Thursday, June 23, 2011

My "New" Baby

A friend roused me from my indolence to write this post - thanks Amy!   This post is dedicated to Sheldon Brown of Newton, MA.   Sheldon Brown's website is a testament to his bike knowledge and sense of humor. 

The actual bike - click to enlarge
Well it's not really new and it's not a baby - a human baby that is.  It's a bicycle,  only twenty-one years old and orphaned on the streets of Cambridge.   I found it stripped of the easy-to-remove things - both wheels (with quick-release skewers),  the seat post and the saddle.   But the key items were intact. The frame, brakes, derailleurs, crank-set, chain were in good condition.    The frame is small - good for a small rider.  The frame graphics identified it as a Miyata 721A.  Note the low and forward setting of the saddle (short legs) and upward tilt of the handlebars  (short arms).  Should I really be riding an adult-sized bike? 

1990 Catalog Page - click to enlarge
After a little googling,  I found someone who likes Miyata bikes enough to scan several years worth of glossy paper catalogs.   One of these,  the 1990 catalog, is a special issue for the  centennary of the Miyata company.    It turns out the Model 721A made it's debut in 1990 and my little orphan is one of the originals.  There is also a decal of the bike shop that sold it - Farina's of Watertown.  
The bike is mid-level road (touring/racing) model designed for hilly terrain.   It has 21-speeds,  most of them useless for the flat lands of Boston,  in a seven rear-by-three front sprocket configuration.  It has a Shimano Hyperglide chain and rear cluster (freehub-cassette) system with a Biopace  front crankset.    The frame is made using the "bonded aluminum" method .   This method uses aluminum tubes and connects them with lugs and glue.   Bicycle frames are typically made from three main tubes in a triangle.  These tubes must be connected to form a strong and stiff stucture.   A classic method is to connect the tubes with shaped "lugs"  ,  thicker hollow forms that accept the tubes at certain angles.  The lugs and tubes are connected using "brazing"  (melting metal into a small gap between the parts).   Other methods include welding the tubes directly together or  using lugs and glue.   In fancy bikes, the frame is constructed of a unified composite material with no obvious seams.  

My other bike is a trusty 1978 Motobecane Sprintour (made in France) with a steel (CrMo alloy) frame.  On the lower end and 12 years older,  the Sprintour model really contrasts with the 721A.   It's much heavier.  The gearing system is much simpler -  a ten-speed using a traditional rear  freeweel  gear cluster (5-sprockets) and two in the front.  The  dérailleur  (French word derived from de-rail which describes the way the chain is pushed off one sprocket on to another) system uses a basic sprocket geometry (the chain only fits on on gear at a time - and slides otherwise).  Shifting levers are continuous (no indexing on the shifters) and they are located on the downtube.  

The Shimano Hyperglide chain and gearing system is much more complex then the 1970's systems.  The sprocket teeth vary in shape and orientation as you go around to allow the chain to grab two gears at one time (the chain is slimmer and specialized as well).  The adjacent sprockets must align (in rotation) to allow the chain to mesh properly - so the entire cassette must be assembled correctly.   Indexed shifting levers are part of the system as continuous control is not really compatible.  The benefits of all this complexity are easy shifting by clicking the shifter into place and changing gears under power.   In the old days,  you had to ease up on the cranks before shifting.  

The braking system on the Miyata is also a big step up from the Motobecane with it's basic Weinmann side-pull, single-pivot, caliper design.   It uses the Shimano 500 EX (Exage?) SLR dual-pivot, calipers,  low-friction cables,  and matched Aero brake levers.   The Shimano brake design is very smooth and powerful (especially on new, clean aluminum wheel rims).  Grime is the bane of most mechanical things - especially bicycle components and brakes importantly.  If you've ever wondered why your brakes are not working as well as when they were new,  it's not age per se - worn down maybe to due the abrasion of sand and grit.  Oils and greases gum up over time due to chemical reactions with oxygen (ozone).  Gums are the opposite of greases in that they promote sticking rather than sliding.  Ironically,  a little layer of grease on your rims will eventually cause them to sound like a really bad violin  (and violinist).   Violin bows are "waxed"  to increase "sticktion".  Also, entrapped sand grains in the brake pads will grind grooves into the rim surface and reduce the contact area available for the brake pad.   And the brake pads, made of rubber, may also degrade as well  (ozone again).

Utility Pole Replacement in Cambridge (Riverside)

Last night a wooden  utility pole  cracked at the base and fell toward the neighboring pole across the street. This caused the wires to d...