Long-Term KTM RC390 Returns To The Track

WRIST: Ari Henning
MSRP (2015): $5,499
MILES: 3,127
MPG: n/a
MODS: Pirelli Supercorsa SC2 rear tire

The first time I took the RC390 racing I placed well and was happy with the bike's overall performance, but I ended up struggling with rear-tire chatter and as I found out later, I'd hemorrhaged a head gasket during the last race of the weekend. With the head gasket repaired and a list of suspension setups to try, I headed into the final round of the Chuckwalla Valley Motorcycle Association season with the intention of making some headway with the RC's chassis. Chatter, after all, is awful.

In preparation for the event I finally put on proper race bodywork. For the past two track outings I've simply taped up the turn signals and slapped a number on the RC's windshield and tail. I was already running a Tyga belly pan from Formula390.com (the same place I got the RC's Tyga rearsets) so I dialed up Matt for the rest of the bodywork.

At the track, I experimented with shock preload and damping settings, as well as ride height changes and tire pressures on the Bridgestone RS10 rear tire. Nothing I tried made much of a difference so I decided to lever on a Pirelli Supercorsa SC2 rear tire, thinking maybe the Bridgestone's traction or carcass characteristics had something to do with the chatter.

Man, what a difference the Supercorsa made! Right away I dropped a second off my lap times. With the softer, stickier, race-spec Pirelli on the rear the chatter was nearly vanquished and the rear end felt calmer and more planted. The only downside was that the Pirelli wore very rapidly on Chuckwalla’s super-abrasive surface, and after just a few sessions the tread was worn down to the wear bars.

The Supercorsa was cooked by Saturday afternoon, so I went back to the Bridgestone for Sunday’s races. I tried one more major suspension change on Sunday afternoon, and halfway through the warm-up lap I knew it was a move in the wrong direction. While the rear was chattering worse than ever and making it really hard to turn a decent lap, the engine started to act up, hiccupping and missing as I rolled on the gas.

When the checked flag finally came out, I’d dropped back to fourth place and was feeling pretty discouraged. But on the drive home I thought about all the progress I’ve made—the bike steers well and the front end is super planted, the ergonomics are perfect, and I did discover that better handling is just a tire change away—and how much fun I have racing the RC and hanging out at the track.

Back at the shop, I went through the RC’s wiring, since the abruptness of the engine hiccup seemed like an electrical issue to me. I eventually discovered that the sparkplug boot—which relies on two little spring clips to attach to the sparkplug—was loose and not making a good contact. I replaced the spark plug boot and the running issue went away. That’s 50 percent of my problems fixed!

Next up, a road trip north to Sonoma Raceway to race with the American Federation of Motorcyclists. I’ve seen how the RC390 stacks up to the competition in SoCal, and now it’s time to see how it finishes at a different track with a whole new group of competitors. Stay tuned for more race updates.