BMW Cafe Racer Rear Fender

Discussion in 'Old's Cool' started by Boxer Metal, Sep 7, 2011.

  1. Boxer Metal

    Boxer Metal Mad Scientist

    Joined:
    Nov 3, 2003
    Oddometer:
    3,608
    Location:
    Chico, California
    Something I have been working on. http://boxermetal.com/?p=180
    This is the prototype. It holds a 12amp hour AGM battery and should work with any of the cafe style seats.

    Attached Files:

    #1
  2. jbcaddy

    jbcaddy Long timer

    Joined:
    Jan 12, 2010
    Oddometer:
    1,292
    Location:
    Oroville & Placerville, California U.S.of A.
    Looks like you are going to cost me some extra money:D.

    Lookin' at those frame braces also. Jan
    #2
  3. Boxer Metal

    Boxer Metal Mad Scientist

    Joined:
    Nov 3, 2003
    Oddometer:
    3,608
    Location:
    Chico, California
    I have both with your name on them:)
    #3
  4. Jon-Lars

    Jon-Lars Jon-Lars

    Joined:
    Apr 23, 2006
    Oddometer:
    569
    Location:
    Beverly
    Placing the weight of the battery out there at the end of the subframe isn't a good design.
    It puts a lot of weight at the furthest point from the center of the MC's mass, and it will vibrate the whole rear end on anything but smoothest pavement.
    Maybe it would work if you filled the subframe tubing with dynabeads?
    #4
  5. Boxer Metal

    Boxer Metal Mad Scientist

    Joined:
    Nov 3, 2003
    Oddometer:
    3,608
    Location:
    Chico, California
    Battery only weighs 6 pounds and that's a lot less than a top case, passenger, saddlebag, duffel bag, stock seat......I'm not seeing an issue here.
    #5
  6. KhaoSanMan

    KhaoSanMan Airhead

    Joined:
    Apr 26, 2009
    Oddometer:
    616
    Location:
    Chico, CA
    You could even go Lithium if that is a concern, not sure this is an apples to apples comparison, but this battery only weighs around 4 pounds: http://www.skyrichbattery.com/Lithium-Ion-Battery/c10/p533/HJT7B-FP%3Cbr-/%3ELithium-Ion-Battery-YT7B-BS/product_info.html


    edit... I personally know very little about batteries, so this was just a what-if. I make no claims as to this particular battery working for any particular bike. I just wanted a rough idea of what Lithium batteries weighed as I had never checked.
    #6
  7. elite-less

    elite-less Been here awhile

    Joined:
    Dec 21, 2009
    Oddometer:
    558
    Location:
    The Puget Sound Convergence Zone
    Man that's a great solution. What's the final material gonna be... aluminum, steel or fiberglass?
    #7
  8. Boxer Metal

    Boxer Metal Mad Scientist

    Joined:
    Nov 3, 2003
    Oddometer:
    3,608
    Location:
    Chico, California
    Aluminum. I'm going to try and make it in 3 pieces so it's easy to ship.
    #8
  9. JonnyCash

    JonnyCash turd polisher

    Joined:
    Jan 22, 2011
    Oddometer:
    1,735
    Location:
    Midcoast, Maine
    A 12 AH battery will spin over an R100 engine? Really? I hadn't tried, but I had wondered if something smaller would do the trick.
    #9
  10. Boxer Metal

    Boxer Metal Mad Scientist

    Joined:
    Nov 3, 2003
    Oddometer:
    3,608
    Location:
    Chico, California
    I think the Bosch starter draws about 4-6 amps. It might suck on a cold day but it's for a Cafe bike:)
    #10
  11. JonnyCash

    JonnyCash turd polisher

    Joined:
    Jan 22, 2011
    Oddometer:
    1,735
    Location:
    Midcoast, Maine
    I believe you're mistaken. I think 4-6 amps might be right, on the little wire going to the solenoid. But going to the motor is another thing.Just try putting even a 25 amp fuse in line with your starter lead. You won't get the bike started, that's for sure. I bet it draws at least 40 or 50. Momentary amperage and amp-hours are very different. Still, have you tried starting one of these bikes with a 12 AH battery? I can totally see how a more modern battery of lower ampacity than a standard battery could do it, but I haven't seen it. I can definitely tell you that I once used a bigger than stock battery to get home on (it was quite a rig, I'll tell you), and that starter was never happier. It makes me think that going smaller than stock might not be so good. I hope that you are right and I'm wrong, because I'd love to get a smaller AGM battery to replace the lead-acid monster I'm now using, and still get reliable starting.
    #11
  12. Boxer Metal

    Boxer Metal Mad Scientist

    Joined:
    Nov 3, 2003
    Oddometer:
    3,608
    Location:
    Chico, California
    I'll plug the 12 amp hour battery into my bike and let you know if 175 CCA is enough.
    #12
  13. ipanemaguy

    ipanemaguy Many bikes & little time

    Joined:
    Jun 3, 2007
    Oddometer:
    76
    Location:
    Rustbelt, USA
    Beta testing: get the little guy, wire it in while located in OEM battery box or just hanging there. Try cold starting with outside temperatures below 50-55 F (most riders will prefer the indoor cafe option colder than that).

    If it passes test, issue resolved. If not try large battery. BTW my concern is the harmonic vibration of the tail light/lic plate tongue sticking out there. How about a little bracing?

    You are showing a block-off plate for where the airbox was. Why not engineer that piece to also serve as a battery box? I have thought of sandcasting a piece shaped much like that the Frenchman has posted, sexy curves and well integrated to the engine casting.

    I am very glad someone has the courage to think creatively and make pieces we others might wish to have but don't have the skill or facilities to fab. I used to have different ambitions, today I drool and envy the inmates that can mill, turn and especially weld. You satisfy some of that craving, keep doing it!
    #13
  14. Boxer Metal

    Boxer Metal Mad Scientist

    Joined:
    Nov 3, 2003
    Oddometer:
    3,608
    Location:
    Chico, California
    We wont see 50 degree for a cople more months. I already do a air box block off plate. Thanks!!!!
    #14
  15. rkatapt

    rkatapt Indo-Kraut

    Joined:
    Jun 14, 2008
    Oddometer:
    263
    Location:
    Dallas, TX
    Won't you wheel hit that battery tray since it's extended down?

    My tire has hit a couple of times and my battery tray is flat.
    #15
  16. xavier296

    xavier296 Alaska n'Back

    Joined:
    Nov 7, 2010
    Oddometer:
    286
    Location:
    Augusta, GA
    It looks like I should stop worrying about my underseat battery box getting hit by the tire. The entire battery and box are above the plane of the frame. I was trying very hard to maximize the available wheel travel. I figure with no passengers there is very little chance of maximum compression.

    Looks beautiful! Mine is crude in comparison.
    [​IMG]
    #16
  17. Boxer Metal

    Boxer Metal Mad Scientist

    Joined:
    Nov 3, 2003
    Oddometer:
    3,608
    Location:
    Chico, California
    What shocks are you running, how long are they and how much sag do you have? What rear tire are you running as well?
    #17
  18. rkatapt

    rkatapt Indo-Kraut

    Joined:
    Jun 14, 2008
    Oddometer:
    263
    Location:
    Dallas, TX
    Stock size rear tire.

    It only hit when I ran the stock BMW shocks. Now I have Ohlins BM141's which raises it a bit and are stiffer. Your battery tray sits a good 3/4" below the frame. My battery tray sits above midframe. Here is a photo of it with the old shocks. You can see where it hit on the pan.
    [​IMG]

    The dropped down portion of your tray may sit far enough back that it will not hit.
    #18
  19. adrenal

    adrenal skrunkwerks.com

    Joined:
    Jun 12, 2008
    Oddometer:
    656
    Location:
    Melbourne, Australia
    This is what I did.
    The Deka battery is pretty nifty - 275CCA and considerably smaller & lighter than stock 20A battery. And because they are sealed AGM battery you can lie them down.
    However, next time I do this sort of thing it will be with a lithium iron phosphate battery - quantum leap in energy density and weight.

    Have to be careful with wheel clearance - the wheel can nudge a flat plate thats just sitting on to of the subframe.

    [​IMG]
    #19
  20. robtg

    robtg Been here awhile

    Joined:
    Jun 29, 2007
    Oddometer:
    757
    Location:
    san jose
    Remove shocks----remove spring from 1 shock---reinstall springless shock---
    compress suspension completely---build whatever it is and if the wheel still
    turns and you have another 1/2' for safety, you/re done. It's really simple and better than guessing.
    #20