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Thread: New chair advice

  1. #1

    New chair advice

    Hi all,

    I'm in the process of ordering a new chair and had a question about COG.

    I'm going from a 18x17, 80 deg ZRA to a 16x17+1, 85 deg ZR. In the attached CAD, the frame depth is wrong (shown as 16x17+2, should be 16x17+1). Everything else matches what I have on my current chair.

    Things not shown in the CAD but important:

    - I'm 180 lbs., 5' 11"
    - I use a Ride Custom cushion (3" thick) on sling upholstery
    - T5 incomplete (I was re-diagnosed after creating my account, never bothered changing the name )

    I like how I sit in my current chair - it's just too damn wide.

    What brings me here today is my COG. From browsing the CAD repository, I noticed a lot of people have COG set to 3" or more. Mine is only set at 2.25". I know moving the COG forward would make my chair more "tippy", but I'm curious what that would mean practically? I don't have any problem with wheelies or tipping back while going up a slope - would there be any benefit to increasing my COG?

    Thanks for your help!

    (also, please point out any issues that jump out at you in the CAD)

  2. #2
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    Increase COG = easier to tip, given ALL other things like your body. head and other parts of body remain in exact same location during movement of chair. You have ability to do this if you have good control of upper body and head while doing any tipping. Meaning leaning forward same time your would be tipping. It is something you would need to learn some. Also depends a lot on the total configuration of the chair. There are a lot of factors go into this. I could tip my chair over forward if I anted to by moving forward on seat and leaning far enough. Things like this go into tipping backward.

  3. #3
    Senior Member tooley's Avatar
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    Quote Originally Posted by T4Gimp View Post
    I noticed a lot of people have COG set to 3" or more. Mine is only set at 2.25". I know moving the COG forward would make my chair more "tippy", but I'm curious what that would mean practically?
    You run a long chair, 17+2", with heav(ier) front casters (5") and smaller (24") rear wheels. A lot of your weight is spread to the front casters with your current COG setting. 3 years ago I had a ZRa and experimented lots with different dump and COG settings. I found that the farther forward I set my COG the easier the chair rolled.

    Rather than being in a rush to get a new chair I would play around with your current chair, the COG is infinitely adjustable. Take some time to fiddle with it. Every adjustment you make will take some time to get used to but may help you in the long run.

    I would also consider switching to 25" wheels. Everyone I've ever talked to prefers them. Combined with a "lighter" feeling front end will increase your pushing efficiency.

    Also, why the long frame? ie. do you need the +2"? I am taller than you and am sitting in a 16" deep chair. Way more maneuverable in smaller spaces.

    Good luck. I too went from an 18" to 16" wide chair and my shoulders thanked me.

  4. #4
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    Nothing better than basing a new ZR off a current, good-fitting ZRA, but do you really need the bottom leading edge of your footrest 3.75 off the floor?

    15” of footrest depth is a well-proven ‘given’ in your case, but you might consider lowering your RSH/FSH half an inch. You’d still have plenty of ground clearance plus maybe gain a better rim grip – the fingertips to axle thing.

    Your same weight and 3” taller, I ride the ZR shown below. I'm pretty sure you can EASILY go 3”+ COG with 1” of additional frame and say, a half inch lower center of mass.

    One final thought FYI: I'm on an 11" V front, size 11 shoe, have just the right room for my FreeWheel (1" clamp width). Almost went 10.5, glad I didn't.

    Good Hunting!
    Last edited by nofuss; 06-04-2013 at 04:30 PM. Reason: punct

  5. #5
    Senior Member ResonantEcho's Avatar
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    Realize, as I found out after the fact, that the 10" width is not what you'll actually get on the footrest width because of the V-shape. It will be more like a little less than 9". As a result, my feet didn't fit on the footrest.
    -ResonantEcho - T6/T7 Complete - October 31st, 1986

  6. #6
    Quote Originally Posted by tooley View Post
    Also, why the long frame? ie. do you need the +2"? I am taller than you and am sitting in a 16" deep chair. Way more maneuverable in smaller spaces.
    The +2" is an error in the CAD. It should only be +1. I'm in a 17" with 80 degree front right now. I'm adding the +1" so I can tighten the front angle to 85 degrees. I don't have too many problems maneuvering - at least not from frame length. I've had far more tight squeezes in the horizontal direction!


    Quote Originally Posted by nofuss View Post
    Nothing better than basing a new ZR off a current, good-fitting ZRA, but do you really need the bottom leading edge of your footrest 3.75 off the floor?

    15” of footrest depth is a well-proven ‘given’ in your case, but you might consider lowering your RSH/FSH half an inch. You’d still have plenty of ground clearance plus maybe gain a better rim grip – the fingertips to axle thing.

    Your same weight and 3” taller, I ride the ZR shown below. I'm pretty sure you can EASILY go 3”+ COG with 1” of additional frame and say, a half inch lower center of mass.

    One final thought FYI: I'm on an 11" V front, size 11 shoe, have just the right room for my FreeWheel (1" clamp width). Almost went 10.5, glad I didn't.

    Good Hunting!
    The 15" seat-to-footrest is just a known quantity in my current chair. My legs splay out with the way I sit. It's a minor annoyance, so I hadn't considered adjusting any measurements for it. Would lowering the RSH/FSH by 0.5" help with this? I have noticed my legs stay closer together when I use my backup seat cushion, which is a thinner than my usual. Now that I think about it, the backup was my main cushion when I got this chair...

    Good point about the footrest width. I was measured wearing my tennis shoes, which I wear 90% of the time. I don't have a freewheel, but I did check my dress shoes and a 10" front would be a pretty snug fit.
    Last edited by T4Gimp; 06-05-2013 at 12:17 AM. Reason: spelling + clarity

  7. #7
    Quick follow-up about COG: the TiLite website says the ZR has 2.25" of adjustability for COG. Will playing with the COG on the ZR conflict with alignment of the front casters?

  8. #8
    Quote Originally Posted by T4Gimp View Post
    Quick follow-up about COG: the TiLite website says the ZR has 2.25" of adjustability for COG. Will playing with the COG on the ZR conflict with alignment of the front casters?
    It should have no effect.
    I have had periodic paralysis all my life. I lost my ability to walk in 2011 beginning with a spinal block, which was used for a hip fracture caused by periodic paralysis.

  9. #9
    Senior Member sowseng's Avatar
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    The more direct body weight you put on your camber tube, the more difficult your chair rolls.

    To have a more forward COG is a good choice to avoid direct body weight on your camber tube.

    A more forward COG also give you a better pushing position, safe your shoulder.
    Life is meaningles, though you create the purpose.

  10. #10
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    Quote Originally Posted by T4Gimp View Post
    ... The 15" seat-to-footrest is just a known quantity in my current chair. My legs splay out with the way I sit. It's a minor annoyance, so I hadn't considered adjusting any measurements for it. Would lowering the RSH/FSH by 0.5" help with this? I have noticed my legs stay closer together when I use my backup seat cushion, which is a thinner than my usual. Now that I think about it, the backup was my main cushionwhen I got this chair... ...
    Assuming same footrest depth and changing an 80º front end to 85º+1 ... lowering your RSH/FSH won't change seated condition. Your whole occupied frame simply drops. Hand-to-rim of course does change.

    Leg-splay with a deeper cushion, legs-closer-together with a thinner cushion? That is stuff for a seating expert as your footrest distance may be in question along with perhaps modified seat dimension, dump and even a need for some seat taper.

    Tread carefully and be PATIENT. Guinea pig your ZRA right and you'll end up with a ZR that will fit like a glove.

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