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  1. #1
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    Opinion : Air shock fitment to 6" plus travel frameset.

    Tim Flooks told me today that air shocks simply cannot work on a 6" plus frameset
    All to do with the spring rate curve being exceeded onto the ramp up point after 70% of stroke.
    Apparently, higher volume air cans will suffer even greater mid stroke blow through than normal volume cans, as they have less capacity for mid stroke damping than smaller reservoir canisters.
    Of course, he suggests a PUSH Ind. kit will assist in the stroke control [RP23, no Monarch kit just yet] as it replaces the flexible stroke washer internally with a more robust 'shim'...
    To be fair, he made a valid point about the mid stroke blow through being in conjunction with air shocks' inability to provide sufficient high speed rebound control. The lack of rebound ability means that most air shocks fitted to 6" travel plus bikes, irrespective of leverage ratio, simply causes pack down and the subsequent effects of such.
    Thoughts ?

  2. #2
    Castron BTT Crew
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    I completely agree. In fact, I've sold my DHX Air and bought a DHX5 coil, just looking for more compression damping and avoid the mid stroke blow. I will tell the results in few weeks, but looking to other guys in my group which have switched from air to coil in LT bikes, the coil shocks give more robust mid stroke and stability in rough terrains.

    Just to finish, this mid stroke blow would be much more marked in clydesdales about 220lb, like me.

    And please, excuse my english. I'm learning a lot of technical words!

  3. #3
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    I've got nothing but respect for TF and his knowledge and experience so I guess he's right(with his busy job does he get to ride as much as us though or is this all dyno testing assumptions?). However, I struggle to see the difference most of the time. The HV monarch and the DHX-C feel very similar on the FR. Both suffer excessive blow through of the mid range. Both are very plush. The air can is easier to tune for climbing etc.Not to mention the air can weighs the same as an empty packet of crisps!

    I do feel rebound control is a struggle for those(me included) requiring more spring rate but I have the same issue on my RocoTSTR coil.

    Is TF just talking about ultimate performance for WC DH or is this a general statement that covers trail riding?

  4. #4
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    Simon
    Why don't we arm ourselves with some spanners and a pile of shocks and go find out for ourselves? We have Monarch Hi and Lo volume shocks, dereks HV RP23 on the air front, Coils we have DHX-C, Roco TSTR and CCDB currently at our disposal.

  5. #5
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    I guess the key point here is whether air cans on work on 6" plus bikes. 6" is a lot of travel and it's a reasonable assumption that at this point, you're not just taking a walk in the park but rather tackling some pretty extreme terrain. I've ridden all over the UK and frankly we don't have trails that can't be handled by 5" travel bikes. Heck even most UK DH courses can be ridden competitively on 6" bikes (although that doesn't stop us wanting World Cup DH rigs ).

    Perhaps what TF is saying is that the performance of a 6" bike is seriously hampered by an air can, assuming you're riding it for what it was designed for.

  6. #6
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    hence my point above

    "Is TF just talking about ultimate performance for WC DH or is this a general statement that covers trail riding?"

    For the riding I do air shocks are sometimes a better proposition. eg. I had no end of grief running a DHXcoil on a turner 6-Pack. Changed to the DHX-A, much the same story. Then to the RP23 and it was a revalation. Horses for courses I think.

  7. #7
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    My rp23 is great, get a grip and stop trying to fix what isnt actually broken.

    Maybe if you had the ultimate shock setup you'd make yourself what 5 secs faster down the hill?

    I dont race so if it feels good who gives a flying F^%$!!!!

    I do recall your statement Simon "You cant run a coil shock on the AM" So just get a RP23 and bin that RS pooooop, job done...

    I think Richard is right TF are prob making a statement based on ultimate performace for racing downhill.

    Just my 2p worth
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  8. #8
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    TLR in 'Not knowing what he wants' shocker

  9. #9
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    I do know what he needs though!

  10. #10
    steep fast and loose :)
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    derekr - i'm trying to fix the mid stroke blow through , which is broken.
    there's little damping control in the mid stroke, hence the issues with pedal strike and stroke wallow, especially when pro-pedal is off.
    i don't race, but have spent a fortune on the rig, hence a desire to tune it so that it works optimally.
    dipper - he's talking about optimisation for trail riding, not racing. he is categoric that air shocks are wrong for 150mm plus framesets. they cannot deliver mid stroke control due to their construction. coil inc. shim stacks are the only controlling method he's proven to be tuneable and workable. understandably. lets take those spanners up the hill and find out my good man

  11. #11
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    Do you know how to use a spanner?

    I get what your saying, I find the AM+RP23 a great combo planted and works well but i am ofcourse easier pleased than you! I'm sure some other combo is even better but i'd rather concentrate on riding the thing and getting used to it than changing it every week (Actually I may have changed alot too ) But i'm happy now!

    That is if Nicolai ever get a mech hanger out to me!!!!!
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  12. #12
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    Again, it sounds like what TF is saying is that if you have an air shock on a 150mm+ bike, then it won't be working properly, although that may not be a problem.

    My suggestion was that if it's not working properly and you can't tell the difference, then you don't need 150mm+ in the first place and you may as well run a lighter bike with less travel.

    Of course the beauty of the AM is that you can do that without having to replace the frame.

  13. #13
    steep fast and loose :)
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    i'm with you geetee - if it ain't working, why have it ? ! ?
    however, me and dipper have planned to hit the hill, spanners and shocks in back-packs and spend a day fettling and taking notes. should happen in a week or so

  14. #14
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    "TF too busy to ride?"

    He's the Enduro National Champion 2008 at the night ride three weeks ago he blew me away on his ti single speed and he's 50!

    I have a DHX on my AM and I am finding the same as TLR hence ordered a Stoy off Tim.

  15. #15
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    Tim was also one of the original 'back in the day' pro riders. I remember him at the NEMBA races in the very early 90s

  16. #16
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    like I said, I've got nothing but respect for TF. I send stuff to him regularly. He is a busy boy though, and riding a SS hardly gives him experience of 6" + trail bikes!

    I'm not saying he's wrong. I just think it's too much of a sweeping statement when there's fat too many variables to generalise. I run coil myself but have nothing against a well set up air shock.

    Anyway, I've got a pile of shocks here and all the time in the world to ride so I'll be doing some testing over the next month to see what works best on the FR(for my application)

  17. #17
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    Garry
    Do you know if Tim is a distributor of BOS gear? If they're as good as the hype I may be interested in selling them myself.

    Maybe we could do a swap for a week or so some time.

  18. #18
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    Tf is the importer/distributor in the uk

  19. #19
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    Quote Originally Posted by The_Lecht_Rocks
    Tim Flooks told me today that air shocks simply cannot work on a 6" plus frameset
    All to do with the spring rate curve being exceeded onto the ramp up point after 70% of stroke.
    Apparently, higher volume air cans will suffer even greater mid stroke blow through than normal volume cans, as they have less capacity for mid stroke damping than smaller reservoir canisters.
    Of course, he suggests a PUSH Ind. kit will assist in the stroke control [RP23, no Monarch kit just yet] as it replaces the flexible stroke washer internally with a more robust 'shim'...
    To be fair, he made a valid point about the mid stroke blow through being in conjunction with air shocks' inability to provide sufficient high speed rebound control. The lack of rebound ability means that most air shocks fitted to 6" travel plus bikes, irrespective of leverage ratio, simply causes pack down and the subsequent effects of such.
    Thoughts ?
    Why, in contrast to the above comments, newer DH forks for World Cup racing use like the ROCK SHOX "Boxxer World Cup" (http://www.sram.com/en/rockshox/downhill/boxxer/#tab1) make no longer use of coil springs but air as their suspension medium for saving weight, and they seem to be indeed able to control > 6" of travel (tbh 200mm = 7 7/8”) without failure in mid stroke damping? Besides, the "leverage ratio" in the case of a fork is 1:1.
    Last edited by Wilhelm6; 01-11-2009 at 03:18 AM.

  20. #20
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    This is a good point but there are two comments to make in response.

    The first is that if you talk to TF or indeed anyone else professionally involved in DH, about improving the performance of the air Boxxer, they all say that the best way to improve performance is to put a coil in. Now the performance gains may be very much more marginal in a fork than a rear damper, but there is no doubt that it is there.

    The second point, which explains why the performance gain is more marginal in a fork than a rear damper, is that the volume of air being used in fork spring is many times greater than that used in a rear damper. This greater volume of air makes a number of differences.

    First, the increased volume gives better management of heat build up, i.e. there is more air to absorb the heat generated by bump absorption so the overall temperature of the air spring is relatively unchanged.

    Second, the greater volume of air means that the change in spring rate is less progressive.

    The thing with air is that the equations governing the relationship between temperature, pressure, volume etc are not linear. Now I'm not a physics expert, so in simple terms it works like, but perhaps not exactly like, this - if you halve the volume you increase pressure by a factor of four, not a factor of two. If you have a very small air chamber already at very high pressure, then the net effect of a change in volume is far greater than if the original volume were three of four times larger.

    This is also the reason why rear air shocks have a much harder time with heat build up - the heat causes the air to expand and increase pressure, thus changing the spring rate.

    All of these problems can be countered by compression damping, but in a rear shock, you just don't have enough space to control all the variables.

  21. #21
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    Quote Originally Posted by geetee1972
    This is a good point but there are two comments to make in response.

    The first is that if you talk to TF or indeed anyone else professionally involved in DH, about improving the performance of the air Boxxer, they all say that the best way to improve performance is to put a coil in. Now the performance gains may be very much more marginal in a fork than a rear damper, but there is no doubt that it is there.

    The second point, which explains why the performance gain is more marginal in a fork than a rear damper, is that the volume of air being used in fork spring is many times greater than that used in a rear damper. This greater volume of air makes a number of differences.

    First, the increased volume gives better management of heat build up, i.e. there is more air to absorb the heat generated by bump absorption so the overall temperature of the air spring is relatively unchanged.

    Second, the greater volume of air means that the change in spring rate is less progressive.

    The thing with air is that the equations governing the relationship between temperature, pressure, volume etc are not linear. Now I'm not a physics expert, so in simple terms it works like, but perhaps not exactly like, this - if you halve the volume you increase pressure by a factor of four, not a factor of two. If you have a very small air chamber already at very high pressure, then the net effect of a change in volume is far greater than if the original volume were three of four times larger.

    This is also the reason why rear air shocks have a much harder time with heat build up - the heat causes the air to expand and increase pressure, thus changing the spring rate.

    All of these problems can be countered by compression damping, but in a rear shock, you just don't have enough space to control all the variables.
    I agree. May be that the "air bladder" technology, patented by CONTINENTAL Automotive, may be helpful in solving some of the above issues (air volume, linearity, heat convection) sometimes in the future. However, besides the constrained capabilities of adjustability, this technology is not ready for MTB DH use yet, and MAGURA will sell the "MX" rear shock exclusively to bike manufacturers and it will not be available in the aftermarket at this time (http://www.magura.com/english/produk...federbein.htm#, see also: http://www.ridemonkey.com/forums/sho...ghlight=Magura).



  22. #22
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    Replying to Dippers Q a few responses back. Tim is the UK importer of BOS and it would be good to do a proper back to back test. Saying that I'm still waiting for mine to arrive.

  23. #23
    steep fast and loose :)
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    geetee - i reckon you've nailed the issue regarding heat build up and lack of compression volume control.

  24. #24
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    Nice of you to suggest so TLR but I was just regurgitating some one else's brain work ;o)

  25. #25
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    "I was just regurgitating some one else's brain work"

    now you've spoiled it! I was impressed for a minute there

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