How not to fall over in Winter!
(or, Triking in Minnesota)
By Dave Krafft
For the last several years I have been trying to get in as many miles as
possible during the winter months so that I wouldn't lose that edge that
came at the end of an active year of racing. Each of the last two years
has seen me take at least one humbling and painful fall that put me off
riding again (except for the ice races) until spring. Since the first race
of each year comes on the last weekend of April, and I keep getting older,
each successive year finds me in worse shape. This year I decided to do
something about this appaling trend and find a new solution.
Two winters of sore elbows and shoulders brought me to the realization that
I needed to move from the realm of two wheels to a more stable and safer
platform of three wheels. As most of you know I have built three previous
trikes. The first two were in the mid 1980's and the only good thing I can
say about them is that I got lots of brazing practice, and didn't get hurt
too bad. The first was too high. The second was too flexible and the front
wheels not beefy enough to handle my 200+ weight. The third was an easy
racer type with two rear wheels built for a friend. This trike has been
quite successful for him but still has some stability problems and has a
few too many custom parts to make it real practical. After having thought
long and hard again about how to build the ultimate winter trike, I again
went looking at the two wheel front single rear drive wheel idea.
The past couple of years I had seen glowing reports about a trike built
in Australia by Ian Simms called the Greenspeed. This trike was much the
same as the first trikes I had built but a little lower and definately beefier.
I was convinced that I could steal most of his steering geometry and add
it to a trike of my own design. So last fall. I began to collect parts.
The front two wheels were 406mm BMX size 20" with hub brakes. I wanted
to be able to put on some of the new high pressure Conti tires and had
found a set of Phil Wood copy wheelchair stub axles and bearings that were
intended to turn a regular hub into a one sided affair. They were about
13mm instead of the 10mm axles that came in the standard Sturmey Archer
hub with brakes. But I had to custom order new bearings and add some shims
as well as beg some time on a lathe to make them work properly. Hub brakes
sure work well in this type of an application and I had found a cable splitter
at Axeman's to brake both off one handle. I wanted to be able to get the
bike through most commercial type doors so wanted no more then a max outside
width of 32" It came out 31.5" and is still just a little too
wide for a home door but will easily go in and out on it's side.
For the rear wheel I wanted to be able to use something available and cheap
so I stuck to a 26" mtn bike type wheel. I had several tires to put
studs in and it is easy to find good high pressure tires in narrow widths
today. This wheel choice set the height of the bottom tube at about 8 inches
above the ground. The front cross tube was originally 40 inches away but
after it broke at the ice races I added two inches to it to give me a little
more hand clearance between the handle bar and the front axle. Because the
front wheel centers are 10" high I had to angle the cross pieces up
two inches from the main tube. Then I had to build in caster and camber
to make it steer right.
Caster is about a seven degree tilt of the steering axis on each wheel to
front of the bike to allow it to return to center if you let go of the steering.
Camber is a degree of tilt to the outside that places a line through the
steering axis to the center of the contact patch where the tire meets the
ground. The pivots themselves were built up using old head tubes, steerer
tubes from forks and head sets. I brazed washers to the bottom of the steerer
tubes to allow the head sets to work properly. Then holes were drilled and
tapped throught the tubes to take the axles. The Ackerman angle was then
figured out. This is a line from the hub center of the rear wheel drawn
through the pivot point of the front axles . If you steering arms are situated
like distances either front or back of the steering pivot point it will
insure that it makes the inside wheel steer tighter. This is the same basic
formula that cars and go-carts use and is very effective.
Then came the part that had so impressed me about Ian Simms's design. To
steer from a handle bar under the seat to the front wheel takes some figuring
out. The first trike I built used cables and initially was hooked up backward.
So if your brain said you should turn right to go right the bike went left
instead. Made for one nasty fall in front of a car because in a bad situation
you always try to do what your intuition tells you is right. One large road
rash and an angry motorist convinced me to change that one and never to
build a steering or braking system that was counter intuitive. That is what
makes Ian's design such a gem is that if you steer to the front of the pivot
point along the ackerman angle you can just use two simple crossed rods
with rod end bearings that are adjustable for length so you can set toe-in
toe-out and the speed of your steering. For all the years I had been trying
to figure this out, this was the answer! It works great, and is very positive
and tight! Alright Ian!
The rest of the bike fell together from there. The front boom brings the
cranks about 21" off the ground so that I can get over curbs and through
drifts without hanging up.I used compound tandem gearing again to getter
a shorter rear shifting chain length to make it quicker. The basic cross
design is pretty good but I tried to just butt braze the tubes up at the
center and eventually someone broke it for me. That is good because now
I could make it a little longer and beef up that joint at the same time.
After about 150 miles, as well as ice racing this winter, I think I have
finally found a "keeper" trike design. Stable, responsive, and
fun, this trike is great on slippery roads. As yet I haven't been able to
assess it's speed potential but will give an update after putting summer
tires on it and trying it out. So If you want to give triking a try definately
consider the Greenspeed type trike.
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