Fork oil, What can I use?

[Gazjacko]

I have a set of clunky forks that I think will need re oiling for damping once I take them apart. Do I really need to buy fork oil? And if so what wt? I’m tempted to buy motorcycle fork oil as it’s cheaper, or even just use some of my car oil which is a synthetic 5w/30w.
Talk me out of it

 

[Drago]

Motorcycle fork oil of the appropriate weight should be fine. Engine oil is of no use as it does not have the anti foam properties that fork oil requires to maintain consistent damping performance.

 

[figbat]

Motorcycle fork oil of the appropriate weight should be fine. Engine oil is of noise as it does not have the anti foam properties that fork oil requires to maintain consistent damping performance.

Not sure I agree with that. Engine oil has antifoam treatment and is required to pass various foam tests to meet most OEM specs.

Fork oil is normally a straight mineral oil, sometimes synthetic but not treated with viscosity modifiers, which engine oil almost always is. Engine oil is tested for compatibility with a number of seal materials too, but I couldn’t say if those in your fork will be the same materials (probably are, but no guarantees).

Motorcycle fork oil of the right viscosity is fine - it’s what I used.

 

[ChrisEyles]

I believe engine oil contains a range of oil weights, while fork oil will all be the same. This would be fine for use in the lowers, where it's just needed for lubrication, but probably not ideal in a damper?

I recently bought some of the following:

Weldtite TF2 Cycle Suspension Fluid - 500ml
£6.99 from ChainReactionCyclesUK

You'll want around 7.5wt for a typical damper or 15wt/20wt for lowers.

Motorcycle fork oil would be fine if you can get it cheaper - I looked for this first locally but couldn't find anywhere with it in stock in town.

 

[raleighnut]

Use Angel tears.

 

[Gazjacko]

It’s going to be a bit of guesswork as I can’t find any documentation for the forks (Magura Rond Quake)

 

[screenman]

How much will you save by not buying the approved product.

 

[Drago]

Not sure I agree with that. Engine oil has antifoam treatment and is required to pass various foam tests to meet most OEM specs.

Fork oil is normally a straight mineral oil, sometimes synthetic but not treated with viscosity modifiers, which engine oil almost always is. Engine oil is tested for compatibility with a number of seal materials too, but I couldn’t say if those in your fork will be the same materials (probably are, but no guarantees).

Motorcycle fork oil of the right viscosity is fine - it’s what I used.

You don't have to agree. I studied fuels and lunricants as part of my Masters (its relevant to rocketry) and engine oil will have some anti foam properties, but of a different type because of the temperatures and pressures they have to endure at the point at which engine oil risks foaming. As such, they dont work in the relatively cool and benign environment of a shock absorber, where different additives are required. Therefore, engine oil does make very, very,poor fork oil, and this why it is not used as such by manufacturers, despite being quite a bit cheaper. Try it and see, no need to take my word.

Alternatively, you can have gas shocks, where oil still does all the damping through orifice or shim stack, but the reservoir is kept under pressure with an intert gas, usually nitrogen, as a means to prevent foaming. Not normally found on bicycle shocks and forks.

So yeah, use motorcycle fork oil.

 

[Levo-Lon]

I use motorcycle fork oil but I have it in different weights from my motorcycle tinkering days.
Fork oil isn't that expensive, and a 500ml bottle will do 3- 4+ services ,or 6-8+ for a 1l bottle
I use 10w as a rule but I will add a heavier or lighter oil into the mix to get a firmer or softer damping effect.
Cold weather, with thicker oil is not always a nice ride and vice versa.
Engine oil for splash in lower leg is fine

Getting the correct level is also very important to achieve a good working compliant fork

 

[figbat]

You don't have to agree. I studied fuels and lunricants as part of my Masters (its relevant to rocketry) and engine oil will have some anti foam properties, but of a different type because of the temperatures and pressures they have to endure at the point at which engine oil risks foaming. As such, they dont work in the relatively cool and benign environment of a shock absorber, where different additives are required. Therefore, engine oil does make very, very,poor fork oil, and this why it is not used as such by manufacturers, despite being quite a bit cheaper. Try it and see, no need to take my word.

Alternatively, you can have gas shocks, where oil still does all the damping through orifice or shim stack, but the reservoir is kept under pressure with an intert gas, usually nitrogen, as a means to prevent foaming. Not normally found on bicycle shocks and forks.

So yeah, use motorcycle fork oil.

With respect, I have been working in lubricant R&D for 28 years. I agree that engine oil is not ideal for a fork although I would add that it is far more formulated than fork oil so it relatively more expensive and essentially over-engineered. Engine oil is around 80% base oil and 20% additives of various types. Fork oil will be more like 99% base oil with a tiny pinch of one or two additives. Engine oil will also tend not to be the right viscosity anyway, as fork oils are in the nominal SAE 5-15 range.

So yeah, motorcycle fork oil.

 

[DaveReading]