Bike Check: Cal Poly Students' Handmade All-Mountain Tandem - Sea Otter 2023

Sea Otter is full of wild and interesting bikes, but there are always a few that catch your attention and draw you in. There were quite a few this year, but this one was pretty hard to miss: the Sea Otter All-Mountain tandem, built by two students in the Cal Poly Bike Builders club. Kevin Zhang and Colin Reay decided two weeks before the event that they wanted to race the 40km XC on a tandem, so they jumped into action and stared designing this beast. They started fabricating the frame on the Monday before the event, finished it Thursday, built it up overnight, and raced it on Sunday. Quite the whirlwind, but with impressive results.


The fabrication of the frame may have been down to the wire with Sea Otter fast approaching, but that didn't stop the two from taking their time and working through the finer details.

The Sea Otter tandem sports a 460mm reach for both captain and stoker, dual 76° seat tube angles, and a 64° head angle driving a 130mm Pike Ultimate. The wheelbase is only a little bit longer than that new Pole downhill bike, coming in at 1950mm tip to tail. BB drop is 65mm for both sets of cranks, which puts it in line with many progressive hardtails out there - you just have to watch out for high-center situations.


They ended up fabricating a few parts for the build as well, adding a few extra touches to the finished product. Colin and Kevin machined the seat collars, front stem, and a T47-to-square taper adapter for the bike, and raided multiple parts bins to scrape together the rest of the components.

All told, they put in over 100 hours of fabrication time on the bike, all in a 5-day window. The frame was also Kevin's first time welding tubular steel, and you can see his skills improve as you work your way down the bike, thanks to some instruction from Colin.


One downside to the spare parts build was the lack of a reverse-threaded tandem crankset, which can lead to some pretty rapid unthreading of the captain's pedals while riding. They doused the front set in Locktite, but unfortunately weren't saved from near catastrophe when riding to the start of the race, as the pedal ejected itself on the side of the trail. They made the game time decision to intentionally cross-thread the pedals, in hopes of holding on for the duration of the race. Due to the mechanical, they hit the start line about 10 minutes after the other tandem racers, forcing them to double their efforts to make up time.


Colin and Kevin had a solid race, managing to pass multiple people in the non-tandem group (two sets of legs may be greater than one), and making up a significant gap set by the leading team. Unfortunately, they lost a pedal once again with only two miles to the finish line, but managed to get a few threads back in to scrape themselves across the line. Finishing proudly in second place, they are rightfully stoked. After crossing the line, Kevin learned that this race was Colin's first time ever riding a tandem, which is quite the trial by fire.


It's always a joy to see weird and wonderful bikes like this come to life, and Sea Otter does a great job of attracting such creations to the dusty pits of Laguna Seca. In the name of full disclosure, I was a member of the CP Bike Builders myself, but any bias I feel for the club feels well deserved when a project like this comes together and survives an entire 40km race as its first ride. The funky spirit of cycling is alive and well in creative endeavours like this, and I look forward to covering more of these wild creations.

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Racing and Events Reviews and Tech Bike Checks Sea Otter 2023