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Sunday, 30 October 2016

Tech Talk: Zerode G Series

Zerode G2 

The derailleur system, been around since 1800’s, still going strong. The parallelogram method has had one hell of a good innings. Campagnolo’s Gran Sport of 1949 vintage, Suntour’s slant of 1964 and Shimano’s index system from 1985 have all advanced the pastime of cycling. Trouble is mountainbiking involves a load of shit being introduced to such systems – mud, grit and finely tuned transfers have never had a fully engaging life off–road. Pure downhill is a sport of few shifts especially on the non–competitive side, many have proved that even a bike less its mode of drive can sometimes be faster…chainless races. 

The idea of a gearbox was intriguing to say. For a start, the gears and the parts used to shift them are packed away in a weatherproof housing. Mud and water can’t get at them, wear is reduced and there are no fragile bits of metal to snag and break on rocks. Shifting is smooth and consistent – smashing in another cog under maximum exertion over the finishing line will feel exactly the same as your first shifts of the day rolling around the car park. But, they have hardly taken off. Heavy, overly engineered and expensive, nobody has really introduced anything that is anything more than a passing flirtation. New Zealand manufacturer Zerode have an answer to many of these questions.

Custom Shimano Alfine Internal Gear Hub

Zerode gearboxes are modified Shimano Alfine planetary hub transmissions. The crankset drives the hub transmission, which then in turn, drives a single sprocket at the rear wheel. The G's high-pivot swingarm would normally create massive amounts of chain growth, but the frame's jack-shaft arrangement allows Zerode to use the placement of the gearbox hub to all but eliminate it.


Two Chainline

Zerode suggest using a 32th ring up front and a 21th at the rear. In the manual that comes with the frame they suggest the recommended different chain lengths needed using these ring sizes. To keep the drive-chain tensioned throughout the suspension cycle, a stock Alfine tensioner is used on the inside of the chainstay. Another benefit of the gearbox is that the chain-line remains straight as an arrow - which takes stress off of the drivetrain and prevents mid-course derailments.

The Chainline was Crankset-Gearbox-Freehub

There is one chain that connects the rear wheel to the gearbox, and another chain from the chainring to the second ring on the gearbox. The chain that attaches to the crankset is also able to be tensioned via the bolts that connect the gearbox hub to the frame. This takes up the slack in the chain and the Alfine.

For those of you out there who maybe worried about the complexities of having a ‘gearbox’ on your bike, you needn’t worry too much. This is actually a Shimano Alfine rear hub, a relatively common item here that can be serviced. This type of hub has been used on folding bikes for years.While the hub maybe a heavy item, with it’s location in snugly above the shock in the mainframe, the weight isn’t so much of an issue. It takes weight away from the unsprung part of the bike, this offers better suspension performance, allowing a more sensitive rear end through the rough stuff.



Glossary:

Chain growth: The distance between the bottom bracket and rear axle lengthening as the bike goes through its travel


Source:
http://www.pinkbike.com/news/Seen-at-Sea-Otter-2013-Zerode-G2-Gearbox-Bike.html
http://ride.io/reviews/zerode-g2-review/
http://www.sicklines.com/2013/12/12/2013-zerode-g2-review-part-1-frame-details/
http://www.bikeradar.com/gear/article/super-bike-zerode-g-1-downhill-bike-33111/


Ride On!



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