MXA TEAM TESTED: PROX 520 X

WHAT IS IT? The ProX 520 X-ring is an O-ring chain that was designed for motocross. It maintains the lubrication, durability and lifespan of an offroad O-ring chain without the weight and reduced efficiency of a typical O-ring chain.

WHAT’S IT COST? $137.78 (120-link chain).

CONTACT? Your local dealer or www.prox-usa.com.

WHAT STANDS OUT? Here's a list of things that stand out with the ProX 520 X-ring gold chain.

(1) Types. There are three principal types of roller chains: roller bushing, O-ring and X-ring. The roller-bushing types date back to the beginning of time and are OEM equipment on every 2023 motocross bike (save for Suzuki). They are strong, light, cheap and relatively friction-free (with the downside that they wear out quickly). O-ring chains have a donut-shaped rubber seal between the inner and outer chain plates. They are also vacuum-packed with grease during assembly. This, in conjunction with the rubber rings, keeps the lubrication in and the dirt out. The inherent problem with O-ring chains is that rubber O-rings create considerable drag, most easily identified when the rear wheel spins sluggishly. X-ring chains don't use donut-shaped seals but instead have a ring with a thin center and four flanges. These flanges provide perfect sealing but create less drag because their flexible shape allows them to flatten under pressure, thus an X-ring chain offers O-ring durability without the typical drag.

(2) Design. ProX has done its homework on this chain. Well, actually, ProX contracted with one of Japan's premier chain manufacturers to design the X-ring mold for them. We assume it to be D.I.D. All ProX chains are pre-stressed and pre-stretched to reduce initial chain stretch. The master link is the standard-issue clip type and can be installed with little fuss—although pressing the plates together with vise grips or a chain press makes the job easier. The chain pins are quadruple-punched to ensure maximum strength. Plus, the heat-treated inner plates are computer-designed to use less material for a 3-percent-lighter chain without compromising tensile strength.

(3) Seals. The ProX 520 X-ring gold chain's X-ring seals have 40 percent less friction and increased durability over the more common O-ring chain. X-ringconstruction reduces friction by twisting between the side plates instead of being squashed. The twisting action ofthe X-ring disperses the pressure and minimizes power loss.

(4) Installation. Removing links from the ProX 520 X-ring gold chain is as easy as with any standard chain and requires only a standard chain breaker. The ProX 520 X-ring chain comes out of the box with 120 links. We had to remove four links for our test bike. It is important to remember when installing the master link that you need to put the supplied black X-rings on both sides

(5) Durability. If you stretch a chain out on a flat surface, you can feel the play in a worn chain by compressing it. With some OEM chains, it only takes a few races before the free-play is noticeable. Not so with the ProX 520 X-ring gold chain. Our test chain still maintained a solid feel after 10 hours of racing. As a bonus, we installed a 51-tooth ProX rear sprocket on our KTM 350SXF at the same time as the X-ring chain to ensure equal wear on both parts. ProX rear sprockets are manufactured from high-grade 7075-T6 and are precision-cut on an automated CNC machine. ProX's mud grooves are positioned to ensure that trapped mud is directed away from the wear areas of the sprocket. Word to the wise, a new chain and old sprockets are a bad combination.

WHAT’S THE SQUAWK? As with all O-ring and X-ring chains, be sure that the master-link clip is bedded into the groove. This is important, since the rubber seals exert outward pressure on the plates when putting the master link on.

MXA RATING: ProX has produced a long-lasting, sealed, X-ring chain that is smooth-rolling enough to use on a motocross bike, and it comes with the benefit of almost double the life of a normal roller-bushing chain.