Mountain Bike Bottom Bracket and Crank Geometry for Stability
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Solution Overview
Problem
Mountain bikes face challenges in achieving stability without compromising safety requirements related to lean angle and ground clearance, while maintaining comfort and ergonomic efficiency.
Innovation Solution
The solution involves lowering the bottom bracket shell and reducing the length of the cranks, which counterintuitively allows for a lower center of gravity without reducing comfort or increasing the bike's weight, while maintaining ground clearance and lean angle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the bottom bracket shell is lowered to reduce the center of gravity, then stability is improved, but ground clearance and maximum allowable lean angle are reduced
Solution Approach 1:
The patent applies parameter changes by lowering the bottom bracket shell position and reducing the crank length from conventional values. This combination of parameter modifications allows the center of gravity to be lowered for improved stability while the reduced crank length compensates for the lost ground clearance, maintaining safe pedal clearance during leaning.
2Stability of the object's composition
If the bottom bracket shell is lowered to improve stability, then weight distribution on the front wheel is improved, but ground clearance is compromised
Solution Approach 1:
The patent employs parameter changes by adjusting both the bottom bracket shell position (lowered) and crank length (reduced). The lowered bottom bracket improves weight distribution to the front wheel enhancing stability, while the shorter crank length ensures that even with reduced ground clearance, the pedals maintain adequate clearance from the ground during maximum lean angle operation.
3Stability of the object's composition
If the crank length is reduced to maintain ground clearance after lowering the bottom bracket, then stability is improved, but this goes against conventional design standards
Solution Approach 1:
The patent challenges conventional design standards by implementing non-standard crank length reduction. This parameter change, combined with lowering the bottom bracket shell, achieves the dual benefit of lowered center of gravity for improved stability while maintaining adequate ground clearance through the shortened crank arm geometry.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design enhances stability and rider experience, particularly in climbing and descending, by redistributing weight onto the front wheel without compromising robustness or comfort.
Implementation Method 1
a rear suspension element connecting the rear wheel to the frame, for allowing the rear wheel to move with respect to the frame
Implementation Method 2
The bike further comprises at least one suspension element connecting the front wheel to the frame, for allowing the front wheel to move with respect to the frame
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
A mountain bike comprises: —a frame (10); —a rear wheel (2) having its axle mounted in rear dropouts (16) of the frame; —a front wheel (3) having its axle mounted in front dropouts (18) of the frame; —a pedal set (20) comprising a spindle mounted for rotation in a bottom bracket shell (19) of the frame, two cranks (22) mounted at the opposite ends of the spindle, and two pedals (21) mounted for rotation at the free ends of the respective cranks; wherein each crank (22) has a crank length L of 164 mm or less; wherein the bottom bracket shell (19) has a Practical Bracket Height PBH of 294 mm or less, wherein PBH=BH−β·(α·FST+(1−α)·RST), wherein BH indicates bracket height, FST indicates Front Suspension Travel, and RST indicates Rear Suspension Travel.