand solubility parameter between the polymer (elastomer) and the solvent (suspension oil) is greater than 2, then they are compatible. This is based on experience and testing.
Now, which elastomer you say. Let's assume that all seals are made of NBR (Nitrile butadiene rubber under trade names such as Nipol, Krynac and Europrene), there is NO PROBLEM AT ALL since this elastomer has a solubility parameter of greater than 20, while WPL oils have a solubility parameter of about 15-17. So, we are all good. Having said this, let's pay tribute to mineral oils and PAOs which have Hildebrand Solubility paramters around ~10.
However, this analysis will depend on the type of polymer that you use....natural rubber (NR), styrene-butadiene rubber (SBR), epoxidized natural rubber (ENR), ethylene propylene diene monomer (M-class) (EPDM). You could just look up the value of the respective polymers and judge by yourself (all in interenet). But I think most manufacturers are using nitrile rubber, so, we can pretty much be cool about the whole thing. If we are talking about natural rubber....then we may have problems.
Does this help?
There are a lot of different additives in various oils, some of them break down relatively rapidly and some don't. In the case of air sleeve services specifically though it's less to do with oil breakdown and more to do with the fact that everything is clean and well lubricated again.
As for how well tuning services work, that is not a realistic generalisation that can be made. Some make a world of difference, some are a complete joke; some are very arbitrary guesses and some are well measured. The end result to the rider depends on how well developed the tuning method is, how well the tuner has managed to interpret the needs of the rider - that one is an art form in itself - and how capable the tuner is of creating measured and quantifiable changes to meet the rider's needs. Read between the lines of anyone's marketing spiel, including ours, and you'll usually be able to get an idea of what you're really getting. This is definitely an industry in which skepticism is warranted.
@VorsprungSuspension my luftkappe was despatched from tftuned today, looking forward to the change it makes.
Keep up the awesome work.