Kronos Springs Rock Shox 95-97 Judy XC SL (over 160 lb)

Kronos Engineering Linear-Rate Coil Springs for 1995 -1997 Rock Shox Judy XC and SL (60mm travel) Models (Medium)

This auction contains the following guaranteed authentic Kronos Engineering product:

• (2) Kronos Steel Coil Springs for Rock Shox Judy XC or SL Models (60mm Travel) for riders between 160 lbs and 190 lbs (Medium Spring Rate)
•  Installations Instructions

The Rock Shox Judy suspension forks utilized very lightweight micro-cellular urethane (MCU) spring blocks instead of the more traditional coil springs or compressed air. The MCU blocks were available in different hardnesses and could be mixed and matched into a 7-inch long spring column for the desired suspension stiffness. At best, the MCU's worked well for awhile until the urethane permanently deformed. And this problem got worse over time until a good amount of the original suspension travel was lost due to the shorter MCU blocks. That wasn't the only problem. On cold days, the MCU blocks were very hard due to urethane's tendency to stiffen when cold and soften when warm. As a result, you could start your ride when it was cold and had very stiff forks that didn't soak up the terrain very well and then once warmed up worked better. On really warm days, the MCU's would soften and give a lower effective spring rate that lead to bottoming if you happened not to run very stiff MCU's to begin with. All told, the MCU's didn't work consistently well for many riders under varying conditions.

In 1995, Kronos Engineering set out to produce a solution to the MCU problem. They had just built their first full suspension XC bike the year prior and were testing many new rear suspension designs on frames using only the Judy fork. After working for awhile on the rear suspension problems that seemed to be very difficult to solve, Kronos determined much of the problem was with the Judy fork. So they designed and engineered a steel coil spring for the Judy in the spring of 1995 that became available that summer. Kronos used the finest ASTM A401 Chrome-Silicon steel wire that was specially wound for the Rock Shox Judy fork. The top of the spring is wound to a smaller diameter than the rest of the spring so that it fit properly into the fork's top cap. Believe or not, one of the other companies that made the first coil springs for the Judy actually ground by hand the smaller diameter to fit into the cap. They also used a weaker Chrome-Vanadium steel that plastically deformed so that the spring became shorter over time - much like the original problem with the MCU's. Because of the 60mm suspension travel, the smaller diameter coil requirement, and the short length of 7-inches the spring is subjected to very large stresses. Kronos engineers determined that a special Chrome-Silicon steel with a minimum ultimate tensile strength of 270,000 psi would be required to meet the strength requirements.

After each spring was wound, it was then pre-set. Pre-setting requires that the spring is fully deformed or blocked to produce a beneficial strain hardening effect. Then, the spring was sent to world-famous Metal Improvement Corp. to be properly shot-peened to enhance the fatigue life of the spring. The shot-peening process involves shooting a precisely sized small steel ball at high speeds at the spring's coils. The complete coil surface is involved since the stresses on the coil are primarily shear stresses and for the shot-peeneing to be effective, the entire coil surface must be processed. If you look closely at the spring, you can see micro-pits from the peeneing process. Most aftermarket springs were NOT shot peened. Oh, and shot-peeneing can increase the fatigue life by over 50% compared with an unpeened spring.

Finally, the spring was PTFE powder coated. PTFE, otherwise known as teflon, was applied for two reasons. Firstly, the chrome-silicon steel would rust if not for a protective coating. Most other spring manufacturers just painted their springs, which is fine to protect them from rusting. But why did Kronos use teflon? Well, the spring resides inside a fork tube and the coils of the spring are in constant motion as the suspension compresses and rebounds. The coils constantly rub on the fork tubes during use. So by using super low friction teflon, the friction within the suspension can be reduced somewhat. How much is it reduced? It is hard to say, but there is some benefit to reducing friction due to the fact that the long slender Judy spring tends to buckle within the tube during compression. When this happens, the spring's mid-section bows into the side of the fork tube with a fairly large sideload. While it is hard to reduce the buckling tendency, it is much easier to just coat the spring with teflon to reduce the friction.

Since all Kronos springs are teflon coated, they needed a simple way to visually differentiate the three different spring stiffnesses available from them. This was achieved using a color anodized aluminum spring cap that fits into the bottom of the spring's inner diameter. I say bottom because the color cap side of the spring is the side that is inserted first into the fork tube. Thus, looking at the bike from the side, the colored cap resides at the bottom of the top fork tube.

Please note, that the spring stiffnesses relative to the recommended rider weight is only a guide. If you are more advanced and ride harder, then you should choose a spring rate that is the next level stiffer. If you are heavier but ride easier, then a less-stiff spring may be better for you. The recommended weights are for average riders.

Kronos Spring Stiffness Cap Color Codes:

Purple: X-Soft - for riders under under 140 lbs.

Silver: Soft - for riders under 160 lbs.

Blue: Medium for riders between 160 lbs. and 190 lbs.

Red: Firm for riders over 190 lbs.

Shipping Information:

In the United States, this item will be shipped using USPS Priority Mail. Each additional set of springs will shipped for an additional $1.00 per pair.

For international shipments, this item will be shipped using USPS First Class Mail.