How Bearing Preload Adjustments Influence Rolling Resistance

Introduction

Bearing preload is one of the most misunderstood—yet critical—factors in wheel performance. Too tight, and you increase friction; too loose, and you risk instability. This article breaks down the engineering principles behind preload adjustments and their measurable effects on rolling resistance, backed by lab data and pro mechanic insights.

The Basics of Bearing Preload

What Is Preload?

1. A controlled axial force applied to bearings to eliminate internal play

2. Common systems:

Cup-and-cone (adjustable via locknuts)

Cartridge bearings (pre-set or via wave washers/spacers)

The Goldilocks Principle

Ideal preload: 0.5-1.2 N·m of rotational torque (measured with a dial torque wrench)

Symptoms of poor preload:

Too Tight	Too Loose
Increased drag (5-15W)	Bearing wobble
Premature wear	Reduced hub stiffness

Lab-Tested Impact on Rolling Resistance

(Data: CeramicSpeed’s bearing dyno @ 40km/h, Shimano Dura-Ace hubs)

Preload Torque (N·m)	Rolling Resistance (Watts)	Bearing Temp Rise (°C)
0.3 (Loose)	8.2W	+3°C
0.8 (Optimal)	7.1W	+1°C
1.5 (Over-tight)	9.6W	+12°C

Key Findings:

· 5-35% efficiency loss from incorrect preload

· Over-tightening generates exponentially more heat (friction ↑)

Pro Adjustment Techniques

1. Cup-and-Cone Hubs

Step 1: Loosen axle nuts until play is felt

Step 2: Tighten gradually (1/8-turn increments) while spinning the wheel

Step 3: Check for smoothness—should coast for 25+ seconds (uninstalled)

2. Cartridge Bearing Hubs

Use preload spacers (e.g., DT Swiss Star Ratchet system)

Torque specs:

o DT Swiss 240: 0.6-0.9 N·m

o Chris King: 1.0-1.2 N·m

3. Thermal Compensation

Aluminum frames expand when hot—recheck preload after 20km of hard riding

Real-World Implications

Time Trialists: Optimal preload saves 3-5W per wheel vs. factory settings

Gravel Bikes: Slightly looser preload (0.4-0.7 N·m) improves bump absorption

E-Bikes: Higher torque demands warrant 10-15% tighter preload

Conclusion

Preload isn’t a "set and forget" adjustment. For best performance:
Measure with a torque wrench—don’t guess
Re-tune seasonally—temperature changes affect tolerances
Prioritize hub quality—high-end bearings tolerate tighter preload

Pro Tip: After adjustment, test roll-down resistance on a 1% gradient—optimal setup should maintain speed within 0.5% of a ceramic bearing wheel.