Mechanics Quick Question Thread [Ask Questions Here]

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Mechanics Quick Question Thread [Ask Questions Here]
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flag ajax-ripper
Posted: Nov 9, 2019 at 16:00 Quote
Bflutz625 wrote:
I see. Just wondering because I've seen a lot of people who just inflate the IFP with air.
Nitrogen looked molecules are larger and don't leak out of the seals over time.
flag R-M-R
Posted: Nov 9, 2019 at 16:23 Quote
Bflutz625 wrote:
Any reason as to why nitrogen is necessary and why normal air won't work?

Not really.

• Air is 78% nitrogen.
• The water vapor in air may condense into liquid at high pressure, slightly affecting the gas charge properties, but since air is less than 1% water vapor, the effect is tiny.
• The argon (1%) leaks through rubber more readily ... but it's only 1%. A Consumer Reports study found the difference in air leakage in a tire over a year with nitrogen vs. air was slightly over 1 psi.
• Oxygen is more corrosive than nitrogen ... but there's oxygen outside the chamber. The oxygen inside the chamber does not cause appreciably more corrosion than the oxygen outside the chamber.
• Gasses other than nitrogen have lower specific heat, meaning their temperature is changed more readily, i.e. they don't buffer the temperature ... but the difference between air and nitrogen is about 10%, and it's 10% of not much, i.e. the temperature change in a shock or tire is due mostly to the properties of the shock body or tire, not the gas.

Go ahead and use 78% nitrogen. If you want to get a little fancier, inflate it in the driest environment you can find, such as:

• In your home, if an air conditioner has been cooling your air
• • Outside during dry weather or a super cold winter day, as the air holds little moisture in cold weather. Note: in cold weather, the relative humidity may be higher, which means "relative to the maximum water carrying capacity of the air". The maximum capacity is super low in cold weather. For example: 70% relative humidity in cold weather is 0.7 × (not much), which is less than, say, 0.3 × (a lot more) in the summer.


Bflutz625 wrote:
I see. Just wondering because I've seen a lot of people who just inflate the IFP with air.

It's fine to do so. The differences are:

• A fractional percent in performance in the expansion chamber, which is a small detail in the overall performance of the shock. If it actually made a difference, there is equal reason to use 100% nitrogen in the main spring chamber, which no one worries about. Also think about the change in friction due to expansion of the rubber seals at elevated temperature and changes in fluid viscosity; not much concern over those, but people get pretty worked up about 100% nitrogen vs. 78% nitrogen.
• A few percent more rapid leak-down in the expansion chamber. Top up the expansion chamber once per year and you should be fine - unless it's a DVO Topaz, in which case you may need to do it every week or two, but at least you can do it yourself. Their rapid leak-down has nothing to do with 78% vs. 100% nitrogen.
flag newbermuda
O+
Posted: Nov 9, 2019 at 16:25 Quote
ajax-ripper wrote:
Bflutz625 wrote:
I see. Just wondering because I've seen a lot of people who just inflate the IFP with air.
Nitrogen looked molecules are larger and don't leak out of the seals over time.

idk about "larger" but nitrogen is inert and won't react with and degrade your seals. regular air has a significant percentage of oxygen and water vapor in it which will corrode your seals.
flag R-M-R
Posted: Nov 9, 2019 at 16:32 Quote
sosburn wrote:
idk about "larger" but nitrogen is inert and won't react with and degrade your seals. regular air has a significant percentage of oxygen and water vapor in it which will corrode your seals.

So does the air on the other side of the expansion chamber. And the air inside your positive spring. Why are those okay, but not inside the expansion chamber?
flag seraph
Posted: Nov 9, 2019 at 16:33 Quote
R-M-R wrote:
sosburn wrote:
idk about "larger" but nitrogen is inert and won't react with and degrade your seals. regular air has a significant percentage of oxygen and water vapor in it which will corrode your seals.

So does the air on the other side of the expansion chamber. And the air inside your positive spring. Why are those okay, but not inside the expansion chamber?

Science?
flag R-M-R
Posted: Nov 9, 2019 at 16:43 Quote
seraph wrote:
R-M-R wrote:
sosburn wrote:
idk about "larger" but nitrogen is inert and won't react with and degrade your seals. regular air has a significant percentage of oxygen and water vapor in it which will corrode your seals.

So does the air on the other side of the expansion chamber. And the air inside your positive spring. Why are those okay, but not inside the expansion chamber?

Science?

Not any science that's known to me. An argument can be made that conditions inside the chamber are more harsh, but the resulting effects are so small that the differences exist in only the most literal sense, not anything practical.
flag newbermuda
O+
Posted: Nov 9, 2019 at 17:03 Quote
R-M-R wrote:
seraph wrote:
R-M-R wrote:


So does the air on the other side of the expansion chamber. And the air inside your positive spring. Why are those okay, but not inside the expansion chamber?

Science?

Not any science that's known to me. An argument can be made that conditions inside the chamber are more harsh, but the resulting effects are so small that the differences exist in only the most literal sense, not anything practical.

Because youre compressing the air in the damper. Compression = heat, and heated water vapor and oxygen = r.o.s.'s which will oxidize the rubber faster.

thats the reasoning why its better to use nitrogen, but the seals are going to wear anyways so doesn't really matter.
flag ajax-ripper
Posted: Nov 9, 2019 at 17:16 Quote
sosburn wrote:
R-M-R wrote:
seraph wrote:


Science?

Not any science that's known to me. An argument can be made that conditions inside the chamber are more harsh, but the resulting effects are so small that the differences exist in only the most literal sense, not anything practical.

Because youre compressing the air in the damper. Compression = heat, and heated water vapor and oxygen = r.o.s.'s which will oxidize the rubber faster.

thats the reasoning why its better to use nitrogen, but the seals are going to wear anyways so doesn't really matter.
What about the air spring that goes through the same effect but isn't charged with n2?
flag R-M-R
Posted: Nov 9, 2019 at 17:17 Quote
sosburn wrote:
Because youre compressing the air in the damper. Compression = heat, and heated water vapor and oxygen = r.o.s.'s which will oxidize the rubber faster.

thats the reasoning why its better to use nitrogen, but the seals are going to wear anyways so doesn't really matter.

All shock components are at a pretty similar temperature. There will be momentary heat spikes in the chamber, of course. I'm not convinced this is enough to cause rapid oxidation on the chamber side of the seal, but I'm not certain enough to rule it out.

If this were true, though, then should we not be similarly concerned about using 78% nitrogen in the main spring chamber? I don't know the typical compression ratio in an IFP chamber, so maybe it gets a lot hotter and crosses some threshold at which oxygen rapidly degrades the seals. I'd be surprised, but it's possible.

I agree the wear from sliding and the degradation of lubrication oil and damper fluids is probably more rapid than the oxidation of the seals, so the service interval will probably always be limited by the life of the oils and seals (due to sliding).
flag newbermuda
O+
Posted: Nov 9, 2019 at 17:31 Quote
R-M-R wrote:
sosburn wrote:
Because youre compressing the air in the damper. Compression = heat, and heated water vapor and oxygen = r.o.s.'s which will oxidize the rubber faster.

thats the reasoning why its better to use nitrogen, but the seals are going to wear anyways so doesn't really matter.

All shock components are at a pretty similar temperature. There will be momentary heat spikes in the chamber, of course. I'm not convinced this is enough to cause rapid oxidation on the chamber side of the seal, but I'm not certain enough to rule it out.

If this were true, though, then should we not be similarly concerned about using 78% nitrogen in the main spring chamber? I don't know the typical compression ratio in an IFP chamber, so maybe it gets a lot hotter and crosses some threshold at which oxygen rapidly degrades the seals. I'd be surprised, but it's possible.

I agree the wear from sliding and the degradation of lubrication oil and damper fluids is probably more rapid than the oxidation of the seals, so the service interval will probably always be limited by the life of the oils and seals (due to sliding).

lmao, "momentary heat spikes" is more than enough to radicalize oxygen.
nitrogen is N2 in an atmospheric setting. unless you have some fancy bacteria in your damper or a lightning bolt's worth of voltage, N2 is going to remain inert.

78% is the majority, but 20% oxygen is a significant amount. if we were just talking about the 1% water vapor then sure, no worries at all.

im not trying to sound like a jerk or anything, but you may as well take care of your expensive suspension products with cheap nitrogen
flag R-M-R
Posted: Nov 9, 2019 at 18:11 Quote
sosburn wrote:
lmao, "momentary heat spikes" is more than enough to radicalize oxygen.

Maybe. Depends on how much heat. I'm not saying it can't happen, I'm just saying I'm not convinced. You can convince me, if you like, by determining the compression ration in an IFP and crunching some numbers. I could do that, too, but I don't currently feel like it. Until someone does this, it's all speculation.

You also ignored two of my three points:

R-M-R wrote:
If this were true, though, then should we not be similarly concerned about using 78% nitrogen in the main spring chamber? I don't know the typical compression ratio in an IFP chamber, so maybe it gets a lot hotter and crosses some threshold at which oxygen rapidly degrades the seals. I'd be surprised, but it's possible.

I agree the wear from sliding and the degradation of lubrication oil and damper fluids is probably more rapid than the oxidation of the seals, so the service interval will probably always be limited by the life of the oils and seals (due to sliding).



sosburn wrote:
im not trying to sound like a jerk or anything

Can you please clarify how we should interpret a response that starts with "lmao"?
flag Nobble
Posted: Nov 9, 2019 at 19:45 Quote
ajax-ripper wrote:
vanillapodfan wrote:
ajax-ripper wrote:

The damper is contained within that shaft, so yes it is difficult.

Any harder than removing a damper from a fork? I'm fairly good with mechanicy stuff.
Significantly. Every small component needs to come out and be re-installed, damper needs to be bled after and charged with n2.
Rockshox shocks can be rebuilt and charged with regular air. Nitrogen is nice if you have it, but not neccesary.

Nitrogen is nice long term because it's usually drier than regular air.

All the old Rockshox service manuals tell you to just pressurize the IFP with a shock pump. IDK about the deluxe/superdeluxe, I haven't done one of those.
flag masonsmith
O+
Posted: Nov 9, 2019 at 21:01 Quote
I just have a few question first being, when I pull my seat tube their is some play. I checked all the pivots and they were all tight. Do I need to replace the pivots or is it something else? Secondly, if I pull my crank their is also play and I checked it as well and it was tight. I think I need to replace the pivots, and bottom bracket, just checking here for some help!
flag R-M-R
Posted: Nov 9, 2019 at 21:10 Quote
masonsmith wrote:
I just have a few question first being, when I pull my seat tube their is some play. I checked all the pivots and they were all tight. Do I need to replace the pivots or is it something else? Secondly, if I pull my crank their is also play and I checked it as well and it was tight. I think I need to replace the pivots, and bottom bracket, just checking here for some help!

In both cases, try to determine the location of the movement.

For the movement you detect when pulling on the seat, first check for movement at the shock eyelets. If that's the location, it could be worn shock bushings, worn pivot hardware, and/or undersized pivot hardware.

The crank issue sounds like a worn BB. Again, confirm the location of the movement before deciding what to replace.

While you're at it, you might as well disconnect your frame elements and check the pivot bearings, even if there's no obvious play. Be careful you don't drop any spacers when you pull things apart and make careful note of the orientation of any spacers.
flag Bflutz625
Posted: Nov 10, 2019 at 6:53 Quote
Just picked up my new bike yesterday (Trance 29) and my rear shock (Fox DPS) is making that zipper noise. Very faint but annoying as hell. Is this just break in or would I have to do something about it?

 


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