Mark Stonich's New LWB Frame
Mark Stonich's New LWB Frame
Mark Stonich brought his latest frame - This is going to be one light bike. Mark's not a strong rider and is trying to turn a 12.5mph average into a 14mph average. At these speeds, weight and rolling/mechanical resistance are a major factor. As speeds increase the power needed to overcome these increases linearly, but the power needed to overcome aerodynamic drag goes up with the 3rd power of the increase in speed. The faster you go the larger the % of total power is used to overcome wind drag. A lower, more aerodynamic bike would be heavier and require power robbing idlers, but would need less total power than Mark's to go 20+ mph. Mark is betting that, at the speeds he rides, his design will be more efficient.
"Light - Cheap - Strong; Pick any two." Framebuilder's Proverb
Cheap, strong bikes are not light. Light, strong bikes are not cheap. Cheap, light bikes are not strong (just ask any ex-Lambert owner). The Holy Grail of bike designers is to combine all three. Back when aluminum was considered an exotic material, the French used to have competitions for touring bike design. There were grueling, long distance tests, with severe penalties for any mechanical failures. Significant bonus points were given for light weight. So French manufacturers made smaller, more elegant parts. That's one way Mark's trying to save weight, another is eliminating parts entirely. The 36h front wheel has 12 spokes and 48 empty holes. Frame, fork, wheels, tubes, tires, dummy headset spacers and rear brakes add up to only 11.5 pounds. Frame alone is 4.5lbs.
Despite trying to build one of the lightest LWBs around, he's using Shimano rear hub and pedals. These are the two areas where Mark feels Shimano gives perfomance and reliability advantages worth accepting a weight penalty. 9 speeds aren't necessary, but a 9-speed Ultegra 12-27 cassette weighs 224 grams, while an 8-speed Dura Ace 13-26 weighs 339grams. That's a quarter pound of weight saving, for just a few dollars, and the wider range will allow him to use only two chainrings.
The rear stays are MTB fork blades. Cute little hanger silver brazed to the inside of the fork tip increases chain clearance. The rear end is considerably offset to allow a dishless wheel and for chain clearance. Used the fork's cantilever brake pivot on left, but the right one would have interfered with the chain and would have been too far from the rim. Therefore he would have had to make a custom, large offset, canti brake pivot for the right side, and mount it on top for chain clearance. For the weight of a max offset pivot he made a brakepad holder. The left cantilever arm is an old French Mafac, about 1/2 the weight of modern ones. With the stiff rim and lightweight spokes, there should be no problem pushing the rim to the pad. Saved the weight of a straddle wire, hanger and a brake arm. Pad to rim clearance is minimal so Mark is committed to keeping the wheel very true. With light spokes, stiff rim and no dish this should be easy.
Modern weight-weenies spend a lot on carbon-fiber and titanium. Mark thinks that is cheating, "Any fool can write a check, but it takes a lot of thought to build a light bike cheaply".
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