Condensed Answer: Downhill bikes have a shorter reach than enduro MTBs to keep the bike nimble despite its long wheelbase and chainstays.
If downhill bikes had the same reach as other MTBs, the bikes would become too long.
Also, downhill bikes are not used uphill and don’t have to provide maximum comfort when climbing.
Reach. The term reach refers to the horizontal distance from the center of the bottom bracket to the middle of the head tube. (image above).
The reach has a direct impact on how big a frame feels. Two frames can be of the same size, but the one with the longer reach would create the feeling of a larger bicycle.
The Geometry of A Downhill Bike
The geometry of a downhill bike has the following characteristics:
1. Long Chainstays
The chainstays are the two rear tubes the closest to the chain (hence the name). The length of the chainstays is a very important measurement as it has a profound effect on how the bike behaves.
Downhill bikes have chainstays notably longer than those found on XC and enduro bikes. The average chainstay length of a downhill bike is about 445mm whereas that of XC and enduro models is about 430-435mm.
Downhill bikes have longer chainstays to increase the bike’s length (wheelbase) and therefore stability while simultaneously reducing the chance of “looping out” (the bike sliding in front of the rider).
Longer chainstays, however, make the bike less nimble and increase the effort needed to lift the front wheel for the performance of tricks such as bunny hops and manuals.
The table below compares the chainstay length of popular downhill, enduro and XC bikes.
|Downhill||Chainstay Length||Enduro||Chainstay Length||XC||Chainstay Length|
|Mondraker Summum||450mm||Cannondale Jekyll 1||435mm||Norco Revolver FS 2||430mm|
|YT Industries Tues 29||440mm||Canyon Torque CF 8||428mm||Sage Optimator||425mm|
|Commencal Supreme DH||439mm||GT Force Carbon PRO LE||434mm||Trek Supercaliber 9.7||430mm|
|Specialized Demo||438-443mm||Nukeproof Giga 290 Carbon Factory||445mm||Mondraker Chrono Carbon||430mm|
|Santa Cruz V10 MX||435-445mm||Orbea Rallon M-Team||440mm||Scott Spark RC||435mm|
|Canyon Sender 6||430-446mm||Pivot Firebird Pro XT/XTR – Air||431mm||Santa Cruz Tallboy||436mm|
|Nukeproof Dissent 920 Comp||445-455mm||Rocky Mountain Altitude C90 Rally Edition||425mm||Cannondale Scalpel Carbon SE||436mm|
|Trek Sessions 29 9.9||452mm||Santa Cruz Bronson CC X01 AXS||438mm||Specialized Epic EVO||438mm|
2. Slack Head Tube Angle
The head tube angle is the angle formed by the head tube and the ground. Since downhill bikes are built for overcoming obstacles during a descent, they have a slack head tube angle.
Or in simpler words, the front wheel is further in front of the rider. As a result, the wheel has an easier time overcoming irregularities. There’s also a reduced chance to go over the handlebars since less of the rider’s weight is on the front wheel.
Out of all MTBs, downhill bikes have the slackest head tube angles ranging between 63 and 65 degrees.
Part of the reason for the extra slack HTA angles on downhill bikes is the dual-crown fork which is longer and therefore taller than standard single-crown forks.
The table below compares the head tube angles (HTA) of downhill, enduro and XC bikes:
|Mondraker Summum||63.5°||Cannondale Jekyll 1||64°||Norco Revolver FS 2||67.4°|
|YT Industries Tues 29||63.5°||Canyon Torque CF 8||63.5°||Sage Optimator||69.5°|
|Commencal Supreme DH||63°||GT Force Carbon PRO LE||63.5°||Trek Supercaliber 9.7||69°|
|Specialized Demo||62.7°||Nukeproof Giga 290 Carbon Factory||63.5°||Mondraker Chrono Carbon||70°|
|Santa Cruz V10 MX||64°||Orbea Rallon M-Team||64°||Scott Spark RC||67.2°|
|Canyon Sender 6||63°||Pivot Firebird Pro XT/XTR – Air||64°||Santa Cruz Tallboy||65.7°|
|Nukeproof Dissent 920 Comp||63°||Rocky Mountain Altitude C90 Rally Edition||65.5°||Cannondale Scalpel Carbon SE||67°|
|Santa Cruz Bronson CC X01 AXS||64.5°||Specialized Epic EVO||66.5°|
The average head tube angle of downhill bikes is the slackest, but that of enduro bikes is very close behind. Unsurprisingly, XC bikes have a significantly steeper head tube angle facilitating climbing and the assumption of a more aerodynamic stance when pedaling.
Comparing The Reach Of Downhill, Enduro and XC Bikes
The table below compares the reach of popular downhill, enduro and XC bikes:
|Mondraker Summum||450 mm||Cannondale Jekyll 1||450mm||Norco Revolver FS 2||448mm|
|YT Industries Tues 29||429 mm||Canyon Torque CF 8||465mm||Sage Optimator||421mm|
|Commencal Supreme DH||445mm||GT Force Carbon PRO LE||455mm||Trek Supercaliber 9.7||440mm|
|Specialized Demo||446mm||Nukeproof Giga 290 Carbon Factory||455mm||Mondraker Chrono Carbon||426mm|
|Santa Cruz V10 MX||402.5mm||Orbea Rallon M-Team||460mm||Scott Spark RC||441mm|
|Canyon Sender 6||440mm||Pivot Firebird Pro XT/XTR – Air||468mm||Santa Cruz Tallboy||450mm|
|Nukeproof Dissent 920 Comp||460mm||Rocky Mountain Altitude C90 Rally Edition||449mm||Cannondale Scalpel Carbon SE||430mm|
|Trek Sessions 29 9.9||461mm||Santa Cruz Bronson CC X01 AXS||455mm||Specialized Epic EVO||436mm|
Note: The reach depends on the frame size. In most cases, the numbers in the table are for medium frames.
The data reveals that on average downhill bikes have a 16mm shorter reach than enduro bikes. Meanwhile, XC bikes seem to have the shortest reach for that particular frame size.
The Need For Short Reach
The slack head tube angle and the long chainstays make downhill bikes longer than other MTBs. That coupled with the fact that downhill bikes are not meant to be climbers, is a strong incentive to keep reach shorter and preserve some of the bike’s liveliness.
The Relationship Between Reach and Height
The taller the rider, the more reach is needed for assuming a comfortable position. For example, 415mm of reach would be too little for someone who is 6’2″ or taller. The downside of riding a frame with an extra short reach is the upright position and the feeling of being restrained.
That said, sometimes even tall people purposefully choose smaller bikes for the ability to throw them around with greater ease.