This BMW Chopper build has been a wild ride, it has been over a year since I unboxed a brand new BMW R Nine T Racer and removed the heart of it for this project. BMW’s support was instrumental in making this project a reality, but don’t be fooled, this is still a budget operation. From the very beginning I had a good understanding of BMW’s heritage, I grew up on the back of one with my dad being a big advocate for the German manufacturer.
Wheels are everything for me, in the beginning this build was meant to be pretty simple, then the invite for the Born Free Show arrived in my inbox and everything went into hyper mode. For over a year I had spent a lot of time thinking about the wheelset, I had Matt (an up and coming Engineer) who was helping me out draw up a snowflake front wheel, he spent a lot of hours perfecting the design for the 5th axis machining process to hog it out of a solid billet of Aluminum. The design was exceptional but the intricacies proved a real nightmare when it came to the proposition of machining. It was estimated that a 5th axis Milling Machine (youtube that for hours of entertainment) would spend nearly 30 hours in two setup stages on each wheel alone. That combined with a $600 billet piece of aluminium and a pre removal process of material on the lathe would cost me around $12,000 for a pair of wheels. Even if I was to be able to afford to do it I had no promises that it was going to turn out ok. So I figured maybe I could get a blank forged in China and then machine it here to remove some cost, still this was to cost around the same amount after shipping and again I couldn’t control the process…… So I needed to think about a few things and I spent months doing so.
I began to think about all my options and continued to gain inspirations from others who had been in this position, being a keen BMX’er I remembered something about the MotoMag and thought I’d dig into that a little more. I contacted Joel from Dsgn.co who was drawing and rendering some insane 3d chopper stuff, I took some measurements and sketched some designs, he simplified a few things and sent me some renders to look at….. I spent a lot of time looking at these renders, I couldn’t help but think about the possibility of fabricating these.
The more I thought about it the crazier I got about the idea, I had finished the TIG welding course (which you can subscribe and learn here) and knew how to minimise the heat effects that could spell disaster if not controlled. I had Matt draw up the wheel in CAD, we sent the rear hub design to a local CNC engineering shop to make it out of stainless steel, the spoke design to the laser cutter and the result is what you see above. Some small changes were needed to make everything fit perfectly and I machined the front hub to suit these.
After hand polishing the spokes with a file and some scotchbrite I took a deep breath and decided to make all of these bits one. Believe me its not easy making it all uniform but the precision of Matts design and the laser cutting accuracy certainly helped.
I decided to slot everything together and get an idea for the finished product so that I could make alterations to my design if needed.
I toyed with the idea of the spokes creating a dished effect, it would look great but the shift from the asymetrical design scared me and once I went this direction I would never be able to go back.
Setup on the aluminum uprights I completely fusion welded (no filler material) all internal spokes 20mm at a time, allowing them to cool between sessions. With heat the spokes would grow individually and tighten up on the outer rim, once cooled the outer rim would be completely loose, stainless steel has very low thermal conductivity and grows rapidly in the heated zone, this is different to higher conductivity metals such as aluminum with quick heat spread that evens out the movement in a wider zone. It was this reason I wanted to make the entire spoked structure and then once complete weld it to the outer rim. This ensured the spokes were all normalized and not fighting the rim, the last process was welding them to the rim on the truing stand ensuring they were true to each other and then the smaller webs were added to finish things up.
With the front tyre now fitted up (Firestone Clincher 28×3 slick on the 22 inch rim) it was time to move onto the rear, but I couldn’t stop looking at the front, I vowed that I would not fit the front wheel till the rear was complete to get the full effect.
With the spoke structure complete on the rear I could break the tacks to normalize the spokes and true the rim before welding.
A dial indicator is perfect for this and I had both wheels within 1mm, keep in mind that these outer rims are fabricated from sheetmetal so they were naturally around .8mm out anyway.
With the rear complete I was blown away, in the beginning I was going to run an old rear drum brake drive system but after building the motor components for performance I deemed it to weak and reverted back to the stock R Nine T drive unit. This meant a 5 stud rear wheel and subsequently a 5 spoke design. With the 22 inch front and 18 inch rear I knew the proportions would be just right.
With the rim complete and true I waited for it to cool and fitted up my M&H Racemaster rear slick, I had this leftover from my Landspeed Record bike as I never used it due to a lack of speed ratings on it. I couldn’t wait to get this tyre on. (Oh and I am also running one on my Triumph drag bike I built)
With the tyre on and pumped up I could go ahead and fit both wheels to the bike.
With the biggest part of the puzzle complete I stood back and took in the sight that was a complete motorcycle. I was a little overwhelmed, I put my tools away and hung up the leads on the welder, this bikes been a massive job, none of the work would be worth it if I didn’t feel butterflies in my stomach when I complete a job such as these wheels, the magnitude of effort and thought that I have put into these two components alone overshadows the whole bike.
Remember the staggering cost of those 5th axis CNC Rims I spoke about in the beginning of this post? Well these cost me just under $1,000 in materials, hours wise I probably spent a good 30 hours broken up into many different sessions to allow for cooling, I found the time to do it because I believed in the process and the outcome, would I ever do it again? Probably not until I get that burning passion to produce something this unique again.
But the bike is a work of art too and together they complete the picture that I had in my mind years ago, I have never worked harder and been more focused than right now. The next post will be the completed machine, hold tight it will be a wild ride.
Thanks for reading, Nigel.