The STI Roctane XD was introduced in December 2012 as an extreme-duty radial tire designed for increasingly large, fast and heavy UTVs. Its 8-ply-rated construction, reinforced sidewalls and unusually broad selection of sizes helped make the Roctane XD a notable tire during the rapid growth of the side-by-side market.
We later used Roctane XD tires on several UTVGuide.net project vehicles, including our long-travel Kawasaki Teryx and Polaris RZR XP 1000. That experience provided a useful look at both the benefits and compromises of installing a large, heavily constructed tire on a UTV.
Editor’s note: This article documents the Roctane XD and its original specifications as part of UTV tire history. Sizes, pricing and retail availability may have changed since its introduction.
STI Roctane XD Introduced for 2013
When STI Tire & Wheel launched the Roctane XD, many sport UTVs still came with 25- or 26-inch tires. Thirty-inch tires were considered large, while the availability of a 32-inch purpose-built UTV radial was particularly noteworthy.
The original Roctane XD range included 11 sizes:
- 25x8R-12
- 25x10R-12
- 26x9R-12
- 26x11R-12
- 26x9R-14
- 26x11R-14
- 27x9R-14
- 27x11R-14
- 28x10R-14
- 30x10R-14
- 32x10R-14
That range allowed the same basic tread design to serve traditional ATVs, early recreational UTVs and heavily modified rock-crawling machines.
Roctane XD Construction and Tread Design
The Roctane XD used an 8-ply-rated radial carcass with heavy-denier nylon cord. STI designed the construction to provide puncture resistance and stability without making the tire excessively rigid over rocks and uneven terrain.
Its non-directional tread pattern used large, closely arranged tread blocks across a wide contact patch. The design was intended to provide predictable handling on hardpack while retaining enough biting edges for rocks, loose terrain and general trail riding.
Several protective features distinguished the Roctane XD from lighter trail tires:
- RocWall sidewall construction reinforced the lower sidewall and shoulder areas.
- Extra-wide tread belts added stability and shoulder protection.
- RocGuard rim guards extended over the wheel lip to help protect it from rocks.
- Wear-resistant tread compound was designed to balance durability with traction on slickrock and granite.
The result was a tire aimed primarily at riders who valued durability, ground clearance and sidewall protection more than minimum rotating weight.
Running 30-Inch Roctane XDs on Our Kawasaki Teryx
We installed 30x10R14 Roctane XD tires on STI beadlock wheels as part of our extensively modified 2011 Kawasaki Teryx build.
The Teryx had previously used several tire combinations, including 26.5-inch Pit Bull Rockers and 31-inch light-truck-style Pit Bull Growlers. The 30-inch Roctanes became a useful compromise between those setups.
They provided considerably more ground clearance than the smaller trail tires without adding quite as much weight and driveline leverage as the 31-inch LT tires. Their strong carcasses and protected sidewalls were also well suited to the sharp granite and ledges encountered on trails such as the Rubicon.
Our Teryx wore the Roctane XD and STI beadlock combination during the 2013 Rally on the Rocks in Moab, where it was displayed at the STI booth when it wasn’t being used on the trails. See more from that event in our STI Rally on the Rocks coverage.
Testing 32-Inch Roctane XDs on a RZR XP 1000
We later used 32-inch STI Roctane XD tires on STI HD5 beadlock wheels on our long-travel Polaris RZR XP 1000 project.
During a rock-crawling trip to Moon Rocks, Nevada, the 32-inch tires worked extremely well on the granite. Their height added useful ground clearance, helped the RZR bridge gaps and allowed it to climb ledges that would have been more difficult with smaller tires.
The Roctanes also delivered strong traction on the rounded granite formations. Their reinforced construction provided additional confidence around sharp rocks and deep crevasses where a sidewall failure could quickly end the day.
The tradeoff became more noticeable when we moved into the faster desert terrain surrounding Moon Rocks. The heavy 32-inch tires added rotating mass and were larger than necessary for the area’s rough, whooped-out trails. For a trip focused primarily on higher-speed desert riding, a lighter 30-inch tire would have produced a better balance of clearance, acceleration and suspension response.
Roctane XD Strengths and Tradeoffs
Our experience showed why the Roctane XD became popular with rock crawlers and riders exploring harsh terrain.
Advantages
- Strong 8-ply-rated radial construction
- Substantial lower-sidewall and wheel-lip protection
- Good traction on granite and slickrock
- Stable feel from the wide tread footprint
- Large sizes that provided additional ground clearance
- Non-directional tread that simplified tire rotation
Considerations
- Larger Roctane XDs added significant rotating and unsprung weight.
- Oversized tires could reduce acceleration and increase CVT load.
- The additional tire leverage placed more stress on axles, wheel bearings and steering components.
- A large XD could be more tire than necessary for lightweight or primarily high-speed machines.
As with any oversized UTV tire, diameter was only part of the equation. Tire weight, wheel weight, vehicle power, clutch calibration and intended terrain all needed to be considered together.
Later STI Roctane Tire Developments
STI expanded the Roctane family after the original XD launch. The company introduced the Roctane XD-K with dual Kevlar belts in 2016. The XD-K retained the familiar tread pattern but added a reinforced internal construction intended to improve puncture resistance.
STI subsequently developed the lighter Roctane XR tire family. The XR used a related tread concept but was positioned as a lighter, more trail-oriented alternative to the extreme-duty XD.
Why the STI Roctane XD Mattered
The Roctane XD arrived while UTV owners were rapidly moving beyond the 25- and 26-inch tires supplied on most production machines. Lift kits, long-travel suspension and more powerful sport UTVs created demand for larger tires with stronger carcasses and better sidewall protection.
Offering sizes through 32 inches at its original launch put the Roctane XD near the front of that movement. It helped demonstrate that a purpose-built UTV radial could deliver substantial ground clearance and rock protection without relying on a much heavier light-truck tire.
Our experience confirmed that the Roctane XD was especially effective in technical rocks. The 30-inch version was a well-balanced match for our built Teryx, while the 32-inch tires gave our RZR XP 1000 excellent clearance and traction at the cost of additional weight in faster terrain.
Although newer tire designs now offer larger diameters and increasingly specialized constructions, the original STI Roctane XD remains an important part of the transition toward the heavy-duty oversized UTV tires commonly used today.
