The DBT4 FWD Race Trike prototype. A custom build featuring David Bruce Trikes FWD technology. Blog from February 2013 to February 2017.
I took the DBT4 "Blue" prototype to the races in February 2013 with the single rear tube test frame with the offset wheel to test the trike and I did poorly. My fitness and the trike's weight with suspension is a little heavy too race I think. Plus the suspension setup didn't like the banking on the velodrome.
So during 2013 I was working on a conventional dual stay rear end with bolt on accessory and head rest mounts among other things and put that new rear frame design to test at the 2014 February races. I had learned some lessons and tried to adjust the trike to perform better but still not where I want it to be performance wise. To be honest, it seemed sluggish and didn't want to turn.
You can see some video taken at the HPRA races from 2013 and 2014: Event Videos
Well, after the last race in February 2014 I'm thinking there has to be something I'm missing on the FWD design so I went online and did more research on FWD handling and front geometry basics. Of course the available data is all about FWD cars, as there no current FWD recumbent tadpole trikes in production that have a internal differential and front suspension.
My focus was on quicker handling and a reduction in drag. I don't have a wind tunnel so I can't tell which areas need streamlining but common sense says the large suspension arms, the front frame and big bulky suspension plates add weight and drag. With the rear frame, who knows? Some folks say a tailbox is the best thing to reduce drag, but that changes the racing class. I want to stay in the stock class, so I went with a single tube design with offset wheel and aero shaped seat mount:
The idea being to leave the rear as clean as possible but still be safe and functional. I've made some wheel cover templates and just need to decide what material to use. I made a custom "training pack" which has a bent tube shaped to fit a frame bag, with a vertical plate to mount a head rest and KMX mud guard fender and red flashy light. The "training pack" can be removed for race events.
Close up of the seat mount. I have another aerofoil shaped fitting that I can use once the training pack is taken off. A lot of work to make these little bits and pieces!
The rear hub is a special narrow hub from BiTek and a 451 rim with ceramic hybrid bearings mounted on a custom made titanium axle. There is a brake mounting flange to mount a 140 or 160 rotor.
Ok, that was the easy part!
The race trike goal was to reduce drag and weight and have quick handling to keep up in the corners so the suspension was taken off, which meant a new front frame design. But I wanted to be able to use the rear frame with existing front frame units already built, so I had new smaller mounting flanges machined just for the race trike. Reducing drag meant using aerofoil shaped tubing, so I ordered three different sizes to use in different areas.
Using the two inch round diameter tubing for the single tube boom was a little heavy so I split the front boom tube into two pieces and machined a joiner section to mount the differential shell. The front tube part has a thinner wall and has a stub for the derailleur mast. My intent is just to use a single chainring, but left open the option to mount a front derailleur with a bolt on tube extension.
I'll be blunt: Working with aerofoil tubing is a bitch! More specifically HOLDING aerofoil tubing while machining is a nitemare as it's not square or round so it won't clamp precisely. I did my best using what I had as another goal was to use as much scrap material or parts and not spend too much! After all, I have no idea if this will work.
After a lot of cussing and screaming I got it jigged to weld. Oh and I had to totally redo the jig as well!
This picture below shows the large aerofoil tubing with the headset steering tubes and center join tube to mount the diff shell on the jig. This is a dedicated jig for the narrower track and cambered front wheels. I didn't really think about the diff shell too much and figured I'd bolt it on in case the frame failed. I got lucky! (more about that later!) I also changed the front wheel and bearing mounts to have a negative camber of 2.5 degrees, and that left no room for the rotors so I had to machine clearances. The bearing / brake mounts are not too aero, but I have these on hand. The tie rod is aero tubing and I have fittings on the end to thread in aluminum rod ends. The left one is left hand threaded and these rod ends are inch standard...everything thing else is metric.
After the welding in late July 2014:
The front derailleur mast has a longer tube that bolts on to allow a front changer. I'm trying to go clean so won't need it here in flat Florida. A couple more bare frame pictures:
It's hard to see and I know the jig and math said the front wheels have a negative camber of 2.5 degrees but damn it's hard to see. I used my machine shop cad to draw and position the angles and parts but...I keep thinking I flubbed somewhere! I changed the front wheels to a 406 size and have Velocity rims on light Halo front hubs. I modified the front drive bearing mounts to increase the gap between bearings for more stability and that meant machining the ujoints to fit a bearing. That was a lot of work! Like most things I had to make a "precision" sleeve jig to hold the ujoint to turn it.
Oh and to add to the fun I machined the new axles out of titanium as I went from .5 inch shaft diameter to 15mm shaft and 20mm bearings on the ujoint. If this thing survives after riding, I'll make a assembly video after paint to show all the bits and pieces.
A lot of stuff happened in August and I stopped doing most everything except eat, sleep and work. Depression sets in after I realize this trike keeps getting heavier every day, and the lack of response from the welder as I'm NOT done! ( changes in work and personal issues add to the depression) I realize I hate social media as that has become a clique for the young cool people and I never was cool, so if your not cool or famous no one wants to follow you or "friend" you. I'm trying to maintain my other business and the lack of social media skills is hurting there too...
Finally I get a call back from the welder, he's taken a new job and they have out of state training so he was in Arkansas for three weeks. Yea, I can get the final welding of the handle bars and diff shell done!
Oh wow I can sit on it and it didn't go POP!
I mentioned earlier I was using scrap, and the bent tubing for the handle bars was from earlier attempts on the rear frame accessory mounts for the other trike frames. Not a lot of adjustment in position. As you can see the "clean aero lines" gets cluttered as more stuff is added. The plan was to make little aero covers for the bulky stuff, but that might be for naught. (more later about that)
In my hurry, which is funny now as I haven't ridden since late July and it's October now, I failed to follow my drawing and so the mount for the rear derailleur is too close. I cut it off and use a new part to mount the diff shell. I mentioned above I got lucky on the diff shell by choosing to use bolts instead of welding...which I found out that I needed to unbolt the diff shell to have clearance to mount the drive shafts! If I had welded it, I would have to have removed the entire wheel unit to get the shaft into the ujoint! As I said, I got lucky.
Once again no response from my welder so I had to use someone else for a small weld. After that was done, I spent some time fitting it together and fine tuning the chainline. The Campy crank won't accept spacers for the large ring, so I had to machine the diff shell and the bearing holders to adjust the chainline for the 8 speed cog. I put "wiggle room" in both to allow custom fits. "Wiggle room" is a favorite term by Harris engineers in case parts don't fit right and with a little machining can be custom fitted with out re-making all the parts.
Friday October 03 2014 I did a short ride to test everything and nothing broke! Yeah! Saturday I checked all the bolts and tightened and loctited the drive line. The head sets were loose, fixed that, adjusted the toe again and of course had to make a bottle holder. Almost ready for a ride:
Dual brake lever on the right handle bar and the 8 speed bar shifter on the left for rear derailleur. I did fit a mirror on the left handlebar as I don't feel safe riding in public without a mirror. (not pictured)
To avoid hitting my heel on the derailleur I made the boom longer than the blue trike. (new DBT4 units have a longer boom tube) I added some links to the chain to allow a larger chainring if needed. The Campy is a 50 tooth and the race cluster is 12 to 23. No boots on the ujoints to test. I was thinking a plain rubber sleeve might work too. Titanium drive shafts and are not drilled yet. I milled flats for the set screws as I found the shafts slipping without a flat on Friday's quickie ride. An aero shield is planned to smooth the lines from the front boom to the diff shell.
I've started on some carbon fiber covers for the frame joining plates and put on a cover over the left side CV shell (left over from the orange trike, not pictured) As you can see, maybe FWD is not the best for "aero" as there is too much clutter up front. To be truly aero everything needs to be enclosed.
A lot of work! And maybe for nothing? Among my FWD research earlier this year I was reading about how FWD cars need less castor and toe in adjust should be either zero or a little out as the FWD tends to pull the wheels in. After the February 2014 races I took the blue trike apart to reset the suspension and found that somehow I had adjusted the castor to almost 12 degrees. The original weld jig was set for a 8 degree castor with rider weight. That 12 degrees is very heavy and likely one reason I couldn't turn on the road course with the Catrikes. The FWD wants to pull straight.
When I reassembled the blue trike I set the castor back to where it should be, near 8 degrees and man it came alive! Well then, I set the race trike castor very light and with the jigging problems machining the aerofoil tubing, the welded in castor is approx 4.5 to 5 degrees. So that is better than the 4 degrees planned. Seems like every time I measure it the number changes...
Anyway Saturday's ride report...The trike seems fast, I have no speedo yet, but the steering is OMG scary, it is extremely light and sensitive to any pressure on the handlebars. I was really scared to even attempt a fast corner. I'll have to ride it more to see the limits. I'll have to see about some sort of steering damper, maybe a simple return spring or maybe a rubber O ring on the headsets.
The weight thing is disappointing too, I'll know an accurate figure once I take it apart. I do know the rear section with the training pack is 11 pounds. The pack frame, fender, light and empty bag weighs 1 pound. I'm guessing 35 pounds total. I'll know later on this week.
And more... just went in the garage to look at it and the rear tire is flat. Great.
Oct 05th 2014 Well the flat was I guess, my fault as I found a aluminum chip in the tire. I patched the tube and added a tire liner. I had posted in BROL and a suggestion to add some castor was to make the rear wheel smaller and that tilts the headsets back a little. Well I don't want to build another wheel so I did something else: I disassembled the trike and bent the rear tube another 3 degrees.
I took all the steering stuff out and trimmed some fits and tightened everything again. I don't want to use the loctite until after paint. I reassembled the trike and went for a 3 mile lap around the neighborhood. All I can say is it's much better in the steering and not as sensitive on the handlebars. I was actually more comfortable. We'll do some more miles before we go out in public!
Nov 14th 2014 I'm expecting my write up in the Human Power News any day now! I did a few more rides and decided to take the trike apart for painting along with some parts for the DBT4's. So in a few days I'll have a nice shiny bright yellow trike to photograph!
Nov 29th 2014 After painting, comes the chore: chasing treads, sanding and filing to get things to fit!
Nov 29th 2014 As you can see, lots of shiny yellow parts! That last picture makes the front wheels look huge! They are standard 406 (20 inch) I even put decals on! (Note to self, wash hands first!) I went for a short ride ride around the house and man I'm so out of shape!!! I'll need to get a bell and speedo so I can see if this thing is even a little faster than the other trikes. The yellow is a little more lemony than I had wanted or I didn't really look at the chart, but I like it.
Dec 28th 2014 I bought an ICE head rest and modified the rails to fit. The seat contour needs some sort of neck rest at all angles. I went for short test ride after the paint and reassembly. First thing I noticed as I tried for some speed is I'm way under geared. I'll have to work on that, and two: The handling is still very light and after my ride I tightened the headsets more and will see how that does.
I ordered some larger chain rings to experiment with as I have to modify the bolt circle as the Campy Athena compact crank has four bolts at a common center (110mm) and one "special" offset slightly. They did this to insure quality shifting with OEM spec parts. I bought two cheap chainrings to test fit with a machined slot to allow it to work on the crank. A 54t and a 60t chainring which will provide a high "gear inches" of 83 and 92 compared to the current 76.8 gear inch.
I installed the 54t and machined a slot on one bolt hole so it will fit the Campy crank. After a recent ride, it does feel like the larger ring is matching the trike and myself a little better.
Training ride ready ( only on the flats and slight inclines!)
Home made wheel covers with .040" clear polycarbonate sheet below. I was gonna do a Knight's Templars cross with the red duck tape but didn't. I went with white paint on the outside as I plan on some decals and stickers. I don't know how the red stripe looks at speed, maybe the red blur will help catch a driver's eye? The plastic covers are not too noisy while riding.
The inside cover is painted black and clear shipping tape is used inside and out to seal the "pie cut". The inside in not painted and sanded. The tape seems very sticky to the unpainted plastic. Aluminum binding posts are used to hold it together with plastic spacers inside to add support.
Compared to a standard 700c rear wheel drive performance trike with it's 116 high gear, it's still under geared a lot. The racing classes don't separate the vehicles based on wheel size so a 20 inch drive wheel will be at a gear disadvantage.
Feb 07 2015 I needed some road miles in prep for the upcoming Catrike Rally and the group just happened to meet today on the WOT for the east side ride. The west side is more hilly and I don't have the hill gears installed...so anyway I went over and did some fast work with the faster guys and then later it became more of a social ride. I had the ride leader do a few short video clips:
A long day with the riding, stopping and lunch as I didn't get home until 5pm. Leaving the house at 8am you can see why I can't do this every weekend!
Feb 28 2015 I had some straight bars welded up to see if that would help slow down the steering. A test ride show they might help a little with the sensitivity, but I believe the steering arm leverage ratio is still very high.
Mar 21 2015 I took the new trike to the Withlacoochee Trail for the annual Clean Air Ride and tested the new handlebars and optimized front toe adjustment. They have a pro photographer on the trail to sell keepsakes photos and I'm always looking for photos of me on the FWD trikes!
June 14th 2015 Sorry I haven't posted in a while! Recent news is that I spent some time in April and May to disassemble the original Red prototype and modify it with the purpose of selling it. Over Memorial Day weekend and the following weeks I reassembled it! Pictures with all the details and updates are here: DBT3 Red Prototype for Sale!!
At the same time I was discouraged by a few things on the yellow Race trike and also took the opportunity to do some rework on that as well. One thing that bothered me was the left axle had some wobble and was creating some serious brake rub. The new bearing mount requires the ujoint to be machined for a bearing shoulder and the axle inserted into the ujoint. The problem is now I have to attempt to machine a axle with bearing tolerances and it takes a lot of time. This allows more of a gap between the bearings so the axle has more support. The farther apart the bearings the more stable the axle is, only I'm limited in spacing.
I am using titanium, so I ordered more stock and turned another axle with close attention to making sure the ends where as true as possible. Everything was fine until I drilled it! It appears the heat from drilling is warping the axle! But turning it again to cut off some excess material and make a taper appears to have reset it a little as it is useable now. So I used it and the wobble is reduced a lot.
I also tried to make the derailleur mount a little better, and the biggest thing I wanted to fix was the steering sensitivity to handle bar pressure. At a recent rally it was suggested to use some O rings under the rod ends to create more "stiction" and that seems to have done the trick!
While I had it apart I also noticed the ujoints were rusting under the powder coat and the inboard CV shells were starting to rust too. I did some research and found out how to dissemble the ujoints. Pretty simple, but you need to cut off a "rivet" and order new ones. I took these apart and got them chromed.
So hopefully no more rusting issues. I was toying with the idea of having a ujoint/shaft/axle machined up as one piece to eliminate wobble. I put the curved handle bars back on and added a short extension on each one and reassembled last week. Now to get back riding and test it!
Jan 24th 2016 I spent some time fixing my computer after it crashed an I believe all my new drawings since 2013 are gone! I've been dealing with family, health and estate issues and slowly seem to getting back to normal! I've been motivated to redo the shop/garage and have been thinking of new ideas!
Mar 27th 2016 Happy Easter! I was supposed to attend the March Clean Air Ride but weather forecast was doom and gloom so I spent the weekend machining parts for the alternate drive line test.
I've been wanting to see if I can eliminate the custom made differential and related parts for the drive line. I was curious about the dual drive ratchet system the UK upright racing trikes use so I bought a couple of inexpensive Samagaga "Easy Gear" units to experiment with. Samagaga makes complete drive lines for the "Adult Trikes" but they are big and heavy with proprietary splines shafts. One version of the "Easy Gear" used a hex drive, so damn I can make one of those! Hers some pics on my work so far!
The large ring is to adapt the new unit to fit inside my diff shell. Luckily the yellow race trike diff shell comes off the frame so I could mill in the inside as the Samagaga unit has a larger diameter.
The silver center part is complex to match the bores and outer races of the Samagaga parts and to stretch the unit to allow a bearing race. I did a lot of match drilling and eyeballing the recesses. The Samagaga units are designed to float between frame members, not to fit inside a shell.
I made another adapter for the non drive bearing side. Parts made for testing!
July 18th 2016 While I had the trike apart for the diff modification ( which did not work like I needed it too) I made a center steering joystick conversion to make it more comfortable to ride. The lower curved handles for the direst steer were hurting my arms and shoulders.
A bit rough and a little heavy but it works fine.
I also added the 60 tooth big ring with a 50 tooth smaller ring with a 12-26 8-speed cassette which is plenty for Florida flats. The larger ring will help bring the gear inches closer to a 700c diameter wheel.
The only problem is I have not been cleared for cardio work, still waiting results back from the doctor as I had some chest swelling and pressure in late June for a few days in a row. So not being able to ride has been frustrating.
February 09 2017 Since my cardio procedures in August, I've changed my diet, and exercising more with weekdays rides on a Trek MTB. The time commitment to break down a trike and travel to a recumbent safe area on a weekday is too much, so I can ride out of the garage with the MTB and be ina MTB trail area only a few miles from home. Still not happy with the performance of the race trike and will tweak it some more! No recent or updated pics! I'll redo the steering column and add a curve to clear the crotch area some more!
If you recall, one of my goals for the race trike build was to determine if the dual shaft FWD driveline takes more watts ( power effort) to get a certain rpm and speed compared to a rear drive performance trike. I can't measure that until I get a power meter that will cross drive platforms.
Dave Bruce, February 2017
Please contact Dave: firstname.lastname@example.org
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