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Bike Fit Terminology: The Complete Glossary for Cyclists

H
Heiko

Triathlete and founder of BikeFittr

When I started getting into bike fitting, the jargon was overwhelming. Stack, reach, KOPS, Q-factor — every article assumed I already knew what these meant. This glossary is what I wish I'd had back then: every term explained with the actual numbers that matter, pulled from the same data our BikeFittr tools use to analyze your position.

Bookmark this page. You'll come back to it.

Frame Geometry

Stack The vertical distance from the center of the bottom bracket to the top of the head tube. Stack determines how high your handlebars sit relative to your pedals. A higher stack means a more upright position. Endurance road bikes typically have a higher stack-to-reach ratio than race bikes.

Reach The horizontal distance from the center of the bottom bracket to the top of the head tube. Reach is the primary number that determines how stretched out you feel on the bike. Unlike top tube length, reach is independent of seat tube angle, making it more reliable for comparing frames.

Top Tube Length (Effective) The horizontal distance from the center of the head tube to the center of the seat tube. This used to be the main sizing metric, but stack and reach are more precise because they separate vertical and horizontal dimensions.

Seat Tube Angle The angle of the seat tube relative to horizontal. Steeper angles (75-78°) push the rider forward over the bottom bracket, common on triathlon bikes. Slacker angles (72-73°) are typical for road bikes and place the rider further behind the BB.

Head Tube Angle The angle of the head tube relative to horizontal. Steeper angles (72-74°) create quicker steering, typical of road and crit bikes. Slacker angles (64-68°) add stability, common on mountain bikes.

Wheelbase The distance between the front and rear axle centers. A longer wheelbase increases stability; a shorter one improves agility. Road bikes range from roughly 970-1010mm, while endurance bikes run longer.

Bottom Bracket Drop The vertical distance the bottom bracket sits below the axle centerline. More drop lowers your center of gravity for stability but reduces pedal clearance in corners. Typical road values are 65-75mm.

Saddle Setup

Saddle Height The distance from the center of the bottom bracket to the top of the saddle, measured along the seat tube. The most common starting formula is the LeMond method: inseam x 0.883. For example, an 86cm inseam gives a saddle height of roughly 76cm. Fine-tuning from there is based on knee angle. Our Saddle Height Analyzer measures your actual knee angle to verify this. Read more in our saddle height adjustment guide.

Saddle Setback The horizontal distance from the tip of the saddle nose to the center of the bottom bracket. Setback determines your position relative to the pedals and directly affects knee-over-pedal-spindle alignment. Adjusting setback shifts your weight distribution between hands and seat. Our Saddle Offset tool measures this.

Saddle Angle (Tilt) The fore-aft tilt of the saddle. Most riders start with a level saddle (0°). A slight nose-down tilt (1-2°) can relieve pressure for some riders but may cause you to slide forward. A nose-up tilt increases perineal pressure. See our guide on setting saddle angle for details.

Saddle Width Should correspond to your sit bone width plus some margin. Typical widths range from 130mm (narrow/race) to 155mm (wide/comfort). Measured sit bone width + 20-30mm is a common sizing rule.

Cockpit and Handlebars

Drop The vertical difference between the top of the saddle and the top of the handlebars. More drop means a more aggressive, aerodynamic position. Beginners often start with zero drop or handlebars slightly above the saddle. Aggressive road fits may have 80-120mm of drop. Our Cockpit Analysis tool evaluates your drop through back and arm angle measurements.

Stem Length The length of the stem connecting the steerer tube to the handlebars, typically 80-130mm on road bikes. Longer stems increase reach and stabilize steering. Shorter stems (50-70mm) are common on mountain bikes for quicker handling. Changing stem length is one of the easiest ways to adjust reach without changing frames.

Stem Angle The angle of the stem relative to the steerer tube. A negative angle (e.g., -6° or -17°) tilts the bars down for a more aggressive position. A positive angle raises them. Flipping a stem with a 6° rise gives roughly 12° of total adjustment range.

Handlebar Width Should roughly match your shoulder width measured at the acromion (bony point on top of each shoulder). Road bars typically come in 38-44cm (center-to-center). Too wide adds drag and strains shoulders; too narrow restricts breathing. See our handlebar width guide.

Handlebar Reach The horizontal distance from the bar center to the furthest point of the drops. Not to be confused with frame reach. Typically 70-85mm on modern road bars. Compact bars have shorter reach for more hand positions.

Handlebar Drop The vertical distance from the bar tops to the lowest point of the drops. Usually 120-130mm on standard bars, 115-125mm on compact bars. Affects how low you can get in the drops.

Hoods Position The position of your brake/shift levers on the handlebar. Most riders spend 60-80% of ride time on the hoods, so their angle and placement significantly affect comfort.

Pedal and Cleat

Crank Length The distance from the bottom bracket center to the pedal spindle center. Standard sizes range from 165mm to 175mm, with 170mm and 172.5mm being most common on road bikes. Shorter cranks reduce hip impingement at the top of the stroke and improve clearance. Longer cranks provide more leverage but require more hip and knee flexion.

Q-Factor The distance between the outer faces of the two crank arms at the pedal attachment points. Road bikes typically measure 145-155mm, while mountain bikes run wider at 170-180mm. A narrower Q-factor keeps your legs closer to the bike centerline, improving aerodynamics and reducing lateral knee stress.

Cleat Position The fore-aft and lateral placement of the cleat on the shoe sole. The ball of the foot (first metatarsal head) should sit over or slightly behind the pedal axle. Moving cleats rearward can reduce calf strain on long rides. Read more in our foot position guide.

Cleat Float The degrees of rotational freedom a cleat allows before unclipping. Ranges from 0° (fixed) to about 15° depending on the pedal system. Shimano yellow cleats offer 6° of float; red cleats offer 0°. Look systems range from 0° (black) to 9° (red). More float reduces knee stress for riders with imperfect alignment.

Cleat Cant/Shims Wedges placed between the shoe and cleat to correct for natural foot cant (inward or outward tilt of the foot). Typically 1-2° per shim. Helps align the knee tracking over the pedal spindle.

Pedal Spindle Length The length of the pedal axle. Standard is about 52-53mm, but extended spindles (+4mm to +20mm) are available to widen your effective stance for riders with wider hips or knee tracking issues.

Body Angles

These are the angles BikeFittr measures from your photos. Ranges vary by bike type because each discipline demands a different balance of power, comfort, and aerodynamics.

Knee Angle (at bottom of pedal stroke) The angle at the back of the knee when the pedal is at the lowest point. This is the primary metric for saddle height.

Bike Type Optimal Range
Road 140-150°
MTB 135-145°
Triathlon 145-155°
City 130-140°
Trekking 135-145°

Too straight (>155°) risks hamstring strain and hip rocking. Too bent (<130°) wastes energy and loads the knees. Measured by our Saddle Height tool.

KOPS (Knee Over Pedal Spindle) The horizontal offset of the knee relative to the pedal spindle when the crank is at 3 o'clock (forward horizontal). Measured in millimeters — positive means the knee is forward of the spindle.

Bike Type Optimal Offset
Road -5 to +5mm
MTB -10 to +5mm
Triathlon +10 to +25mm
City -15 to -5mm
Trekking -10 to 0mm

Triathlon bikes push the knee well forward for hip-opening and sustained power at low aerodynamic positions. City bikes keep you further back for an upright posture. Measured by our Saddle Offset tool.

Back Angle The angle of your torso relative to horizontal. Lower angles are more aerodynamic but demand more flexibility and core strength.

Bike Type Optimal Range
Road 40-50°
MTB 50-65°
Triathlon 20-35°
City 70-85°
Trekking 55-70°

Measured by our Cockpit Analysis tool.

Arm Angle The angle at the elbow when your hands are on the hoods or aero bars. A slight bend absorbs road vibration and prevents locking out your elbows.

Bike Type Optimal Range
Road 85-95°
MTB 80-95°
Triathlon 70-85°
City 100-120°
Trekking 90-105°

Measured by our Cockpit Analysis tool.

Hip Angle The angle at the hip joint at the top of the pedal stroke (when the thigh is closest to the torso). A too-closed hip angle restricts breathing and power.

Bike Type Optimal Range
Road 45-55°
Triathlon 35-45°
MTB 50-65°
City 65-80°

Steeper seat tube angles (as on tri bikes) open the hip angle despite the lower torso, which is why tri-specific geometry exists.

Ankle Angle The angle at the ankle joint during the pedal stroke, typically 85-115° depending on pedaling style and bike type. A neutral ankle (around 90-100°) is most efficient. Excessive toe-pointing (plantarflexion >115°) or heel-dropping (dorsiflexion <85°) wastes energy and can cause Achilles or calf issues.

Riding Position Modifiers

These preferences shift all the base angles for a given bike type. BikeFittr applies them automatically when you select a riding preference.

Performance Prioritizes power and speed. Shifts knee angle +2°, KOPS +3mm forward, back angle -5° (lower), arm angle -5°. Suits racers and fast group rides.

Balanced The default — no modifications to the base bike type angles. A good starting point for most riders.

Comfort Reduces strain with a more upright position. Shifts knee angle -3°, KOPS -3mm back, back angle +8° (more upright), arm angle +8°. Ideal for riders with flexibility limitations or those prioritizing joint health.

Endurance Optimized for long-distance sustainability. Shifts knee angle -1°, KOPS -2mm, back angle +5°, arm angle +5°. A middle ground between balanced and comfort for century rides and touring.

Aerodynamic Maximum aero, aggressive positioning. Shifts knee angle +3°, KOPS +5mm, back angle -10°, arm angle -8°. For time trials, triathlons, and riders with excellent flexibility. Not recommended for rides over 2-3 hours unless you've trained in this position.

Quick Reference: Which Tool Measures What

Measurement BikeFittr Tool
Knee angle Saddle Height
KOPS offset Saddle Offset
Back angle Cockpit Analysis
Arm angle Cockpit Analysis
All angles + bike switch Full Analysis

For a complete walkthrough of doing this yourself, check out our DIY bike fit guide. If you're dealing with knee issues, our cycling knee pain guide covers how these measurements connect to common problems.

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