Introduction: Pimp Your Kids Ride

With summer about over, give your kid something that they'll be proud to swing a leg around for that fall ride to school. With a quick fork extension you can quickly build a great looking and fun to ride chopper.

Step 1: Start With Your Kids Bike


Step 2: Take Off the Handle Bars So That They Aren't in the Way

It's also a good idea to take the entire fork out of the headset. unfortunately, the reflector mount sometimes becomes loose and strips the threads on the stem of the fork. If this happens you might want to leave the fork and frame together.

Step 3: Draw a Line on the Forks Before Cutting

Drawing a line on the forks makes it easier to line up later when you weld them back together. This is easier to see in the later steps.

Step 4: Cut the Forks

You can cut the forks using a variety of different metal saws. Here I'm using a pneumatic auto body saw. This saw works great, doesn't require that much air, and only costs about $20 from Harbor Freight.

Step 5: Forks Cut Apart and Grinding Them Down to Remove Paint for Welding


Step 6: Test Assembly of Forks

The assembly of these forks was especially easy. I used 1" .040 steel for the new fork tubing. it turned out that the inner diameter of the original forks was just slightly bigger than the 1" steel. This allowed for the extensions to fit inside the original fork.

Step 7: Draw Alignment Lines on the Fork Extensions

we'll use these makes as an alignment aid when we assembly the final forks.

Step 8: Use the Alignment Marks to Line Up the Forks


Step 9: Tack Weld Everything Together First


Step 10: Weld Forks


Step 11: Finished


Comments

author
wyldestyle (author)2014-04-09

talk about a lot of heat... from the comments... firstly i am not a big chopper fan but this is a really good mod. why? 1. its simple design and easy to do 2.it only modifies only the forks so you could return to the original setup once the thrill is gone. 3. gets a little more life out of something that potentially end up in the dump. 4. yes if we all respected safety and engineering laws we would have banned skateboards

author
oggryn (author)2014-02-27

Thankyou!!!

author
HammE (author)2013-05-30

I want to do this to my bike, but not weld it. I really can't weld, but I might post an Instructable on the no-weld version

author
Psychonautilus (author)2011-08-10

I did a double take on this... I thought at first that this was an instructable on how to "pimp your kids"... I missed the word ride. Lol, sorry, but I think that word is a poor choice for describing making something look cool. There's nothing cool about pimps.

author
jvetterick (author)2011-05-23

Check out THIS site for pimping your bike. Totally rad:

www.NiteSring.com

author
knexman123 (author)2010-02-18

haha lol i made me one of these and i sold it for 40 dollers on the side of the road lol

author
callmeshane (author)2008-02-15


I applaud the idea of doing cool stuff for your kids, friends and favourite squeeze.

But this kind of workmanship - including the lack of forethought is legally negligent.

Ok without getting into maths that I have mostly long forgotten, such as triangulation etc...

We shall go probably into incorrect vectors and simple comparisons.

Probably the more mathematically adept can clarify it all later.

Please do.

OK - why this alteration is a BAD idea.

The average bike (like so), with average quality welding, average strength and wall thickness tubing, under the weight of an average rider, doing average riding - will with a very high probability - give excellent service with NO structural failure.

This is why the average bike has labels on it such as "Rider weight must not exceed X Kg. - Do not use for stunt riding. Do not use for off road racing or sporting events" etc.

The whole unit is designed and built to a price and a purpose.

Ok now to implement what is left of my retarded mathematical skills.

The stock forks extend from the center of the head stem, at a rake of say 15*.

This means that if you draw a vertical line from the center point in the head stem, to the axle height, that the axle is about 150mm ahead of this head stem center.

This design, with the riders weight, bumps and pot holes and up and down gutters and the forces under braking.... means that the whole package holds together nicely.

It's strong, it steers well and gives reliable service.

Now my for what is left of my retarded maths.....

OK so by extending the forks so that the axle center is now about 700mm ahead of the center point in the head stem, this now gives a "LEVERAGE RATIO" of about 5 X that of the stock setup.

So with the stock bike, the center point is say 5 X the distance of the vertical line, to the axle.

Now if one were to put a 50kg force onto the stock handle bars... that would through the resultant forces put about a 10Kg force to push the front axle forward.

Because I don't know all the lengths and it's a long time since I qualified as an engineer and then moved into another trade...

Assuming that the fork is 1/2 a meter in length, his would give a TWISTING force of about 10Kg meters (actually about 5 newton meters of torque).

With the extended forks, extending the vertical distance from the center point of the head stem, horizontally along to the axle, now being about 5 X that of what they previously were, this means that with a 50Kg weight on the handle bars, one has about 50Kg of horizontal force, pulling or pushing the front axle AWAY from the bike frame.

Assuming the extended forks are about 1 meter in length, this force multiplies through the application of the extended forks, from the original to about 50 Nm or Newton Meter (or is that Kilo Newtons Kn?).

This feeds a stress from the axle, up the fork legs, into the head stem bearings, and the tubes of the frame, (50 / 5 =) about 1000% greater than the original bike "composition" was designed for.

Given that most engineers are not idiots, and that the people and companies avoid public liability suites (being sued) and getting done for criminal negligence; and they usually calculate in about a 500% safety factor... this means that if the bolt can take 1000Kg, before it begins to stretch and does not return to it’s original size when the load is released, that one has exceeded the UTS or Ultimate Tensile Strength.

So they toss in bolts that take 5000Kg.

You have the STATIC loads, then you have the shock loads of pot holes and gutters etc.. that greatly multiply and add to the weight or force being thrust down on the bike frame.

And worsera – you have cyclic stressing – the loading and unloading of stress in the parts.

Cyclic stress will seek out any weakness in any part or assembly and usually cause catastrophic or sudden failure in parts, that could have held 10X the load if it was a static load.

Then you have an AVERAGE frame with AVERAGE welds, and these can act as stress concentrators.

The welds and joints are taking loads that they were NEVER EVER designed to take, in ways that they were never ever designed to take them.

The tubes are apparently not the appropriate wall thickness, or quality for a high stress component.

You have changed the fork tubes to a SMALLER outside diameter, - this concentrates the stress of compression on the upside and tension on the underside of the tubes.

The tubes are set like a rat trap – one decent knock and they will buckle.

In your exhuberance to create a "fashion accessory”, what you really have created is a rolling death trap for your kid.

I was talking with a cop friend of mine one day... about motor cycle crashes, and in one scenario we discussed, the phrase she made went like this; “Landing in the middle of the road ain’t good, but it’s the car following behind you that is the bad thing – "Badooomp - Badoomp"

I am OK with tricked frames, but I suggest that you go and see some professional frame builders who do build "choppers" and ask for their opinions and expertise on how to make a GOOD strong and safe design.

While your on your way there, make an appointment to see an qualified engineer who works in public liability insurance - and ask for their opinion of your current design – and ask them is your modification marketable.

If I were you, I'd take them forks off the bike immediately, I'd check the head stem and welds for cracks or signs of stressing in the paint or metal, and then if the frame looked OK, I'd go buy a decent set of brand new ordinary forks and head stem bearings.

If the frame showed signs of distress, such as cracking or stretching of the paint or metal in the joints around the head stem etc.. I'd either get a NEW bike or a NEW frame.

author
minerug (author)callmeshane2009-07-13

...............................

author
jeaper99 (author)callmeshane2008-04-01

You are absolutely correct, but for one glitch. Let's just ballpark this at a factor of five for the sake of convenience. By extending the forks, he has created a lever that will exert five times the force on the headset. By extending the forks without modifying the frame, he has pushed the seat rearward to the point where there is reasonable concern that the front tire won't stay on the ground. In other words, the tire just kind of hangs there acting as ballast keeping the front end down. Trying to kill someone's fun in this way only makes you look smart in passing, but it won't hold up to scrutiny. Ask Jesse James to show you his engineering degree. Try it in person. His bikes roll down the highway with hundred cubic inch engines. It's about the feel dude. Ride on. Enjoy!

author
Rishnai (author)callmeshane2008-03-07

excellent point-- I see I'm not the only one that thought as much. Folks, when modifying something like this, always OVERengineer it. Brace the heck out of it. Put gussets on the inside of all angles and fishplates overlapping all the welds, same as if you're shortening or lengthening the frame on a car. As long as a competent person does the welding, it'll be as strong as you need it to be. Still, beware your forks bending. Take Shane's advice here, bud, inspect the heck out of that thing NOW (tell your kid you're improving it if he puts up a fight), inspect, reinforce (weld, don't bolt), and make sure your wheels are up to snuff. If it passes inspection and the wheels are still rolling true, I would say let the kid ride it again once the reinforcements are welded in.

author
Rishnai (author)2008-03-07

Also--I would be falling over backwards all the time on this one. You might want to consider putting a stretch in the frame behind the seat, moving your wheel back & lowering the center of gravity. This would probably also involve changing the rake of the headstock itself & a bunch more bracing. Basically, I like the way the lines flow on your design, but when I'm customizing a frame I prefer my bars to be closer to the ground. It really helps keep stuff more upright. Right now it's kind of like riding a bigwheel, which is cool, but it's not that cool when you lay it over, and.... if it was me I'd eat pavement a lot.

author
shamuslauer (author)2008-01-25

i used to do that but to add to the affect i put a small tire in the frunt

author
karsten.hain (author)2007-12-27

You see, these projects are great. When I was a kid we used to ride the ole radio flyer down a hill along the road and twist the handle at the last second to dump us all out of it to avoid going through a stop sign. I may have a few facial scars, but kids are supposed to have dangerous things to do, so I applaud this project.

author
MadMechanicMike (author)2007-09-25

wow, we been makin those around my town for years. now we actually chop the bikes, not just extend the forks. im making one now that has a riding mower wheel on the back.

author
AKinBK (author)2007-09-05

throw on a longer seat, a sissy bar, and a coat of paint.... and im stealing your kids bike!

author
Person486 (author)2007-08-24

If you just extend the forks these things get impossible to ride. You have to know how to, (or, like in my case, have a friend who knows how to), weld, and then you can just sawzall the frame apart from the handlebar mount, sawzall a lower angle into the frame, then weld the handlebar mount back on. Then you will have added a good rake to your bike, and you can make your forks as long as you want without having to ride it sitting back at a 90 degree angle staring up at the sky. Just dont go over big curbs... the forks and frame wil be set apart at such a wide angle underneath the bike that a jolt upward could split the welds if not done properly, and then your bike literally falls apart as you're riding it... (not good).

author
ajanderson77 (author)2006-12-18

dude that bike is gangster i want my dad to make my bike like that

author
longboarder (author)2006-10-19

Its easy enough to ensure the metal you put in is up to the job but there is now a considerably greater bending force at the lower side of the headstock. You have no idea how much of a safety margin the original manufacturer built into the forks to stem joint. What are the chances of your child snapping the forks at this point and rearranging his/her face or worse.

author
buildingteen (author)2006-09-28

I'm builing a chopper for my home coming parade except I'm using a lawn edger engine a little more complicated but that's the way I like to do it it's kind of a chalenge obsession. but I'm making mine more like g_freckleton's. Oh and where did you get the wide rear tire I can't find one.

author
orangeindiana (author)2006-05-13

Make sure that you have the stem tightened down VERY well once you reattach it. Place the wheel between your legs, swing the back of the bike up so the stem is vertical, and try twisting the handlebars from side to side. If you can move the handlebars while keeping the wheel still, then it's not tight enough. Also check the seat to make sure that it's at an angle where it won't come off. Finally, make sure your kid is wearing a helmet while riding this... it's not going to be the safest bike.

author
orangeindiana (author)2006-05-13

If your kid's bike has a reflector mount which strips the threads off the stem, it's time to throw away your kid's bike and get a new one -- it's poorly made and dangerous. Having worked in a bike shop, I can't think of any reputable manufacturer that would make a bike with such an odd flaw.

author
DeniziaDiGatti (author)2006-04-23

I made a chopper very similar, and yes, it was a real pain to ride. Sure, I looked cool, but it was a balancing act every moment, and don't think about hitting a curb! If I had it to do again, I would definitely change the geometry. Cheers to sCary, he is a pimp.

author
clint eastwood (author)2006-04-07

sweet bike

author
g_freckleton (author)2006-04-06

take a look at this guy http://knifeyland.blogspot.com/
he makes some really well finished chopped bikes, to add to stability and better weight distribution, i would suggest elongating the drivetrain, and rear triangle.

sadsd1_(5).jpg
author
sCary Cary (author)2006-01-31

We did a Burning Man bike workshop at my house and made a similar chopper. Changing to a smaller diameter front wheel helped alo with rideability and stability.

author
pennswoodsed (author)2006-01-08

Pimp? Having built a chopper 20" in 1973 or 74? this will be uncomfortable and difficult to ride.There is too litte weight on the front wheel.A nice revision would be to move the visual length above the steering neck.And to move the front axle frontwards by bending fork tubes.Please accept in spirit offered.I still have the lumps on the back of my head.we didn't wear helmets. Ed

author
neuralstatic (author)2006-01-03

what is the metal involved? are kids bikes alumninum or steel or something fancy?

author
Harald Hansen (author)2005-09-20

Not quite... What about a lick of paint to keep the rust at bay?

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