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Thread: Help with seat height

  1. #1

    Help with seat height

    I am finalizing my order for a Tilite 2GX and dont feel real comfortable with the seat heights my rep is recommending and would appreciate any help in making sure I get these right on my order. I measure 18" from floor to back of knee so he is recommending. Rear seat height 17"; Front seat height 18". Also I am not sure if 1" dump is enough but he said 2" is quite a bit.

  2. #2
    A CCC member (SCI_OTR, a professional wheelchair seating clinician) wrote the attached fabulous article. Maybe he'll chime in here.

    Having determined only my own measurements, I am an amateur, but the TiLite AeroZ1 ordered per my measuring fits really well, so I'll offer an opinion. Getting these values right is a bit complex.

    My method: Determine what Front Angle you want. Make a to-scale sketch of that angle and the floor. Assume your footrest will be level, and sketch it in horizontally (parallel to the floor) about 2.5" above the floor. (That height is the bottom of your shoe, and allows some ground clearance below for the thickness of the footrest tubing.). When you're seated with feet flat on the floor, have someone measure the back of your leg from the floor (bottom of your heel with typical footwear on) to the back of your thigh at the knee. Sketch that length along the angle of your Front End starting at the footrest line (or use trigonometry to calculate it). From the upper end of your leg-measurement line, draw a vertical line to the floor. Measure that vertical line and subtract your compressed cushion thickness (often about 2" but varies). The result is your FSH. (See EDIT below.)

    To me RSH is mostly independent of FSH. IMO RSH should be set for best pushing efficiency, and dump should just be the resulting difference FSH-RSH whatever that may be. The RSH should put your middle fingertip at the same height as the center of your rear-wheel axle.

    To determine RSH, sit on a solid chair (e.g., wooden kitchen chair). Let you arms hang naturally. Have someone measure the vertical distance from the floor to your comfortably extended middle finger tip (F). Measure the height of the chair's seat (S). Compressed cushion thickness (same as for FSH above) = C.

    RSH = WheelDiameter + F - S - C (See EDIT below.)

    For Example: I sit on a hard chair. My middle fingertip is 12.5" above floor (F=12.5"). The hard seat is 19.5 above the floor (S=19.5"). My wheels are 25". My compressed cushion = 2" (C=2"). RSH = 25 + 12.5 - 19.5 - 2 = 16". (see EDIT below: for solid seat pan, RSH=16; for sling RSH=17.)

    If you want, I can sketch up the FSH for you if you like. Just give me your desired Front Angle and your lower-leg length.

    PS: I can't get the article to attach ("The Quest for the Perfect Lightweight Wheelchair" by Steve Mitchell, OTR/L,ATP); I'll keep trying. It was published online at http://www.rehabpub.com/issues/articles/2011-03_02.asp but the link no longer works. I'm glad I kept a copy. I wish it would attach :(

    EDIT: The above calcs are for a solid seat pan. For a sling add about 1" to the RSH and 1/2" to the FSH

  3. #3
    BTW, I love my 3.5" of dump. It keeps me from sliding out of chair when the city bus stops and when I stop when going down a hill. (I don't wear a seat belt in the bus because I have good trunk control.) I used to have 2.5", but it wasn't enough. With 1" of dump, I could wheel only slowly on flat surfaces. I can stand up, and I still love having 3.5". (I also have an ergo seat; without it my back hurts.)

  4. #4
    Thank you so much that is very helpful. My lower leg measures 18" without shoes and I am looking for 70 degree front angle. I will get my RSH measurement tom. I don't see the attached article would you mind reattaching or sending to me directly.

  5. #5
    Here's the article (I hope): [ATTACH]n2918365[/ATTACH]

    The problem was operator error :)

  6. #6

    No Title

    Based on this sketch, IMO minimum FSH = 17.5", so his suggestion of 18" is real good. If you'll be wearing shoes, that allows 1/2" for heel. I might even suggest 18.5" to account for a little error or for more ground clearance under your footrest.

  7. #7
    Oh, just having reread the article, I remembered the above calcs do not account for sag in the seating fabric. I have a solid seat pan (i.e., no sag). You will have sag because you have a folding chair, so add about one inch to the RSH calc above. The front won't sag as much as the rear, but in a folding chair it will sag some, so I'm leaning more toward an 18.5" FSH.

  8. #8
    Thank you for the sketch that really helps me visualize it. 18"5 sounds about right, then I can start with 17.5" RSH. Do you know if the dump can be adjusted once I purchase. From reading the manual looks like there is some adjustment but doesn't really tell how much.

  9. #9

    No Title

    Because of the design of the 2GX frame, I presume the full adjustment range will be available to you, but I'm not positive. Pic is a screen shot of the 2GX order form.

  10. #10

    No Title

    And here is what the 2GX manual says about adjusting the FSH. I raised the FSH on my AeroZ by installing fork-stem extensions.

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