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Building Custom Seat Question

This is a discussion on Building Custom Seat Question within the Technical forums, part of the Caferacer.net Forums category; Hi, I'm building a custom seat for my café racer project and have a few questions. I am going with a flat piece of stainless ...

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  1. #1
    Junior Member ams14's Avatar
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    Building Custom Seat Question

    Hi, I'm building a custom seat for my café racer project and have a few questions. I am going with a flat piece of stainless sheetmetal for the pan. I will put foam on it, wrap the leather around to the underneath and hold in place with rivets.

    question: I want the seat to ramp up slightly towards the tank and have a nice snug fit against the tank. Would you recommend I extend the pan up vertically by cutting/welding a piece of sheetmetal that rises up vertically against the tank? or do I just cut the foam the way I want and upholster over it? The seat foam near the tank will be around 2.5" high and I'm worried that when upholstered it will deform that section somewhat.

    the foam in this pic is temporary, just for getting an idea of the shape I want.

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  2. #2
    Senior Member woodsman's Avatar
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    If you are going to use leather and want a proper fit you'll need to do some cutting and sewing. Make the cover to fit the foam.

  3. #3
    Senior Member Cyorg's Avatar
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    Quote Originally Posted by ams14 View Post
    Hi, I'm building a custom seat for my café racer project and have a few questions. I am going with a flat piece of stainless sheetmetal for the pan. I will put foam on it, wrap the leather around to the underneath and hold in place with rivets.

    question: I want the seat to ramp up slightly towards the tank and have a nice snug fit against the tank. Would you recommend I extend the pan up vertically by cutting/welding a piece of sheetmetal that rises up vertically against the tank? or do I just cut the foam the way I want and upholster over it? The seat foam near the tank will be around 2.5" high and I'm worried that when upholstered it will deform that section somewhat.

    the foam in this pic is temporary, just for getting an idea of the shape I want.

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    Hard to tell from the photo, but it looks like a DIY mono shock conversion. If so, how well it is welded and braced should dictate what you make the seat pan out of. It might also dictate the shape.... I'm thinking something that resembles a jock?..... and yes I'm an asshole.
    Last edited by Cyorg; 04-10-2019 at 06:10 PM.
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  5. #4
    Junior Member mkwilcox's Avatar
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    Agreed that getting the seat cover to fit properly is critical, which will likely involve some sewing. Instead of rivets, which can easily cause puckering, I'd suggest using contact cement to stick the leather to the underside of the seat pan. This will allow the cover to be easily be re-positioned to allow micro adjustments. You will need to put multiple coats on the leather to saturate the edge of the leather so that it will stick.

    As for extending the seat pan, it will depend on the geometry of the gap. I am guessing that the gap is where the 2" Styrofoam is placed, which might require the support of extending the pan, easily done if you glue or rivet a bit more stainless sheet in place.

    Have you figured out what foam you want to use? I have had trouble finding foam firm enough for a motorcycle seat, and have gone to using under carpet padding (very firm, but can be layered, cut and shaped to build a foundation), and then a layer of 1" latex foam to increase the cushy-ness. I use spray adhesive to tack it all together.

    Just some thoughts.

  6. #5
    Senior Member Geeto67's Avatar
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    use closed cell foam for the seat padding. it's weeatherproof and it's what most modern motorcycle seats are made of:

    https://www.grainger.com/product/5GC...!471318999323!

    if you don't want that, go to joann fabrics and tell them you want an outdoor upholstery foam and they will probably show you all the high density seat foam they have.
    https://www.joann.com/sewing/foam-and-fiber/foam/

    carpet pads come in two varieties: prime foam and frothed foam. Prime foam is less dense than upholstery foam and tends to move around a lot, frothed foam is as dense as upholstery foam and is pretty much the same thing although made slightly differently.

    as far as wrapping around the tank at the back, there is no wrong way to do it. The oem's in the 70's usually just left this upholstered without a seat pan, but if you look at any 1970's honda there is always a wear mark in the paint from where the seat wore it away while moving around. Starting in the 1980's the OEMs began to make pans that had a little front support so the seat didn't do this as much. aftermarket seat makers like corbin are the same way - I have an old corbin for my beemer that wraps around the back of the tank without a supporting pan (it's just foam and leather), but the corbin I had made a couple years back for my 1979 cb750F has a bit of the pan come up to wrap around the back of the tank.

    One thing I would suggest is forget the "stainless steel" pan and make it out of fiberglass directly on the bike. You'll get a better fit and if you want the seat pan to wrap around the back of the tank, it's way easier than bending, weldign and shaping sheet metal (esp stainless sheet which is a bitch and a half to work with).

    Here is a tutorial:



    and yes, I am an asshole also because I am pretty sure your mono-shock conversion is a death trap - mostly because for every 1 I see that takes real engineering into consideration there are 100 that are just slapped together using pictures off google image search as a "guide". But prove me wrong - post some pics of it up.
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  7. #6
    Senior Member woodsman's Avatar
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    I would make the entire pan from fibreglass, use closed cell foam and a jell pad and barb strips to hold the cover. If your cover is sewn to fit the seat there shouldn't be a need to adjust it. Make your cover, steam it before you put it on (a bit of water in a steel bucket drop in oven heated rocks), which will give it some stretch, put it on and it will contract to tighten things up. Any small creases or puckers I work out with water in a spray bottle, my fingers and a warm smooth river rock.

    Personally I wouldn't use leather for a seat.

  8. #7
    Senior Member irk_miller's Avatar
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    Except for the choppers I build, I make the base out of epoxy fiberglass and I carve the seat pad shape out of insulation from. Then I make a plaster mold of the insulation foam form and cast it in FlexFoam-iT 7 FR.

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    Last edited by irk_miller; 04-17-2019 at 09:06 PM.
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  9. #8
    Junior Member ams14's Avatar
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    Thanks for all the responses and good info! I think I follow everything for the seat. I plan to shape the foam myself then get it upholstered by someone (that knows what they are doing) so they will definitely be able to sew it in the required shape. Yes, the area I was talking about is up near the tank. I like the idea of contact cement vs rivets. I may add a small pan upright extension at the front, just to help with shaping and give the upholsterer something to stick to.

    What do you use if not leather? Some type of synthetic?

    I bought foam already. I read this article (linked) and went with their recommendations of Sunmate brand foam, 1" of extra firm on bottom and 1" of medium for top layer. I got it already, seems decent, like a stiff memory foam.
    https://www.sunmatecushions.com/page...m-applications

    I like the epoxy fiberglass idea. For this I like the asthetics of seeing the whole frame rail.

  10. #9
    Junior Member ams14's Avatar
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    As far as the monoshock goes, your point is well taken (now that I understand what you mean).

    Firstly, my calling this a café racer is a bit of a stretch, it is more of a custom/frankenbike with a vintage tank. The frame, which started out with a monoshock, is now highly custom. The swingarm was a monoshock as well. I spent considerable time (in solidworks) designing the linkage actuation so it pivots correctly and with the appropriate amount of spring load on the shock and cnc'd the various components. I didn't run a finite element model on the upper frame where I moved the mount, but used similar construction as the original (and ran it by a stress engineer). I will post some pics!

  11. #10
    Senior Member brad black's Avatar
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    modelled in solidworks would make you the 1 in 100 that has a clue. good work.

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