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BH GC Aero

By Tom Demerly with assistance from Jaclyn Applegate.

The BH GC Aero is a high head tube, variable geometry seat angle bike well configured for the short torso, long leg rider- a fit category that has been underserved by the tri bike industry.

Spain’s BH Ultralight Bicycles is a company steeped in tradition. Triathlon is a sport that resists convention. The two seem an unlikely match. When I began my survey of BH’s GC Aero triathlon bike I was impressed by their G5 road bike, but cynical about the GC Aero’s foray into triathlon geometry.

On my first pass of the geometry chart I was concerned about the seat tube angle claims and the changes their steeper orientations may have on stability. I shouldn’t have worried. BH built a stable, relaxed front end with 72.5 and 72.8 degree head angles on their 52cm and  54cm frames. The largest 56 cm uses a 73 degree head tube angle.

BH Pro Angela Naeth sits at a moderately steep effective seat tube angle on her BH. The top tube length and reach match her torso dimensions well at this effective seat tube angle. Naeth has produced impressive bike course results including a new record on the difficult St. Croix 70.3 bike course.

BH Ultralight Bicycles (their U.S. name) also took a practical approach to head tube height on the GC Aero. The head tube on a 54cm BH GC Aero is 130 millimeters high as compared to 110 millimeters for a 54cm Felt “B” series bike and 120 millimeters for a 54cm Cervelo P2. The only bike in this category with a higher head tube is Kuota’s K-Factor at 135 millimeters for their size “Medium” with an advertised 54.5 cm seat tube according to their geometry chart. A higher head tube is a practical approach to rider positioning, especially if you find your fitter adding an increasing stack of 1 centimeter spacers under your stem on a low head tube bike. It’s better to fit the bike with the frame rather than buying a low head tube bike and adding spacers. For an athlete on a 54cm Cervelo P3 with a 70 mm (very short) stem but 4 cm of headset spacers under the stem and the stem angled upward- a BH GC Aero would have been a better fitting bike with its higher head tube and shorter reach dimension. The BH GC Aero is “High and Short” as opposed to a bike like the Cervelo P3 or Felt B12 which is “Low and Long”. If you have a shorter torso and longer legs the BH GC Aero may be on your fitter’s short list.

Using stack and reach comparison along with head tube heights the BH GC Aero is located toward the top of this comparison with its high head tube, high stack and short reach. Only Kuota's K-Factor is higher and shorter.
Naeth's bike is configured with a moderate rise stem and almost no headset spacers. At the top half of her pedal stroke, as seen in these photos, her knee still remains below her elbow for most of the pedal stroke, suggesting a high trend in cockpit position.

While this geometry trend smacks of being leisurely the BH GC Aero was ridden to the fastest ever St. Croix 70.3 bike split by Ultralight Bicycles athlete Angela Naeth. Naeth is an “uber biker” who has rapidly become one of the strongest cyclists in the sport, even challenging the bike splits of Wellington on some courses. Her tendency toward the slightly higher head tube, shorter reach of the BH GC Aero is typical of very powerful cyclists who tend to build a position firstly around power numbers and bike handling rather than drag coefficient and effective seat angle. Naeth’s performance may confirm that the BH GC Aero is a good geometry set for technical, rolling to very hilly bike courses. Naeth’s setup typically includes a moderate rise stem with minimal spacers. At the top of her pedal stroke a quick comparison of the proximity of her knee to her elbow reveals her elbow slightly above her knee- an attainable, functional, comfortable posture for the majority of riders and a practical orientation for grinding up long climbs at Pentiction, Lake Placid, Wisconsin and other hilly bike courses.

BH Pro Eneko Llanos uses no headset spacers and a negative rise (drop) stem on his BH. Note that his knee is still roughly horizontal in comparison to elbow position, suggesting a moderate degree of drop. The BH GC Aero is a strong choice for riders who prefer a slightly higher front end position.

Top Ironman pro Eneko Llanos, also on the BH GC Aero, uses a lower cockpit orientation on his BH that includes a negative rise stem that slopes downward from the head tube with no spacers. Based on photos Llanos may sit at a slightly steeper effective seat tube angle and have longer humerus bones (biceps) than Naeth, accounting for some the difference in cockpit orientation between the athletes.

I love the Vision cockpit in this parts kit but would prefer the older (albeit heavier), stiffer aluminum elbow rests. Once the elbow rests are replaced with stiffer aluminum ones to replace the flexible composite/polymer versions this cockpit is excellent.

From front to back the BH GC Aero starts with a great cockpit: Vision alloy “J” bend aerobars and alloy, wing shaped base bars. This is the cockpit I’ve swooned over on Cervelo and other bikes and ridden to race finishes at every distance. I’ll argue it is the best bend, especially as distances get longer. The one let down on the cockpit are the new polymer/composite molded elbow pads that replace the previous alloy pads. The new pads are lighter weight, but extremely flexible. It is worth it to source the previous alloy versions to shore up the stiffness of the elbow pads on this otherwise excellent cockpit.

Controls are Vision’s fine (and my favorite) crab-claw brake lever. This is the newest version with the polymer/textured grips. Shifters are Shimano’s more recent 10-speed bar ends, version SL-BS79, without the D-ring friction shift option. The cockpit is clamped to a Vision stem with a two-bolt front mounting plate and +/- 10 degree rise. This alloy stem is available in 70, 90, 100, 110 and 120 mm lengths to provide your fitter with a full range of reach options.

The BH GC Aero has a high, aero-styled head tube and an aero shaped, carbon fiber steer tube fork that melds nicely in appearance with the frame.

The head tube of the BH GC Aero features a pointed flourish that continues an aerodynamic-styled theme throughout the frame. I haven’t seen any wind tunnel development information on the tube shapes of the BH GC Aero other than a brief mention of wind tunnel testing in their sales literature. Because of that, I’ll place the BH GC Aero in the “Aero-styled” category as opposed to bikes with tube shapes developed in the wind tunnel specifically for low drag. If you are a wind-tunnel weenie who buys a bike from a spread sheet showing lowest drag coefficient the BH may not appear on your short list. If you are more pragmatic about fit and position the BH GC Aero’s higher head tube may become attractive. Fork on the BH GC Aero melds into the design of the down tube with further aerodynamic styling. The fork uses a carbon fiber steer tube to reduce weight and enhance ride quality.

Rear derailleur cable routing passes through the right seat stay instead of the more typical chain stay. This design keeps the rear derailleur cable straight for great rear derailleur performance.

Practical features on the frame are excellent. Cable routing is internal and uses cable housing throughout its length. The rear derailleur cable routes through the right seat stay instead of the chain stay to maintain a straighter cable and reduce friction. Nice design. There is one bottle mount on the frame so you’ll be referring to our article on hydration systems for anything longer than a one hour ride.

The main triangle and rear triangle are thick and substantial providing good ride stiffness. One bottle mount on the down tube means you'll likely need a handlebar mount hydration rig or rear saddle bottle carrier.

The BH GC Aero main frame has an aero-styled down tube, curved seat tube, sloping top tube and a minor seat tube extension attached to a robust rear triangle. The low top tube keeps the frame compact and stiff and helps with stand over clearance when climbing out of the saddle. Rear wheel dropouts are angled about 40 degrees downward, rear facing and have no dropout screws. The derailleur hanger is replaceable and wheel removal and installation is easier that with an entirely horizontal rear facing dropout.

Angular and fore/aft saddle adjustment require an open end wrench and can be a bit fumbly. It does clamp securely and has a wide range of adjustment. The seatpost binder collar is robust and modular, but be certain the torque on both bolts is equal using a torque wrench.

The seatpost on the BH GC Aero is a simple and effective design that requires at open end 13 mm wrench for angular and fore/aft adjustment. Some saddles with low sides will make using this bolt tricky. The seatpost binder collar uses a replaceable alloy collar with two bolts. The entire saddle adjustment system is well designed and practical for flight casing.

The curved seat tube has become a common styling theme since Cervelo innovated it in wind tunnel development of the iconic P3. BH shares this styling theme on the GC Aero.

The out of the box component spec on the BH GC Aero includes a full Shimano Ultegra drivetrain complete with a genuine Shimano chain and cogset. Gearing is a 12-25 cogset turned by a full size, 130 bolt pattern 53/39 crank. The fantastic Shimano Ultegra crank with hollow-forged large chainring provides exceptional shifting from small ring to large.

A mechanically solid and stylistically pleasant drivetrain and brake ensemble provide great shifting and braking performance.

The FSA Gossamer brake calipers add a functional accent and have cartridge style pads with alloy barrel adjusters and lightweight polymer quick releases.

On the road the high head tube of the BH GC Aero gave the front end wonderful comfort. This would be a great bike to lean on for 112 miles if you trend toward short torso/long leg. The higher head tube mitigates road shock. Handling is stable owing to the unique front end geometry. Because the top tube is low, the rear triangle tight and the wheel tucked-up well the bike is responsive to acceleration and punching it on the climbs. Chainstays on this bike run a half centimeter shorter than a same-size Cervelo P2 and that may contribute to a stiff, snappy rear end.

Rear wheel dropouts on the GC Aero slope downward and negate adjusting screws. Most wide-aero wheels will fit in the rear triangle of the BH GC Aero. This view also provides a look at the robust seat stays and chain stays.

The triathlon bike market is packed with great choices for the low head tube, long torso fit rider but the short torso fit rider has been limited to brands like Scott and Kuota. The BH GC Aero adds another fit option for the long leg, short torso triathlete and comes with a proven racing heritage thanks to Angela Naith and Eneko Llanos. An additional logistical feature of the BH Ultralight Bike brand is they permit mail order distribution, enabling to fulfill bike orders online and by phone for shipping to anywhere in the U.S. Most other brands have restricted mail order fulfillment. BH deserves notice for this bold distribution strategy.

The BH GC Aero fills a niche for a high head tube, short torso fit tri bike with nice styling, a great component spec and proven competitive results.