Machine Design

Svelte suspension springs hit the track

Yamaha designers are the first to spec titanium rear-suspension shock springs as original equipment.

Weight reduction on a motorcycle can greatly improve performance. A 1-lb reduction on a 200-lb, highperformance motorcycle is equivalent to a 14.1-lb drop in the weight of the already exceptionally light Ferrari Challenge Stradale (curb weight: 2,822 lb), a $300k sports car.

Yamaha designers are the first to spec titanium rear-suspension shock springs as original equipment. They will be standard equipment on four of their five 2006 YZ Series of motocross bikes. The bikes range from 146 to 220 lb and compete in amateur and professional racing classes where agility, strength, power, and lightweight are a premium. Relocating even a small amount of weight can give riders a competitive edge in handling and performance.

The springs, manufactured by Chuo Spring Co. Ltd. (CHKK), Japan, are made from a variation of Beta-C titanium (Ti-3Al-8V-6Cr-4Mo-4Zr) called Timetal LCB (low-cost beta, Ti-6.8Mo-4.5Fe-1.5Al). Conventional Beta-C titanium has an inherently expensive chemistry and gets its strength through long, 24-hr age treatments, cold-work steps, or both. The costs involved rule out motor-vehicle applications.

In contrast, Timetal LCB from TiMET Automotive, Morgantown, Pa., with its altered alloy formulation and substantially less-expensive Fe-Mo ( ironmolybdenum) master alloy gets its strength through chemistry rather than additional extended aging and cold work.

Aging times are compatible with thermal-cycle treatments used by conventional steel-spring processors. And from a structural efficiency perspective (spring response per unit of mass), the alloy's low shear modulus (45% less than CrSi spring steel), combined with its high strength, reportedly make it the best spring material currently available. Timetal LCB suspension shock springs vary in size and specification from model to model, but are typically 30% lighter than steel springs on Yamaha 2005 motocross bikes and weigh 1.1 lb less than steel counterparts.

Volkswagen was the first carmaker to use Timetal LCB on the rear springs of its 2001 Lupo FSI. That car was noted for being a small automobile with surprising performance and high fuel efficiency, thanks in part to its lightweight. More recently, the 2004 Ferrari Challenge Stradale became the first production car to use Timetal LCB titanium springs throughout. Ferrari selected titanium springs to reduce vehicle weight and unsprung weight, and improve performance.

Chuo Spring Co. Ltd. (CHKK),

TiMET Automotive,
(610) 286-1200,

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