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Old 12-26-08, 11:34 AM   #1
LWB_guy
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New idea for wooden seatback - your thoughts ?

Last year, my wooden seatback, which is about a foot wide by seven inches from top to bottom, started hurting my back after two and a half hours of pedalling my homebuilt LWB. At least, it became quite uncomfortable.

I was thinking about using a plastic-metal-foam seatback that came off one of those black made-in-China swiveling cushioned office chairs made of plastic and metal. It's a lot more comfortable. After carefully measuring, though, I discovered it would be about six inches thicker than my wooden seatback. I cannot afford to put my hips six inches closer to the pedals, without rebuilding the whole frame. The fit is just right as is.

Somewhere I read that a wooden seatback can be curved in one direction, but not in two orthogonal directions. And I prefer using wooden plywood to CF or fibreglass because I can get scrap pieces of it free from a local furniture maker. And my experience is with wood, but not with synthetic composites. So I thought about making a seatback that is curved so that the middle is farther aft of its left and right edges.

So, since Christmas I've been thinking about making a larger seatback out of a couple layers eighth-inch (4mm) plywood epoxied together and laminated with half-inch closed cell foam. This is the technique I used for the old seatback, which has held up well.

Last night, I thought maybe the most comfortable seatback might be one shaped like the back of an adirondack chair.
Like this: http://www.woodworkersworkshop.com/r...unge&andor=and

I don't have an adirondack chair, so I don't know if this idea would indeed work, seeing as my frame geometry doesn't allow for seatback force to be transmitted to the base of the chair. So, obviously it's not going to support my back from tailbone to shoulders the way a real adirondack chair would. (This area of my back measures 15 inches wide at torso by 28.5 inches from chairbottom to top of shoulders.)

So I'm considering making a real adirondack chair back and then using it as a mold against which to bend, laminate, and epoxy a couple of plies of thin plywood, which I would then trim to final size and cover with half inch foam. In other words, the final seatback would be a double-ply thickness cushioned hardshell in the shape of an adirondack chair seatback, but without the actual five slats of the adirondack chair back. And unlike a real adirondack chair, the back would not extend to the seat bottom. I could, however, add a lumbar cushion (like this: http://k2healthproducts.com/Products...hion-3-S_1.jpg)
if I felt like it.

Regarding the frame, the seatback attachment point is 11.5 inches above the top of the seatbottom. The top edge of the seatback can be much higher than this. (This is simply the point to which pressure on the seatback will be transmitted to the rest of the frame.) The side-to-side distance is also unlimited by the frame. And the frame geometry allows a seatback angle of 69 degrees between the seatback and the frame extension.

I haven't yet measured the seatback angle of an adirondack chair.

Good idea or bad idea? Your thoughts?

Last edited by LWB_guy; 12-26-08 at 12:04 PM.
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Old 12-26-08, 02:17 PM   #2
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I'm trying to wrap my mind around an Adirondack chair (back) on a bicycle. What comes to mind are the plastic Adirondack chairs.
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Old 12-26-08, 03:59 PM   #3
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All the Zox bikes have laminated wooden seats.

I don't know if something similar would work on a long wheel base?
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Old 12-26-08, 04:36 PM   #4
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I would think that having a seat back that supported all the way up to your shoulders would be more important than having the proper lumbar curve. It only needs to be 8-11 inches wide, but it should be 15-18 inches tall (from the top of the seat pad.) Seven inches tall is just too short. The EasyRacers Cobra seat is a good example; it is tall but narrow. There's no lumbar curve, the padding compresses where it needs to. Here's a picture of a Recumboni seat, just for reference.

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Old 12-27-08, 03:41 PM   #5
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No, JanMM, here's a better picture of the real adirondack chair:

http://www.cedardelight.com/images/F...ndackChair.jpg

I was wrong --its back has seven reclined slats, not five as I originally
stated. If you've ever relaxed in one, then you know the adirondack chair has several characteristics that give it its renowned comfort:

* It is wide enough to seat the biggest person
* The armrests are flat wooden surface comfortable for the biggest, fatest arms plus
your beverage of choice.
* Its seat bottom is curved so that one's butt sits lower than his` knees, forcing one to recline when he leans back.
* Its bottom has a comfortable curve that supports the thighs.
* The curved back tends to center a thinner person in the middle of the back.


This last feature is the only one I was thinking of copying. The adirondack chair is notoriously comfortable -- as if it were sculpted to fit your back. That's what made me think of copying its curvature.


Imagine you have a bowl of uncooked rice and you want to pour the rice into an empty ketchup bottle. You need a funnel. You don't have one. All you have is a blank sheet of paper. So you grab the paper's two left corners, the top left corner in your right hand and the bottom left corner in your left hand. You bring the two corners together, making one overlap the other, forming a little circle small enough to fit into the top of the empty ketchup bottle. Then you hold the two corners together securely, twisting a little tighter, and voila -- a makeshift funnel.

The curved side of the funnel is the shape on the adirondack seat back that I was planning to replicate.

Read on....


yangmusa,

Thank you for posting that picture. The black seatback on that red Zox lowracer looks extremely comfortable. It looks comfortable enough to sit in, pedalling, for hours and hours without discomfort. That is my goal.

It doesn't look like wood. It looks like some plastic material. If I decide to go with an integrated (one-piece) seatback-seatbottom, I will defibitely replicate that black seat. It looks even more comfortable than what my adirondack chair seat back.

Is it?

Now imagine you have a blank, perfectly uncreased sheet of paper on a tabletop laid out completely flat. Firmly press down the paper's bottom edge with the fingers of your left hand. Firmly press down the paper's top edge with your right hand's fingers. Now maintaining downward pressure on both hands, slide your right hand half an inch closer to your left hand while keeping your left hand fixed. What happens?

The middle of the paper bows up, making a curve convex upward. Another hand could slide that bow up or down the paper, and make it exactly match the curvature of that Zox seatback. Then the paper would be curved just like the seatback on that red Zox lowracer.

Notice though, the curvature is different from the funnel-shaped back of the adirondack chair. This curvature looks more comfortable to me. So long as you position that "bulge", convex bump, so that it fits into the curve of your lower back. In this case, you don't need the little lumbar cushion if it's built permanently into the seatback.

How long can you sit in that seat, yangmusa, before it starts hurting? I"d be highly interested in any details you care to post. It looks like a real winner of a seat. I don't read German, so I gave up on the Zox website. I wonder how to take a mold of my back in order to make the seatback align with my back's natural curve perfectly? Maybe some quick setting glue, clear poly sheeting, and a huge pile of styrofoam peanuts?

Blazingpedals,

I think you're right that shoulder support would make the seatback comfortable for long hours of pedaling. Especially with my underseat steering. I posted a side drawing of my recumbent so you can see the geometry. (Please note the existing seatback is concave to my back. ) That's why I think the black seat on that red Zox lowracer looks so comfortable -- it supports all the way from the buttocks to the shoulders. It looks comfortable.

So maybe the curvature of the second sheet of paper would be more comfortable after three to six hours of riding than the curvature of the first sheet of paper (adirondack chairback).........What do you think?
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Old 12-28-08, 03:38 PM   #6
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Looking at the ZOX above reminds me of the new version of the Ground Hugger. It too has a 'segmented' seat that I have thought of trying {haven't yet** with wood and then putting padding on each segment.
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Old 12-29-08, 01:03 AM   #7
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Quote:
Originally Posted by LWB_guy View Post
yangmusa,
It doesn't look like wood. It looks like some plastic material. If I decide to go with an integrated (one-piece) seatback-seatbottom, I will defibitely replicate that black seat. It looks even more comfortable than what my adirondack chair seat back.

Is it?
....
How long can you sit in that seat, yangmusa, before it starts hurting? I"d be highly interested in any details you care to post. It looks like a real winner of a seat. I don't read German, so I gave up on the Zox website. I wonder how to take a mold of my back in order to make the seatback align with my back's natural curve perfectly? Maybe some quick setting glue, clear poly sheeting, and a huge pile of styrofoam peanuts?
I'm afraid I can't give you first hand info on the seat, all I know is from reading about it. It's definitely wood, it says so in the text and you can see it in some of the other pictures from behind. The top layer is closed cell foam (camping mat type stuff) that is cut away to aid airflow - apparently still quite warm though.

You could use Google's language tools to translate the website, but it only seems to work 2-3 pages deep. Hence you loose some detail.

I think laminated wood is shaped by steaming the wood until soft, then gluing layers together under pressure. Easy for production runs, but I don't know how one could replicate that at home.
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Old 12-29-08, 07:35 AM   #8
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Well, I zoomed in on the picture of the seat on the red lowracer and
took a few measurements. If I can find a source for thin plywood (thinner than eighth inch), I imagine I can replicate that curve with a couple layers of plywood pressed together. First I'm going to look for a leaded curve that's about 29 inches long. I don't know leaded curves are made that long. I don't even know if they are still made at all.

The ZOX seatback is supposedly 93cm x 33cm (36 5/8" x 13"). I measured my back with a tape measure. It seems to be 28 1/2" by 18 1/2 " wide. So I'll shoot for that size or larger.
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Old 12-29-08, 07:22 PM   #9
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Depending on the budget, you might also consider this ready made anatomical wooden seat:
http://www.geocities.com/atombikes/seat.html
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Old 12-29-08, 10:41 PM   #10
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yangmusa,

Thanks for the link! That sounds like it might be a good deal for a wooden seat. Wonder if ten inches is wide enough....
That Actionbent Tidalwave 3 FRP seat looks nice with a big vent in it.

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Old 12-30-08, 06:47 AM   #11
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Word of warning: The seats you are looking at are all designed for SWB bikes, which all use more recline than the drawing of LWB Guy's bike. They're made for lying, not sitting. To adapt it to LWB, you'd need to make the seat base bigger and make the angle between the base and the back more acute.

You can make a wooden seat to just about any form you want. Simply take two 'ribs that are oriented lengthwise and perpendicular to the seating surface. Cut the facing edge to the desired lumbar curve. Place them about 8 inches apart and use slats to create the seating surface. Ironically, that's the way an Adirondak Chair's seat base is made. Except in this case, you'd cantilever the slats and make the seat wider than the ribs. Cover the slats with a foam pad and voila!
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Old 12-30-08, 11:11 AM   #12
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Word of warning: The seats you are looking at are all designed for SWB bikes, which all use more recline than the drawing of LWB Guy's bike. They're made for lying, not sitting.
Oh yes, good point...
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Old 12-30-08, 11:27 AM   #13
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LWB Guy, if you like the idea of a lumbar curve, maybe you should look into this:

http://www.recycledrecumbent.com/Parts%20Page.htm

I've met AD Carson and seen his work, and it's very nice. He sells a seat frame designed for his LWB bikes/kits for $60, which is very reasonable, IMHO. You'd just need to make the mesh out of some Pet-Pruf screen material, which could be done by hand if no sewing machine was available. In fact, if you tell him that BlazingPedals sent you, he might only charge you $65! Just kidding! I'm not sure how he mounts his seats or how it would mount on your bike. I bet he could help you, though.

Disclaimer: I have no business relationship with the guy, just impressed with his work.
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Old 12-30-08, 12:42 PM   #14
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I think you are quite right, BlazingPedals. There is no need for me to learn how to bend plywood. The seatback need not be a monolith. I will simply make plywood slats overtop three bottom-edge-to-top-edge curved "ribs". That way,

(1) I can easily attach mounting hardware to the ribs.
(2) Lighter weight than a monolithic seat. (well, maybe)
(3) I can use the quarter inch plywood I already have rather than order thinner plywood.
(4) I can add ventilation if I want to (by putting holes in the foam pad).

Great idea! Thank you, BlazingPedals.

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