For the weight I decided concrete blocks would be handy, and the pair shown was 70 lbs. I made temporary brackets welded to the frame and hung the bricks from them. The weight pushed the limits of the frame and steering but I decided to give it a try. It turned out to be extremely top-heavy and impossible to control. The frame flexed a lot, the fork creaked loudly, so it was declared a total failure.
As usual, other hobbies and interests have cut into my development time for ProjectVF, but progress was still made. The existing front suspension has been dismantled in order to build a new suspension, this time with a shallow, chopper-type rake. The long-suffering Test Mule has been altered several times to test new theories about steering.
A successful recumbent builder in the U.K. suggested my “turning force” test data might be flawed because there was no significant weight over the front wheel (like an engine), thus the different rake and trail combinations might not work so well on a heavier machine. He said other builders used very steep rakes and small amounts of trail with great success.
Naturally, I had to test it myself, as follows:
An hour later I tried suspending one block beneath the frame using steel cables and a couple of bungee cords. It was no longer top-heavy, but the reduced weight of 45 lbs still strained the lightweight frame. When I tried to ride it, the weight shifted back and forth like a pendulum. I would turn in one direction but the weight moved in the opposite direction, throwing off my balance. I'd try to compensate, turn back toward the center, and the weight would swung the other way with more force. It was a feedback loop and made the Test Mule nearly unrideable. Worse yet, the block hung too low and on the next run it scraped the street during turns. Like before, this design was a failure.
The basic plan was to test five rake & trail
combinations. Each combination would tried with and without the weight. The
static tests were done in my garage, using scales to measure the force
required to turn the handlebars. The kinetic tests were done on the little
hill up my street.
When the rake and trail are altered, the distance
between the front ball joint and the rear ball joint changes. Rather than
adjust the length of the arm each time I changed rake or trail, I made a
preset version, shown here in a lovely shade of orange. The drilled holes
connect in various ways for specific lengths. Labeled holes makes it easy to
use. It came from recycled materials, so the only cost was the electricity
used to cut and weld.
The current control arms use 1-1/4” DOM tubing. I
wanted to use the same size tubing but with a thinner wall to save weight.
However, doing that requires the use of larger rod ends and new hardware such as
threaded bungs, cone spacers, jam nuts and the new tubing. Add
shipping and it comes to $105.
I'll need a lot of miscellaneous parts, like ball joints, tools, hardware,
raw materials and outside machining for the triple clamp adapters. An
estimate for these came to $195, plus the above price of $105 gives
a total of $300 which I have to admit is higher than expected. There's going
to be other things I haven’t thought of, but for now I think it's a fair estimate.
If I use the same size tubing as before and reuse the hardware I can save about $90. No matter which design I choose, some things have to be bought such as the ball joints, the tubing, the machining and raw materials, but knocking a third off the price is pretty significant. Given that, I don’t think the weight loss at this point is worth the extra cost.
I’m going to build a new suspension, this time with a 40-degree rake. I need to know if it works full size before I commit myself to a final version. I’m keeping all of the existing pieces in case I want to switch back, and making all new parts for the experimental assembly. The existing mounting points on the frame will remain untouched by using a bolt-on adapter which holds the new control arms where needed.
I’ve learned a lot about steering and suspension since this photo was taken back in 1971, but that crude setup worked as well as needed for a sloped dirt road. It was a riding sulky from a farm mower combined with plastic wheels and metal axle from a broken chaise lounger, a piece of 2x4 with bent-over nails to hold the axle in place and a loop of clothesline for controls. That day was the birth of my adaptation skills.
The next step is to order parts and raw materials and start fabricating. Snowboarding season is still two months away and motorcycling season is just ending so I should make good progress in between. A little more testing until the parts arrive and I'll be ready to go.
On a side note, I was able to obtain a second VF750 Interceptor frame on eBay. Once I have everything working on the prototype, I can make a nice, clean transformation to the new frame without all the grinder marks and sloppy welds and crooked pieces.