All the Rage: Suzuki GN125 “TNT” Custom

Suzuki GN125 Custom

Pint-Size Stick of Dynamite: Suzuki 125 by Cus’Tom Motorcycle…  

Around 1980, Suzuki introduced their GN series of single-cylinder, air-cooled SOHC machines. Major models would include the GN125, GN250, GN400, and GN600, each with the funky “cruiser” styling so popular at the time. While these were no-frills machines, the GN125 and its larger siblings proved themselves as hardy workhouses with ultra-low running costs.

The Suzuki GN125 is a tough little bike with a trusted engine and ideal about-town motorcycle or leaner bike.” –MCN

Suzuki GN125 Custom

The low barrier of entry and high parts availability have made these bikes ideal as donors for 125cc custom builds. This one comes from our friend Tom Boissel of Cus’Tom Motorcycle, whose late father taught him to ride the twisties around their home in rural France — experiences that would culminate with Tom racing supersports in the Coupe de France Promosport 600cc class before opening his own workshop near Toulouse.

Suzuki GN125 Custom

In the past, we’ve featured some fairly high performance machines from Tom’s shop, including a Honda CB1000 Super Four and one of our favorite builds of 2023, a Yamaha RD350 that his father used to pick him up from school. He’s also hard at work on a Yamaha V-Max we’ll be featuring soon.

For You, Old Fox: Yamaha RD350 Custom

In the meantime, Tom just completed this 125cc Suzuki GN as part of his “Rage” series of full-blown customs:

“It bears the ‘Rage’ coat of arms, which represents the complete and unique preparations from Cus’Tom Motorcycle. This means a change in general style, complete rebuild of the motorcycle, increase in power, custom parts made in the workshop, and the details that mark such preparations (X-stitched leather grips, Rage engraving, stainless steel screws, titanium nuts, Cus’Tom details).”

Suzuki GN125 Custom

Starting with a “completely ordinary” Suzuki GN125, still in its Japanese mini custom style, Tom set out to make it a fun little café racer.

Tom details all of the modifications below, but highlights include a rebuilt engine with performance cam, stainless steel exhaust, rear disc conversion, upgraded front brake, blaze orange saddle and grips, and lots of high-quality finishes and one-off custom touches.

The result is a sweet little 125cc custom that punches above its weight class, with style to boot.

125 Suzuki GN Custom: In the Builder’s Words… 


Creation of a custom upper tee using traditional machining to accommodate a Motogadget speedometer with “neutral” and “full headlight” indicator light.

Suzuki GN125 Custom

The front wheel has been kept despite a new tire size and painting of the original rim and hub.
The front disc has gained 20 mm in diameter and the single-piston caliper has given way to the double-piston caliper of the 250cc version.

Suzuki GN125 Custom

Note in passing, the small front wheel spacer (Cus’Tom detail).

Suzuki GN125 Custom

New front mudguard and mounting bracket. The fork has not undergone any modification; however, its caps were re-machined (Cus’Tom detail).

Suzuki GN125 Custom

Replacement of the original 16″ rear wheel and its drum brake with an 18″ disc rim borrowed from a MUTT 125 Akita.

Suzuki GN125 Custom

It was necessary to adapt a rear brake master cylinder mounted on a custom plate welded to the frame, modify the brake pedal to connect it to the cylinder with the right lever arm proportions, and a caliper housed on a machined support, coupled to a custom connecting rod fixed to the frame. Note a stainless steel tube covering the master cylinder rod in order to streamline the details.

Rim spokes were replaced by stainless steel models.

Suzuki GN125 Custom

The rear part of the original GN frame does not have a “straight” line, so it was necessary to cut behind the tank and rebuild this entire part of the frame, and in the process, raise the tank a little.

Suzuki GN125 Custom

Two Shock Factory shock absorbers, 10 mm longer in order to abandon the original mini custom line. Note the “Cus’Tom detail” washers, which hide the rubber of the shock absorber eyelets.

Suzuki GN125 Custom


A “Rage” must also be faster. In addition to an engine and carburetor repair which only brings a small gain, the camshaft has given way to a “racing” model which gives a greater opening time of the valves — the power goes from 10 hp to 15 hp.

Suzuki GN125 Custom

And a stainless steel exhaust made to measure in the workshop, in a half-moon shape and TIG-welded.

Suzuki GN125 Custom

The Fun Part:

Light gray powder-coating of the frame.

Body paint in a similar shade with “dynamite” and “Rage” logo under varnish, done with an airbrush stencil.

Suzuki GN125 Custom

The plastic side covers have given way to steel covers made in the workshop, with 90° bends on all their contours.

Suzuki GN125 Custom

The keyswitch has been moved to the front, mounted in one of the headlight supports with an aluminum “Cus’Tom detail” nut.

Suzuki GN125 Custom

And to increase the fun, a combo: saddle (support + foam + leather covering) + tailor-made “X” stitched leather handles in blaze orange color.

Suzuki GN125 Custom

Follow the Builder

Facebook: Cus’Tom Motorcycle
Instagram: @custom_motorcycle_tom_boissel
Youtube: @custommotorcycle8364



  1. I grew up with an SP125. What a wonderful time I had with that bike! There have been others but to be honest looking back I enjoyed it most of all.

  2. Martin Breakwell

    I had a GN400. I don`t remember there being a GN600 though.

  3. Needs a back fender if a sort.
    Otherwise it would be outstanding

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