Mk III

Frame

     Here's the 3D rendering of it using 3D Studio Max.  Nice thing about basic trike design is it's very easy to make it look almost identical, plus the scaled sizes of all the trike parts makes the measurements, of the actual metal, a breeze.

     This frame is the same as the previous one in that it's made of 1" mild steel box tube with 1/16" walls.  I tried to simplify the design by making the 2 side rails from single pieces, and making them 5" apart and parallel.  The boom was also simplified to a single top tube, and a single lower tube acting as a truss to minimize boom bounce.  There seems to be a small amount of boom yaw when I'm in a tall gear and cranking really hard at low pedal RPMs, but there is no twisting or bounce, so I'm pretty happy with that.  The single tubes on each side of the rear wheel give it a very mellow ride and it takes bumps much smoother than the 2nd trike with its triangulated rear end.  While there is a fair amount of wheel and frame twist when cornering hard or at speed, it isn't felt much and doesn't seem to affect the handling.

     I actually sketched up some plans for this one and made measurements and recorded angles on a full scale drawing on my table top.  It helped quite a bit to get the bike as low to the ground as I wanted it.  The bottom of the frame rails are 6" off the deck and it is very stable considering how narrow it is.  I tried to be very tight with my angles and ended up with about 1 to 2 degrees of negative camber on the front wheels, but it doesn't seem to do much to hamper the steering aside from adding a little push when cornering hard at speed.  It is very slow to come up on 2 wheels while cornering and very easy to ride once it is up on two wheels.  It has about 11 degrees of caster and I planned for 10.  The harder you try to turn it, the more it tries to straighten the wheels.  It is very easy to ride at speed compared to the 2nd trike I made.  I'm very happy with the steering on this one and it turns very tight if you keep your feet and legs clear of the wheels.  It comfortably corners tighter than my 2nd trike but the wheels can contact the pedals or your thighs when cornering hard.  A very manageable problem though.  I welded the steering/brake tubes onto the bottom of the king pins at 45 degrees this time instead of 90 degrees (roughly parallel to the ground) like on trike #2.  I wanted to simplify the construction and have the handle bars coming out of the end of the tube instead of being welded on top.  Much easier to build, lighter and works great for anyone up to about 5' 6" - no good for shorter riders, so back to the drawing board for the handle bars. :(  I found some nice twist grip shifters off a scrap bike and they work pretty well but aren't really matched to the rear derailler so the indexing isn't always accurately changing gears, but I might be able to tune it a bit with patience.  First time I've ever used anything like them so the novelty factor is still higher than the inaccurate shifting factor :)

     I used the same type of seat adjustment rails on this trike, and this time, it's much closer to the optimum x-seam measurements than the 2nd trike was.  I also decided to make the seat adjustment tool-less so I made a T-handled pin out of 5/16" mild steel rod to pin the seat in place on the adjustment rails.  A simple hitch pin clip goes through a hole on the other end of the seat pin to hold it in place.  I also changed the way I mounted my chain guide rollers as the chain stayed very close to the right frame rail due to the fact that I kept them parallel this time.  I used a piece of 1" x 1/8" angle iron and welded triangular pieces of 1/8" plate mild steel to the sides to form small gussets.  The ¼" bolts hold the roller only on the right hand side and I don't know if the stock roller blade bolts will be strong enough to take the stress.  If not, I'll swap them out and replace them with grade 5 bolts or stainless ones.

     I was told about a company in Barrie, ON (The Finishing Center) that would powder coat my frame for $40 to $60 Canadian, so I took it to them and they did a masterful job on it.  I could have painted it myself but the whole process would have taken me 6 or 7 hours from the time the bike was torn down til the time the paint gun was cleaned, plus a day or so for the paint to cure, so I took the easy way out with the powder coat and it only took a few hours from the time I dropped it off til the time the frame could be handled.  Too easy :)  I also added a small 4" long tube on the left side for my safety flag, and small brackets back near the dropouts for trailer hitches and fender/rack mounting at a later date.

Seat

     As intended, I made the seat 1" shorter on the front, 2" lower on the back, moved the bottom seat support forward an inch, and the back seat support down 2".  I thought the 15" seat width might have been too narrow, but it feels pretty comfortable.  There is a lot less frame flex on this seat and lengthening the height of the seat supports by ½" has also helped stop my butt from occaisionally hitting the seat support bar.  I managed to get a single seat angle adjustment on this bike too, but it is noticeably less rigid than the small dual supports on the 2nd bike and creaks a bit when I am cranking hard.  I'm wondering how much of an effect the seat support flexing will have on its durability.  If it can take my 230 lbs, it should be good to go though.

     This seat was made out of the same ¾" stainless tubing and 1/8" mild steel as the 2nd bike.  The seat covering was simplified into a plain rectangle, reinforced at the edges, with #3 grommets every 3".

Wheels

     The rear wheel is standard 26" wheel with a 6 speed cassette on it.  The front wheels are heavy duty 20" wheels with 48 spokes and 14mm axles.  I wouldn't mind getting higher pressure tires with a narrower profile to see how free it rolls with them as compared to the 2.125 Mongooses (Mongeese?) on the front right now.

Misc Hardware

     The brakes, levers and deraillers were all salvaged parts.  The only store bought items were the front wheels, tires and nice new pedals.  With lessons learned from the first two trikes, I tried to keep the cable runs for the deraillers as straight as possible and give large radii for and changes in direction.  I have space to add a rear brake at a later date if I so choose and I'll have to add a splitter if I add the third brake as well.  I added the perfunctory green garden hose to act as chain guide/guard and this time I ran it all the way up to the chain wheels to keep chain oil off your leg or pants.  I plan to switch over to ½", flat black garden hose as soon as my supply of green hose runs out :)  The handlebars are made of the same material as the seat and I added a small tube stub to mount a U shaped bike lock on top of the boom.

Specs:

Modifications:

• replaced the 30/40/50 chainwheels with a 40/52 chainwheel from a racing 10 speed
• zip tied a water bottle mount to the rear of the seat.  On future bikes, I'll weld small brackets to the frame so they can be more rigidly mounted.  Exact location to be determined later . . .
• added a plastic MTB fender for the rear wheel that a friend wasn't using anymore.  Still need to come up with some front fenders as they throw a LOT of water when it's wet out.
• added a cycle computer.  I just wrapped the wire around the tie-rod and mounted it center-line so it can easily be viewed between my legs by just glancing down.

In the following picture, the wheel sensor for the speedometer was too far away from the magnet attached to the spokes.  I had to shim the sensor out closer to the spokes by using a small piece of ½" steel square tube.  It works quite well and I secured it using 4 small zip ties.  On future bikes, I'll weld a small piece of ½" tube to the steering arms when I'm building them so I don't have to shim it out later.

• added a trailer hitch to pull our small kid's trailer.  I simply cut part of the left rear dropout off of an old scrap frame and welded it to a small piece of 2" square by 1/8" thick steel plate and bolted it on.  I left the section of seat stay a little long so I could hook an induction LED tail light to it.  The tail light requires no batteries.  It operates by having a small magnet attached to the spokes and when it rotates past a small coil in the LED light's housing, it induces a small current and makes 3 LEDs flash.

• installed a new 100 psi rear tire and a friend and I experimented with making wheel disks out of some thin white plastic that was kicking around.  The disks are held on with small clear zip ties - 8 on each side of the wheel.  Aside from the cosmetics, they have negligible benefit so I doubt I will make more unless my friend gets bored and decides to make some for the front wheels (as his trike has 20" rims on all corners).  Even at higher speeds, they only amount to 1 or 2 kph benefit.
• as I only have 2 chainrings on the trike, some of the hills are pretty killer to pedal up.  I bought a new rear wheel and put a 13/34 mega range cassette on it and aside from making a huge improvement with regards to ease of pedalling on hills, it also gave me a small boost on top end. :) All good.

• added a new, used, long cage rear derailler as the old one was damaged and has a fair bit of slop in it now.  Also, contrary to popular opinion, you do NOT need a long cage derailler to use mega-range cogs.  The short cage on the original drailleur worked fine.
• added bar ends to the handle bars.  I found that on long cruising where you didn't need to work the brakes or gears, it could get a little tiring to maintain the high hand position.  I put a set of $2 bar ends near the brake mounts and they are VERY comfortable for relaxed cruising.  I would recommend them for anyone's trikes or bents.

• added a fish eye rear view mirror that I picked up for a whopping $4 at Wal-Mart.  It actually is a pretty good little mirror with very little or no vibration.  It's most effective at checking my left rear for approaching vehicles.
• added a normal bike rack and some small saddle bags as I was doing increasing amounts of longer rides and had no place to carry/store items.  The rack mounts to the rear tabs I welded to the frame above the rear dropouts, and I made small 1/4" x ~9" mild steel rods with a 1" square by 1/8" tab welded on one end, and a 1" piece of 1/8" angle iron welded to the other.  The angle iron end attached to the rack and made a rigid connection, while the 1/8" tab connected to the top of the seat support bolts.  One of these rods on both sides and the rack is very rigid.  This simple mod would likely work to mount just about any standard bike rack on any trike with the only major modification being to change the length of the steel rods.

For later . . .

• front fenders and maybe start toying with a small fairing of some sort

Next time . . .

     First of all, I am VERY happy with the performance of this trike.  It is so smooth and so stable, it really is fun to ride fast.  After sorting out the toe-in, a friend of mine had it up to a little over 50 kph.  With the addition of the speedo, I've had it up to a little over 60 kph on a short downhill.  It is very easy to maintain a constant 25 kph cruise on level or slightly hilly ground even into the wind.  I can hold 28 to 30 kph for few kilometers and have had it up to 43 kph in bursts on flat ground.  Having said that, there are a couple things I want to try . .

• higher pressure tires
• I want to lower the boom at least an inch, possibly 2".  It is definitely a steeper angle than trike #2, but it is still pretty comfortable to ride.
• move the lower seat support forward another ½" to further clear the rider's butt, and stiffen up the front of the seat rails.  Make the seat back 1" lower and the front 1" shorter.  Move the seat back support 1" further down and maybe change the seat angle from a 60 degree bend to about 70 degrees.  A slightly flatter angle will put more weight on my back and less on my butt to hopefully minimize or delay the appearance of "recumbent butt".
• maybe make the seat ½" wider, just for comparison with the new design
• use a 27" 10 speed racing rear wheel and add an intermediate cassette and derailler
• use triple brakes if I install the 27" rear wheel.  Even pulling a small child trailer tends to overpower the old side pulls I'm using ATM.  I shop at a cool little bike shop that sells BMX brakes and adapters that are very powerful and work every bit as good as disks at a fraction of the cost.
• move the steering arms/brake mounts back to horizontal to minimize interference with rider/seat
• possibly try USS if space and routing allows it

5 Dec 2006      The Mk 3 had been sitting for a while because I had other bents to ride, so it was getting little use.  I wanted to get it to someone else to enjoy, but thee were a few things that were bothering me, namely the seat and the old king-pins.  So, I finally dragged it down and started its make-over.  I did the following to it: stripped it all back down to bare metal so I could have it re-powdercoated and also so I could check the status of the welds stripped and reinforced the seat frame sewed up a new seat cover in the same style as the one I had on the Mk 3. took the kingpins and reinforced them where the axle tube meets the king-pin rebuilt the rear wheel installed a new BB axle, races and bearings installed new BMX side pulls trimmed 4" off each handlebar (the part that slides inside the square tubing) had it powder coated again, and they just happened to be running white :)      It was, and still is, a great trike. Very comfortable and one of the fastest I've built to date.  Hopefully the new owner has many years of enjoyment out of it.  It had a total of about 1600km before being sold.

More bike details when more bikes are built :)

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