Long-Term KTM RC390 Suspension Upgrade: JRi Shock Installation

Less Sag Means Less Parts Drag

JRi Double-Adjustable Shock for the KTM RC390
JRi Double-Adjustable Shock for the KTM RC390
Exhibit A: JRi’s “double adjustable” shock. The North Carolina-based company also sells a simpler “single adjustable” shock for $799. All units are made to order and entirely rebuildable, unlike the RC’s stock WP shock.©Motorcyclist

WRIST: Ari Henning
MSRP: (2015): $5,499
MILES: 2,790
MPG: 58
MODS: JRi shock

For the most part the KTM RC390 belies its modest $5,499 price tag, but the bike's suspension is definitely one area where cost cutting is evident. Sure, the RC has a beefy and sophisticated-looking inverted fork, but it's non-adjustable and inside it's pretty basic. The shock is as elemental as they come, and even though I can adjust the spring preload, that's never going to counter the fact that the spring is simply too soft for my 175 pounds. (As a side note, if you want to learn more about springs, damping, and suspension in general, (click here for our "Making Sense of Suspension" tech articles.) As with most stock suspension setups the RC's fork and shock are designed to accommodate a wide range of riders and also be cheap to manufacture.

That's all well and good, but I want to ride my RC hard and fast so I turned first to Tige Daane at JRi Shocks (jrishocks.com). I've known Tige for years (he helped fine tune the suspension on my championship-winning CBR300R racebike) and he just recently started developing products at JRi, so I was keen to give his new shock a try. JRi's double-adjustable shock is built to order and tunable for compression and rebound damping plus spring preload and ride height. It costs $899, which sounds pricey until you realize that the WP Cup-bike shock that everyone is after costs $1450! For those that want the best price possible, Öhlins has a fully adjustable shock for the RC390 for $750.

KTM RC390 suspension upgrade
The Right Suspension
Why do journalists always gripe about suspension? Because it’s what keeps your wheels on the road! The more you ride, the more you understand the importance of proper spring rates, damping, and weight balance. Spring rate (and rider sag) are the foundation to a good suspension setup, and unfortunately the RC’s shock is sprung for a rider much lighter than me. The main benefit of the JRi shock was not only getting the right spring rate under me, but being able to adjust the damping to control how quickly the suspension strokes.©Motorcyclist

The shock bolted up easily once I’d removed the rear fender, which was a total pain in the ass. The shock is only held in place with two bolts, but the fender is secured with about a dozen, and they’re all different! I’ll be leaving the rear fender off since I don’t’ want to deal with that debacle ever again…

I mounted the reservoir to the subframe, but I think there’s room for it under the seat as well. Even before I left the garage I knew the shock was a big improvement. It didn’t sag excessively like the stocker and didn’t rebound uncontrollably either. I set sag (at 35mm), set the length to 303mm (the same as stock), and left the other adjuster where they were.

Even during my freeway commute the difference in ride quality is profound, and I'm glad I had the shock installed for our Small Sportbike Tire Comparison. During that tire test at the track the shock's added ride height (from lower sag figures) meant I wasn't dragging hard parts as much, and I was cornering with a lot more confidence since the back end wasn't wallowing and pogoing along. It's amazing what having the right spring under you will do, and since the JRi was handbuilt for me the spring rate was selected based on my weight.

KTM RC390 WP Performance shock
WP Shock
The factory built Cup bike comes with WP’s fully adjustable racing suspension, and KTM offers all the Cup-bike parts separately for those that want to upgrade their RCs. This shock will set you back $1,450. It’s a nice piece and does offer one additional form of adjustment over the JRi (high-speed compression damping), but I’d rather spend the extra $550 on tires.©Motorcyclist

A few weeks later I was back on the stock shock (I was helping Tige develop the JRi and he had a damping update he wanted to do, so I sent the shock back temporarily) and I couldn’t believe how sloppy it was. I guess I’d just gotten used to the loose, springy feeling before. Needless to say, I was relieved when I got the JRi back on the bike! Before I reinstalled it though I threw it on the scale and discovered another benefit: The JRi shock is 2.4 pounds lighter than the stocker. I love losing weight off a bike!

I’ve had the JRi on the RC390 for several months and I’ve ridden with it at several tracks. It’s improved the RC390’s handling quite a bit, but it’s also exposed the fork as being sprung too soft and inconsistently damped. That’s kind of the way these things go: You improve one thing, which reveals weaknesses elsewhere. Luckily, I really enjoy developing and tuning bikes, so I’m up to the challenge. I’ve already got the fork upgraded, but that’ll have to wait for another update.

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