Common e-bike geometry terminology
The following list contains the most common terms used to describe the geometry of e-bikes as well as descriptions for each term. Riders of more specialized types of bikes (e.g. road bikes or enduro mountain bikes) may be concerned with a variety of other, more specific elements of geometry. However, for the average recreational e-biker, the following basics should be helpful when analyzing the geometry tables found on many e-bikers’ websites the e-bike brands we have worked with.
Some of the following descriptions refer to specific parts of the frame; We’ve included a reference image above that identifies the key elements of bike frame anatomy.
Effective top tube length
Deviating from the actual length of the top tube, this can be angled effective top tube length is a horizontal measurement from the center of the seat tube to the intersection of the top and head tubes. This measurement can be used to indicate the size of the frame as well as its feel.
Riders feel more stretched on bikes with longer top tubes and more compact on bikes with shorter top tubes.
To reach
To reach is the horizontal measurement from the center of the bottom bracket to the center of the top edge of the head tube. Like effective top tube length, it can be used to interpret frame size and the rider’s stretched feel, although actual rider position and comfort can be adjusted at the stem, saddle, etc.
Shorter range bikes generally feel more compact, while longer range bikes feel longer and are better suited for performance-oriented cycling.
stack
Related to range, stack indicates the vertical distance from the center of the bottom bracket to the center of the top edge of the head tube. This measurement can help determine the lowest possible handlebar height without spacers.
Lower stack bikes typically have a more aggressive, forward-leaning riding position, while higher stack bikes are more upright and comfortable.
Standing height
Standing height is the vertical distance from the ground to the center of the top tube. This measurement primarily influences the fit; Riders should have at least 1 to 2 inches of clearance over the top tube when standing to allow for comfortable dismounting.
City cruisers like the iGO Core Elite 3HD value comfort and an upright seating position.
Seat tube length
Seat tube length is the distance from the center of the bottom bracket to the top of the seat tube, measured along the length of the tube. In the past this was used to distinguish a bike’s frame sizes, but is no longer considered correct due to the differences between different types of bikes and even the same types of bikes from different brands.
In terms of fit, this distance can indicate the lowest possible saddle height (with the highest determined in combination with the seat post length). When taking the stack into account, the length of the seat tube can also provide information about the standover height.
Seat tube angle
Measured from the back of the seat tube relative to the horizontal line of the ground, Seat tube angle indicates how far back the seat tube is tilted and how the rider’s weight is positioned. It is usually between 71 and 76 degrees.
This angle can be described as shallow (a smaller angle with more slope) or steep (a larger angle with more straight-ahead direction). A steep seat tube makes climbing easier by shifting more weight to the front wheel. A loose seat tube shifts weight backwards and can make the rider feel more stretched out.
It is important to note that the effective seat tube angle can be adjusted by changing the tilt of the saddle (its adjustable fore-aft position).
Head tube length
The Head tube length is simply an end-to-end measurement of the head tube, which can be an indicator of bike positioning when fork length and wheel size(s) are also taken into account.
Given two bikes with the same fork length and wheels, one with a shorter head tube would have a lower, more aerodynamic riding position that would be better suited for racing. One with a longer head tube would have a more upright position and would be suitable for casual riding.
Hybrid commuter/e-MTBs like the Specialized Turbo Tero X 5.0 are characterized by a moderate forward lean.
Head tube angle
Like the seat tube angle, that Head tube angle is measured towards the rear of the bike relative to the ground. The temperature is often between 72 and 65 degrees and can also be described as flat or steep. The head tube angle affects the steering of the bike.
Bikes with a steeper head tube (larger angle) have more responsive handling and often feel nimble and agile. Riders with a slacker head tube (smaller angle) may require more effort to steer but are also more stable at speed.
Chain stay length
Measured from the center of the bottom bracket to the center of the rear wheel dropouts. Chain stay length can influence handling by determining the driver’s weight distribution and wheelbase (see below). Note that bikes with larger wheels require longer chainstays.
Bikes with shorter chainstays tend to have a more responsive and nimble ride, while bikes with longer chainstays sacrifice some agility to feel more stable.
wheelbase
A bicycle wheelbase is the distance between the wheel dropouts or axles and has a major influence on driving behavior.
With longer wheelbase bikes, the rider’s weight shifts less when going over bumps or applying the brakes, making the rider feel more stable. Shorter wheelbase vehicles may feel less stable, but are far more maneuverable and responsive to steering input.
Some foldable e-bikes like the Denago Folding Model 1 have an upright seating position with a relatively long range.
