Fork air Pumps

Yamaharider1474
Edited Date/Time 9/4/2012 10:23pm
Does anyone who owns a new model CRF or KXF use or purchase a small hand pump to adjust PSI in the forks ?
What model and make did you get? cost?
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newmann
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newmann 9/4/2012 3:26pm
9/4/2012 3:26pm
You would think it would come with one. Do the forks have the standard air valve stem or something special?
newmann
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newmann 9/4/2012 3:28pm
9/4/2012 3:28pm Edited Date/Time 9/4/2012 3:29pm
Here you go.

"New 2013 KX owners will have to invest into an accurate pump to set the fork air pressure before each ride. The good news is that it’s as easy as setting tire pressure. Kawasaki sells a pump for $49.95, part number (K56019-060A). The air fork pressure adjustability is like having several spring rates at your fingertips. We messed with pressures but found 35 worked best initially."

http://www.motocross.com/features/first-impression-2013-kx450f/
BAMX
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BAMX 9/4/2012 3:42pm
9/4/2012 3:42pm
Use nitrogen....Air expands too much with normal changes in temp.
ML512
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ML512 9/4/2012 3:45pm
9/4/2012 3:45pm
DRC is making a trick one that Enzo racing is selling, and its cheaper than the kawi one too i believe...

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tobz
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tobz 9/4/2012 3:45pm
9/4/2012 3:45pm
Does anyone know if pros have been using th air forks? Just wondering if it's a gimmick, like the dual exhausts.
newmann
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newmann 9/4/2012 3:54pm
9/4/2012 3:54pm
BAMX wrote:
Use nitrogen....Air expands too much with normal changes in temp.
If not mistaken, people are claiming these are not supposed to be affected as you are thinking.
Bret
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Bret 9/4/2012 3:58pm
9/4/2012 3:58pm
BAMX wrote:
Use nitrogen....Air expands too much with normal changes in temp.
Spend a day testing two sets of forks, one with nitrogen and the other with air, and you will discover that it isn't worth worrying about. Bret
bradmx421
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bradmx421 9/4/2012 4:09pm
9/4/2012 4:09pm
ML512 wrote:
DRC is making a trick one that Enzo racing is selling, and its cheaper than the kawi one too i believe...
you can purchase these from Langston Motorsports.....we sold out of the first batch of them and are expecting to get another shipment this week.

Ive used it a few times to play around with the forks with the bikes on the floor, and it works really well
T-MAC
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T-MAC 9/4/2012 4:37pm
9/4/2012 4:37pm Edited Date/Time 9/4/2012 4:41pm
Yeah, like I said in a thread about this a while back (but someone said that I was wrong and you just use a regular floor pump). Lots of options out there already that are sold as mountain bike shock pumps.
BAMX
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BAMX 9/4/2012 4:43pm
9/4/2012 4:43pm
BAMX wrote:
Use nitrogen....Air expands too much with normal changes in temp.
newmann wrote:
If not mistaken, people are claiming these are not supposed to be affected as you are thinking.
I don't understand how something that is made to be adjusted by air pressure isn't effected by changes in air pressure. I'm not trying to be a dick. It just doesn't make sense that on one hand you adjust with pressure but on the other hand, they aren't effected by it. I thought that I read 3 lb is equal to on spring rate. Does anyone have any real info on this?
bayodome
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bayodome 9/4/2012 6:08pm
9/4/2012 6:08pm
As long as the MTB-style shock pump has small enough increments on the PSI dial, it will work. The Kawasaki comes with a valve adapter since their Schrader valve is recessed. We have been using a Bontrager shock pump on our test bike, that I also use for my MTB, and it works just fine. One side of the meter has higher pressure increments, while the other has a smaller dial for more precise measurement.
Camp332
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Camp332 9/4/2012 6:15pm
9/4/2012 6:15pm
bradmx421 wrote:
Pretty interesting. I thought the "Compressed Air Chamber" would be a lot bigger.

Don't try to figure it out. Japanese Engineers who are way smarter than us figured this stuff out. It works. Now they sell it.
crashnburn11 9/4/2012 7:37pm
9/4/2012 7:37pm
BAMX wrote:
I don't understand how something that is made to be adjusted by air pressure isn't effected by changes in air pressure. I'm not trying to be...
I don't understand how something that is made to be adjusted by air pressure isn't effected by changes in air pressure. I'm not trying to be a dick. It just doesn't make sense that on one hand you adjust with pressure but on the other hand, they aren't effected by it. I thought that I read 3 lb is equal to on spring rate. Does anyone have any real info on this?
Basically, the reason that is not the case is that the 35 psi you put in it to set the spring rate is not the pressure it is under as it compresses. As it compresses, the pressure becomes relatively large compared to the effects of heat exciting the air into a higher pressure. The basic equation is PV = nRT, (where T is the absolute temperature, in Rankine or Kelvin), but since you always have the same number of molecules in the chamber, and it is just pressure and volume changing (with minor changes in temperature), you can ignore the n. R is the gas constant, so it can also be ignored as far as changes go. So basically, PV/T is constant, or P1V1/T1 = P2V2/T2. Since pressure and volume change much more than the temperature, they tend to dominate this equation.

In all that equations, the R is what would actually be different between Nitrogen and Air. Yes, you would see LESS change with temperature since R is lower for nitrogen, but the difference is minuscule compared to the other effects in play.
Derpin' DJ
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Derpin' DJ 9/4/2012 7:57pm
9/4/2012 7:57pm Edited Date/Time 9/4/2012 8:00pm
Actually, it's an adiabatic process, so P1*(V1^1.4)=P2*(V2^1.4). Temperature increases quite alot when the air is compressed, but it cools back down when it expands. The issue is that air generally has alot of moisture in it, which tends to hold its heat much differently than nitrogen and oxygen. Dehumidified air will act almost identically to pure nitrogen
crashnburn11 9/4/2012 8:13pm
9/4/2012 8:13pm
It can be approximated as Adiabatic, but it isn't. The Air chamber would need to be insulated from the surroundings for it to be adiabatic. You could claim the system was isentropic, but I don't think adiabatic is correct. The air is going to gain heat from the output off the damper during a moto, and maybe a little from.

Also, both equations apply. My equation would be used to determine the temperature at two states, where as yours is the polytropic equation that would help you relate the volume with the pressure at different points. The point isn't the temperature gradient during compression, but the amount it changes as the temperature rises due to heat gain being small.

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Derpin' DJ
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Derpin' DJ 9/4/2012 8:17pm
9/4/2012 8:17pm
Ahk, I see the point you are trying to make. I probably should have read your comment a bit better, lol.
wow123
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wow123 9/4/2012 10:23pm
9/4/2012 10:23pm
BAMX wrote:
Use nitrogen....Air expands too much with normal changes in temp.
Thats more to do with shocks as they get very warm and the gas is at much higher pressure so can have a greater effect.
And i think its about the shock exploding more than ride, air burns nitrogen doesn't
Much to my suprise my suzuki RM 250 manual says if nitrogen is not available
then you can use air when regassing a shock.

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