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Bike Geometry Explained

Understanding Bike Geometry: A Guide for Beginners

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We have all seen them, those huge tables of numbers that do little more than intimidate. Understanding geomtery is the key to choosing the right bike. Let's demystify some of the numbers and get you started.

Ask yourself a few questions like, “Do I need a bike for gravel racing or or all day comfort?” or, “Am I looking for power and optimized aerodynamics?”. Questions like these will help you determine the best bike for you. Consider these three main requirements first and feel free to further tailor them to your liking from there.

Position

A relaxed rider position will provide longevity and stronger endurance. Placing the rider in an upright position allows them to breathe easier and balance their center of gravity. If you're planning on long backcountry adventures, choosing a relaxed geometry hardtail or gravel bike is the way to go.

Comparatively, the aggressive rider position of many gravel bikes will improve power and give you the advantage of speed. Positioned to help you lean forward for more efficient wind resistance and powerful pedal strokes.

Steering

Choosing between slow or fast steering can be more complicated than you might think. Slow steering provides the rider with the ability to feel more stable and perform better at high speeds. Fast steering will allow the rider to have more control over the path the bicycle is taking and dodging debris.

For those traveling at a face pace, slow steering is the best choice for a stable ride. Otherwise, choosing fast steering for biking on roads will increase your ability to control the bike and avoid accidents.

Turning

Otherwise known as cornering, bikes can either have stable cornering or nimble cornering. Stable cornering allows the bike to smoothly turn with you in a controlled motion at high speeds. Nimble cornering is good for stable turning at lower speeds.

Depending on your personal speed goals, stable is best for speed racers. Nimble is a good choice for leisure riders and those who require a tighter turn radius.

The Geometry of a Bike

Let's explore the full geometry of a bike, starting with each individual part. The dynamics of each piece work together to create the best experience for the rider depending on how they choose to use the bicycle. By combining all optimized parts together leads to better achievement and endurance.

Frame Size

Though most retailers sell bikes in small, medium, and large, these sizes aren't exactly dependable. Choosing a customized bike based upon standover height is a far better way to guarantee a comfortable stable ride.

Seat Tube Length and Angle
Bike geometry - seat tube length

The seat tube is located below the top tube in front of the back wheel. This tube keeps you well centered and does not vary further than 71-77 degree angles. Using this measurement to find the perfect bike size for you ensures your bike will be optimized and ready for your specific needs.

Stack and Reach
Bike geometry - stack

Stack is the distance from the centre of the bottom bracket to the mid point of the head tube. Reach is the horizontal distance from the centre of the bottom bracket to the middle of the head tube. Together these two measurements determine the feel and use of a bike. If you are looking to go fast for racing or whatever reason, look for something with a long reach and short stack (also known as aggressive). If you plan on doing long days in the saddle bikepacking you want to stick to short reach and high stacks (also known as slack or relaxed).

Top Tube Length
Bike geometry - top tube length

Similar to reach, top tube length can help determine the length of a bike and its ride. There are a few ways to measure top tube length. In todays world, top tube length is measured as an imaginary level tube that runs from the center of the seat post to the top of the head tube.

Head Tube Length and Angle
Bike geometry - head tube length

The head tube resides right under the handlebars connecting the front wheel and the frame of the bike. The angle of the head tube can either be slack or steep. A steep head tube provides more controlled steering for road biking, while a slack head tube gives you stability for fast rides.

Fork Rake and Fork Offset
Bike geometry - fork rake and fork offset

Fork rake or offset is the measured distance from the steering axis to the front axle. Fork offset is linked to the Trail of the bike. Together these two measurement's affect a bike's wheelbase and handling.

Chainstay Length
Bike geometry - chainstay length

The length from the centre of the bottom bracket to the centre of the rear dropouts. Long chainstays keep you stable and create a longer wheelbase. Shorter chainstays provide crisp movement and controlled handling.

Bottom Bracket Height and Drop
Bike geometry - bottom bracket

The bottom bracket connects the crankset to the bike.Consider length from pedal to ground, higher is typically better for off-road bikes.

Understanding Your New Bike

Whether you choose a bike for increased performance speed, traveling, adventures, or pleasure, knowing the geometry of your bike is crucial. With the right information choosing an ideal bike is easier than ever. So what are you waiting for? Use your new knowledge to find your perfect fit and start riding!

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