Presentation of the KTM RC4 by Werner Koch

Presentation of the KTM RC4 from Werner "Mini" cook

RC8 in small?

Content of

Powerful single cylinders in sporty road chassis are in short supply, fans miss them tremendously. One of them is colleague Werner “Mini” Koch. Without further ado, he built his own speedster: the KTM RC4.

He’s done it again. In the past three decades, colleague Koch has already developed numerous bikes. In most of the projects he created and realized himself, “Mini” was way ahead of its time, and it was not uncommon for the manufacturers to be inspired by his machines for large-scale production – as was the box during the RC8 development. So now a single cylinder. “I wanted to build an athlete that was as light as possible and still powerful,” said the busy tinkerer, explaining the starting shot for the KTM RC4.

Presentation of the KTM RC4 from Werner "Mini" cook

RC8 in small?

A small KTM RC8 – that sucks!

The KTM RC4 also offers Sturm und Drang. Not overhanded, but with very little effort, the fully fueled runabout weighs only 143 kilos. A great, almost forgotten feeling that the author only knows from the stump-driven little athletes from the 90s. Even better than the playful handling of the RC4 is its high level of precision, with which it maintains the targeted line: set course, steer precisely with the laser, done. “It wasn’t always like that,” grins colleague Koch.

"Because of the initially extremely manageable geometry, I knocked over unsuspectingly on the first test ride and drove inward almost into the rebates far in front of the apex!" The screwdriver quickly grabbed the flex and welding device, defused the steering head angle from a violent 77 degrees to its moderate 66, increased it the caster by means of exchangeable triple clamp inlays from 90 to 96 millimeters, lengthened the wheelbase to 1425 mm and lowered the center of gravity of the bike by 20 mm.

The speedster weighs only 143 kilograms with a full tank.

The cure was well received by the gray sweeper. Wonderfully stable, it chases the radii, not the slightest trace of nervousness or wobbly. This is reminiscent of the unique Ducati 916 or an MV Agusta F4, which is also fascinating in this regard, and raises the following question: Which chassis components serve as the basis for the KTM RC4?

“The steel tubular space frame comes from one of the first KTM RC8s,” explains Mini. “However, the shock absorber does not work via a deflection, but is screwed directly onto an arm of the swing arm. Incidentally, the original RC8 also donated that. ”In contrast, my colleague Koch himself designed the rear frame, which consists of round tubes. “The main pipe runs in the middle and is offset downwards. This creates space for the exhaust and the shock absorber. Both are attached to the side. "

Handling and accuracy inspires

If the handling and accuracy of the little racer are enthusiastic, it jumps over edges and heels a bit insensitively. According to Mini, the chassis of the KTM RC4 is just as stiff as that of the factory Honda NSR 250 from the former two-stroke World Championship. But precisely because of this, the frame transfers unevenness directly to the fork and shock absorber. The parts, which tend to be tightly dampened, seem a bit overwhelmed. The Bridgestone rubbers RS 10 in 120/70 dimensions at the front and 180/55 at the rear are too stiff for the light racer and offer hardly any self-damping.

In addition, the front structure dips a long way when anchoring hard, and at the same time the rear slides slightly to the side due to the front-heavy weight distribution. “So far I have only worked out the setup while standing. I have to work on the fine-tuning again. "

The strut is on the right side. It is linked directly to the swing arm without any deflection and works in a sporty, taut way.

According to Mini, the fork was developed for a Honda NSR 500 in two-stroke times and now works with just one spring. “It’s about ten percent too soft, I still have to change that too.” Despite these small inadequacies, the KTM RC4 inspires. Also because a lively stew drives the speedster.

“The engine is one of the first KTM 690s. The guys in Mattighofen matched it to the exhaust and the open air filter. Actually the manifold is too short, but because of its conical shape the engine still works quite well. ”You could say that. The single sends a full 72 hp to the gearbox!

New project is in the starting blocks

The two hangs at medium and high speeds are noticeable, but do not stop the load from moving forward. The throttle response is also top notch. The characterful vibrations typical of stews – life unplugged – go well with such a puristic conversion!

When asked what he’s doing with the KTM RC4, Mini just shrugs his shoulders: “As always, put it under the tree in front of the workshop. I urgently need the space for my new project. Maybe it will one day be used in the new summer semester. “It absolutely has to! Because the KTM RC4 is far, far too good for the tree in front of the workshop. But wait, didn’t Mini just mention a new project? So he’ll do it again. splendid!

Technical data Koch-KTM RC4

Price: Not for sale single item.


  • Single cylinder four-stroke engine
  • oven valves
  • 53 kW (72 PS) at 8200 rpm
  • 64 Nm at 6500 rpm
  • 654 cc
  • Bore / stroke: 102.0 / 80.0 mm
  • Compression: 11.8: 1
  • Ignition / injection system
  • 46 mm throttle bodies
  • hydraulically operated multi-disc oil bath anti-hopping clutch
  • Six-speed gearbox
  • Chain

landing gear:

  • Steel space frame
  • Steering head angle: 66 degrees
  • Trail: 96 mm
  • Wheelbase: 1425 mm
  • Inner fork tube: 41 mm
  • Spring travel from / h .: 120/100 mm

Wheels and brakes:

  • Light alloy cast wheels, 3.50 x 17 / 5.50 x 17
  • Front tires: 120/70 ZR 17, rear: 180/55 ZR 17
  • 280 mm double disc brakes with four-piston fixed calipers at the front
  • 220 mm single disc with two-piston floating caliper at the rear


  • (full tank) 143 kg
  • Tank capacity: 11.5 liters of super

Base price:

  • Not for sale single item

Performance measurements

Power on the crankshaft, measurements on Dynojet roller dynamometer 250.

The engine comes from the first 690 series from 2008. At that time it had a rated output of 65 hp. Except for the exhaust, an open air filter and the mapping, the drive corresponds to the series. All the more astonishing that it delivers 72 hp from a standing start. The two hangs around 5000 / min and 7500 / min are noticeable, but do not disturb. Because of the very short manifold, tuning the 690 single turned out to be a bit tricky.

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