BICYCLE DESIGN PART 2:

Bicycle Components and changing standards:

Continuing from last week, this is part of a series of weekly blogs about bicycle design.   This will be on route to explaining why and approach that I took when I designed the Ram / Swan Frame for the Pinion gearbox.  I will take you on the journey of bicycles that have influenced me and then why I took the less conventional path;  
I will answer those questions and let you glimpse into my design mind...  


Strong, Light, Cheap - Pick Two.

The bicycle is something that will always keep evolving in design as engineers look for something stronger and lighter. The components that sell or have potential to sell, get value engineered and stripped down to made cheaper.

In the 1980's you can forgive the early MTB "pioneer" framebuiders for getting components came from road bike and beach cruisers. But with impact, sand, mud and rocks components started failing.  Lets look at 2 component on your typical mountain bike, where they started and where they are today.

HEADSETS:

Headsets got larger bearings for stiffness and less bearing slop.  Especially the bottom headset bearing.  Old 4130 steerers were 1” (25.4mm).  The standard was changed in the 1990's to 1 1/8” (28.6mm) with the popularity of the mountain bike.
Carbon forks are stronger if they have less stress raisers.  It makes more sense to have a tapered steerer, where the bottom of the steerer blends with the fork crown.  
The 11/8" top bearing is the same, but increases the bottom bearing to a 1.5" (38.1mm)  
Klien was a head of this in the 1980's with a 1.5" steerer on their oversized aluminium frames and forks.  These were like the "intergrated" headsets, but Klein pressed them into the frame.

Headsets are a minefield of tolerances and sizing choices, which becomes confusing for the customer.  Canecreek have developed the SHIS system, which helps but there are still too many headsets on the market.

BOTTOM BRACKETS

Bottom Brackets got stiffer and lighter.
Old bottom brackets were bomb proof, however the Square taper axles were heavy.
Shimano managed to develop a hollow axle around the same BSEN68 threaded bottom bracket. This was marred by Raceface blaming frames not being faced on bearing quality.  But it did catch on, because it solved some other issues.

Again Klien had their bottom brackets pressed into the frame, much like todays pushfit bottom brackets.  This gave Klien the clean look and allowed them to get a good weld junction on the chainstays and bottom bracket.
Now there are almost as many bottom brackets as headset sizes.  24mm and 30mm axles. 
BSEN threaded for 68,73,83 and 100mm.  Pushfit 41mm for 86mm (road) and 92mm (mtb).  
PF46 for BB30 and BB30 itself and the new threaded T47 to fit 30mm axles.  
At the end of the day road bikes will always have a narrow Q-factor so BB30 suits road bikes.
Mountain bikes with tyre and chainring clearance on the chainstays need to have a bottom bracket shell that enables the chainstays to be as wide as possible.  
For me BBPF92 is hard to beat. 

Next week I will look at a few other frame "standards" and how they have changed for the better.  

Steven OlsenComment