Frame Geometry

Why Frame Geometry is Critical

Geometry directly influences:

• Riding Position - From aggressive-aerodynamic to upright-comfortable
• Handling - Agility in corners vs. stability on straights
• Comfort - Load on back, neck, and wrists
• Power Transfer - Efficiency when pedaling and sprinting
• Stability - Safety at high speeds and descents

A frame with wrong geometry can never function optimally, even with the best components. Geometry is the foundation on which everything else builds.

The Most Important Geometry Measurements Explained

Stack and Reach - The Base Parameters

Stack (vertical height):

• Distance from bottom bracket center to top of head tube
• Determines how high the handlebar can be positioned
• Typical values: 500-600mm (depending on frame size)
• Low Stack (500-540mm) = Sporty, aerodynamic position
• High Stack (560-600mm) = Upright, comfortable position

Reach (horizontal length):

• Horizontal distance from bottom bracket to top of head tube
• Determines how stretched the riding position is
• Typical values: 360-420mm (depending on frame size)
• Short Reach (360-380mm) = More compact, upright position
• Long Reach (400-420mm) = Stretched, aerodynamic position

Top Tube Length - Classic Measurement with Pitfalls

The horizontal top tube length used to be the main measurement for frame size:

• Measured from head tube center to seat tube center (horizontal)
• Typical values: 520-575mm
• Problem: Says little about actual riding position
• Stack/Reach are more precise and meaningful

Virtual vs. actual top tube:

• Many modern frames have sloping top tubes
• Virtual top tube = horizontal projection
• Enables lower standover height with same geometry

Seat Tube and Seat Angle

Seat Tube Length:

• From bottom bracket center to top of seat tube
• Less relevant with modern frames with sloping top tubes
• Important: Is sufficient seatpost extension possible?

Seat Angle (Seat Tube Angle):

• Typical: 72-74.5°
• Influences riding position relative to bottom bracket
• Steep Seat Angle (73.5-74.5°):
  • Saddle further forward over bottom bracket
  • More power on pedal, better for climbs
  • Less load on arms/handlebar
• Flatter Seat Angle (72-73°):
  • Saddle further back
  • More balanced weight distribution
  • More relaxed position

Head Tube and Head Angle - Critical for Handling

Head Tube Length:

• Determines minimum handlebar height
• Race: 100-130mm (flat position possible)
• Endurance: 150-200mm (higher handlebar without many spacers)
• With short head tube: More spacers under stem needed

Head Angle (Head Tube Angle):

• One of the most important values for handling
• Typical: 70-75°
• Influences trail and thus steering behavior

Trail:

• Determined by head angle and fork offset
• Critical value for steering feel
• More trail = more stable, less agile
• Less trail = more agile, less stable
• 55-60mm is the "sweet spot" for most riders

Wheelbase - Stability vs. Agility

The wheelbase is the distance between front and rear axle:

Short Wheelbase (960-990mm):

• Agile, nimble handling
• Quick direction changes
• Better acceleration
• Ideal for: Criteriums, technical courses, climbs

Medium Wheelbase (990-1010mm):

• Balanced handling
• Good balance between agility and stability
• Ideal for: All-round race, training

Long Wheelbase (1010-1040mm):

• Very stable, smooth handling
• Safe at high speeds
• Comfortable on long distances
• Ideal for: Gran Fondo, long distance, descents

Bottom Bracket Height - Cornering vs. Ground Clearance

Bottom Bracket Drop (BB Drop):

• How much lower is the bottom bracket below the axle line?
• Typical: 65-75mm

Bottom Bracket Height (BB Height):

• Absolute height above ground
• Typical: 265-280mm

Chainstay Length - Traction and Handling

Chainstay Length:

• Length of rear stays from bottom bracket to rear axle
• Typical: 400-420mm
• Influences weight distribution and rear wheel traction

Short Chainstays (400-410mm):

• More weight on rear wheel
• Better traction on climbs
• More agile, "poppy"
• Can feel unstable

Long Chainstays (415-420mm):

• Better weight distribution
• More stable, predictable
• More tire clearance
• More comfortable

Fork Offset (Fork Rake)

The fork offset is the forward offset of the fork ends:

• Typical: 40-55mm
• Works with head angle to determine trail
• More Offset (50-55mm):
  • Less trail with same head angle
  • More agile steering
  • More direct feedback
• Less Offset (40-45mm):
  • More trail with same head angle
  • More stable steering
  • More damped feedback

Geometry Types by Purpose

Race Geometry - Maximum Performance

Characteristics:

• Stack/Reach Ratio: 1.30-1.40
• Low stack for flat aerodynamics
• Long reach for stretched position
• Steep head angle (73-75°)
• Short wheelbase (970-995mm)
• Low bottom bracket (265-270mm)
• Aggressive riding position

Advantages:

• Maximum aerodynamics
• Direct power transfer
• Agile handling
• Optimal sprint position

Disadvantages:

• Less comfortable
• More load on back/neck
• Less stable at high speeds
• Requires good flexibility

Ideal for:

• Competition races and criteriums
• Short to medium distances
• Experienced, flexible riders
• Sprint and climbing specialists

Endurance Geometry - Comfort for Long Distances

Characteristics:

• Stack/Reach Ratio: 1.45-1.55
• High stack for upright position
• Shorter reach for less stretch
• Flatter head angle (72-73°)
• Longer wheelbase (1005-1025mm)
• Higher bottom bracket (273-278mm)
• Comfortable riding position

Advantages:

• High comfort even after hours
• Little load on back/neck
• Stable at high speeds
• Safe descents
• Relaxed posture

Disadvantages:

• Less aerodynamic
• Sluggish in corners
• Somewhat harder to accelerate

Ideal for:

• Gran Fondo and sportives
• Multi-day tours
• Hobby and pleasure riders
• Older riders or those with back problems
• Training for long distances

Aero Geometry - Time Trials and Triathlons

Characteristics:

• Very low stack
• Very long reach
• Steep seat angle (74-76°)
• Medium-long wheelbase (990-1010mm)
• Integration for minimal air resistance

Special Features:

• Optimized for time trial position with aerobars
• Seat angle extremely steep for forward position
• Short head tube for low handlebar position
• Often limited everyday usability

Size Determination and Bike Fitting

Correctly Measuring Body Dimensions

Measuring Inseam:

1. Stand barefoot with back against wall
2. Clamp book between legs (firmly against crotch)
3. Measure distance from floor to top of book
4. Note value in cm

Considering Torso Length:

• Two riders of same height can have very different torso lengths
• Long torso → rather larger frame or longer stem
• Short torso → rather smaller frame or shorter stem

Stack/Reach for Your Measurements

Rule of thumb for Reach recommendation by inseam:

• Inseam (cm) × 0.475 = approximate Reach in mm
• Example: 84cm inseam → 399mm Reach

Rule of thumb for Stack recommendation:

• Race-oriented: Reach × 1.35
• Balanced: Reach × 1.45
• Comfort-oriented: Reach × 1.55

Deciding Between Two Sizes

If you're between two frame sizes:

Choose smaller frame if:

• You prefer agile handling
• You ride race-oriented
• You're above average flexible
• Short torso
• You like rather sporty-aggressive position

Choose larger frame if:

• Comfort and stability are important
• You prefer long distances
• You have rather limited flexibility
• Long torso
• You prefer upright position

Professional Bike Fitting

Professional bike fitting is the best investment:

What happens during fitting:

1. Measure body dimensions and flexibility
2. Discuss riding style and goals
3. Analyze current riding position
4. Calculate optimal geometry parameters
5. Make frame recommendations
6. Adjust saddle, handlebar, stem
7. Position pedal plates (cleats)
8. Test ride and fine-tuning

Cost: €150-350 for comprehensive fitting
Benefit: Priceless for performance, comfort, and health

Geometry Adjustment Through Components

Stem Length and Angle

If frame geometry doesn't quite fit:

Adjusting stem length:

• Standard: 90-120mm
• Shorter Stem (80-90mm):
  • More upright position
  • More weight on rear wheel
  • More nervous steering behavior
• Longer Stem (120-140mm):
  • More stretched position
  • More weight on front wheel
  • More stable steering behavior

Stem Angle:

• Negative angle (-6 to -17°): Sportier, lower
• Positive angle (+6 to +17°): More comfortable, higher

Seatpost Offset

Setback (Seatpost Offset):

• 0-25mm offset backward common
• Influences effective seat angle
• Can make steep seat angle somewhat flatter
• Or conversely: Inline post makes flat angle steeper

Handlebar Height and Spacers

Spacers under stem:

• Increase effective stack
• 5-40mm common
• More spacers = higher, more comfortable handlebar
• Fewer spacers = lower, more aerodynamic handlebar

Handlebar width and shape:

• Influences effective reach
• Narrower handlebar = somewhat more reach felt
• Wider handlebar = somewhat less reach felt

Geometry Trends and Developments

Longer Reach, Shorter Stems

Modern road bikes focus on:

• Longer reach for better weight distribution
• Shorter stems for more direct handling
• Result: Better control with maintained stretched position

Slack and Long - Adopted from MTB

Influence from mountain bike sector:

• Flatter head angles than before (72° instead of 73.5°)
• Longer wheelbases
• Result: More stability, especially on descents
• Perfect for Gran Fondo and fast descents

Larger Tire Clearance

• Before: Maximum 25mm tires
• Today: 28-32mm standard
• Result: More comfort, better traction
• Geometric adjustment: Longer chainstays, more fork clearance

Integration and Aerodynamics

Geometry is increasingly optimized for aerodynamic integration:

• More compact front ends
• Head tube and fork crown integrated
• Influence on handling must be compensated

Special Geometries for Different Disciplines

Track Bike Geometry

Special requirements for velodrome:

• Very steep head angle (75-76°)
• Short wheelbase (960-980mm)
• Very steep seat angle (75-76°)
• High bottom bracket for banking
• Extremely agile, direct handling

Gravel Geometry

For mixed terrain:

• Longer wheelbase for stability
• Higher bottom bracket for ground clearance
• Flatter head angle for control
• Higher stack for comfort
• Wider tire clearance (40-50mm)

Women-Specific Geometry

Differences to unisex frames:

• Often shorter reach (women on average have shorter torsos)
• Higher stack (for same stack/reach ratio)
• Shorter chainstays (smaller shoe sizes)
• Adjusted touchpoints (saddle, handlebar)

Avoiding Common Geometry Mistakes

Mistake 1: Frame Too Large

Problem:

• Too long reach
• Too high stack
• Overstretched position
• Too long standover height

Symptoms:

• Pain in shoulders and neck
• Too much weight on hands
• Feeling of "over the bike" instead of "in the bike"
• Difficulties when dismounting

Solution:

• Choose smaller frame
• Shorter stem (only limited help)
• Saddle further forward (compromise)

Mistake 2: Frame Too Small

Problem:

• Too short reach
• Too low stack
• Cramped position
• Too many spacers needed

Symptoms:

• Knee problems (knees too close to elbows)
• Too much weight on rear wheel
• Unstable handling uphill
• Much too long stem needed

Solution:

• Choose larger frame
• Saddle further back (only limited possible)
• Longer stem (max. 130mm sensible)

Mistake 3: Wrong Geometry Category

Problem:

• Race geometry for long-distance tours
• Or: Endurance geometry for competitions

Symptoms:

• Race on long distance: Pain, exhaustion, limited position
• Endurance in race: Too slow, no pressure, poor handling

Solution:

• Second bike with suitable geometry
• Or: Compromise geometry (All-Road)

Reading Geometry Charts Correctly

What Manufacturers Specify

Typical specifications in geometry chart:

• Stack and Reach (most important values!)
• Top tube length (horizontal)
• Seat tube length
• Head tube length
• Head angle
• Seat angle
• Wheelbase
• Bottom bracket height and BB drop
• Chainstay length
• Fork offset
• Standover height

What You Should Pay Attention To

Priority 1: Stack and Reach

• Do these values fit your body measurements?
• Does the Stack/Reach ratio match your goals?

Priority 2: Wheelbase and Head Angle

• Agile or stable handling desired?

Priority 3: Seat Angle

• Does it fit your riding style?
• Sufficient adjustment range for saddle position?

Priority 4: Special Requirements

• Sufficient tire clearance?
• Bottom bracket height for your use?

Testing Geometry Before Purchase

Conducting Test Ride Correctly

Minimum Duration: 60 Minutes

• Short test rides say little
• Book extensive test rides

What to test:

1. First 10 minutes: Basic feel, handling, position
2. 20-30 minutes: Comfort, do pressure points develop?
3. 30-45 minutes: Does position become uncomfortable? Pain?
4. Sprint test: How does power transfer feel?
5. Corner test: Handling in tight and fast corners
6. Descent test: Stability at high speed

Comparison to Current Bike

If you already have a road bike:

• Measure Stack/Reach of your current setup
• Compare with new frame
• Consider spacers, stem length, etc.
• Think: What should improve?

Summary and Decision Guide

Checklist: Finding Perfect Geometry

• Measure body dimensions - Inseam is critical
• Define purpose - Race, Gran Fondo, training?
• Determine geometry type - Race vs. Endurance
• Determine Stack/Reach - Matching body measurements and goals
• Handling preference - Agile or stable?
• Compare sizes between manufacturers - Not just frame size
• Test ride extensively - At least 60 minutes
• Plan bike fitting - €150-350 well invested
• Think long-term - Geometry is hard to change

The Most Important Geometry Rules

1. Stack and Reach are more important than frame size
2. The Stack/Reach ratio determines your riding style
3. Head angle and wheelbase fundamentally influence handling
4. Test ride extensively - numbers alone aren't enough
5. Bike fitting is the best investment
6. Components can only change geometry to a limited extent
7. The right geometry is more important than expensive components