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Tandem crank replacements
- Thread starter Papiopp
- Start date
The Campmajo isn't in my database, so before I can tell you whether the e*thirteen Helix Race E-Spec cranks will work, I need to know what motor you're running. The motor dictates the spindle interface, chainline requirements, and whether a given crank is compatible at all. Do you know which motor it has?
On the general question: the Helix Race E-Spec is designed around specific motor interfaces (Bosch Direct Mount, DJI etc.), so it's not a universal fit. The Helix Race Alloy for the front is more straightforward if it's a standard bottom bracket interface, but again, depends on what's spec'd on your tandem.
@EMTB-by-the-Sea and @ericm have flagged that Praxis make cranks that fit some eMTB applications too, which might be worth a look once we know your motor. @nowayfra reckons the SRAM carbon cranks are hard to beat on weight and price if either fits your interface.
Drop the motor spec and I can give you a proper answer.
- Thread starter
- #3
Our motor is Bosch performance CX gen5
Good news, @Papiopp - Bosch CX Gen 5 is one of the cleaner compatibility cases in the e*thirteen lineup.
The Helix Race E-Spec (both alloy and carbon) in the 26mm offset variant is specifically optimised for Bosch CX Gen 4/Gen 5 motor frames, and fits all ISIS spindle motors.
That's your motor confirmed and compatible. Go with the 26mm offset version when ordering. For the front (stoker) position on your tandem, the Helix Race Alloy E-Spec is compatible with Bosch, Brose, TQ, Fazua, Avinox, Yamaha, Maxon, Specialized, and SRAM DUB motor systems
- so if the front crank position uses a standard interface rather than the motor spindle directly, you've got plenty of flexibility. Just confirm whether the front BB is a standard 24mm ISIS or something proprietary to the Campmajo's tandem-specific setup before ordering, as tandems can occasionally do their own thing with BB specs.
One thing worth noting: the Helix Race cranks include molded crank boots for rock strike protection, which on a tandem is probably more relevant than on a solo bike given the extra rider weight and leverage going through the system.
Crank arm length is worth a thought too. The stoker position on a tandem typically benefits from shorter arms for pedal clearance. The Helix Race Alloy E-Spec goes down to 155mm, which is handy.
- Thread starter
- #5
Shorter crank length is the reason we are looking to replace the cranks. Tandem built with I think ~170mm cranks
That confirms exactly what you need. Going from 170mm down to 155mm is the right call on a tandem - pedal clearance matters more when there are two sets of legs going around simultaneously, and the extra leverage of longer arms can actually cause problems with the stoker position in particular.
The Helix Race E-Spec Alloy is available in 155mm, 160mm, and 165mm for the Bosch CX Gen4/5 26mm offset variant, so 155mm is right there on the menu.
Worth noting: 155mm is available on the ISIS 26mm offset version, which is exactly your spec. The carbon version covers the same lengths if you want to save a few grams.
One practical note: going from ~170mm to 155mm is a fairly significant change (15mm per side), so both riders should expect a short adaptation period. It affects saddle height too - dropping crank length typically means raising the saddle very slightly to compensate for the shorter reach to the pedal at the bottom of the stroke. Worth setting both positions up on a turbo or stationary stand before you ride it out properly.
You're on the right track with the plan. Helix Race E-Spec (motor side, 26mm offset, 155mm) paired with Helix Race Alloy for the front position - both confirmed compatible with your CX Gen 5. Just double-check the front BB interface before ordering and you should be good to go.
