Once upon a time in the late 20th century, the folks at GT were on one.  While there is no formal documentation as to what they were ON, it’s clear from the bikes coming out of their warehouses that it was something strong.

Out of all the great paint jobs, triple triangles, and slightly off-beat bikes they cranked out, there was one that stood out as a little bit extra and once I became aware of its existence was one that I coveted.

Eventually, a frameset popped up on eBay and I snapped it up.  And here we are, my GT Tachyon dad-bike.

Originally designed for drop bars and 700d (yes “D”) wheels the original spec of these bikes was bananas and like the Gary Fisher Sphinx and a few other odd ducks at the time, foretold the coming of gravel bikes decades too soon to a largely apathetic audience.

But I digress.  I started with a frame, fork, and stem so things barely resemble the original.

Let's begin at the beginning.  Weird triple triangle cromoly frame?  Check.  ADJUSTABLE rake fork?  Yup.  Reversible angle QUILL stem.  You betcha. 

You can’t forget the use of two completely different brake standards for the front and rear wheels.  Massive tire clearances?  Oh yeah! And last but not least, the 700d wheel size.   What is funny is that quite a bit of this came back into stye with a vengeance as gravel bikes became the norm.

Adjustable rake forks are common.  Just about all stems are reversible these days. And here’s the really funny one…. That 700d wheel size that popped up and quickly vanished?  Well, it happens to be mere millimeters in diameter form 650b or 27.5.

Modernizing things just a bit to fit my needs was a cinch.   I started with some tubeless ready 650b wheels built by yours truly and took advantage of the large tire clearances and installed some Teravail Sparwood 27.5x2.1 tires.  Since this bike largely sees duty riding with the kids I decided to keep the drivetrain simple and nothing is more simple than a single speed.  With the help of the brilliant eccentric bottom bracket from Velo Orange and some parts in my bin, I was able to make this happen with ease.

The funky mis-matched brakes meant I used a super cheap but utterly cromulent BMX U-brake in the rear and a fancy pants cyclocross racing cantilever up front.  With the practically free Sunlite 3-finger short pull levers the brake feel is somehow completely matched between wheels and works amazingly well.

To finish off making things extra useful I bolted up a Soma Lucas rack to a Wald basket and dropped a Swift Industries Sugar Loaf bag in there to hold snacks, tools, and whatever else. 

Of course, I tucked a dynamo light under there too.

Flat pedals for chilling hard and a comfy Brook Cambium C17 saddle to carry my posterior around the neighborhood.

Last but not least is the one spot where I had to go a little overboard.  Given when the bike was designed, it is no surprise that the stem clamp was the relatively obsolete 26.0mm standard.  These days all the best bars are bigger and after putting my hands on the Velo Orange Seine bar a while back I knew this was the only option I would be truly happy with. 

When one is trying to fit a square peg in a round hole, it helps to have a frame builder around to pester. 

I asked the mad scientist behind Swood Bikes to chop that 26.0 clamp off the GT stem and braze up a modern 31.8 clamp.  He could smell what I was cooking and was down for the cause.  After some time cobbling together a custom fixture to put the stem on the mill and some time with the torch, the final piece of the puzzle fell perfectly into place.

Full Build Specs.

• Frame/fork - GT Tachyon Crossover
• Headset - mystery threaded loose ball
• Rear brake - Diatech U
• Front brake - Avid Shorty Ultimate
• Brake levers - Sunlite short pull
• Rear hub - Shimano
• Front hub - Shimano Dynamo
• Rims - Velocity A23 650b with machined sidewalls
• Tires - Teravail Sparwood 27.5x2.1 tubeless
• Bottom bracket - Velo Orange BSA eccentric
• Cranks - FSA Comet
• Cog - Box BMX
• Chain - 11 speed
• Seatpost - alloy
• Saddle - Brooks Cambium C17 all-weather
• Front rack - Soma Lucas
• Basket - Wald 137
• Bag - Swift Industries Sugarloaf
• Light - Trelock VEO50 dynamo
• Grips - Supacaz
• Pedals - VP
• Bars - Velo Orange Seine
• Stem - customized by Swood GT Cromoly