Chris Siebenhaar is the product manager at Dunlop tires. That means he is one of the most well-connected people in the motorcycle industry, so when he built a dual-sport bike for himself, you know it’s going to have all the right stuff. His KTM 500EX-C impressed us so much that we asked him to tell us about it. Here is a little of what he said. The full story will be in the December, 2024 print edition of Dirt Bike.
Chris Siebenhaar’s 2024 KTM 500EXC project
“I started off by replacing the OEM fork and shock with a set of WP XPLOR Pro spring forks and XPLOR Pro shock tuned by REP Suspension out of Murrieta, California. Owner Mark Johnson is an ex-WP Suspension technician for Ryan Dungey, KenRoczen and Marvin Musquin. He started by adding stiffer springs to the fork and firming up the valving by swapping out the spring perches to better control oil flow, all in an effort to increase bottoming resistance. He applied an anti-friction treatment to all the bushings and seals. He also FDE-coated the lower tubes for less stiction–Mark estimated around a 50-percent reduction compared to stock.
The Dunlop AT82 isn’t necessarily a dual-sport tire, but by the time Chris finished, this wasn’t a fully-compliant dual-sport bike by the rules.
“The progressive-rate shock spring was swapped out for a standard-rate spring, and rather than relying on the spring to progressively get firmer through the stroke, he relies on the sophisticated internals of the WP XPLOR Pro shock. By doing this, Mark is able to create a very consistent feel by removing a changing variable from the damping equation. Installing those beauties in the stock cast triple clamps almost seemed sacrilegious, so I swapped them out for a set of Xtrig billet clamps. I personally like split clamps because I feel it allows for extremely precise torque settings when clamping the fork tubes, and this is key to proper fork performance. Too loose and the front end can feel sloppy; too tight and it will bind up the fork through its stroke. Plus, they’re also sexy.
Chris Siebenhaar
Faster USA Wheels manufactures their own hubs in-house from a block of USA aluminum to a finished anodized unit. Their hubs also feature double bearings on the drive side to better manage the torque of modern four-strokes to reduce stress and add durability. I opted for Galfer’s oversized Tsunami front rotor and Tsunami rear rotor.
I lent Yoshimura my bike for a few weeks. When I returned, I was greeted with their brand-new RS-12 slip-on, featuring gains of 7.5 horsepower and 2.3 pound-feet of torque! Being that this bike is going to be primarily used for off-road riding and some racing, I reached out to my friends at Rottweiler Performance for their plug-and-play smog-removal kit. This not only cleaned up the engine compartment of the bike, but also removed over a pound of canisters, wires and plugs, and will help with overall tuning.
I picked up the GET SX-1 ECU unit with a map switch and Wi-Fi connectivity that allows you to change maps via their phone app. The map switch was a key addition, because it allows the bike to have dual personalities with a map that maintains its original mellow, tractable power feeling and a second map that is an all-out fire-breather. The maps installed were created by Rottweiler. Altogether this has taken the stock KTM 500EXC-F from 38 horsepower to 60 horsepower!
More parts:
ICW Radiators
IMS 2.8-gallon tank.
Baja Designs XL80 headlight
KTM Power Parts carbon-fiber disc guard and skid plate.
BRP chain guide
D.I.D gold chain
KTM Power Parts sprocket.
GutsRacing seat.
Sypher Coatings Cerakoting
“Finally, being that I am the product manager for Dunlop Motorcycle Tires, I chose our latest off-road tire set, the Geomax AT82 in the larger 90/100-21 for the front and 110/100-18 in the rear wrapped around Dunlop mousses.”
See you next time!
–Ron Lawson
Source : DirtBikeMagazine