Installing vs. Fitting: Why Your Crank Still Binds

You bought the best ceramic bearings, the stiffest carbon frame, and a premium crankset. You torqued everything to spec. But it still binds. Why? Because "installing" parts isn't the same as "fitting" them. In this workshop deep dive, we explore "Tolerance Stacking"—the engineering reality where micro-differences in your bicycle frame, Bottom Bracket cups and caps, bearings, and crank spindle add up to a potential disaster. We explain why the most expensive, tightest-tolerance bearings often perform worse than standard ones in a press-fit application, and why a "perfect" spec sheet doesn't always equal a perfect fit. We go on to show skilled mechanical fitters can solve design and manufacturing issues to get to a smoothly spinning crank and bearings. In this video: The TIME Demo Fleet: Why we are testing 145mm cranks for 2026. The Math: How a 0.05mm variance stacks up to kill your bearings. Decoding Bearings: ABEC ratings, C3 vs. CN clearance, and why "loose" is sometimes better. The Debate: Why T47 Threaded BBs aren't the magic bullet everyone thinks they are (The weight penalty). Mapdec Cycle Works Precision Cycle Works & Technical Analysis https://mapdec.com ⏱️ Chapters (Timestamps) 00:00 Building the 2026 Demo Fleet (145mm Cranks) 00:40 What is Tolerance Stacking? 01:40 The "Cheap Fix": Why Plastic Shells Work 02:43 Decoding Bearing Standards (ABEC, ISO, P5) 03:53 C3 vs. CN Internal Clearance Explained 05:06 Are Ceramic Bearings Worth It? 05:48 The Stack Up: How Errors Accumulate 07:05 Measuring the Spindle (DUB Tolerances) 07:58 The Truth About T47 & Threaded BBs 09:00 The Weight Penalty of Threaded Systems 09:23 Summary: Installing vs. Fitting Correction: 7:03 The measurement is 28.98mm, as shown on micrometer