Getting your hands on a big wheel kit for ktm 85 is usually the first thing on the to-do list once a young rider hits that inevitable growth spurt. It happens almost overnight. One weekend they're looking perfectly balanced on their bike, and by the next race, their knees are practically hitting their elbows when they stand up in the corners. It's that awkward middle ground where they've outgrown the small wheel setup but aren't quite tall or strong enough to jump straight onto a 125cc two-stroke or a 250cc four-stroke.
The KTM 85 SX is a beast of a machine, but the "small wheel" version (running the 17-inch front and 14-inch rear) can start to feel a bit cramped and twitchy as a kid gets taller. Swapping things over to a big wheel setup—which moves you up to a 19-inch front and a 16-inch rear—doesn't just change the seat height; it completely alters how the bike handles the track. It's a way to stretch the life of the bike for another season or two without having to drop eight grand on a brand-new motorcycle.
Why the jump to big wheels makes sense
When you start looking into a big wheel kit for ktm 85, you're mostly looking for stability. Small wheels are great for tight, technical turns because they make the bike feel like a mountain bike on steroids. You can flick them around easily. But the downside is they fall into every hole and every rut on the track. When the track gets "clapped out" at the end of a long day, those small wheels are working overtime just to stay on top of the chop.
By moving up to the larger rims, the bike suddenly has a much better "angle of attack" on obstacles. Think of it like a 29er mountain bike versus an old-school 26-inch bike. The larger diameter means the tire doesn't drop as deep into the holes, which smooths out the ride significantly. For a kid who is starting to carry more speed into the rough sections, this is a massive safety boost. It keeps the bike settled when things get hairy.
What usually comes in the kit?
If you're shopping around for a big wheel kit for ktm 85, you'll find a few different ways to go about it. Some people try to piece it together from used parts on eBay, while others go for a complete aftermarket package. A standard kit is going to include the obvious: the 19-inch front rim and the 16-inch rear rim, usually already laced to hubs with heavy-duty spokes.
But here's the thing—it's not just about the wheels. To do it right, you usually need a longer swingarm. The KTM 85 small wheel swingarm is shorter, and while you can sometimes squeeze a 16-inch rear wheel in there with the axle pulled all the way back, it doesn't leave you much room for mud clearance or chain adjustment. Most proper kits or conversions involve swapping to the OEM big wheel swingarm or an aftermarket equivalent. This extends the wheelbase, which adds to that stability I mentioned earlier.
You're also going to need to look at your brake lines and potentially your gearing. Since the wheels are larger, the overall "final drive" changes. If you keep the same sprockets, the bike is going to feel a bit sluggish off the line because the larger circumference of the tire acts like taller gearing. Most riders will go up a tooth or two on the rear sprocket to keep that snappy KTM power delivery.
Handling the height and weight
The most immediate change you'll notice—aside from the look—is the seat height. It's going to jump up a couple of inches. This is usually exactly what a growing teenager needs, but it does change the center of gravity. The bike will feel a little more "top-heavy" at first.
It's worth mentioning that you'll likely need to mess with the suspension settings. Since the wheels are heavier and the leverage on the swingarm has changed, the rear shock might feel a bit softer than it did before. If the rider has grown enough to need the big wheels, they've probably put on a few pounds too. It's a good time to check if you need stiffer springs to keep the bike balanced. You don't want a "chopper" feel where the back is sagging while the front sits high.
Is it a DIY project?
Actually, installing a big wheel kit for ktm 85 is a pretty straightforward weekend project if you've got a decent set of tools and a sturdy bike stand. If you buy a kit where the wheels are already laced and trued, you're mostly just doing a parts-swap. The biggest hurdle for most people is the swingarm pivot bolt, which can sometimes be a pain to get out if it hasn't been greased in a while.
You'll also need to break the chain and likely install a longer one. It's one of those jobs where you should take the opportunity to grease everything—linkage bearings, pivot bolts, and axles. If you're going through the trouble of taking the back end of the bike apart, you might as well make sure it's all buttery smooth when it goes back together.
The cost factor: Kit vs. New Bike
Let's talk money, because that's usually why we're looking at a big wheel kit for ktm 85 in the first place. A full kit with wheels, tires, and a swingarm isn't exactly cheap—you could be looking at anywhere from $800 to $1,500 depending on the brands you choose. However, compared to the loss you take on selling a small wheel bike and the premium you pay for a factory big wheel model, the kit often saves you a couple of thousand dollars.
Plus, if you keep your old small wheels and swingarm in a box in the garage, you can swap them back when it's time to sell the bike. This gives you two chances to sell it—either as a small wheel or a big wheel—widening your pool of potential buyers. Or, if you have a younger kid coming up through the ranks, you can just swap it back down for them later.
Final thoughts on the swap
At the end of the day, putting a big wheel kit for ktm 85 on the bike is about confidence. When a rider feels like they're "on top" of the bike rather than cramped "inside" it, they ride better. They're more willing to attack the jumps and hold the throttle open through the whoops because the bike isn't dancing around under them as much.
It's one of the most common modifications in the pits at any local motocross race, and for good reason. It's the bridge that gets a young racer through those middle-school years when they seem to grow three inches every time they sleep. If the motor is still strong and the bike is in good shape, there's no reason to ditch it just because the rider got taller. Toss on the big wheels, adjust the sag, and let them rip for another season. It's a solid investment in their progression, and honestly, the bike just looks way cooler with the bigger setup anyway.