KTM 530 EXC supermoto build for the twisties

Brilliant. Take a plated dirt bike, swap in some street wheels & tires, and now the 530 EXC chassis is transformed into an entirely different machine. The build deserves its own introduction, derived from the bike’s Adventure Build for TAT.

It starts with a 17″ wheelset in order to run modern tubeless street tires. In other words, sticky sport tires, 300mm of front suspension travel & 335mm in the rear, and a single cylinder dedicated to dropping the hammer.

After searching the local secondary market, found a complete set of used wheels, mounted tires, rear sprocket, brake rotors, and chain off a late model KTM 350 EXC. They are a custom build of Excel rims laced to Talon hubs, shod with Continental Tires at 120/70R17 front and 160/60R17 rear.

The rear fit with without a fuss despite the 160/60R17 back tire, and am now dealing with fitting the front hub. 350’s use a smaller diameter axle at 22mm, while the 530 uses a larger 26mm. Dubya, the distributor of Excel hubs and wheel spacers, hasn’t had the proper wheel spacer adapters in stock for weeks, and it’s mildly irritating that a couple of aluminum spacers are preventing the entire bike from being ridden in supermoto format; admittedly, the mod tends to never be straight forward when going from bike to bike.

Decided to call around and sent the spacers out to a local machine shop to be bored out to a 26mm ID while the proper adapters come into stock. After coming back for a test fit, the spacers appear to need some slight width offset toward the rotor side, which can be temporarily resolved by a short stack of washers under the caliper to reposition its centerline.

Upon fitment to the 530, the rear went on surprisingly without a fuss. Wheel spacers, offsets, and axle sizes all fit up. The brake caliper and lower chain guide indeed need to come off to make room for wheel fitment, but it’s a manageable swap that won’t prevent frequent wheel changes. (This becomes an addition to the basecamp project list for a wheelbox to store the other set, and perhaps also the 19″ dedicated rear paddle for the sand.)

On the rear drive side, the previous owner had experienced chain rub against the leftmost edge of the tire, because squeezing a 160mm wide rear into the swing-arm about maxes out any static lateral clearance. It’s when the chain is whipping at high rpm, under sag and compression does it slacken enough to twist and contact the tire. And of course, KTM’s are known for their notoriously loose appearing chain tension. My take on this characteristic is the distance and ride height angle between the countershaft axis, swing arm axis, and finally the rear wheel axis. It’s a dynamic angle yet will always be longest when they are all in a straight line.

To check chain tension, KTM typically has a procedure to take a measurement from a reference on the swing arm. It’s best to use this as a guideline, then actually sit on the bike and load the suspension by bouncing up and down on it to check chain tension through the travel of the rear wheel. Keep in mind, there is a huge difference in chain tension between the bike at full suspension droop off a workstand, and under compression when the rear wheel travels. Folks that mistakenly run a chain too tight put excessive wear on the machine, and in some cases catastrophic failures like chains snapping or shafts breaking off, in particular on a landing that yanks the chain.

At first, I’m seeing bits of rubber getting flung up into the fender along with moisture from the manually soaked air filter and chain lube. It’s a bit of a hot mess right now that i’m not sure how i feel about it all yet (but can clearly see why pre-oiled air filters are brilliant), especially because i do like stuffing the widest tire possible. There is an ability to perhaps further dish the wheel but it’s on the order of millimetres of clearance toward the rotor side. Can also swap out the o-ring chain for an even thinner street chain.

My solution at the moment after the first handful of tuning rides, is to bolt up a piece of angle iron under the rearmost M6 mounting bolt of the upper chain guide, and screw in a block of engineering plastic and over-hanging piece to help guide the chain.

The front swap proved to also be an indirect fit attempting to hop from bike to bike. The late model KTM 350 uses a smaller axle at 22mm, while the larger 530 has a 26mm through axle. The wheel spacers from the OEM dirt front hub do not carry over because the Dubya is designed with a smaller ID hub sleeve between its bearings. While we wait on parts to come in to stock at Dubya, i sent the original spacers off the supermoto wheelset out to a local machine shop to be bored to 26mm. They now fit the hub and axle, but the widths need shortening toward the rotor side in order to retain the brake caliper centerline without using a stack of washers.

Also in the front, the fork guards need notching on both inward sides to clear the point of the tire where the tread ends and sidewall begins. The 530 already had some clearance holes at the correct height that i slightly enlarged, so perhaps it very well was a supermoto under a former pilot. The street front wheel also came with a magnet so the 530’s speedometer functions at the dash, and can be re-calibrated to a 1880mm tire circumference.

The procedure to recalibrate a KTM speedometer is as follows: unplug the 3wire connector wiring harness leading into the dash, behind the number plate. Use the Mode button to cycle into the dashboard computer units, scroll over to WS -wheelsize- and manually use the +/- keys to increase/decrease the stored tire circumference in units of millimetres. (For reference: 2205mm circumference for a 21″ dirt front tire, 1880mm for a 17″ street front tire; measure actual tire for accuracy.) Reattach the 3wire harness behind the dash, and reattach number plate.

To date, am still shaking down the supermoto format and have since been up and down Highway 9, which the upper half to Skyline Boulevard was repaved last year and is incredibly smooth. The bike handles exceptionally well without even getting to suspension tuning yet, it eats up the 15 mile an hour hairpins in both up and downhill directions, and the XC4’s torque rolling on the throttle is sensational. =)

Couple of details still being addressed. The kickstand needs to be swapped out for a shorter unit after the supermotor wheels really dropped the stand-over height of the bike. As is with the dirt kickstand, it is very tipsy on flat ground, and simply turning the bars to the right and attempting to park it will tip the bike. Sourced a supermoto specific kickstand from Warp 9, along with their front and rear axle sliders. In the meantime to park, i’ll first pull the bike over on to the kickstand so the rear tire comes off the ground (like a dog taking a leak), then kick a 2×4 under the rear tire before setting it back down.

Next, the dual sport flimsy plastic mirror needs to go. While making the bike street legal, it’s useless at speed and vibrates to the point the reflection is a complete ripple. Am opting for round bicycle concave mirrors to clip below the handlebar.

Published by Manolo al Sol

Learning by adventure.. will curiosity kill the cat ?

One thought on “KTM 530 EXC supermoto build for the twisties

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: