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Thread: help before I order ZR chair

  1. #1

    help before I order ZR chair

    I am ready to order my new ZR chair and the rehab engineer did some measurements but she confused me. I have a Tilite TR and I have a 3.5 COG and I like the way it it. She said if I want to have the same the COG should be 1.5 because the frame on the ZR is different. I like the way my chair is now and I do not want to make any mistakes so please if you can help me. thanks

  2. #2
    The engineer is correct. The center of gravity is significantly different on a z frame and 3.5 could be dangerous because it is really tippy. The good thing about cog on a zr is that it is movable which means you can start at 1.5 and move forward to find your sweet spot. For comparison my aero t is set to 3.5 and I have never tip back. My aero z was at 2.

  3. #3
    I have a TR3 (COG 4.25") and a ZR2 (COG 4.0") -- the difference in feel and responsiveness between the two is negligible. (I don't find the chair dangerously tippy, but user ability/wheelchair skills comes into play here.) The COG on the TR3 is "infinitely" adjustable, not discrete 1/4" adjustments on the ZR.

  4. #4
    Senior Member tooley's Avatar
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    hmmmph. I'm not quite sure what the rehab "engineer" is thinking - the lower box-frame tubing of your current TR is filled with lead? That's the only reason I can think of making such a drastic change in COG, assuming there aren't major changes of frame geometry. I think this "engineer" person is incorrect in their assumptions of the center-of-gravity between the two styles.

    The only difference that would warrant such a huge change in COG would going to a very reclined backrest, or an after-market backrest positioned inches behind the vertical backposts of the new chair.

    The other possibility is if the new ZR is being spec'd with a shorter front end - ie. moving from 70-degree downtubes to 90-degree.

    If these are not changes being made then you need to make this re-think their reasoning, or at the very least explain it. Let them know, in no uncertain terms, that _you_ need to see the CAD drawing that TiLite supplies to the DME vendor prior to building the wheelchair. If they balk at this idea you need to look into finding an alternative. I realize this isn't ideal, but you don't want to end up with a brand new wheelchair that you won't use.

    If there aren't major changes they are spec'ing you a chair that is going to be incredibly front-heavy in comparison to your current setup and will push like a tank, you will feel ever little pebble and sidewalk crack.

    Look at the length difference in the 2 chairs on the left - this is going to make smaller spaces seem tighter, ie. turning around in bathroom stalls, etc. Many people (especially walkers) don't take this factor into consideration, a shorter chair (up to a point) makes our quality-of-life better because of its increased maneuverability.


    Name:  TRvsZR.jpg
Views: 301
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    (btw, this little drawing didn't take up much time, not to worry. In school I drew a "dynamic block" using AutoCAD that allows me to quickly manipulate the dimensioned geometry to compare changes)
    Attached Images Attached Images  
    Last edited by tooley; 01-25-2015 at 05:28 PM.

  5. #5
    Going that conservative with a ZR2's COG is likely to put it outside of the range of adjustment that you need and you will get a front heavy chair. If you like your current COG and your frame length feels right, make sure you get a CAD with the OFL and compare it with your current chair's dimension (blue circle). There is a difference in where the bend begins (red arrow) and the point that the mark the frame depth (purple line). As a result, the ZR's frame will be shorter than your TR unless a custom frame depth is specified. You can only compare apples to apples by measuring your current chair and comparing it with the CAD.

    http://sci.rutgers.edu/forum/showthr...=1#post1626812
    Attached Images Attached Images  


  6. #6
    Quote Originally Posted by SCI_OTR View Post
    Going that conservative with a ZR2's COG is likely to put it outside of the range of adjustment that you need and you will get a front heavy chair. If you like your current COG and your frame length feels right, make sure you get a CAD with the OFL and compare it with your current chair's dimension (blue circle). There is a difference in where the bend begins (red arrow) and the point that the mark the frame depth (purple line). As a result, the ZR's frame will be shorter than your TR unless a custom frame depth is specified. You can only compare apples to apples by measuring your current chair and comparing it with the CAD.

    http://sci.rutgers.edu/forum/showthr...=1#post1626812
    +1

    When I ordered my TR3 I spec'd it to have the identical OFL (occupied frame length) as my ZR2 to ensure as best as possible that the feel between the two chairs would be as close to identical as possible. They are.

    I'd bet dollars to donuts (or a more current expression!) that your seating "engineer" is not familiar with the OFL spec. TiLite will include this dimension on the CAD drawing but only if you request it. And if your "engineer" neglects to inform you (or is simply unaware) that you're entitled to a free CAD drawing then that's another reason to reconsider his/her level of expertise.

  7. #7
    Hi Stephen and Tooley - I don't want to hijack this thread but I see you all are experts in this stuff. Could I request your opinion in another thread as I am currently ordering a new Tilite ZR chair this week and don't have the confidence about the order.

    Danita72 - you are in good hands if you listen to these pros....

  8. #8
    Quote Originally Posted by arndog View Post
    Hi Stephen and Tooley - I don't want to hijack this thread but I see you all are experts in this stuff. Could I request your opinion in another thread as I am currently ordering a new Tilite ZR chair this week and don't have the confidence about the order.

    Danita72 - you are in good hands if you listen to these pros....
    You can hit me up at stephen@bike-on.com

  9. #9
    thank you so much for your help , I am getting the cad drawings and I will check on that

  10. #10
    thank you for the help the graphs were really helpful

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