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Thread: Advice for new chair setup

  1. #1

    Advice for new chair setup

    Hi all,

    I'm hoping that you could give me some advice regarding my new chair as I've, apparently, been in the wrong setup for years now.

    I have Charcot-Marie-Tooth and have been using a chair full-time for 16 years now. I've always had folders that were, for the first 13 of these years, entirely too large. I'm 5'6" and weigh 120 lbs. My thighs are 18" and lower legs 15.5". My chairs were 16wx18l (someone goofed).

    Three years ago, I was measured for a new chair and was recommended a 16x16 TX which I loved...until I started playing rugby. I realized that I don't need a 15" backrest (as I have trunk) and I'd like to make the chair more compact, rigid, and thus lighter.

    Now my dilemma:

    I'm considering a ZR with a 14-15" wide and 14-16" deep seat. I'm not to worried about the width because that choice doesn't affect other parameters. My depth, however, does. I'm concerned about transfers and stability. I'll give you my proposed setup and see if you can probe me for anything I've missed.


    14-15 wide
    14-16 deep
    8.5-11.5 backrest
    3" COG
    17.5-18 RSH
    18.5-19 FSH
    85-90 front end
    14.5" STF
    2" cushion
    10" V-front
    24" wheels
    4x1.5" casters (FL softrolls)
    solid seat pan

    Thanks so much for any advice.

  2. #2
    Ok, let me try it this way:

    What combinations of a 14-16" deep seat and 85-90 degree front end would be dangerous? i.e. How short is too short?

    Thanks?

  3. #3
    Senior Member jschism's Avatar
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    i am about the same size as you and my first chair was also a 16x18. i have a 14x16 zr, the frame can't be any shorter but i wouldn't mind trying a 15 deep seat on my 16 chair, i like my feet kinda tucked under. i wouldn't go any shorter on frame at all. you are only getting 1" of dump? skip v front, save the extra cost, not much different. minus 1" on seat to footrest when ordered, tilite will make it exact with no room to shorten, only to make longer. skip FL and go with tilite softrolls, i also use 3"COG and have 10" high back
    Last edited by jschism; 12-30-2010 at 08:34 PM. Reason: added info

  4. #4
    What seems like a decent setup is a 15 deep + 1 in frame depth and 85 degrees. My feet would be slightly tucked and it doesn't make the frame too long.

    I thought the V-front was a no-charge option, no?

    As for the STF height, 15.5" (my lower leg length) - 2" cushion = 13.5". If I order 13.5 STF, how much adjustment would I have, 1-2"?

    Oops, I meant the Uni-tine forks, not the FL suspension forks.
    Last edited by Rodrigo; 12-31-2010 at 12:28 AM.

  5. #5
    I could not be sure for certain , but I would have concerns that the relatively high STF heights combined with a a 16" seat depth and 85/90 degree frame would make a ZR endo prone (especially sitting up on a seat pan). .It would have a very high center of mass. I would definitely make sure your fork selection will allow you to use a 4x1.5 FLAHSR.

    If you want fixed STF heights and are looking looking to keep them roughly the same as your TX, you may get a lower center of mass and lighter weight by going with a TR. I imagine your configuration would look similar to the TR pictured below.

    Maybe totoL1 can provide the details because I believe he knows the owner of this chair.

    Transitioning from a TX folding frame to any rigid frame with fixed STF heights is a risky undertaking. The ZRA S2 would give you some adjustability without that many compromises.


  6. #6
    Quote Originally Posted by Rodrigo View Post
    Ok, let me try it this way:

    What combinations of a 14-16" deep seat and 85-90 degree front end would be dangerous? i.e. How short is too short?

    Thanks?
    With the high of your chair, dump and your 3"COG i wouldn`t go under 15" deep and 85ยบ.

    When i ordered this chair i did it with 8cm(3.14") COG and Oracing told me that they wasn`t going to do that chair with that COG because it will be dangerous because the distance between axles will be very little, so they did it with a 6cm(2.36") COG.
    And this chair is much lower than yours and with more dump, so yours ...
    Last edited by totoL1; 12-31-2010 at 08:27 AM.

  7. #7
    Quote Originally Posted by SCI_OTR View Post

    Maybe totoL1 can provide the details because I believe he knows the owner of this chair.
    .
    The chair was ordered with 3" casters, now have 4".

  8. #8
    How much higher would the seat pan put me? Assuming I have an inch of sag (sling + old cushion), if I have a 16.5" (42 cm) rear and a 19" (48.25 cm) front seat height and a seat pan/better cushion, I hope it would leave me where I want to be with the top of my wheels close to the tops of my thighs. Am I way off?

    As for the depth, If I have a 16" frame with an 85˚ front end and 2" COG (which is still slightly adjustable on the ZR), would that be more stable coupled with the 2.5" of dump?

    Sorry for all of the questions. I'm new to the physics of a cantilevered frame.

  9. #9
    Quote Originally Posted by Rodrigo View Post
    How much higher would the seat pan put me? Assuming I have an inch of sag (sling + old cushion), if I have a 16.5" (42 cm) rear and a 19" (48.25 cm) front seat height and a seat pan/better cushion, I hope it would leave me where I want to be with the top of my wheels close to the tops of my thighs. Am I way off?
    TiLite's seat pan is mounted on top of the frame. Although TexasWheelz could tell you for certain, I'd say you would probably need to add about 3/16", . The seat pan on this Terminator is mounted between the frame rails (Top End welds a couple of ~1/2" diameter crosstubes between the seat rails to support it. They will do this custom on a Crossfire, BTW). Remember to factor in the type of cushion you plan to use because its thickness is going to make a big difference in the stability. You can always insert a piece of 1/8" ABS plastic under the cushion cover to rigidize it and eliminate the uncertainty of a seat pan.

    Quote Originally Posted by Rodrigo View Post
    As for the depth, If I have a 16" frame with an 85˚ front end and 2" COG (which is still slightly adjustable on the ZR), would that be more stable coupled with the 2.5" of dump?
    It comes down to what type of stability we are talking about and your individual body characteristics.

    Despite the extremely short wheelbase on this 15x15+1 90 degree Terminator which had 20"F/17"R STF heights, it wasn't very endo prone at all. I think this was because the rear axle was so far forward. There was very little weight over the front casters and the lower frame rails reinforced the caster housing to keep the front end from flexing when hitting cracks in the pavement. They also lower the center of mass slightly. You'll note that Oracing reinforced the bend in the cantilevered frame in toto's pic and I'm wondering if that was done for that very reason. I describe this type of stability as dynamic forward stability.

    On the other hand, the rear axle setting combined with the low back and elastomer suspension made the Terminator rear tippy for some. It did not seem excessively tippy for me or the other veteran who received it, but another one of my colleagues flipped within a minute of sitting in it. This was a function of our individual height and weight on the chairs dynamics.

    Quote Originally Posted by Rodrigo View Post
    Sorry for all of the questions. I'm new to the physics of a cantilevered frame.
    "Cantilevered physics" is an emerging field and I'm not sure there are many experts because there are so many variables involved. I'm actually finishing up my syllabus for the International Seating Symposium and will be talking about this as part of my presentation in March. Seating therapists, manufacturers, and end users all need to understand these things because there are significant safety implications and manufacturers alone can not be expected to identify all configurations which may be high risk for certain end users.
    Last edited by SCI_OTR; 12-31-2010 at 01:16 PM.


  10. #10
    Quote Originally Posted by SCI_OTR View Post


    You'll note that Oracing reinforced the bend in the cantilevered frame in toto's pic and I'm wondering if that was done for that very reason.
    That was done for just give rigidity to the chair, the girl wanted as light as posible, and she weight only 100lbs, so they did a L frame using the same tubes that they use for box frames and with that reinforce for give enough rigidity.

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