KTM 640 Supermoto LC4 [1999 – 2005]: A Raw Symphony of Urban Agility and Off-Road Grit

When KTM unleashed the 640 Supermoto LC4 in 1999, it wasn’t just launching a motorcycle—it was dropping a Molotov cocktail into the supermoto segment. This Austrian brute, with its liquid-cooled single-cylinder engine and rally-bred DNA, redefined what a street-legal dirt bike could be. Six years of production saw subtle tweaks, but the core ethos remained: a lightweight, high-revving machine built for carving asphalt and embarrassing sport bikes in tight corners. Let’s dissect why this orange menace still makes riders grin like fools two decades later.

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Design & First Impressions: Function Over Fluff

Climbing onto the 640 Supermoto’s 910mm (35.8") saddle feels like mounting a particularly angry horse. The minimalist cockpit—analog tach, basic speedo, and a fuel light that might as well be a resignation letter—screams "no nonsense." KTM’s signature chromium-molybdenum frame isn’t just pretty; it’s a exoskeleton that keeps the dry weight hovering between 137-149kg (302-328 lbs), depending on model year. Translation: you could lift this thing off its sidestand with one hand… if the 625cc thumper between your legs wasn’t trying to vibrate fillings loose.

The USD forks (48mm WP units in later models) and monoshock rear suspension give away its dirt pedigree. Those 17-inch hoops wrapped in 120/70 front and 160/60 rear rubber? Pure supermoto swagger. This isn’t a bike that apologizes for its dirt heritage—it weaponizes it.

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Engine Performance: Single-Cylinder Sadism

Fire up the LC4 mill, and the world narrows to three sensations:

1. The Bark: That Mikuni BST 40 carburetor (later models kept it despite the EFI revolution) delivers a shotgun blast of induction noise. No electronic nannies here—just raw fuel-air alchemy.
2. The Throb: 625cc of single-cylinder fury hammers out 49-60HP (37-45kW) depending on year, with torque peaking at 52-60Nm (38-44 lb-ft). It’s not smooth—it’s alive, vibrating like a paint shaker at stoplights before smoothing into a frenetic wail above 4,000 RPM.
3. The Rush: With a power-to-weight ratio up to 0.44 HP/kg, the 640 SM doesn’t just accelerate—it detonates. 0-100 km/h (0-62 mph) vanishes in about 4.5 seconds, though the upright riding position makes it feel faster than a crotch rocket. Top speed? 160-168 km/h (99-104 mph), but you’ll feel every wind blast.

The 5-speed box is agricultural—clunky shifts that demand deliberate bootwork. But get it right, and you’re rewarded with a machine that pulls like a freight train from 3,000 RPM onward. This isn’t an engine you short-shift; it’s a beast that demands to be ridden at 80% throttle minimum.

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Handling: Urban Assassin, Canyon Carver

Throw the 640 into a corner, and physics laws get rewritten. The 1,510mm (59.4") wheelbase and 27° rake angle make direction changes so quick you’ll think the bike’s reading your mind. Those WP suspenders—270mm (10.6") front travel, 300-335mm (11.8-13.2") rear—swallow potholes whole while staying composed mid-corner.

Braking? The 320mm front disc with 4-piston caliper (single 220mm rear) offers stoppies on demand. ABS? Don’t make the LC4 laugh—this is a bike that rewards skill and punishes ham-fistedness.

In city traffic, it filters like a bicycle. On twisty backroads, it humiliates heavier nakeds. And when you spot that dirt access road? Crank the bars and let the long-travel suspension eat ruts for breakfast. Just don’t expect comfort—the seat’s as forgiving as a concrete park bench after an hour.

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Competition: How the Orange Menace Stacks Up

Husqvarna SM610 (2006+)
The Swede counters with smoother power delivery and better road manners. But at 146kg (322 lbs) wet, it’s porkier than the KTM. LC4’s raw aggression wins for hooligans; Husky’s better for daily commutes.

Suzuki DR-Z400SM
The Japanese entry is bulletproof reliable and 12kg (26 lbs) lighter. But 34HP vs KTM’s 50+? No contest in straight-line thrills. DR-Z owners wave; KTM riders wheelie past them.

Aprilia SXV 5.5
Aprilia’s V-twin screamer makes 70HP—on paper. In reality, its 15-hour engine rebuild intervals make the LC4 look Toyota-reliable. KTM for riders; Aprilia for masochists with deep pockets.

KTM’s Edge: The 640 SM didn’t just compete—it defined the big-bore supermoto class. While others focused on refinement, KTM bottled the essence of a motocross bike with a death wish and let it loose on city streets.

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Maintenance: Keeping the Beast Alive

Owning a 640 Supermoto is like dating a fiery artist—thrilling but high-maintenance. Key considerations:

Valve Checks: Every 1,000 km (600 mi). Shim-under-bucket design needs 0.12-0.15mm (0.005-0.006") clearance. Neglect this, and you’ll be shopping for new rockers.

Oil Changes: 2.1L of JASO MA-rated 10W-50 every 3,000 km (1,800 mi). The single-cylinder engine treats oil like a disposable commodity.

Carb TLC: That Mikuni BST 40 needs regular cleaning—especially if you’re running ethanol blends. Consider upgrading to a JD Jet Kit from MOTOPARTS.store for crisper throttle response.

Chain & Sprockets: 17/42 gearing wears fast when you’re constantly lofting the front wheel. Swap to DID 520ERV3 chains and hardened steel sprockets for longevity.

Vibration Management: Check every bolt monthly. Handlebar clamps, footpegs, and exhaust mounts are notorious for shaking loose. Loctite is your co-pilot.

Upgrade Potential:
- FMF/Q4 exhaust (+5HP, apocalyptic soundtrack)
- Twin Air filter (better breathing, easier cleaning)
- Braided brake lines (improved lever feel)
- Gel seat (your butt will thank you)

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The Verdict: Unapologetic, Uncompromising, Unforgettable

The 640 Supermoto LC4 isn’t for everyone—it’s for someones. The kind of rider who values character over comfort, thrills over practicality. It’s a bike that demands to be ridden hard, maintained religiously, and loved despite (or because of) its quirks.

Twenty years on, well-kept examples are becoming collector’s items. But this isn’t a garage queen—it’s a machine that begs to be abused on backroads, flicked through traffic, and occasionally tossed down a fire trail. For those willing to put in the wrench time, the 640 SM remains the ultimate urban predator. Just don’t expect it to coddle you. Or start on the first kick every time. Or stay shiny. But when it’s on song, nothing else matters.

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Specifications sheet

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