The Robert Taylor suspension thread

[Robert Taylor]

I've read conflicting things about this. Is altering the viscosity of the fluids in suspension components a valid way of changing their behavior for the better?

I can understand if I filled my suspension with treacle it would be terrible, and likewise I guess if I filled it with something very thin the suspension wouldn't do much except bounce around.

But are smaller changes something that can be done to alter characteristics for the better?

Very quickly and simplistically, altering viscosity primarily affects by pass bleed ( clicker positions ) by about 95% and will affect flow through deflected shim stacks by only about 5%. If you have made a substanial change in viscosity you may have to move the clicker setting by an enormous and ''inappropriate amount'' Excepting on a limited number of top shelf suspension components the tapers on adjustment clicker needles only have a single taper and therefore dont have a linear response range. There is a sweet spot of response range. If you are only a few clicks out from ''fully in'' one click can be a huge change ( excepting if the shim stack opening pressure is very weak ) Conversely, if you are nearly all the way out, one click will do almost nothing as the needle is already so far withdrawn.

So tuning by viscosity is in most ways a myth, especially with modern high spec high performance suspension units.

And not all oils are the same, sae ratings are not ''gospel'' by any means. But please ask me about that another time or read an upcoming issue of Kiwi Rider. I need sleep!

[Robert Taylor]

Very quickly and simplistically, altering viscosity primarily affects by pass bleed ( clicker positions ) by about 95% and will affect flow through deflected shim stacks by only about 5%. If you have made a substanial change in viscosity you may have to move the clicker setting by an enormous and ''inappropriate amount'' Excepting on a limited number of top shelf suspension components the tapers on adjustment clicker needles only have a single taper and therefore dont have a linear response range. There is a sweet spot of response range. If you are only a few clicks out from ''fully in'' one click can be a huge change ( excepting if the shim stack opening pressure is very weak ) Conversely, if you are nearly all the way out, one click will do almost nothing as the needle is already so far withdrawn.

So tuning by viscosity is in most ways a myth, especially with modern high spec high performance suspension units.

And not all oils are the same, sae ratings are not ''gospel'' by any means. But please ask me about that another time or read an upcoming issue of Kiwi Rider. I need sleep!

Further to that, in fairness you will notably see a difference in rebound speed if altering the viscosity of fluid in damper rod forks as primary rebound control is ''fixed orifice'' only...through a hole drilled in the rod. As such bikes require such heavy viscosity oils for control they are VERY affected by the atmospheric conditions of the day. On a cold frosty morning the forks will be very ''lethargic''

[sAsLEX]

.. one of the current crop of 600 sportbikes has the cheapest nastiest front fork cartridges that you have ever seen. As a term of relativity last years cartridges look as if they would have come out of the Ferrari factory ( although that rather flatters them ) This years look like a lowest level budget replacement that would be made in China for resale by SuperCheap auto.

I realise you might not want to name and shame for commercial reasons but is there a reliable source one could be pointed to to ascertain what is beneath the skin of modern sprot bikes? I mean the most people really get before purchasing is a shortish test ride and a few articles in magazines or off the net. Not many of which point to the tunability/rebuildability of the internal cartridges....

[Pussy]

Just a point here for all those using Roberts services.
Being able to give him informed feedback will mean you'll get best bang for buck from his trackside services.
Having notes clearly showing what suspension settings you are using really are like gold.

Go on!! You mean that I shouldn't just hand RT a shock and say "fix this"

[FROSTY:Me]

Go on!! You mean that I shouldn't just hand RT a shock and say "fix this"

Dude have a look around the pits at the next vic club round. See how many riders havent a clue of the fuel load needed,Suspension settings, or even in some cases the gearing.

[slowpoke]

Much more so than a Japanese fork the overlap where the lower tube threads into the lower castings is substanially longer and stronger than in a Japanese sportbike fork. There are 2 current popular litre class Japanese sportbikes that will develop movement between the lower tube and bottom casting over time, especially if the rider likes pulling wheelies and is a late braker.

Hmmm, as the owner of an "old" modern sportsbike ('00 R1) I'm wondering if this means it is actually possible (within monetary reason) to replace the lower casting of my forks with a radial caliper design.
Would it be as simple as finding a virtually worthless pair of trashed later model R1 forks and swapping the cast sections?

[roogazza]

Great reading from you Robert and TDC . A far cry from the seventies Prod/bikes that we stuffed engine oil and packers into the forks and put the preload on the rear to full and just hoped our TT100's would grip ? I'm now in the 21st century........Gaz.

[TDC]

So tuning by viscosity is in most ways a myth, especially with modern high spec high performance suspension units.

And not all oils are the same, sae ratings are not ''gospel'' by any means. But please ask me about that another time or read an upcoming issue of Kiwi Rider. I need sleep!

At the risk of sticking my nose in... the whole oil things I feel needs some considerable expansion.

Firstly that stuff many of us buy based on the price tag rather than the specification or quality, or worse have fallen victim to a completely dubious marketing campaign based on catch phrases rather than fact....

The considerable technology and ongoing R&D invested in oil products would astound all of us if we could comprehend the extents of the technology, budget, and qualifications and experience of the numerous white coated technicians manipulating molecules to make ever better oils.

Anyhow, as Robert alluded to the S.A.E. numbers don't really mean much when used in suspension. All quality suspension fluids have their viscosity expressed in centistrokes at a temperature reflective of its mean operating temperature. Why is this important? We first have to understand the S.A.E. viscosity numbering systems intention. When we think about oil destined for a engine application we assume that the the viscosity rating is a measure of the "flowability" of an oil. More specifically, it is the property of an oil to develop and maintain a certain amount of shearing stress dependent on flow, and then to offer continued resistance to flow. This is important because of the way a plain bearing works. It is not the oil pressure generated by the oil pump that keeps the crank separated from the crank bearings. Rather, it is a local area of higher pressure generated by the shearing action of the parts moving relative to each other. This "hydro-dynamic bearing" layer is what resists the forces of pistons and so on. As a result the S.A.E. developed a number of approved methods for measuring the shear strength of oil, and oil weights are representative primarily of their shear strength not their flowability. The centistrokes measure is however primarily concerned with the flowability of the fluid, which in the case of suspension components is of far greater importance. To a lesser extent we don't care what the shear strength of the oil film is but rather how it is going to perform when being passed through an orifice. While the shear strength and flowability are related they are not as closely related as you might instinctively think. This is why three brands of the same weight oil will perform quite differently in a suspension application as their centistrokes measurements will vary considerably.

Then we need to be concerned with the viscosity index. This is a rating of how well the fluid holds its viscosity when exposed to temperature, the bigger the number the better (pretty much). Many multi grade engine oils claim to be able to maintain their viscosity over a wide temperature range. They do this by additives to the base oil (usually some form of polymer) that has a positive viscosity temperature coefficient, so as the base oil thins as a result of heat the polymer thickens, hence keeping the observable viscosity static over a wide range of temperatures. Usually the better the oil the longer this effect will last for. However one particular oil that is popular in motorcycle applications looses its viscosity index so alarmingly quickly I wouldn't put it in a lawn mower, and worse it has a 0% zinc content!! For a suspension component this is ultimately the ability to have consistent damping over a wide range of operating temperatures, again cheap or poorly specified suspension fluids either degrade quickly in service or simply don't manage to remain stable over the working temperature range of the suspension and deliver unpredictable results at best.

We also need to be concerned with PH in suspension components, most modem suspension components have a number of different materials present in them. If the Ph is too far from the neutral range, galvanic corrosion can destroy things up internally at a rate that deifies belief! Many people incorrectly diagnose erosion on the damper pistons as cavitation scaring when in fact it is exactly the same thing that destroys the props on boats in salt water. The Ph of the oil is really affected by the water it picks up because the water will react with gasses to form acids. This means that suspension fluids need to handled with the same care as brake fluid! Many lower grade suspension fluids have a significant water content sitting in the sealed bottle on the shelf.

Oil is not the simple stuff you can easily mistake it for. In times gone past when the front forks of basically everything had damper rod forks pretty much any semi reasonable oil of the right grade was just fine, it was under very low levels of stress. When dealing with modern high performance cartridge forks the oil is under enormous stress, there are disturbingly few oils that will give acceptable performance across the temperature ranges experienced in New Zealand, and if you want them to offer consistent performance past a few hunderd K's the choice gets very small indeed.... Then spare a though for the extraordinarily highly stressed oil in your rear shock working under pressures often in excess of 12 Bar and temperatures easily exceeding 80 degrees C, A poor choice of oil here can have dire consequences.

[HenryDorsetCase]

Holy shit, would anyone mind if I printed this thread off, bound it up and sold it on trademe? (HDC's big book of wisdom sounds like a catchy title....)

There is some amazing techy insight going on here. Thank you to the people with the knowledge and the ability to express it in terms a munter like me can understand.

[HenryDorsetCase]

Dude have a look around the pits at the next vic club round. See how many riders havent a clue of the fuel load needed,Suspension settings, or even in some cases the gearing.

Oooh thats me!


Next time you see me, come up and introduce yourself!

[TDC]

Hmmm, as the owner of an "old" modern sportsbike ('00 R1) I'm wondering if this means it is actually possible (within monetary reason) to replace the lower casting of my forks with a radial caliper design.
Would it be as simple as finding a virtually worthless pair of trashed later model R1 forks and swapping the cast sections?

Technically very probable in theory, however there are some likely sources of problems.

Firstly because you can not "shim" the distance from the caliper to the rotor with a radial caliper you may have problems with the offset of the disk rotors mandating the purchase of different rotors, trust me when I tell you that trying to source a rotor with the right diameter, the right offset, and the right number of mounting holes of the right diameter and the right pitch circle diameter is often very difficult! All the suppliers want to discuss is for "what model bike are you looking for a rotor for"! The other way that this problem can be addressed is by manufacturing triple clamps to suit the new requirement. You will almost certainly need the matching front axle (from the fork lowers) that may not match the bearings (an easy fix usually) and the width of the forks may not suit the new combination which would require the fabrication of a new axle and spacers. Unfortunately this kind of a job can get really silly due simply to the number of custom pieces that need to be manufactured and can quickly end up costing more than a set of after market forks that bold right on. Having said that some are very simple to do because they accidentally line up out of the box. I can't comment on the R1 its not a job I have done before.

While radial mount calipers look cool they don't offer a quantum leap in brake performance. You might end up with a better thing by upgrading the internals of the forks rather than the outside?

Oh and as its your life you are effectively playing with you will need to have this work done by somebody experienced and competent.

[Robert Taylor]

I realise you might not want to name and shame for commercial reasons but is there a reliable source one could be pointed to to ascertain what is beneath the skin of modern sprot bikes? I mean the most people really get before purchasing is a shortish test ride and a few articles in magazines or off the net. Not many of which point to the tunability/rebuildability of the internal cartridges....

There used to be a totally up front source in the States, ''Road Racing World'' Trouble was the distributors / manufacturers blacklisted them from having test bikes....imagine if one of the magazines here in NZ was totally candid. Not only do we have a Government that exercises press censorship, commerce exercises its own effective form of censorship. Our small population exacerbates the effect of these realities.

There is of course a difference between subjective reasoned judgement of products and open slather bad mouthing. Those that engage in the second option know who they are.

I would expect that we will see more non rebuildable / non tunable cartridges like the ones I mentioned. And ( sorry ) no, Im not going to put my head on the chopping block over this.

[Robert Taylor]

At the risk of sticking my nose in... the whole oil things I feel needs some considerable expansion.

Firstly that stuff many of us buy based on the price tag rather than the specification or quality, or worse have fallen victim to a completely dubious marketing campaign based on catch phrases rather than fact....

The considerable technology and ongoing R&D invested in oil products would astound all of us if we could comprehend the extents of the technology, budget, and qualifications and experience of the numerous white coated technicians manipulating molecules to make ever better oils.

Anyhow, as Robert alluded to the S.A.E. numbers don't really mean much when used in suspension. All quality suspension fluids have their viscosity expressed in centistrokes at a temperature reflective of its mean operating temperature. Why is this important? We first have to understand the S.A.E. viscosity numbering systems intention. When we think about oil destined for a engine application we assume that the the viscosity rating is a measure of the "flowability" of an oil. More specifically, it is the property of an oil to develop and maintain a certain amount of shearing stress dependent on flow, and then to offer continued resistance to flow. This is important because of the way a plain bearing works. It is not the oil pressure generated by the oil pump that keeps the crank separated from the crank bearings. Rather, it is a local area of higher pressure generated by the shearing action of the parts moving relative to each other. This "hydro-dynamic bearing" layer is what resists the forces of pistons and so on. As a result the S.A.E. developed a number of approved methods for measuring the shear strength of oil, and oil weights are representative primarily of their shear strength not their flowability. The centistrokes measure is however primarily concerned with the flowability of the fluid, which in the case of suspension components is of far greater importance. To a lesser extent we don't care what the shear strength of the oil film is but rather how it is going to perform when being passed through an orifice. While the shear strength and flowability are related they are not as closely related as you might instinctively think. This is why three brands of the same weight oil will perform quite differently in a suspension application as their centistrokes measurements will vary considerably.

Then we need to be concerned with the viscosity index. This is a rating of how well the fluid holds its viscosity when exposed to temperature, the bigger the number the better (pretty much). Many multi grade engine oils claim to be able to maintain their viscosity over a wide temperature range. They do this by additives to the base oil (usually some form of polymer) that has a positive viscosity temperature coefficient, so as the base oil thins as a result of heat the polymer thickens, hence keeping the observable viscosity static over a wide range of temperatures. Usually the better the oil the longer this effect will last for. However one particular oil that is popular in motorcycle applications looses its viscosity index so alarmingly quickly I wouldn't put it in a lawn mower, and worse it has a 0% zinc content!! For a suspension component this is ultimately the ability to have consistent damping over a wide range of operating temperatures, again cheap or poorly specified suspension fluids either degrade quickly in service or simply don't manage to remain stable over the working temperature range of the suspension and deliver unpredictable results at best.

We also need to be concerned with PH in suspension components, most modem suspension components have a number of different materials present in them. If the Ph is too far from the neutral range, galvanic corrosion can destroy things up internally at a rate that deifies belief! Many people incorrectly diagnose erosion on the damper pistons as cavitation scaring when in fact it is exactly the same thing that destroys the props on boats in salt water. The Ph of the oil is really affected by the water it picks up because the water will react with gasses to form acids. This means that suspension fluids need to handled with the same care as brake fluid! Many lower grade suspension fluids have a significant water content sitting in the sealed bottle on the shelf.

Oil is not the simple stuff you can easily mistake it for. In times gone past when the front forks of basically everything had damper rod forks pretty much any semi reasonable oil of the right grade was just fine, it was under very low levels of stress. When dealing with modern high performance cartridge forks the oil is under enormous stress, there are disturbingly few oils that will give acceptable performance across the temperature ranges experienced in New Zealand, and if you want them to offer consistent performance past a few hunderd K's the choice gets very small indeed.... Then spare a though for the extraordinarily highly stressed oil in your rear shock working under pressures often in excess of 12 Bar and temperatures easily exceeding 80 degrees C, A poor choice of oil here can have dire consequences.

Thanks for doing a much more thorough and detailed job of explaining suspension oil issues than I would have. Its worth mentioning that temperature stability at the lower end of the scale is important when selecting fork oils. As there is a lot of metal mass in forks and they are always exposed to the cooling airstream ( and are not in close promity to a warm engine and headers ) they will usually run at ambient temperature or slightly below.

I am sure we race motorcycles during our winters in conditions that the Europeans would usually stay home at....please somebody correct me if Im wrong. Fork action can feel very lethargic first thing on a frosty race morning at Taupo or Teretonga. But come early afternoon when the sun is out the action becomes a little happier. A fork fluid that ''thickens'' only slightly as the barometer drops is called for.

In pushing my own barrow Ohlins make a high percentage of the worlds snowmobile shock absorbers so are neccessarily pedantic about oils with great flow characteristics at sub zero temps. Their branded oil ( supplied by a Norwegian company ) provides the neccessary characteristics. Also, to the best of my knowledge they are the only supplier of suspension oils to label their bottles with the first and very most important part of selection, the centistroke rating.

[Robert Taylor]

Great reading from you Robert and TDC . A far cry from the seventies Prod/bikes that we stuffed engine oil and packers into the forks and put the preload on the rear to full and just hoped our TT100's would grip ? I'm now in the 21st century........Gaz.

Yes and I remember well sweating away fitting those TT100s. Still a great brand of tyre as Bugden and Smith proved.

[Pixie]

In truth the biggest immediate improvements are going to come from those newer tyres and your own personal riding development. As will ensuring you stay lean and mean and sharp. Ie no mind altering substances etc.

Brings to mind an acquaintance from many years ago.
When he started recounting how he was going to work over his Benelli 250 to make it perform better, his wife suggested that loosing 3 stone would be cheaper and have more effect on the bikes performance.