Cuda-W front sub frame part 3

Cuda-W front subframe III

By Warren Beauchamp

Aside from a chain-derailment during the 100 lap race in Northbrook, the Cuda-W performed well in 2007. At the 2007 Hawkeye downs races, conditions were good and the track was plenty big enough to be safe at the near 40MPH speeds I ran at, but I was still unable to beat Dennis Grelk in my old Barracuda 'liner. He was consistently about 1/2 lap ahead of me.  Curses!

So 2008 is here and I need to go faster this year. How do I do it?

Training in the 'liner position.
The streamliner is much more upright than the Nocom which I normally train on, so I really need to train in that position to be competitive.

Better aerodynamics.
Hmm. All I can do there is add the little door for the landing gear, finish fairing in the rear wheel disk, and see if I can close in the front wheel a little. But not too much! I need some air in that thing!

Improve the drivetrain efficiency.
While the Rohloff hub works nicely, offers a very wide range of gearing, and makes for a very simple drivetrain, I can't help but think I am losing a bunch of precious watts making all those little tiny gears spin around. I will build a new derailleur based drivetrain to replace the trusty Rohloff.

It looks like if I use the 85T chainring that Dennis made for me at the high speed events, and the 67T chainring I am using now at the HPRA events, in conjunction with step up gearing and a BMX hub, I will have a versatile and high efficiency drivetrain.

I found this very interesting article from IHPVA Human Power #52, detailing testing of internal hubs vs a standard 27 speed derailleur system.

Basically it says that at 200 watts, the derailleur system is on the average 2% more efficient than the Rohloff 14 speed hub. 2% of 200 watts is 4 watts, which doesn't seem like much.


When you look at the Rohloff hub efficiency for each of the gears, you can see that the upper 3 gears were only about 89% efficient. I spend all my time in those gears while blasting around the track!

The top 3 gears of the derailleur system in this graph seem to be more variable in efficiency than I can believe, so I'm going to arbitrarily throw out the 90% data point and say that that system is around 93.5% efficient for top gears on the derailleur system.

This gives 4.5% difference in efficiency. I can work with that!

4.5% of 200 watts is 9 watts, which still doesn't seem like much, but...

According to the HPV speed simulator, the Cuda-W goes 39.942 MPH with 200 watts, and goes 40.77   MPH with 209 watts. That's .828 MPH, which also doesn't seem like much until you realize that during a 1 hour time trial on the Hawkeye downs track, that makes me 2 laps faster! That may be all I need!

This 2% efficiency gain may be further mitigated by the multi-chain step up drive needed to construct the derailleur gearing system. Because of this I'm going to keep the old drive system around, just in case the new one doesn't seem any faster.

According to the gear inch calculator:

Battle Mountain drivetrain
85T chainring + 11T -> 30T step up gearing + 18T BMX hub gear  = 68MPH at 100RPM with a 406mm (18") Stelvio drive tire (75MPH at 110RPM).

HPRA drivetrain
Changing to the to the 67T chainring gets me to a speed of 54MPH at 100RPM. That's a bit high for HPRA racing. I will need to change the intermediary gearing as well. Looks like I will be using a custom mid-drive cluster to allow for track specific gearing changes. I always was a gearhead...
67T chainring + 11T -> 24T step up gearing + 18T BMX hub gear  = 39MPH at 90RPM with a 406mm (18") Stelvio drive tire (47MPH at 110RPM). Perfect.


I brazed up the fork for the narrowed hub with BMX freewheel. This makes a nice narrow package.
I temporarily attached  a cog set and derailleur to the top of the Cuda-W subframe. This position would allow the large cog to be used to drive the BMX Freewheel.

The derailleur is attached directly to the axle shaft. The derailleur bolt is the same size as the axle shaft, so a long axle nut attaches them nicely.

Unfortunately, my knee hits the derailleur. I tried everything I could to work around the issue, but apparently this type of drive only works if you have short legs.

Unless the many fine people that have suggested possible solutions to this dilemma can figure out a workaround, it will be back to the old drivetrain.

Along those lines, I changed the old skate wheel idler to the larger NoCom Idler. That should be slightly more efficient plus it will give me tire clearance so I can use the 85T Grelk chain ring.

Larry Lem supplied suggested moving the mid drive forward as far as possible. This way the chain ring drives a small cog on the mid-drive, with no idlers needed due to the close proximity. Also My knee won't hit it.  On the hub side of the mid-drive, the chain would pass through several idlers as well as the derailleur guides. I still think this would be more efficient than the Rohlhoff, especially while coasting which seems to be particularly draggy. Rube Goldberg, here I come.
After some thinking and drawing  I noticed that the derailleur cluster cannot be mounted that close to the chainring unless I invent a new power side derailleur for the cluster. Because I don't really want to do that, it's back to the drawing board.

Eric Ball suggested I try the Dahon Neos (Suntour) derailleur. It mounts forward of the axle, routes the cable forward, and is very low profile. I ordered one from the LBS.

Here's the latest drivetrain mockup. After some pedaling with the drivetrain screwed to my workbench, it appears that this configuration may work with the low profile derailleur.

I will need to raise the cluster about another 1/2", and be sure to add a knee guard to prevent accidental bumps into the cluster from getting bloody when getting bounced around at speed. I'm hoping to be able to add the mount for the cluster to the existing frame.

I picked up the Neos derailleur and though nothing fancy, it looked good. Over the weekend I mounted the derailleur on the mocked up drive-train, and raised the cassette about a half inch. My knee now clears the cluster, and it appears it will only rub on the derailleur when my knee gets bounced to the inside during a wind buffet or while flailing. It should be a soft hit on a rounded portion of the derailleur. I cut a couple parts for the actual mid-drive mount. Initially  Because the chain has to flex over an inch to the outside when I'm in the top gears, I need to make some different spacers for the chain-ring, to ensure it is mounted as far out toward the crank as possible.
Here's the new derailleur mount, ready for brazing, but it's too cold outside today for brazing, so instead I'm typing away on the computer.

It stands about 1.5" above the top frame tube. I mount this assembly to the frame temporarily, then mount the sub-frame back into the 'liner and do some more testing before I make it permanent. I don't want to burn any bridges and will keep the capability of using the old drive-train on the same sub-frame. Once I have determined it's all good, I'll slather it in epoxy and CF.

Here's the wide range cluster I will be using, with the Neos derailleur mounted to the axle bolt. The silver tab below the mounting bolt will be connected to an aluminum strap to keep the derailleur in place and provide a guard to keep my knee out of the gears.
Work has stalled on the new Cuda-W drivetrain. The chain angle between the chainring and the cog set is so severe that when I'm in the smaller gears the chain rubs the derailleur cage on the non-power side, and rubs the chainring guard on the power side. In addition to that, the drive chain that goes to the wheel is so close to the frame that it will rub with the slightest turn. Because of this I have decided I will need to create a crossover drivetrain where the cogset is mounted to a narrow BB, which transfers the power to a cog on the left side of the bike, then down to a lefty drive on the wheel. Because I don't have time to do all that now, I just repainted the old drivetrain and put it back together with the Rohloff hub.
I have finally decided to restart this project. I'm building a new subframe that will be just for the derailleur system. In spring 2010 I ovalized some 1.625"x.049 wall tubing for the main tube, and I built and brazed in the "T" bracket that attaches the subframe to the front bulkhead.

Last weekend I took measurements from the old drivetrain and cut the head tube holes in the main tube. This picture shows the tube being cut in the jig.

Here's the drivetrain mocked up on the new main tube. Of course I ran out of gas for my torch so I could not braze any of it together, but I got lots of parts cut out and ready to go.
Here's the two sections of the main frame that will be brazed to the head tube. The mitering jig does a nice job.
Here's an image of the Neos derailleur on a Dahon folder that shows how it mounts forward of the dropout rather that behind and below like a standard unit.
I had a good day of brazing, and got the main components of the new drivetrain spot brazed together. After some mucking about I determined that due to chain alignment I could only use about 4 gears.  Now I need to find more chain and then run it through the gears several times to ensure it runs properly. If these are not enough gears I may look into adding another gear to the hub, which currently uses a BMX freewheel.
After another day of tweaking, I now have it to the point where it shifts properly through all 4 gears without derailing. I may even be able to add a 5th gear. I also added the shock mount, so now I can mount it in the 'liner and see if my knee bashes the derailleur. If my knee hits I can raise the whole mid-drive assembly up a bit.

I put the drivetrain in the 'liner and spun it up. Miraculously, my knee (barely) clears the bulk of the derailleur, even when I'm flailing. The idler cage is also enough inboard that it's out of the way. I can still hit it if I try, but it's a soft hit so I think it's a go to finish brazing this thing up.

I was a cold day to be outside brazing, and the quality of the beads certainly suffered, but now I have a brake mount for the new drivetrain!
Here's the current drivetrain (3A). The brake is mounted. Next I need to braze on the chainwheel chain keeper, a spring loaded idler for the drive side chain, and the bracket for the lateral movement inhibitor arm.
I had another productive day of work on the drivetrain. It now has chain management and a power side idler. It's actually time to bolt it into the 'liner and see how it works around the block. I still need to see if it's possible to cram another gear it there to being it up to an amazing five gears!

Currently it's set up for 70MPH top end, so it needs to be de-tuned it a bit for 40MPH top end if I want to have any chance of climbing the hill at the Waterford Hills race track in Michigan.

I found a 15T BMX cog to replace the 18T. This will help with the top end speeds. With the 85T chainring, it's good for 82MPH at 100RPM cadance.
Probably a bit high. With the 67T ring I can still go 65 MPH.

HPRA - 67T chainring -> 28T -> 24T -> 18T = 15 MPH
HPRA - 67T chainring -> 11T -> 24T -> 18T = 43 MPH

WHPSC - 85T chainring -> 11T -> 24T -> 15T = 17 = 66 MPH
WHPSC - 85T chainring -> 11T -> 28T -> 15T = 17 = 77 MPH

I installed the new drivetrain into the streamliner. It was difficult to do. I had to remove the wheel and then it was tough to install it. Apparently I did not build it straight as the wheel was not in the middle of the wheel hole. I am disheartened and have no time to work on the streamliner now. I will need to cut it apart and fix the head tube angle. I have abandoned drivetrain 3A for a while...


After racing the Cuda-W a few times with a new fork in the old Rohloff drivetrain, I have decided to start work on rebuilding the new drivetrain.

As seen in this picture, which overlays the drivetrain3 onto drivetrain2, I really messed up. The headtube angle is about 15 degrees off and the BB is mounted an inch or two farther back than the old one.

I'll need to cut the headtube and BB out of the subframe and  remount them. Arg.

Aside from that, this time I will build a crossover style drivetrain, and use a BMX left hand drive hub. This will allow me to have a couple more gears, and hopefully better efficiency.

I have cut apart the V3A drivetrain to rebuild it again. shown here are the major components, including the lefty drive wheel.

Now I just need some quality time to build a jig I can use to ensure that this new V3B drivetrain has the same geometry as the existing one.

After building a jig, spending much time grinding, tack brazing, and doing several test fits, I once again have something resembling a front subframe. The geometry is now the same as my old Rohloff subframe.

I rebuilt the drive wheel with a Profile Racing MINI BMX CASSETTE REAR LHD hub with a 10T cog.

The next step is to build the crossover drivetrain. I will be using a 5 speed freewheel 14 - 24 hub for the shifted gears.

Here I am a year later and I have done very little with the new drivetrain. I have been racing the 'liner with the old drivetrain which has been working well.

Recently I have begun working on it again. One issue was that because of the fork rake the chain drive would rub on the back of the fork. Also the wheel was too far forward in the fairing's wheel slot. To fix that I took the rake out of the fork by heating the fork with the torch and bending it.

I think I have critical mass on the parts for the crossover drivetrain. The last part of the puzzle was the left side drive gear, which needed to attach to the 2" square taper BB. I cut the arm off of an old 39T steel BMX crank. A bit heavy but it should work well.

I put the new subframe back in the 'liner again to check clearances to my legs and I think it will work well mounted right to the top of the frame tube just in front of the head tube. A small miracle.

The drivetrain calculator says I need a 13T cog on the hub to replace the 10T cog. Profile wants big $$$ for these parts. Your donation dollars at work.

Here are the crossover drive parts. The freewheel hub has a Wianecki freewheel to square taper adaptor mounted in it.

Latest gearing: 39T chainring -> 14T gear on crank side of  intermediary drive -> 39T on hub side of  intermediary drive -> 13T on lefty BMX hub at 90RPM cranks = 40 MPH.

Interestingly, with this gearing the number of teeth on the front chainring corresponds almost exactly to the bike speed at 90 RPM.

Here's the crossover drive assembled.


I built a bracket to clamp the crossover bearings, and after many fits and starts and keepers and making of small pieces of metal out of large ones, it's tacked in place in the right place and is straight.

No 39T chainring to be found in the box-o-chainrings, but I found a 36T chainring and see now I need different spider bolt spacers to prevent the chain from catching on the crank arm.

Next step is to build the derailleur bracket.

I ended up just using washers to space the chainring properly, and the chainline has clearance in all 5 gears. A couple days of above freezing temperatures allowed me to finish the steel derailleur hanger, and it is shifting great, except for the high gear which is most outboard. I will need to tweak the derailleur cage a bit to allow the chain to get onto the bottom idler without skipping to fix that. I installed the 13T cog on the Profile left drive cassette and the chainline on the left looks good. I just need to install an idler and some chain keepers to make the drivetrain bulletproof.

Drivetrain 3B is the first time I have gotten this far with a super-narrow derailleur based Cuda-W drivetrain without abandoning it due to insurmountable problems. Happy days!

Here's the remote steering linkage. It's made fronm the shaft of a carbon fiber golf club that I picked up at a thrift store for $4, and some Aurora rod end bearings. The threaded bolt part of the rod end bearing is held in the hollow shaft with JB-Weld.

I also finished the brakes and handlebars, worked the bugs out of the shifting, and finished the secondary chain idler, so it's getting close to done.

Yes, that's my workbench. I cleaned it shortly after this picture was taken, and now it's already strewn with tools and detritus again. A clean workbench is an unused workbench...

I took the drivetrain apart and brazed all the joints that were tack-brazed previously, then sprayed a coat of gloss black onto the frame. It's amazing how much better it looks with a coat of paint (not that anyone will ever see it once it is hidden inside the Cuda-W fairing).

I re-assembled the drivetrain and am pretty close to installing it back in the 'liner for an actual test ride. The chain wants to skip off of the inside of the cog on the wheel hub under adverse conditions. A wheel disk will fix that, but I may have to kludge something so I can try it out at the Waterford races this weekend. 

Pictured - Left side of new drivetrain

I ran out of time so I put the old drivetrain back in the 'liner.

Pictured - Right side of new drivetrain.

During the 2014 Michigan races I got a flat tire in the streamliner during the Sunday "short" race. In that race there's a very tight corner. It's the crash corner. I had a sudden flat in that corner and was able to keep the bike upright long enough to dump it in the grass. Today I looked for debris in the tube and didn't find any, then replaced the tube and pumped it up. At about 100 PSI it went "bang". Took the tube out again and inspected it and it looked like maybe it was defective. Repeated tube replacement and this time it held. For a while. While I was working on the new drivetrain it blew out again. This time I found a slit in the sidewall down by the bead. Scratch 3 tubes and a vintage Stelvio tire...
I finally put the new drivetrain in the Cuda-W and rode it up and down the block until the chain fell off. It's hard to get started with only 5 speeds! I decided that the way to fix the chain issue was to add a wheel disk, which will keep the chain from falling off toward the inside.

I dug the old foam wheel disk molds out of the attic and found one that had the right offset dish. Here it is after I used some drywall compound to fix a scrape and fill in the joint where the foam was cut to make it cone-shaped. After that dried I spent several days coating the foam mold in several coats of green water soluble mold release.

After the mold release agent dried, I laid in 2 layers of fiberglass, coating each in epoxy. Here's the fiberglass wheel disk is the mold after I trimmed the excess and cut the hole in the middle.
After washing the water soluble mold release off of the fiberglass and giving it a quick sanding, I mounted it to the wheel and did some spin testing. Looks good and definitely keeps the chain on better. Paint is next. On the other side of the wheel will go a wheel disk half from the old 20/20 Barracuda frame rear wheel that had the right dish.
Painted the wheel disk yellow and mounted both sides. Not perfect but it should make it though the Northbrook races. Chain seems to be staying on, I went and bought a BMX chain thinking that it would stay on better than the derailleur chain but it was worse. Go figure. Next step is to reinstall the new drivetrain into the 'liner and drive it around a little.

Today was a major milestone. I reinstalled the new drivetrain and rode it up and down the block with the canopy off. The chain wasn't popping off of the hub cog anymore, now it was popping off of the upper chainring. I took off the upper chainring and reshaped the teeth a bit to prevent that, then back out on the road. Success at last!

I felt confident in the bike enough for higher speeds, so I rode the 'liner to a faster albeit more heavily trafficked road. I had to ride it up a largish hill to get there, which was tough with the lack of low gearing. A roadie dude passed me on the way up and astutely ignored me. After sitting at a light for a while he took off and I slowly cranked it up. About half a mile down the road I blew by him like he was standing still. I was able to get it up to high speed on the way back (slight down hill) but no speedo so I don't know how fast I was going. I'll have to take it along next time to see if the bike feels right at 36 - 40 MPH.

No chain loss, no major rubbing, and it felt pretty responsive. Better than the old Rohloff drivetrain? Dunno yet. When I crank the drivetrain by hand it does spin much easier than the Rohloff drivetrain. We will see at Northbrook!

Cuda subframe3 did make it through the Northbrook races, but not without issues.

After about 20 minutes the drivetrain had something rubbing, It was making interesting noises that Garrie Hill said sounded like Anakin's pod racer. I slowed down a bit to make sure I finished the race. Then the old tape holding my canopy on got melty in the sun and came loose. Eventually the canopy blew off onto the track. That's when I really slowed down.

Tucker (Northbrook,IL) 100 lap race video - 12 minutes of thrills, spills and high speed action taken from the back of my streamliner.

The other thing is the the nose is higher with this drivetrain. I don't think that is good from an aerodynamics standpoint.

I do not have a Power Tap that works with the streamliner, but I was wearing my heart rate strap and I do have a pretty good idea of how my wattage correlates to HR now, so looking at the Garmin data for the race I can say I started out at about 250 watts, then backed off to about 180 for about 15 minutes. Race pace for me is about 172 BPM.

In the graph you can see when the rubbing started and my heart rate went up, then down, then up again as I tried to figure out what was rubbing and if it was going to make me crash and burn. I was cranking and my speed wasn't increasing so I backed way off. You can see where my speed dropped off more with about 10 minutes to go when the canopy blew off. My HR says I was loafing then.

After taking the drivetrain apart, I could clearly see that the secondary chain and chainring were rubbing on the frame and headset. Also I found that the bolts holding the crossover drive in place were not tight, which allowed it to shift over. Tolerances are very close. I tightened the bolts and added a pop can shim to the BB to space it out a few millimeters.

I will take both the old and the new drivetrain to BM. I will make a spacer to replace the shock to lower the new drivetrain as the BM road is very smooth so the shock should not be needed.

I made a shorter non springy replacement for the front subframe shock to lower the front end. The bike seems to be level now. No shock absorber is needed for Battle Mountain.

For Battle Mountain this year I will move the 63T chainring from the old drivetrain to the new one. With that chainring the speed at 90 RPM will be 67 MPH. It should be perfect for a 70MPH top speed (I can dream, right?). I'm going to take the old drivetrain too in case the new one has problems. With the 80T chainring it will max out at 64.3 MPH at 110 RPM, which coincidentally is close to my max speed from my last Battle Mountain in 2008.

Stuff to do before BM2014
- train on the Cuda-W trainer bike
- make a new front wheel fairing
- sand and repaint the body
- test ride
- install big chainrings.



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