This post compares the advantages and disadvantages of slack and steep head tube angles.
Head Tube Angle.
The head tube angle is formed by the head tube and the ground (or a horizontal line passing through the center of the bottom bracket. (image below)
What is a steep head tube angle?
The larger the head tube angle is, the steeper it is. For example, head tube angles around 71-73º or more are considered steep.
Steeper head tube angles are common for bicycles designed for efficient pedaling (e.g., road bikes, gravel bikes, urban commuters…etc.)
What is a slack head tube angle?
The smaller the head tube angle is, the slacker it is.
In general, angles under 70º are considered the beginning of the slack range. Slacker angles are common for mountain bikes designed to overcome massive obstacles during descents.
What Are The Advantages of Steeper Head Tube Angles
A steeper head tube angle positions the rider’s mass closer to the front wheel. Consequently, it becomes easier to assume a more aerodynamic position. Reduced drag equals greater average speed and efficiency.
For that reason, road and TT bikes do their best to minimize the drag created by the torso by making the rider’s back angle as horizontal as possible to the ground.
- Climbing Power
Bicycles with steep head tube angles excel at climbing because the front wheel has better traction and there’s less mass over the rear end making it easier to spin the rear wheel.
As a result, the rider has an easier time maintaining a higher cadence. Cadence is a term indicating the rotations of the cranks per minute.
A higher cadence such as 90RPM or more produces a greater average speed and spares energy.
Also, the extra mass on the front wheel reduces the chances of accidental front wheel lifting when overcoming a section with a steep gradient.
If the front wheel goes up involuntarily, the rider loses control as well as the ability to maintain a steady pedaling output.
- Technical Control as Slow Speeds
A steeper head tube angle makes tight turns at slow speeds easier. This is beneficial when the rider is covering technical terrain. For that reason, XC bikes have steeper head tube angles than trail models.
- More Glute Involvement
The aerodynamic position resulting from the steeper HTA brings more of the rider’s hip extensors into the pedal stroke.
As a result, the rider can produce more power because the glutes are among the strongest muscles of the human body.
The Disadvantages of Steeper Head Tube Angles
- Obstacles = Problem
The more aggressive an MTB is, the slacker its head tube angle becomes. This geometry makes it easier to overcome road irregularities.
When the head tube angle is slack, the front wheel is further in front of the rider and there’s less weight on it.
Consequently, the front wheel has an easier time rolling over obstacles. And if the front wheel overcomes an obstruction the chances that the rear wheel will follow are very high.
Steeper head tube angles have the opposite effect. The extra weight on the front end and the position of the front wheel closer to the rider’s mass make it more difficult to get over irregularities.
- Falling Over The Handlebars
The steeper the head tube angle is, the easier it becomes to flip over the handlebars due to the extra mass on the front end.
- Horizontal Back Angle
The horizontal back angle is beneficial from an aero standpoint, but it does stress the rider’s back more. If the bike fit is poor, and the rider isn’t fit enough for the riding volume, chronic pain may arise.
- Wrist Stress
The shift towards the front end stresses the wrists, elbows, and shoulders because they have to support more of the rider’s weight.
The Advantages of Slack Head Tube Angles
Slack head tube angles weren’t a thing until MTBs acquired long travel suspension and became extremely aggressive downhill.
Until then, MTBs were essentially gravel bikes (although used on much harsher terrain) and had a very steep geometry.
The head tube angles of MTBs are getting slacker and slacker for the following reasons:
- Stability Downhill
By putting the front wheel further in front of the rider, it becomes easier to ride fast downhill on off-road terrain because the front wheel has an easier time overcoming obstacles. Hence the extremely slack HTAs on downhill bikes.
- Longer Travel Forks
A super slack head tube angle allows the user to run a fork with massive travel.
When the fork compresses, the head tube gets closer to the ground, and the head tube angle becomes steeper.
The slacker the starting head tube angle is, the more the fork can compress until it reaches its final position without putting the rider in danger.
Meanwhile, if you put such a fork on a regular bike with a steep head tube angle, the post-compression HTA will get dangerously sleep.
Also, the stress on the head tube itself will be massive, and sometimes the frame may crack (or completely disintegrate).
- Harder To Flip Over The Handlebars
The slacker the HTA, the harder it is to get over the handlebars because the rider’s mass is closer to the rear wheel.
- More Aggressive Front Braking
Thanks to the two points above, it’s possible to use the front brake slightly more aggressively. Of course, the extent of this technique depends on the rider’s skills, the terrain, the braking mechanism...etc.
- Tricks Are Easier
Slacker head tube angles facilitate the lifting of the front wheel – an essential move for the performance of many tricks such as the bunny hops and rear wheel manual.
In the case of MTBs, lifting the front wheel is also used to overcome obstacles such as tree roots, rocks, small logs…etc.
The Disadvantages of Slack Head Tube Angles
- Difficult Climbing
Slack head tube angles make climbing more difficult because the rear wheel is supporting more weight whereas the front wheel has less traction.
It’s also more difficult to exert force due to the body position of the rider. As a result, downhill bikes are rarely if ever used for climbing.
- Slow Speed Steering = Weird
The slack HTA makes steering at slow speeds a bit uncomfortable and “boat-like”.
As a result, going around tight corners is difficult, especially uphill.
- Turning Requires More Leaning In
Riders used to steeper head tube angles will find that steering via the bars only is not ideal when the HTA is extra slack.
The slacker the HTA is, the more the rider has to lean in the turns. Not everyone will like that.
- Upright Position
Slack HTAs put the rider in a more upright position creating more drag.
Steeper Seat Tube Angles Come to Save The Day
The slacker the HTA, the steeper the seat tube angle becomes. This engineering aims to negate some of the downsides caused by the slack head tube angles.
A steeper seat tube angle places more of the rider’s weight towards the front wheel and thus allows more efficient pedaling and improves front wheel traction.
The Average Head Tube Angles Of Road Bikes
The table below contains the head tube angles of some popular road models.
Note: The data in the tables focuses on medium size frames.
|Giant Contend SL1||72.5º|
|Giant Propel Advanced SL||73º|
|Boardman SLR 8.8||72.5º|
|Canyon Ultimate CF SLX||73.3º|
|Mason Definition Chorus||71.5º|
|Fara Cycling F/AR||72º|
|Enigma Evoke MK3||73º|
|Mason SLR SRAM Force||70.5º|
|BMC Roadmachine 01 ONE||72º|
|Cannondale SuperSix EVO Hi-MOD||73º|
|Canyon Grail CF SLX 8 eTap||72.8º|
|Cervelo Caledonia-5 Dura Ace||72º|
|Mason Resolution EKAR||71º|
|Merida Scultura Endurance Custom||73º|
|Orbea Gain M20i||72º|
|Rose Reveal Four DISC Ultegra Di2||72º|
|Scott Addict eRIDE Premium||73.3º|
|Specialized S-Works Aethos||73.5º|
|Storck Fascenario.3 Comp Disc Ultegra||73.5º|
|Trek Domane+ LT 9||71.9º|
|Wilier Filante SLR||71º|
Conclusion: Road bikes’ average head tube angle is 72.475º and is therefore on the steeper side.
The Average Head Tube Angles Of Gravel Bikes
The next table shows the average head tube angle of gravel bikes.
|Canyon Grail CF SLX 8.0 Di2||72.5º|
|Canyon Grizl CF SL 8 1by||72.5º|
|Giant Revolt Advanced Pro 0||71.5º|
|Trek Checkpoint SL6 eTap||72.2º|
|Lauf Seigla Weekend Warrior||72.5º|
|TERRA M21e TEAM 1X||71º|
|Vitus Venon EVO-GR Rival AXS 1x||72.1º|
|Cannondale Topstone Carbon Rival AXS||71.2º|
|Specialized Diverge STR Expert||71.75º|
|Boardman ADV 8.9||71.5º|
|Mason Bokeh Ti GRX Di2||71.5º|
|Moots Routt 45||71.5º|
|Marin Nicasio +||72º|
|Cinelli Nemo Gravel Disc Ekar Mendini||71.5º|
|Ribble CGR 725 Steel||72º|
Conclusion: The average head tube angle of gravel bikes is 71.79º or about 1% slacker than what we observe on road bikes.
The ever so slightly slacker head tube angle isn’t surprising given that gravel bikes are designed to conquer light off-road terrain.
The Average Head Tube Angles Of Touring Bikes
The next table focuses on the head tube angles of popular touring bikes.
|Model||Head Tube Angle|
|Salsa Marrakesh Sora||70.8°|
|Trek 520 Disc 2020||71.8°|
|Giant ToughRoad SLR GX 1 Drop Bar||70.5°|
|Bombtrack Arise Tour 2020||71°|
|Salsa VAYA GRX 600||71.5°|
|Norco SEARCH XR STEEL RIVAL 1||71°|
|Genesis Tour De Fer 30||71°|
|Surly Disc Trucker||72°|
|Marin Four Corners||71.5°|
|Co-Motion Deschutes 2021||70.5°|
|Riverside Touring 900||72°|
|Rose Multisport 1||70°|
|Focus Atlas 6.7 EQP||70.5°|
|Brodie Mega Tour||69°|
|Panorama Taiga EXP||69.7°|
|On-One Rocky Road||70°|
Conclusion: Touring bikes have a much slacker head tube angle than road and gravel bikes averaging at 70.77°
Why? The slacker head tube angle puts the rider in a more upright position which relieves wrist and back stress. The relaxed stance is especially beneficial over long distances.
The Average Head Tube Angles Of XC Bikes
The next table focuses on the head tube angles of popular XC bikes.
|Lapierre Prorace CF 9.9||68º|
|Specialized Epic Pro||67.5º|
|Vitus Rapide FS CRX||67º|
|YT Izzo Uncaged 7||66.5º|
|BMC Fourstroke 01 Two AXS||66.5º|
|Cannondale Scalpel HT Carbon 4||66.5º|
|Canyon Exceed CFR Team||69º|
|Giant Anthem Advanced Pro 29 1||67.5º|
|Intense Sniper XC Expert||67.5º|
|Merida Ninety-Six RC 9000||68.5º|
|Orbea Oiz M-Team||67.9º|
|Pivot LES SL 29 Pro XT/XTR||68.5º|
|Santa Cruz Blur C X01 AXS RSV||68.3º|
|Scott Spark RC Team Issue AXS||67.1º|
Conclusion: The angles of modern XC bikes are quite slack at 67.59º on average. Not a surprise since modern XC bikes have become way more aggressive than their ancestors.
The Average Head Tube Angles Of Trail Bikes
The next table focuses on trail bikes.
|Bird Aether 9||65º|
|Boardman MTR 8.9||66º|
|Cannondale Habit 4||65.5º|
|Canyon Neuron 5||66º|
|Merida One-Forty 700||65º|
|Propain Hugene Custom||65.5º|
|Vitus Escarpe 29 CRS||65º|
|Boardman MTR 9.0||66º|
|Canyon Spectral 125 CF 7||64º|
|Carrera Titan X||67º|
|Focus JAM 8.9||65º|
|Kona Honzo ESD||63º|
|Marin Rift Zone XR 27.5||65.6º|
|Polygon Siskiu T7 29||65.5º|
|Privateer 141 SLX XT||64.5º|
|Santa Cruz 5010 CC X01 RSV||65.2º|
|Specialized Stumpjumper Comp||63.5º-65.5º|
|Trek Fuel EX 8 Gen 6||63.5º-65.5º|
|Vitus Escarpe 29 CRX||65º|
|YT Jeffsy Core 3||66.2º|
The Average Head Tube Angles Of Downhill Bikes
The next table contains the head tube angles of popular downhill bikes.
|Canyon Sender CF 7.0||63º|
|Nukeproof Dissent 290 Comp||63º|
|Saracen Myst AL||63º|
|Scott Gambler 900 Tuned||62.9º|
|Commencal Supreme DH||62.2º|
|YT Industries Tues||63.5°|
|Atherton Bikes DH Prototype||63°|
|Specialized Demo 29||63.2º|
|Polygon Xquarone DH||63º|
|Santa Cruz V10||63.7°|
Conclusion: Unsurprisingly, downhill bikes have the slackest head tube angle on average at 63.09º.
The Average Head Tube Angles Of Dirt Jump Bikes
The next table focuses on the head tube angle of dirt jumpers.
|Saracen Amplitude CR2||68.5°|
|Santa Cruz Jackal||68.7°|
|NS Bikes Metropolis 3||70°|
|Scott Voltage YZ 0.1||68.5°|
|Canyon Stitched 720||68.5°|
|NS Bikes Movement 3||69°|
|NS Bikes Zircus||70°|
|Haro Steel Reserve 1.1||69°|
|Polygon TRID 2021||70°|
Conclusion: Dirt jumpers have a conservative head tube angle of around 69° that’s neither steep nor as slack as what we observe on aggressive MTBs.
The Average Head Tube Angles Of Race BMX Models
The next table analyzes the head tube angles of RACE BMXs.
|Model||Head Tube Angle|
|BMX Race Chase Edge Pro XL||73°|
|Haro Pro 24||73.3°|
|Haro Pro XL||74°|
|Chase Edge Expert BMX||72°|
|Chase Element Pro||74°|
|Redline 2022 Proline||74°|
|Redline MX Expert XL||73°|
Conclusion: Race BMX bikes have steep head tube angles averaging 73.2°
The Average Head Tube Angles Of Freestyle BMX Models
The next table presents the seat tube angles of freestyle BMX bikes.
|Model||Seat Tube Angle|
|Mongoose Legion L100||75°|
|Sunday Street Sweeper Pro||75.25°|
|Performer 20.5 Mercado||75°|
Conclusion: Freestyle BMX bikes have very steep head tube angles averaging at about 75°. The goal in this case is to increase the responsiveness of the bike – a critical property when performing technical stunts.
Meanwhile, race BMX bikes do not have to be as technical and thus can get away with slightly slacker head tube angles (values above) making it easier to overcome obstacles in front of the rider.
The list below contains the average head tube angles in the tables going from the steepest to the slackest.