Step 5: Ballast

Weight, its your friend in this sport. Where the weight is located is also important. Pushing as much weight as possible below the axle height will give you a much more maneuverable bike.  So what you can do is drill a hole in the frame and fill parts of it full of lead or concrete. Some builders will bolt on lifting weights this is nice because you can easily move the weight on the bike and or increase decrease the amount.

What we have done here is taken two steel hemispheres drilled a half inch hole in the center of both hemispheres. In one hemisphere we welded a piece of 1/2" all thread through the sphere. Leave a few inches on the inside and enough on the outside of the hemisphere to mount it to the frame. Then weld the two hemispheres together. Next, ground off excess weld to create a smooth looking sphere. A tube was welded to the sphere for a "wick" to be added later making a classy looking little bomb. 

Now for the awesome nasty dangerous part. Filling the hollow sphere full of heavy stuff. Using a gas forge we melted lead pellets and then poured the melted lead into the sphere. A funnel is of great assistance during this process. Ours is an Ace model for about three dollars. This created a 25lb ballast. There was still room for more weight so we drilled a hole in the bottom tube of the frame and filled that full also. Do not try to cool these parts down with water. Just let them do there thing. It may take an hour or more. If you do not have a gas forge at your disposal an oxy/acetylene torch or MAPP Gas torch will also get the job done. If you go down this road please where a proper respirator and do it outside if possible. 

The excess all thread that was left protruding from the sphere was enough to safely mount it in a vise for the pouring of lead. After the lead has cooled we drilled a half inch hole in the frame and mounted the ball. You can bolt the weight on using a nylock. We chose to cut the all thread down until only .125" was protruding out of the frame, and then welded it on. 

<p>Yeah! I am creating this work of beauty. I am making an ible about it. (CREDIT GOES TO YOU ;) ) It's going to be made out of an old BMX bike. hope to post it soon!</p>
<p>Definitely one of the<em> coolest </em>instructables ever. After I read this I favorited it immediately. I hope to make this. Quick question though. How would you wire it to make it electric? Thanks</p>
<p>what did you use for the back to hold the tire and weld the pegs on?</p>
<p>Hi!</p><p>We are a team of 15 people trying to make a bike quite like yours. We would like to make a bike that gives the same feeling of speed as yours, though we would like it to have pedals so you can also bike uphill. I added a picture of an early sketch and appreciate all sorts of comments and help! </p><p>What do you think? Is it possible and what is important to think about during this process? :-)</p>
Just finished making this as my project for my senior engineering class in high school along with 2 friends. Added a 36v hub motor using 3 12v deep cycle lead acid batteries works great. Thank you for the instructable. Used an ammo box to hold the batteries.
<p>This is awesome! I want to do the same thing except 48-60v and using lithium batteries (to reduce weight). How well did it preform? And does it turn well?</p>
Works great. I would recommend building an aluminum frame. It will help with the weight issue. As mine is now it can go up some inclines but with my heavy frame you can severely notice the reduced speed. The bike however turns great. We are currently working to paint the bike to prevent rust as well. Hope your build brings you as much fun as mine did.
<p>What is your top speed on flat land?</p>
I would say about 15-20mph on flat but have not actually done calculations though I plan to in the coming week or so I will post the definite speed then.
<p>It's been a few months. Any updates on your bike?</p>
Painted product
<p>Came out nice! You should post up a youtube video of it in action!</p>
<p><iframe allowfullscreen="" frameborder="0" height="281" src="//www.youtube.com/embed/vJSmPAGhf6A" width="500"></iframe></p><p>Here you go hope you like it. Just tell me if you want to see more.</p>
<p>Woa man that is sick! I'm going to have to make one with the leftover tubing after I finish my dirtsurfer.</p>
<p>Thanks it's so worth it. And good luck with your dirtsurfer. </p>
What would be the measurements for a kids gbike?
<p>my two top full length bars were 54in across so based off of my hight take what ever your child's height is in inches and divide by 1.33 and that should give you a good length for the laying down portion the rest is up to preference on positioning the knee pads and handle bars as well as how low to the ground you want it. </p>
<p>this bike is awesome<br>I would like to make one but with a 50cc pocket bike engine and mountain bike gears at the back<br>has anyone got any tips or advice?<br>thanks</p>
<p>Depends if you already have the 50cc pocket engine I hope all goes for the best in you build. However if you are looking to buy a motor i would recommend using a hub motor there is no worries about how it will fit or be integrated and you can use the batteries that power it as a weight for going down hill.</p>
<p>cool, thanks :)</p>
Does riding this hurt your back at all? Also, what happens when you come across an uphill? Do you just have to walk it up??
Instead of filling the tube along the bottom of the frame could you just use a solid bar instead of the hollow?
Hey guys. Just wondering how you would make a gravity bike from a regular BMX frame. I know that you turn it upside down and obviously adjust a couple of things so that the handle bars arent on the ground ahaha. But how would you make the kneeboard for it??
Relly good
How hard do you think it would be to put an electric motor on one of these?
You could add some hub motors, then you could even use couple sealed lead acid batteries as more ballast.
Bingo!!! my thoughts exactly
The frame would have to be modified to accommodate a chain, but other than that, it'd work. If you were going to do so and use it to cruise around town, I'd suggest putting a large / tall flag on the back like some recumbent riders do. This way people have a better chance of seeing you considering it is so close to the ground.
HEY this is really great i want to build for my self. i think this is first Gbike gona build in India. <br>Just need little help plese guys i want to iknow the measurement of the frame full frame. <br>what is the size of frame and lower frame. plese <br>
That is just so awesome it's not funny. I saw this and immediately decided to build one. I have never been so inspired by an instructable! It's all i've been thinking about for the last few days! Went to the local junk yard and picked up a couple of (darn good) bikes for $20 and some steel for $10. Should give me about 95% of the stuff i need to make it. Also, i found some very cheap 160mm discs/calipers for US$26 express shipped from china and i am going to see what i can do to machine a hub to mount the disc to a *standard* hub. Fingers crossed it all works out and they are not total crap. Cant wait to start building it!
Well, as i said, i just HAD to do it. This is my effort so far. <br> <br>VBrake rear, 160mm Disk front, fully suspended. Total build cost, about AUD$100 but that uncludes 3 donor bikes (from my local scrap yard). The bottom bar is full of lead. The only thing really left to do is put a seat on it. Rides well, spring rates are perfect. Now i just have to find some hills to run it on (and make some brackets to strap it to the roofracks on my car). Still trying to source some wheel covers at a reasonable price but with my feet further forward, they tend to stay out of the spokes anyway. <br> <br>Thanks Harlan for such an awesome inspirational instructable!
I have never heard of G-Bikes but thanks to you I have now seen an amazing addition to the bicycle world! This looks like on heck of a lot of fun and building it yourself just makes it more fun! I was a cyclist for many years and have been 50+ mph a few times but the thought of it being so close to the ground sounds wild! Well done good luck racing your fantastic Instructable.
I've raced motorbikes all my life, thought I'd retired from the sport till i spotted this stuff on Youtube, I'm hooked and as yet haven't even attempted to squeeze all 6ft 2in of me onto one. <br> <br> However I'm already scavenging parts for my own build. the only thing is I figure as I'm on the downhill slide to becoming 60 I reckon my old knees and wrists are going to need suspension :) <br> <br>God damn it i feel young again, I might not be able to keep up with you young whipper snappers (yet) but I'll have a blast just the same. <br> Cheers guys <br>You're never too old to be a dick.
Your Rear wheel covers are easy to find, look at the Thrift Shops for the Stationary Bikes that have the covers on the wheel. They have been kept inside and never have been crashed. Nice job on the machine. To bad the guys here play polo and nobody does any bombing here in Idaho.
i bomb quite frequently in your state sir.
Good call never thought of that!
im building a bike for this but im starting with a frame for a stingray chopper.. i may post a build for it<br>
what length is the kneeler all way through??
how do you stop them like once you want to stop
Brakes we have never built a downhill machine without them!
Is there A possibility this could be made of wood? If so, would there need to be some modifications considering this?
Totally possible! It would take some tinkering no doubt. <br>
Very coo! <br> <br>On another note, I recall carrying a 200lb., two person, elephant costume down Main St. that your company designed for the Lion King Celebration back in 94. I remember meeting Michael a couple of times. Seemed like a nice guy. Was attentive to our puppeteers.
RAD! Bet that was a memorable experience! Yeah the puppeteers come first if they are not happy no one will be :)
Could someone please tell me the measurements and sizes of the metal frame he used, as i dont understand what he means by 8ft of .75 x 1.5 x .125 mild steel. thanks
What I believe he means is that the square tube he bought was eight feet long, three quarters of an inch wide, an inch and a half high, with an eighth of an inch thickness.
will it work if it has suspensions
This is very, very cool. If I could weld, I would build one! <br>I especially like the &quot;bomb&quot; between your legs. You should add a fuse on top to complete the picture... <br>Have you ever considered using solid wheels? (for weight but for a very strong gyroscopic effect and thus stability as well).
About how much did this cost???
Not sure that it's for me, but nevertheless, a fantastic instructable with excellent supplemental documentation. Five stars for you.

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Bio: The word I hear most explaining me is whimsical. I'm an artist designer crafter person. By day I work for Michael Curry Design making ... More »
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