Gravity racer - Calling all daredevils!

Discussion in 'BUILD CHALLENGES' started by breakurnees, Jun 17, 2011.

  1. Philphine

    Philphine

    0   0   0

    Joined:
    May 6, 2009
    Messages:
    876
    Location:
    just a wind on the road
    what's a good size tire to use? i've been looking on ebay and seeing high pressure 20" tires from about 1.35"-2.3". just from trying to look at g-bike pics it looks like they're around the 2" range.

    nothing i have around the house is more than the usual 40-60lb range, except a 1.5" 100psi i got for a specific bike that i don't want to take off, and a flea market find (hoffman 110psi 1.9") i put on the poseur 'cause it had white letters like the occ tire.

    since i'll have to buy them i might as well be looking for the best size. thanks.
     
  2. breakurnees

    breakurnees

    Rating - 100%
    1   0   0

    Joined:
    Sep 6, 2010
    Messages:
    35
    Schwalbe Marathons are the standard. I am buying Primo Comets.
     
  3. Philphine

    Philphine

    0   0   0

    Joined:
    May 6, 2009
    Messages:
    876
    Location:
    just a wind on the road
    looked at the primos on ebay. the price isn't too bad and they come in sizes i think i'll want. i may try for a pair.

    unless someone recommends against it, i'm meaning to get two different sizes 'cause the front rim i've found is a little narrower than the rear. i think i'm gonna try for a 1.5" front and somewhere around 2" for the rear.
     
  4. kingfish254

    kingfish254 Check out the 30+ Items in my FOR SALE thread! Pro Member

    Rating - 100%
    65   0   0

    Joined:
    Aug 31, 2009
    Messages:
    18,476
    Location:
    Historic Savannah
    I was playing around with the mock up of my Fugsley (folding Pugsley) build and thought you guys would get a kick out of it in this config. Has anyone tried using a Dahon folder frame for a gravity bike? You could even attach two Dahon frames together front to back and have a double folding gravity racer.

    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
     
  5. Philphine

    Philphine

    0   0   0

    Joined:
    May 6, 2009
    Messages:
    876
    Location:
    just a wind on the road
    i can see it. push everything down for aerodynamics going down, pull it all up to pedal back up the hill.

    i'm on hold for tires. i got what i think are decent to pretty good wheels over the last few weeks.

    looks like all i'll be doing is trying the same hill again when i get the new tires/wheels on, like an a-b test to see if it's any faster. still haven't found another hill i want to try.
     
  6. breakurnees

    breakurnees

    Rating - 100%
    1   0   0

    Joined:
    Sep 6, 2010
    Messages:
    35
    That's basically what I am doing. I took a kids full suspension MTB and flipped it, removed the shock and will be replacing it with a couple of heim joints and a turnbuckle. I can extend it until the seat post drags the ground.
     
  7. snydur

    snydur

    0   0   0

    Joined:
    Mar 3, 2011
    Messages:
    1,100
    Location:
    riverside
    IM DONE!! not just with the build, but with going 32 that low to the ground. went to the beach today, would i bring a beach cruiser? nahh, ill toss my gravity bike on the storage rack. about 1 30 or so, roll into my dads boss's beach house over looking a cliff. see the street out front and about a third mile back theres a speedo on a pole. swam, bbq'd and decided to try it out an hour or so ago. held onto my sisters cruiser going up the hill, and came down the other side. it was wobbly, and fast, shoes were scraping, people were looking and half a breath laster i was flying by the speedo pole, kept on going down a bigger hill and decided to call it luck and stop. . . ish. brakes dont help alot. so i got a good rush, sister has a picture of the sign on her ipod ill post it when she's home. but i think this one is just going to stay up on the shelf for a while. haha oh and an fyi, two piece twist bars are a horrible idea.
     
  8. breakurnees

    breakurnees

    Rating - 100%
    1   0   0

    Joined:
    Sep 6, 2010
    Messages:
    35
    Way to GO!
     
  9. Philphine

    Philphine

    0   0   0

    Joined:
    May 6, 2009
    Messages:
    876
    Location:
    just a wind on the road
    you're a faster man than i gunga din

    my spare cash has kinda dried up, so i may not get more tires before the deadline. unless i find another hill or get the faster wheels/tires on (which may not make much difference anyway), i guess my 22mph is all i'll have by the deadline.
     
  10. Three-Wire

    Three-Wire

    0   0   0

    Joined:
    Dec 11, 2010
    Messages:
    56
    Location:
    Goddard, KS
    Well, you guys have inspired me... The Coaster's are hosting a Gravity Shoot-Out in a few weeks and I thought it looked interesting, but Philphine's, Fej's, and Snydur's bikes along with Snydur's experience put me over the edge. I'm in. May not get to run it until after the deadline, but we'll see.

    I don't have the gear or time right now for welding, so it'll all be bolt-on stuff. We'll see how my ideas for that play out.... Here's where we are tonight:

    [​IMG]
     
  11. chubs68

    chubs68

    0   0   0

    Joined:
    Aug 29, 2011
    Messages:
    8
    i think im gonna join in with this, its gonna be my first build off. ill post a pic later. :)
     
  12. breakurnees

    breakurnees

    Rating - 100%
    1   0   0

    Joined:
    Sep 6, 2010
    Messages:
    35
    I just got the tires on and kneelers built. I took it for a ride down the driveway brakeless. Oh boy it is gonna be fast! The steering is twitchy due to the rake. I also scrape my butt on the tire a lot. I may have to make a seat. 35 won't be a problem, not doing 80 or crashing hard might be tricky.
     
  13. Three-Wire

    Three-Wire

    0   0   0

    Joined:
    Dec 11, 2010
    Messages:
    56
    Location:
    Goddard, KS
    Took a night off from chores to get some work done. Call it a mental health evening...

    Got the majority of the frame work done. Still some tweaking to be done, but this is the basic layout... I need to add a member where the red line is drawn.
    [​IMG]

    To keep the pivot point locked into the dropouts of the purple frame, I had to fab up some plates that have a hole for the new pivot bolt. [​IMG]

    For steering, I want to put the MTB bar ends on the tripple-trees like I've seen done elsewhere on this thread but I can't make the pair I have fit. Still thinking about alternates for that...
     
  14. aka_locojoe

    aka_locojoe

    0   0   0

    Joined:
    Sep 21, 2006
    Messages:
    7,509
    Location:
    Kansas
    Cool. I hope you get it finished in time for the race. See ya there.
     
  15. Philphine

    Philphine

    0   0   0

    Joined:
    May 6, 2009
    Messages:
    876
    Location:
    just a wind on the road
    the bar ends i put on didn't fit either. it's one of my later worries, like if i stressed the metal bending it out or something.

    but on one set i just stuck a screwdriver or something in the screw hole and bent it out. on the second pair i had a seat post that was i guess 7/8" at the top, but fit into a 1" seat post hole. so i stuck them on the seat post and hammered them down till they expanded onto the 1" part. then i drilled out the old bolt holes (couldn't get them to line up again plus the old bolts were then too short) and added new nuts and bolts to tighten them down.

    like i said, i can't say it's 100% safe. seems ok so far.
     
  16. Three-Wire

    Three-Wire

    0   0   0

    Joined:
    Dec 11, 2010
    Messages:
    56
    Location:
    Goddard, KS
    Thanks Randy. We plan to be there... My wife is gonna ride her 'Lil Chick - first time she's been on it since she was a 'lil chick. We'll take off the chain and put on caliper brakes just for this. 8)

    I suspect you'll be ok, but if you're not confident in it then I'd find something else to try. Tonight I gave up on the bar ends and just flipped the bars that came with it. This should work fine but I may try a different stem, bars, and brake levers from an old 10-speed.

    Tonight's progress:
    [​IMG]

    [​IMG]

    Extra member is installed. Frame is very rigid with the extra member and pretty heavy. Now, I've got to figure out how to ride it! Not sure how to sit on the thing... I also have to make retainer plates for the rear wheel, similar to what I fabbed for the pivot point. And hook up the rear brake, true and overhaul the wheels, ditch teh reflectors, and install a bald set of 60psi 20" MTB tires... One more complete evening out to do it.
     
  17. breakurnees

    breakurnees

    Rating - 100%
    1   0   0

    Joined:
    Sep 6, 2010
    Messages:
    35
    Witchita is a long haul from here, but it would be fun to race a fellow member. Hmmm...
     
  18. Philphine

    Philphine

    0   0   0

    Joined:
    May 6, 2009
    Messages:
    876
    Location:
    just a wind on the road
    how wide are those two pieces of angle iron? maybe just a pad bettween them on top? the occ chopper seat i started out with wasn't too bad, if you have one and/or don't find something else. i switched mainly 'cause it wasn't working with my kneeler plan (plus since i was kinda going for style, i didn't like how it looked as much as the one i used). it would bolt right to the two pieces (i think, just going by the pic) and also give you a little flip up in the rear so you don't slide back to the wheel.
     
  19. Philphine

    Philphine

    0   0   0

    Joined:
    May 6, 2009
    Messages:
    876
    Location:
    just a wind on the road
    well skip all that. i forgot you're using the x-games bike. if you have the seat from it you ought to be able to get it to work well enough.
     
  20. breakurnees

    breakurnees

    Rating - 100%
    1   0   0

    Joined:
    Sep 6, 2010
    Messages:
    35
    I have brakes! Tomorrow I have to work out better pads for the kneelers, a seat and weight. I hope to do some real test rides tomorrow night.
     

Share This Page