|Betty's Composite Bike
by Damon Rinard
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This is Betty. She's 78 years old and loves to ride. This October (2000) she and a friend are taking an Elderhostel tour of Wisconsin on their bikes. She can't lift her leg as high as she used to, and she had trouble stepping over the frame to get on and off her old bike. Even the frames on girls' bikes are too high for her. She didn't want to stop riding just because of that. She also wished her bike weighed less. Not for performance, but to make it easier for her to lift the bike onto her car's trunk rack when she takes it out on the weekends. To solve these two problems, I built her a custom bike with much lower step-through height and much lighter weight than her old bike. Betty's bike is almost two years old now. She estimates it's got about 2000 miles on it, since she hasn't been putting as many miles in recently as she used to.
This is the bike I built for Betty. The main feature is very low step-through height. The forward part of the frame is carbon-fiber and epoxy composite; the rear triangle is lightweight steel. The finished bike weighs 23 pounds. That's 15 pounds less than her old bike. Although the composite frame probably weighs a few pounds less than her old one, much of the weight savings comes from lightweight components. I've weighed a lot of bike parts; see weights.htm.
I joined the front and rear at the time of manufacture by laminating the carbon fiber over the bottom-bracket shell and the bottom part of the seat tube. Carbon wraps completely around the seat tube and the bottom-bracket shell. The rear triangle was custom brazed for Betty's bike by Holland Cycles.
Here you can see the main feature - the low step-through height. Betty doesn't have to lift her leg nearly as high as she did with her old girl's bike. You can see that the water bottle was a tight fit. There is barely enough room for Betty to miss hitting it with her knee when mounting.
In fact, I had to move the water bottle higher after the frame was done to keep it as much out of the way as possible. I did that by adding a third T nut above the original two. Here you can see the old T nut on the down tube below the water bottle.
After the frame was done, I had to route the cables. I made custom carbon-fiber cable stops right on the frame. Here is a single cable stop. I formed the back side of the stop right on the frame surface, and the cavity for the cable using a quarter-inch-diameter steel rod. I wanted to bond the stop on after it cured, so I put a layer of thin plastic packing tape on the frame as a release. I also wanted to be able to get the rod out, so I waxed it and coated it with release agent. To make the stop, I thoroughly wetted the carbon plies through with epoxy, wiggled the rod through the weave, and vacuum-bagged the wet carbon right on the frame. After cure, I sanded the rough edges smooth and filed the cable opening to shape. I cut the slot with a hacksaw, then bonded the stop in place on the frame.
Here is a double cable stop on the other side of the down tube. I made doubles the same way, only with two rods, of course. I taped popsicle sticks together to act as spacers between the rods. That way, they remained parallel during cure.
Here is a stop located on the corner of the down tube near the head tube. You can almost see the curve in the stop where it wraps around the contour of the frame.
Betty loves her Rinard bike. Her friends want copies of it, but I've told them it's too much work for me to break even. Betty believes the bike industry is missing out on a lot of sales because it fails to cater to older folks who don't want a racing bike. Even hybrids or comfort bikes don't solve the two main problems Betty had: low step-through height and very light weight.
Copyright © 1995-2001
Last Updated: by Harriet Fell