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Thread: Gas shocks

  1. #1
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    Default Gas shocks

    I want to learn more about gas charged shocks and how the gas changes handling and feel. Not specific to late models or modifiers but I do race a modified following USRA rules.
    I have the AFCO 73 series, mono tubes, these are new to me this year.
    How does the gas pressure effect handling?
    Does gas pressure effect the spring rate?
    Does the gas pressure effect valving or is it just to prevent cavitation of the oil?
    Does gas pressure effect slow speed and high speed shaft performance?
    Do bumpy/rough tracks need more gas pressure then slow/slick/smooth tracks?

    I have so many questions but finding information is hard. It’s like it’s either top secret, or guys claim it’s voodoo, especially shock rebuilders. I mean, do the guys that harber UFO’s at Roswell even have the security clearance for this kinda shock information or what? Is shock tuning just so widely variable and specific to discuss between cars and types of cars/shocks/drivers/ etc.

  2. #2
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    Handling effect = yes. The car will more quickly return to ride height, from compression, with the same springs on the car.

    Spring rate = sort of. Spring rate results in a load that is proportional to spring displacement. The rod force from a gas shock is closer to constant. There isn't a big difference related to travel.

    Valving = It has no effect. Valving is shock oil being forced through an orifice when the shaft moves. Resulting force is proportional to shaft speed.

    It is typically suggested to increase gas pressure on rough tracks.
    Droop isn't the problem.

    Arizona Speedway - 2 ........ Brushcreek -1
    Alltech -1 .................... Eldora - 8
    East Bay - 6 .................. Richmond -1
    Florence -1 ................. Lawrenceburg -1
    Atomic -6 .................. Circle City -1
    Tazewell -1 .................. Mudlick-1
    Moler -4
    Portsmouth -3 .....................Tyler Co. -1

  3. #3
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    Thanks for that info.
    How does one know what gas pressure to start with and which direction to go?
    Is it based strictly on car/driver/track/testing and note taking or are there generalities that can be applied?
    Does the adage of “shocks are timing devices” still mostly apply? Are there other factors to consider?

  4. #4
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    One thing that most drivers notice when switching from twin tube to mono tube (gas) shocks. Is the feel especially in the steering wheel. With twin tubes you could feel every Crack in the racetrack it felt like. With gas shocks you don't feel as much. Most manufacturers have recommended starting points aswell as suggestions for rough and smooth conditions. Good rule of thumb is more gas pressure everywhere when rough. Lower gas on the right sides when more sidebite is desirable. Be aware Their are minimums on gas pressure and that number can vary quite a bit between manufacturers

  5. #5
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    How or why does a twin tube have more feel?

  6. #6
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    Some one more educated in the subject could shed more light on the subject I'm sure but in my head it's always seemed as though the gas charged area acts as a additional spring of sorts with in the shock that the oil can compress before being forced through the valving. That added cushion area acts somewhat as a disconnect between the shaft and the body. And I believe that extra dampening witch is one of the same things that help in rough conditions leads to less feel and or overall grip. I was once told that twin tubes were all around better on a glass smooth slick as ice surface but the mono tubes are a better compromise because of the better performance in most every other condition

  7. #7
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    Makes sense. Thanks!

  8. #8
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    Has anyone experimented with using Argon or C02 for shocks?
    Both are stable and doesn’t contain water.

  9. #9
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    Did I ask the wrong question or am I missing the security clearance for some top level speed secret?
    Ha! Just goofin.

  10. #10
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    Quote Originally Posted by Lizardracing View Post
    Did I ask the wrong question or am I missing the security clearance for some top level speed secret?
    Ha! Just goofin.
    I have been told you can use air if you have a really good air drier, but I've never tried it or seen anyone do it for sure. So I would imagine either of those 2 are fine but can't say with 100% confidence.

  11. #11
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    In a "air" shock configuration I could see their being differences but in a traditional gas shock such as a canister double adjustable. I don't think the particular gas much matters. It's just the effect of having the pressure on the fluid. Nitrogen I could imagine is popular for the same reasons it is in tires it has a really stable and considerably smaller variance in head pressure vs temp. It's also a larger molecule so it doesn't leak out as fast creating less matters and more consistency

  12. #12
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    A couple of things and ideas I've been playing around with.

    AFCO has a Youtube video posted that compressed air could be used long enough to get ya home again to a proper repair.

    First is the volume of air in a gas shock, It's quite small even if a canister style is used. I don't have a canister available to me to measure but my own non canister style shock is less than 2sq inches of volume. Since the water content is also very small, I would think it would have to take a fairly large water vapor content to have corrosion or fading issues due to water present. That said, I would think a quality compressor dryer would do the job, the style used in auto body paint sprayers for example. That still leaves the fact that many standard shop air compressors can't make the upwards of 300psi needed to fill a shock though. Especially, but not limited too, the lines/hose are long and pressure tends to be lessened at 50 foot or more of hose through 1/4 fittings.
    Second, N2 is cheap and can be had about any welding supply house. Most guys already have a welding tank and buying a $350 set up (tank/fill/regulator hose and manifold) for shocks doesn't make much dollar sense on top of the typical lower budget $200/each gas shock on the market.
    Chemistry says N2 and Argon are both inert gasses and SHOULD act close to the same as long as they are pure. Most MIG welding uses Argon/CO2, The C02 is the variable here.
    Tank pressures are about the same, around 2-3000psi.
    Third, I built my own manifold for shocks using a Schrader valve, a 0-300 pressure gauge and No loss chuck. A length of 1' T6 aluminum dowel, gun drilled and tapped for 1/8 NPT on both ends and 1/4 NPT for $50. That beats the $130ish for the one in popular motorsports and aftermarket shock catalogues prices. I took me an hour from start to finish. If a person doesn't have a lathe or mill, then a simple brass tee fitting gets the job done.
    Fourth, Using my new manifold I filled the RF shock on my car and asked my shock guy to run it "hard" on the shock dyno to "test it out" and I used that as a base line. I then took the shock home, filled it with Argon and took it back the next day and asked him to test it again in the same mannor. I got some weird looks but he's a good guy so he did it anyway.
    Once again I took it back home and filled it with compressor air without a dryer at all. All three times tested were at 50psi, the recommended pressure for the RF tie down shock. After the test on the 3rd time I told what I was up to and I didn't want his knowledge to skew results.
    In this blind test of the sorts, all three dyno graphs were identical or well beyond the scope of the graduations of the dyno it self and we both agreed any variances are beyond the tolerance of the shock dyno he uses. Without my own shock dyno, I wasn't able to do any further testing but it seems, the dry air, N2 or Argon will work well enough for a dirt car for the average weekend warrior or for any one in a pinch trying to get to the track.
    If I were chasing regional or national points I'd still go with N2, for everyone else like me brewing up junk in there home shop, I'd 100 percent say Argon or Argon/C02 gets the job done and if you build your own manifold from parts on Amazon, one can save a bunch of money and spend it on things like tires and fuel and seat time.
    Finally, in some other of my interests beyond CT racing, I found some off road guys and some Motorcross guys using gas shocks have also been using Argon for a long time as a alternative so apparently it's not a new idea at all but seems novel in the CT roundy round crowds.
    Not tested would be the effects of pressure and valving and long term excessive heat build up like you might get a long rough track. IT would be interesting to see those results if I had the ability to do that sorta level of reasearch.

  13. #13
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    Quote Originally Posted by Lizardracing View Post
    A couple of things and ideas I've been playing around with. AFCO has a Youtube video posted that compressed air could be used long enough to get ya home again to a proper repair. First is the volume of air in a gas shock, It's quite small even if a canister style is used. I don't have a canister available to me to measure but my own non canister style shock is less than 2sq inches of volume. Since the water content is also very small, I would think it would have to take a fairly large water vapor content to have corrosion or fading issues due to water present. That said, I would think a quality compressor dryer would do the job, the style used in auto body paint sprayers for example. That still leaves the fact that many standard shop air compressors can't make the upwards of 300psi needed to fill a shock though. Especially, but not limited too, the lines/hose are long and pressure tends to be lessened at 50 foot or more of hose through 1/4 fittings. Second, N2 is cheap and can be had about any welding supply house. Most guys already have a welding tank and buying a $350 set up (tank/fill/regulator hose and manifold) for shocks doesn't make much dollar sense on top of the typical lower budget $200/each gas shock on the market.Chemistry says N2 and Argon are both inert gasses and SHOULD act close to the same as long as they are pure. Most MIG welding uses Argon/CO2, The C02 is the variable here.Tank pressures are about the same, around 2-3000psi. Third, I built my own manifold for shocks using a Schrader valve, a 0-300 pressure gauge and No loss chuck. A length of 1' T6 aluminum dowel, gun drilled and tapped for 1/8 NPT on both ends and 1/4 NPT for $50. That beats the $130ish for the one in popular motorsports and aftermarket shock catalogues prices. I took me an hour from start to finish. If a person doesn't have a lathe or mill, then a simple brass tee fitting gets the job done. Fourth, Using my new manifold I filled the RF shock on my car and asked my shock guy to run it "hard" on the shock dyno to "test it out" and I used that as a base line. I then took the shock home, filled it with Argon and took it back the next day and asked him to test it again in the same mannor. I got some weird looks but he's a good guy so he did it anyway. Once again I took it back home and filled it with compressor air without a dryer at all. All three times tested were at 50psi, the recommended pressure for the RF tie down shock. After the test on the 3rd time I told what I was up to and I didn't want his knowledge to skew results. In this blind test of the sorts, all three dyno graphs were identical or well beyond the scope of the graduations of the dyno it self and we both agreed any variances are beyond the tolerance of the shock dyno he uses. Without my own shock dyno, I wasn't able to do any further testing but it seems, the dry air, N2 or Argon will work well enough for a dirt car for the average weekend warrior or for any one in a pinch trying to get to the track. If I were chasing regional or national points I'd still go with N2, for everyone else like me brewing up junk in there home shop, I'd 100 percent say Argon or Argon/C02 gets the job done and if you build your own manifold from parts on Amazon, one can save a bunch of money and spend it on things like tires and fuel and seat time.Finally, in some other of my interests beyond CT racing, I found some off road guys and some Motorcross guys using gas shocks have also been using Argon for a long time as a alternative so apparently it's not a new idea at all but seems novel in the CT roundy round crowds. Not tested would be the effects of pressure and valving and long term excessive heat build up like you might get a long rough track. IT would be interesting to see those results if I had the ability to do that sorta level of reasearch.
    I like your enthusiasm and enginuity but you may have missed some things. Bicycles have be using gas shocks for years. You can buy a fill tool from any higher end bike shop or Amazon for around 30$ and it works really well. Nitrogen is cheap and at the rate we use it a small bottle can last a racer a very long time. I think you may have more invested in fuel material and time than this project was worth. Jmo

  14. #14
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    also , N2 greatly extends the life of rubber based seals , just like with tires , when I started using N2 in my motorcycle tires , they last nearly twice as long , as finicky as these shocks are , I would be afraid of any moister getting in them ....jmo....

  15. #15
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    Quote Originally Posted by Jking24 View Post
    I like your enthusiasm and enginuity but you may have missed some things. Bicycles have be using gas shocks for years. You can buy a fill tool from any higher end bike shop or Amazon for around 30$ and it works really well. Nitrogen is cheap and at the rate we use it a small bottle can last a racer a very long time. I think you may have more invested in fuel material and time than this project was worth. Jmo
    I did read that on the nets but I didn't know anyone I trusted in that sport so I didn't explore that direction. It's very interesting in any case. Are those kind of shocks just air springs or are they oil filled as well?

  16. #16
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    Quote Originally Posted by fastford View Post
    also , N2 greatly extends the life of rubber based seals , just like with tires , when I started using N2 in my motorcycle tires , they last nearly twice as long , as finicky as these shocks are , I would be afraid of any moister getting in them ....jmo....

    Very interesting. I hadn't consider that a possibility other than thinking about the molecule size comparison for leakage. I assumed, perhaps wrongly, the shock glands were chemical resistant like Viton or something similar.
    In any case, I wasn't attempting to be comprehensive or anything, it's just a rabbit hole I got into. Our season has begun over a month ago and we have had 5 rain outs so I'm just keeping my mind busy. I'm not a very good driver but I do like the shop time....I can build anything but a trophy shelf lol.

  17. #17
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    Quote Originally Posted by Lizardracing View Post
    I did read that on the nets but I didn't know anyone I trusted in that sport so I didn't explore that direction. It's very interesting in any case. Are those kind of shocks just air springs or are they oil filled as well?
    I honestly don't know anything about the bicycle stuff I think it's just a air spring. In my opinion on extra shop time besides the obvious things like servicing birdcage and other maintenence items these days should be spent on the smasher playing with different combos and plotting their numbers for comparison. The better educated and informed you are about those things the better your at the track adjustments are. Just like playing on the scales in years past you can look at dynamic wedge and things

  18. #18
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    I would agree to that races are won in the shop...
    I actually have a USMTS/USRA modified and so with one spring per corner and shock limits we don't get to play with that kinda stuff too much. With a stock type front end, the front ends of these things are very sensitive so most of the technology is hiding in there as well as tires and chemical prepping. Oops, I didn't mean to say that.

  19. #19
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    also nitrogen does not change pressure with temp like air , this could be the main reason to use it...jmo

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