©2019 by MBD - Mini Bike Drags. Proudly created with Wix.com

May 13

My build: Here's a quick look at my bike. It went together well enough, but it took a bit of figuring to made things work.



I'm lucky to have a great trike builder here in Raton, who has a tubing bender for the 1" DOM tube I made the frame with. He is JP Rodman (look him up online to see what he builds) & does some incredible trikes. Here's the frame in it's rough starting stage. I'm not a great welder, it's been 40 years since I did any metal work, so I'm a bit rusty. It's still rewarding to have some progress. Having a shop to work in makes a huge difference for a build, having some basic tools helps as well.


Basic frame

The front end is made with 7/8" DOM & seems to be plenty strong. It's a bit stiff on bumps, since I'm used to riding an old Baja Warrior with front suspension & softer tires.


10" Michelin tire, 5/8" grade 8 axle

The rear axle is a 1" X 16" steel type with a 1/4" keyway cut along one side, so it's a live axle. It's a standard setup for karting, but hubs, tires & other parts can be a problem at times. I'm running a dual piston hydraulic unit with a steel hub from GoPowerSports (MB200-2) which is pretty good for braking. I use a cross-drilled rotor & it has good stopping power so far. The rear sprocket on the live axle is a 48 tooth steel one for 420 chain.


For now, the rear tire is a 19" Kenda 572 Road Go with pretty heavy tread. It's certified in Europe for 43 MPH, but I will be turning it a bit faster than that. The rim is an aluminum Douglas which is 8" in diameter. When I set up the axle, it didn't balance well at all. The tire kept turning until it stopped at the same place each time. I had to use adhesive weights along both sides of the rim to finally get it balanced correctly. It spins well now, but again, I need to keep an eye on it in the future.


Kenda 572 Road Go 19X7-8 tire

PMR jackshaft on the output side with #35 primary drive & 420 secondary to the rear wheel. I need a better clutch!

May 16

There are a couple of things I would have done differently, but as this is a first time build from the ground up, I'm satisfied with it (for now...). One thing which was a real PITA on the build was figuring out the brake setup. The MB200-2 hydraulic reservoir has a lot of stopping power & works flawlessly, but due to my axle location & the mounting bracket location on the frame, I didn't have much room for the brake caliper. I ended up having to mount the caliper on a plate, then make another plate to fasten to the frame. It was difficult set all of it up, align it properly, drill & tap the plates, then weld it to the frame. It took more time than it should have.


Since the brackets for the axle were already located, I had to work around them. If I made one plate to mount the caliper to the frame, there wasn't room for the bolts to go in place on the bracket. That's why I had to make 2 plates instead of just one. It was more work, more weight & more bolts, but it was OK in the end.

Clamping the 2nd plate prior to welding, checking the fit & alignment


Rear view showing all the stuff in place

As you can see, it's 10# of $hit in a 5# bag, but it works. I had originally ordered a 14" axle, but once all the parts arrived, there just wasn't room for the tire, sprocket, disc, hubs, caliper & bearings. Ah well, live & learn.


Another thing I should have done, lift the frame another inch or two & then locate the foot pegs on top of the frame rails, not sticking straight out from them. I don't have much room for them when going into a turn. Fortunately, I used pegs which will flip up when the bike lays over, instead of solid mounts which would dig into the pavement and spin the bike like a top on a turn. It takes a bit of getting used to on corners, I hate that grinding feel of the pavement on my foot, but it's a straight line bike as designed, so turning isn't really a big deal (right!).


Basic parts

The pegs were ordered from ebay & the plates were just fabbed in the shop. One tool I use more than I though I would for welding is a knife grinder & coarse belt which I made for working on blade steel. It's pretty handy for shaping parts, grinding welds & finishing stuff when you weld like I do...


Grinder for 2" X 72" belts, coarse for the welding stuff, fine for blades

Shaping things, grinding down the welds & cleaning lines is faster & easier than using the 4 1/2" Makita, at least on the small stuff. On big stuff, there's nothing like a hand-held grinder.


Ready for welds


Finished, should have welded this on top of the frame...

Here's one of the blades from the grinder. D2 steel with an ironwood grip, tempered to 61, so it's a booger to sharpen, but holds an edge pretty well. This is my design on the blade, lifted (loosely) from a Spyderco Mule shape & changed a bit.


Sharp & cuts well, hard to make & could be a bit better in fit & finish, but it cuts well enough


May 18

One of the things I've had trouble finding is a good rear tire which is actually rated for higher speeds. The Kenda Road Go rear tire in place now is not rated for road use (in Europe only not a DOT rated tire here in the states), Road Go at 43 mph? Finding a rated tire which will spin up to 100 mph is tough. At some point I may want to run on a longer course for a top speed, like a measured mile or flying mile. The main problem is tires, there is a pretty tough tech inspection since the sanctioned events don't want bad PR with people smeared across the pavement from blown tires at speed.


I've been talking with an aircraft tire sales rep in California a bit & may have found a solution. There are some 650 8-8 tires available for general aviation use, like those used on a Cessna or Piper. As is always the case, there's a good side & a bad side to using them. The good side is that they're rated to 120 mph, it says so right on the side wall of the tire for the tech inspection guys, that's good! They're 19.85" tall, mount on an 8" rim and are very similar to the Kenda, just a bit narrower on a 6" rim. The bad side is weight & cost. They're pretty spendy at $200-$300 each, depending on the type & ply design from Goodyear or Michelin (some are running Kevlar belts). There's also a weight penalty with them, they're a beefy 12-14 pounds per tire. They're strong-like-buffalo, since each tire is rated at between 2300 & 3150 pounds for those hard landings. My skinny butt & the bike aren't quite that heavy yet.


Trying to stretch these things on an aluminum Douglas rim might be a challenge as well. It's bad enough with the Kenda or Jr. dragster slicks, but the 8 ply tires would be nearly impossible to get over the edge without destroying the rim, or at least bending it pretty badly. I'm still thinking about them & trying to decide if it's worth the cost & effort, but it's simmering on the back burner for now.

This is a Condor tire, similar to a Goodyear or Michelin & cheaper by a few dollars. Same speed & load rating so they would run OK too.

Jun 1

Changed the header brace to another bolt (lower on the head) & chopped off about 4" of length. It broke the head, so I've put it back together with a shorter header & new bracket mount.


Jun 24

Added a spun aluminum tank from Sandstorm. Had a little trouble with splashing around the cap when it was full & running up through 4000 rpm. Added a vent with a drilled out zerk fitting & hose. It's a lot better now. I was getting a bunch of fuel spilled & thrown back on my balls as it was. Fortunately, I didn't catch fire down there, so better now that it's fixed. Always something, unintended consequences...

Zerk, tubing & zip tie