Just wondering the reasoning why there is so little oil in pike lowers or any other fork ?
My current forks are 2015 pikes and it is 5ml and 15ml. Newer pikes were 10ml and 10ml. Still doesn’t seem a lot. My raidons on my sons bike were grease.

So why so little ?

Weight.

Realy ?

I would happily carry the extra 20 grams for 30ml if extra lube.
Is that realy why ? If so I’ll pop a bit more in.

The oil doesn’t do anything other than provide a bit of lubrication. It’s not there to provide any damping, and as it (generally) can’t escape you don’t need any more.

Do you think 5ml is enough to live the bushings in the lower leg ?

Back in the heyday of Marzocchi bombers, it was not uncommon to have 125ml to 200ml per leg. They ran super smooth for ever, with the same oil sometimes being used for the damping too, but they were criticised for being too heavy and competitors moved to less and less oil.

After all, 400ml of oil is what, 375g? When you’re making incremental weight savings across the fork chassis so you can make your fork lighter than the competition, that’s a pretty easy win right there.

No matter what the main purpose of the oil is, oil height is always going to influence the performance of the fork. It’s like using volume spacers.

Do you think 5ml is enough to live the bushings in the lower leg ?

Personally, no. I don’t think 5ml is enough. There’s no appreciable splash lubrication with low volume semi-bath. As a liquid, even a viscous one, it’s going to find itself at the bottom of your fork under the action of gravity, with only a film remaining anywhere near the bushes.

A film is fine for lubrication of course, but it doesn’t give much overhead for running dry or dealing with wear particles and trail contamination.

No matter what the main purpose of the oil is, oil height is always going to influence the performance of the fork. It’s like using volume spacers.

In the air spring it does but not in the lowers.

In the air spring it does but not in the lowers.

The lowers are effectively an air spring so yes it could make a difference.

This oil only is for lubrication.

5 ml or 10 ml or or are plenty.

NO OIL is bad. And hate when RockShox ships their stuff without any oil in lowers…

My recipe for RockShox forks: plenty PM600 military grease for upper seals / foam rings. And roughly the right oil (viscosity) and the correct amount of oil for the lowers. And the fork will go at least for two years super smooth.

Fox: seems they do a better job when shipping forks. They are smooth from day one. At least mine…

In the air spring it does but not in the lowers.

The lowers are effectively an air spring so yes it could make a difference.

Exactly, outside of the airspring and the damper cartridge you still have a sealed compressable volume of air. Air being more compressable than oil.

Yeah but its at atmospheric pressure in the lower legs and its a much, much bigger volume than the air chamber. The seals are just dust seals that trap air at low pressures. Must people actually run a slight negative pressure in there due to assembling the forks fully sagged. You would literally have to chuck the entire bottle of oil in there to notice a difference. You could certainly triple those tiny oil volumes easy.

NO OIL is bad. And hate when RockShox ships their stuff without any oil in lowers…

There are better than they used to be! Remember seeing someone in chatel with an almost brand new pair of boxxers, stanchions scored as there was no oil in them.

Any new fork I buy or fit for mates, the lowers come off for lower leg service before they get ridden. Surprising how many forks are lacking in grease/oil round the seals/wipers and in the lower legs.

Rockshox reckon 50hours between lower leg services, I prefer to do mine a bit earlier than that, more so in the winter/wetter conditions. My old boxxer teams had a 10hour service life, even shorter with the low friction seals!

Can’t beat an old marzocchi for smoothness!

@ndthornton I agree, going from 5 or 10ml to 30ml is unlikely to make any noticeable difference. But, chuck say 100ml or more in there in an attempt to have a load of oil sloshing around for lubrication is quite likely to be noticeable. Those dust seals don’t allow air to pass at the speed a fork works.

Yeah but its at atmospheric pressure in the lower legs and its a much, much bigger volume than the air chamber. The seals are just dust seals that trap air at low pressures.

This is something that has always confused me. In theory the above makes sense and Rockshox don’t seem to offer any advice on what pressure should be in the lowers. But I’ve found it makes a huge difference to performance in practice.

If I assemble the forks fully extended so the lowers are effectively at atmospheric pressure I find it quite hard to fully compress the forks (even if I let almost all the air out of the main air chamber). If I compress the forks then slip a zip tie past the seals to let the air out (creating a negative pressure in the lowers when the fork is extended) the fork behaves very differently. But I’ve never worked out which of these two situations is “correct”.

I was under the impression that it’s now 10ml in 2015 pikes. Also I thought overfilling can cause the damper to ingest more oil and split the bladder.

It’s a sealed cartridge unit. How do you propose the oil is ingested?

its a much, much bigger volume than the air chamber.

The air chamber is the entire inside of the stanchion isn’t it? I haven’t checked but I would have guessed that’s a lot larger than the internal volume of the lowers, once the end of the stanchion, push rod, etc is taken into account.

It is! Not sure how the two volumes compare though. On the damper side though, the cartridge pretty much fills the stanchion so at full compression there wont be much space left in the lowers for air, oil or anything else.

Both stanchions are effectively solid in most forks I’ve serviced. When you consider at full compression there will be a tiny bit of space between the lowers and stanchion ends – the shaft diameter + any air volume between stanchion and lowers along their length (remembering bushings take some of this space) I think you’ll be looking at a significant compression ratio at full compression.

It’s a sealed cartridge unit. How do you propose the oil is ingested?

Through the lower seal head.

I think you’ll be looking at a significant compression ratio at full compression.

It cant be that high or it would blow the dust seals out – I once had a leaky negative air chamber due to not using enough grease on the seal – The leak from the air spring into the lowers popped the dust seal out at as soon as started trying to inflate the air spring.
If you think about it – in the air spring you have a static pressure of at least 60 PSI before you even start compressing the forks….I am sure it spikes to many times that on full compression especially running tokens.

A rough example using guessed dimensions. Say an effectively solid 34mm stanchion travels 130mm into the lowers and leaves 20mm space before the bottom of the lowers. That’s a compression ratio of 7.5:1. Assuming the internal bore of the lowers is 34mm(in reality it will be slightly more but you also have a shaft in there taking up space) 7.5 x 14.7(atmospheric pressure) = 110.25psi.

So you measure the amount of air in the “spring” with your (digital) shock pump to high precision. Then there is this extra positive spring (the two lowers) but the amount of air in that is pretty much random (depending on whether the legs were compressed, extended or somewhere in between when you did up the foot bolts). It doesn’t make any sense. If the lowers are sealed (making them an extra positive spring) at least tell us how much air should be in them.

@roverpig. They do tell you in a round about way. You should assemble the forks according to the service guide (full compression in the case of my forks). This will be known volume to the designer so they can take it into account.

I have some wireless TPMS sensors – would be a interesting to drop them in the lower legs and measure this properly so we can stop guessing.

roverpig

We can only assume rockshox accounts for the extra springiness. There is no way for the user to control it apart from running atmospheric pressure or a very slight vacuum. I run atmospheric – works fine for me.

@jordan was going to post a very similar example. So for someone adding an extra 10ml of oil could effectively double the compression ratio.

Edit just realised you gave 20mm or space rather than a volume so probably not doubled.

@ndthornton great idea! Do it! btw if you are correct that the dust seals lose air then it makes no difference whether the forks are assembled compressed or exteneded as they are going to equalise eventualy anyway.

Thanks @nixie I guess I should read the manual then 🙂

The 2015 manual states 5 and 15. In my 2017 pikes it is 10 and 10. I don’t know if the fork internals are the same and RS just changed their minds ? I’m gone put a few more Ml in I think.
Most of 5 ml will hopefully stuck to the lowers.

Didn’t the manual get revised to say 10 in both legs? That’s what I’ve been putting in and mine haven’t set on fire or anything

It did mate.
I just downloaded the 2015 manual . The 2017 is 10 and 10. I just assumed that they had changed something in the fork. I’m going to put a bit more in .

The manuals are confusing but do warn that too much oil in the lowers can damage the forks. Can’t believe that a few extra ml would though.

I also doubt that lube oil will find its way into the damper cartridge and bladder via the seal head. The other way around however….

I take it no one has ever had their lowers “fill” with water and effectively hydroloc the forks, it takes a surprisingly small amount to do so.

No!

I’ve heard of hydrolocking the forks but never done it. Did they change the damper in 2016/2017 or is my 2015 forks the same ? .

I filled my old RST mozo pros with water fording a river. Not deliberate, they road like crap afterwards until I stripped them down.

I put a few ml extra on one oil change – the fork ramped up more quickly at the end of the travel. IIRC about 10ml was enough to do it. In another set I put in 100ml extra – no differnce in performance noticable – so it very much depends on the design. ie how much volume is left when the fork is fully compressed

Old Marzocchis were ace, not only was the oil a lube bath and damping medium, but it was also a volume spacer!

I would just do what the manual says. Except that I put 5ml in my 2015 Pikes after reading the lowers bolt that said “5ml max”, despite the manual saying 10. I think.