2019 Factory Off-Road Bikes—Mikayla Nielsen’s KTM 105 SX

We check out the bike ridden by 2019’s AMA Female Racer of the Year.

Mikayla Nielsen plans to be a two-sport athlete (water polo and track) in high school this year and previewed that versatility last year by capturing AMA National Championships in both MX and GP aboard her KTM 105 SX, which starts out as an 85 SX before Pro Circuit goes to work modifying the 105 kit for her.
Mikayla Nielsen plans to be a two-sport athlete (water polo and track) in high school this year and previewed that versatility last year by capturing AMA National Championships in both MX and GP aboard her KTM 105 SX, which starts out as an 85 SX before Pro Circuit goes to work modifying the 105 kit for her.Mark Kariya

Mikayla Nielsen enjoyed a banner year in 2019, accruing three AMA National Championships in two different disciplines. The now-14-year-old high school athlete from Southern California romped to AMA National Championships in two classes in the new FMF AMA National Grand Prix Championship (NGPC) Series—Women, where she won the first seven of the eight scheduled rounds (missing the finale due to injury), as well as Super Mini, where she raced heads up against the boys, winning six of the eight rounds.

In addition, she made it to the AMA Amateur National Motocross Championship at Loretta Lynn’s for the first time and won Girls (11–16).

To top it off, Nielsen then received perhaps her most prestigious award after traveling to Ohio for the KTM AMA Championship Banquet last month where she was announced the 2019 AMA Female Racer of the Year.

The bike she used to earn those honors started as a standard 2019 KTM 85 SX. (She actually has three with one used strictly as a practice bike.) One of the first things that her mechanic/dad, Mike, does is swap the stock top end for one from KTM PowerParts to make it a 105. But that comes after the top end has been to Pro Circuit for a little work on the ports that yield gains mostly in top-end power. A 40:1 mix of VP’s MRX02 and Maxima 927 flows through those ports via the standard 38mm Mikuni TMX carburetor, jetted for whatever race venue they’ll be at and after air passes through a DT1 air filter. A Pro Circuit expansion chamber and shorty silencer assist in power enhancements.

Besides a little porting to go along with the Pro Circuit pipe and silencer for more top-end hit, a Hinson clutch and VHM head are employed. Pro Circuit also personalizes the suspension for Mikayla. A Nihilo Concepts seat cover and Frame Grip Tape, and IMS Core pegs help keep her where she wants to be on the bike.
Besides a little porting to go along with the Pro Circuit pipe and silencer for more top-end hit, a Hinson clutch and VHM head are employed. Pro Circuit also personalizes the suspension for Mikayla. A Nihilo Concepts seat cover and Frame Grip Tape, and IMS Core pegs help keep her where she wants to be on the bike.Mark Kariya

It doesn’t stop there. Mike adds, “[Pro Circuit] developed their own head insert for the 105, and we use a VHM head that gives us better cooling. Pro Circuit, it’s very interesting working with them because the whole bottom end is stock besides the clutch—we run the Hinson clutch components.

“That’s what they’re saying, is don’t put too [many] modifications into the motor because it’s a good motor to start off with.”

Although the radiators are standard, Mike fills them with the waterless coolant from Zip-Ty Racing. Other fluids come from Maxima with 80W MTL the choice for the six-speed transmission.

While the standard WP suspension components are retained, Pro Circuit works on the internals to suit Mikayla’s speed and weight, as would be done with a top pro. For her, that means stiffening both ends, both pressure in the AER fork (now 85–90 psi) and using a 5.4 kg/mm spring on the Xact PDS shock, with Pro Circuit also replacing the piston in the reservoir with a PC bladder kit. “It’s more consistent and stays cooler [with the bladder],” Mike says. Static sag is set at 30mm.

The Dubya wheelsets feature orange Talon hubs and black Excel Takasago rims. Although the WP AER fork remains, it gets the Pro Circuit treatment for her weight and speed.
The Dubya wheelsets feature orange Talon hubs and black Excel Takasago rims. Although the WP AER fork remains, it gets the Pro Circuit treatment for her weight and speed.Mark Kariya

The wheels get upgraded to Excel Takasago rims laced via stainless steel spokes to the orange Talon hubs from Dubya. Mikayla runs Dunlop tires, mousses, and rim locks with Mike sharing, “For some of the faster courses, like the hardpack, [she likes] the MX53. If we get into the softer stuff like at Gorman or something like that, we run the MX33.

“They send us big-bike mousses and we cut them down to fit the minibike. We get the rear ones in [105’s rear tire],” he insists. “Zip-Ty [Racing’s] Ty Davis helps us with the mousses. He helps me cut them down and install them front and rear so we do run a front and a rear from the big bikes. He’s like the master of that stuff!” (For her dedicated motocross racer, however, they forego the mousses in the interest of saving weight.)

Although Mikayla runs tubes for motocross, Dunlop big bike mousses go into her favored MX53 tires front and rear with Zip-Ty Racing’s Ty Davis helping to cut them down correctly. Note too the rear rotor—it’s a larger item sourced from a KTM 250 to better cope with the larger Super Mini wheel, added weight of the mousse, and her speed.
Although Mikayla runs tubes for motocross, Dunlop big bike mousses go into her favored MX53 tires front and rear with Zip-Ty Racing’s Ty Davis helping to cut them down correctly. Note too the rear rotor—it’s a larger item sourced from a KTM 250 to better cope with the larger Super Mini wheel, added weight of the mousse, and her speed.Mark Kariya

Taking a cue from top Super Mini motocrossers—and to help compensate for the larger Super Mini wheel plus mousse—the rear brake rotor is actually off a full-size KTM 250, and a Nihilo Concepts kit adapts it to the smaller hub. This also requires modifying the brake line slightly, though the caliper is left alone. “It holds up pretty well,” Mike observes. The brake pads and the entire front-brake system is standard KTM though.

Up top is a Mika Metals handlebar in the KTM replica bend, though her father, Mike, is weighing going to taller bars if she continues growing. Note the larger IMS tank, though no dry-break is needed.
Up top is a Mika Metals handlebar in the KTM replica bend, though her father, Mike, is weighing going to taller bars if she continues growing. Note the larger IMS tank, though no dry-break is needed.Mark Kariya

Mika Metals provide final drive components with gearing at 14/48 or 49 depending, of course, on the course. The Mika Factory Series chain is non-O-ring. Mika’s handlebar replicates the stock KTM bend with ODI half-waffle grips—her choice, as are retaining the OEM levers. “She’s tried other levers, but she likes the stock ones,” Mike muses.

IMS Core footpegs give Mikayla a comfortably wide and secure place for her boots, and a Nihilo Concepts seat cover over a standard base and foam keeps her from sliding fore and aft uncontrollably.

Since most of her GPs are around 45 minutes to an hour, Mikayla uses an IMS 2.5-gallon fuel tank, though she doesn’t need a quick-fill.

Since GPs generally don’t throw many rock gardens or other abusive obstacles at riders, especially for the mini races, Mike says, “If it’s real muddy, I’ll put the Acerbis skid plate on and OEM KTM hand guards.”

As it sits, Mikayla’s 105 wears graphics from Motocutz.

Mike adheres to regular service intervals, the results of which show in Mikayla’s outstanding record. The piston gets replaced every 15 hours “just because it’s a 105 and they’re harder on everything,” he says. “The clutch, we can go 40 hours on a clutch on these.” (The bike shown here had only 13 hours on it.)

At 14 years old—and with her recent growth spurt—this will be Mikayla’s last season on the 105 she’s had so much success on. As the year progresses, she’ll start racing a 125.
At 14 years old—and with her recent growth spurt—this will be Mikayla’s last season on the 105 she’s had so much success on. As the year progresses, she’ll start racing a 125.Mark Kariya

This will be Mikayla’s last year on minis though. She’ll race Super Mini in NGPC again, but when she lines up for the Women’s class, she’ll transition to a 125 later in the year. “We’re hoping to get a year out of the Super Mini, but if it’s way too small [later in the year], I don’t want to chance her getting hurt or crashing because she’s too big for the bike,” Mike notes. “We’re going to start testing new [taller] bars now because the way she is growing so fast, I just haven’t done that yet.”