Factory bike Test - Knight’s Steed!
Published: 07th February 2008
Author: Words and photos by Jonty Edmunds
Despite 250cc two-strokes being preferred by most top US GNCC racers, David Knight dominated America’s largest off-road motorcycle series - and the indoor Endurocross championship - in ’07 on a 450cc KTM thumper. DBR got to ride it…
Before the start of the ’07 US Grand National Cross Country series there was an unwritten rule that all top woods racers subscribed to – you needed to be mounted on a 250cc two-stroke if you were to stand any chance of winning the championship. Easier to start, less tiring to ride and more reliable, strokers were the only choice for those serious about winning.
Fast forward to the end of the ’07 US GNCC series and the preconceived notion that ‘only a two-stroke would do’ lay in tatters thanks to the skill, determination and sheer strength of David Knight. Knighter actually started the season on a 250cc two-stroke but it only took him two races to decide to revert to a bike he knew. A bike he enjoyed racing. A bike he had won on before. Even if few others believed it was the right thing to do….
So Knighter made the switch, climbed back onto a four-stroke and despite having to overcome numerous stupid little mechanical problems during the 13-round championship added the US GNCC title to his two WEC crowns.
The bike David reverted to was not a million miles away from the bike he piloted to the ’06 E3 world title – a factory-built four-stroke KTM. He decided to compete on a 450 rather than a 525cc machine but in switching back to a four-stroke he also reverted to settings he knew and a power delivery he didn’t need to adjust to.
The motor used in the bike Knighter raced to the ’07 US GNCC title is all but the same as the one used by KTM’s WEC E2 star Samuli Aro. David’s bike features an electric starter like the production machine - something that’s removed from Aro’s WEC bike – but apart from this the motors are otherwise pretty much identical. The biggest difference is that DK’s engine has a different CDI - one which allows the motor to rev a little quicker and gives slightly more torque. Put simply the motor’s smooth power is jazzed up a little with an aggressive CDI.
The biggest difference between David’s 450cc KTM motor and a production engine of the same capacity is a relatively small one - 8mm to be exact. Featuring a ‘tuned’ cylinderhead fitted with titanium valves, lighter valve springs, a standard camshaft and with different timing to standard and a bore and stroke of 72mm x 89mm, at the heart of the motor is a con-rod eight millimetres shorter than standard. The second significant difference is a crank that is 600 grams lighter than a stock part.
Just like many of KTM’s factory prepped ‘off-road’ four-stroke motors, the one David used during last year’s US GNCC series featured less compression than standard. Fitted with a 41mm carb as opposed to a 39mm part, the bike’s ignition is retarded slightly and then fitted with an FMF exhaust system.
With many of KTM’s factory riders preferring to use a six-speed motocross gearbox, Knight opted for the six-speed MXC unit which is basically a mixture of enduro and motocross gears. Each of the gears is slightly different to those in a standard EXC enduro gearbox with first, second and third being a little longer, fourth about the same and fifth and sixth a little shorter.
Despite KTM’s engine builders being able to save 5.6kg by removing the electric start system, its battery and all the required knobs and switches, David prefers - as he did with his WEC bikes - to retain the electric starter system. The bike does however have a shorter primary gear which helps make the engine smoother under acceleration.
The aim of all the modifications is to produce a motor that is responsive, builds quick yet manageable power and has handling that’s improved over standard. While engine modifications are rarely known to improve a bike’s handling - that’s normally the job of the suspension and chassis - by shortening the con-rod the cylinder also has to be shortened which lowers the numerous moving parts found within the cylinderhead. Although less than one centimetre lower than on a standard bike, the difference according to KTM’s engine builders is a noticeable one and one well worth the effort.
David has an immense amount of skill on a bike – although the sepies seem to think of him as brute-strength rider who muscles his way onto the podium. Truth is DK rides with finesse. Trials trained and speed driven, the big guy can weave through trees and pop over rocks at ridiculous velocities without so much as denting a rim.
What you get when you kick DK’s bike over is a buttery smooth delivery of ground-grabbing power. The motor has low compression and starts easily with the foot or the button. Standard KTM hydraulic clutch goodness keeps the easy sensation at the hands and a clean, crisp throttle response gives you that oh-so-good feeling when you whack the carb slide up. When you get to the trails it gets even better.
It doesn’t take long to learn what the monster living inside the KTM cases craves. The motor loves to be ridden responsibly, with power that comes on quick and strong but totally under control. It has a great torque feel - smooth and linear through the mid-range with a top-end surge that comes on just before you’d expect to shift. The whole bike is comfortable running a higher gear and just motoring around, not revving. This type of power produces great traction on flat, fast corners and can have you ripping out of deep ruts with enough snap to get the front up. Same goes with track obstacles. If you need to loft the front the bike will do it. But it rarely spooks you with an unpredictable, over-aggressive hit.
Coming out of the woods and into the daylight of the fast and flat cornfield sections, the bike shows that it seemingly wants to win as much as David does. With a top-end surge there if you need it, the motor almost always delivers great traction. It’s a free-revving motor that takes its time reaching high revs. It rarely spins up quickly unless you really drop the hammer. Really, this bike is happiest with a short shift and a lot of mid-range throttle.
David Knight is both taller and heavier than most other riders and as such you’d expect his suspension to be firm, if not hard. Initially the fork action is stiff but the factory 52mm tubes settle into the mid-stroke like a dream and are close to being the best feeling off-road or motocross forks I’ve ever felt. The movement and control was phenomenal and gave a confidence rating that’s off the scale. The shock was stiffer but if I really settled back and loaded it up it would perform happily. The rear worked best for me at high speed where I could scoot back with my weight but even in the tight stuff and up steep climbs it rarely knocked me out of line.
Most of David’s bike is simple and clean. The handguards aren’t ‘bark busters’ as David doesn’t, well, bust bark. Fitted with simple plastic handguards, David opts to not over-protect his hands as he doesn’t want to ‘get lazy’ and start clipping trees. The reason? He feels full wrap-around guards might stop him manoeuvring as precisely as he does now which would reduce his speed.
Control set-up is fairly normal on Knight’s bike. The clutch is level with the bar which is probably a little higher than the average rider would have theirs but his front brake is fairly neutral - down a bit from level. Speaking of brakes, the factory Brembo calipers are supreme giving the same bite as stock KTM units but with a much healthier control and more linear grab. The Renthal Twinwall bar bend is nice, neutral and comfortable and not too tall.
Having ridden David’s KTM at the final round of the ’07 GNCC series I learned a lot about the champion’s bike. More than anything I learned the bike would work every bit as hard as you ask it. But I also learned that provided you’re as talented as Knighter you can win a US GNCC championship on a four-stroke, no matter what anyone else says.
Tech specs
Engine
Modifications: Factory specification with tuned cylinderhead, titanium valves, lighter valve springs, reduced compression and cylinder length reduced by 8mm over standard
Bore x stroke: 72mm x 89mm
Piston: Standard
Exhaust: FMF Power Bomb with FMF Factory 4.1 silencer
Carburettor: Keihin PWK 41mm
Crankshaft: Factory specification, lighter, 8mm shorter connecting rod
Transmission: MXC six-speed
Ignition: Factory specification, retarded
Spark plug: NGK BR8CP
Clutch basket: Hinson
Lubricants: Motorex
Fuel: VP racing C12
Flywheel weight: Standard
Chassis
Front brake: Factory Brembo master cylinder with Brembo KTM Hard Equipment SXS caliper
Rear brake: Factory Brembo master cylinder with Brembo KTM Hard Equipment SXS caliper
Triple clamps: KTM factory to fit 52mm forks
Bars: Renthal 996 Twinwall
Levers: Standard
Grips: SDG
Handguards: KTM Hard Equipment
Fuel tank: IMS 2.9gal
Plastics/bodywork: Standard
Air filter: Twin Air
Radiators: Standard
Sumpguard: KTM Hard Equipment - poly resin skidplate
Chain: Regina 520GPZ
Chainguards: KTM Hard Equipment
Sprockets and gearing: Renthal/KTM Hard Equipment 13-51
Rear wheel: Excel A60 rim with Talon carbon hub
Front wheel: Excel A60 rim with Talon carbon hub
Tyres: Michelin MS3 19” and Michelin MH3 21”
Suspension: Forks - WP MXMA5200, shock – WP PDS 5018
Footpegs: Standard
Graphics: Image Werx
Seat: SDG
Other >>
Enduro Engineering clutch, rear brake line and rear brake discguard. Motion Pro brake saver. KTM Hard Equipment hour meter. KTM Hard Equipment clutch cover kit. KTM Hard Equipment SXS 4-stroke CNC-machined oil plug. KTM Hard Equipment WP fork protection stickers. KTM Hard Equipment skidplate foam