Rim profile & aerodynamic CFD optimisation: Paul Lew
Finite Element structural Analysis: Performance Engineering Solutions (UK)
Materials and rim layup: Textreme Innegra/Toray carbon spread tow – Paul Farrell
Spokes & nipples: Sapim D-Lite spokes with black brass Polyax nipples
Hubs: Industry 9 Hydra Classic Boost centerlock hubs featuring Enduro sealed bearings
All mass produced carbon composite wheel rims are constructed in one of two ways using an intermediate “sporting grade” modulus of carbon fiber thread. Almost exclusively P.A.N. (propylene+ammonia) based fibers are used and as a general rule ‘the better the PAN the better the fibre’ is true.
Japanese Toray is an industry leader but despite common claims, not all wheels use Toray fibres. Many cheaper inferior fiber grades are now commonplace. Visually they are impossible to tell apart to the consumer.
All composite components are manufactured using multiple layers of pre-cut fibres in either woven or uni-directional form. All other parameters being equal, the number of layers and orientation of the fibres determine the final mechanical properties of the product once cured in a mould which is heated and thermally activates and sets the epoxy resin surrounding the fibres.
Cutting the required fibre shapes and ‘laying up’ to create the final structure has traditionally been done exclusively by hand and is therefore intensely labour dependent and final quality depends on skill established over many years.
Recently expensive semi-automated equipment has been developed to build up parts of the rim structure using the tape winding method. This has many advantages including highly accurate and repeatable fibre orientation, consistent fibre overlap and most importantly, the fibres are kept under tension (which is not possible using hand layup). Nex-Gen rims use the automated tape winding process.
Traditional hand-layup sporting grade carbon composites have amazing properties when the material layups are designed an implemented properly. In general they can be up to 20% lighter than the best equivalent alloy profile and can withstand approximately 15% higher impact energy (140J carbon only compared to 120J for alloy) before structural failure – or deformation in alloy. Alloy rims although being significantly(14%) heavier are significantly more vertically compliant (approx. 25%).
The most significant problem with carbon composites is with brittle fracture which occurs when the designed limit of structural integrity is exceeded. Experts refer to this a structural dissociation where the rim physically separates or remains connected with only a few fibres – Rendering it useless.
ISO 4210 impact at 150j comparison.
ISO 4210 alloy at 120j (similar rim profile to composite)
LET’S DEFINE ENDURO
Enduro in its most basic definition is a type of mountain bike racing where the down hills are timed and up hills are mandatory but not timed. Riders are timed in stages that are primarily downhill, with neutral “transfer” stages in between.
Serious enduro riders require wheels that can withstand the extreme rigors of their riding conditions and styles week-in, week out, with minimal failures.
Failure to finish is worse than setting a poor time!
Traditional carbon composite and alloy wheel rims have almost reached the limits of their physical mechanical properties, especially when the market is demanding ever wider but lighter, rims.
Innegra / carbon spread tow by Textreme is a unique woven composite material which combines the tensile strength of Toray carbon fibres with Innegra polyolefin fibers which have a density less than aramid fibers yet twice the toughness, thereby dramatically increasing impact strength yet lowering weight.
WHAT ARE THE BENEFITS OF USING INNEGRA FIBER?
• Reduced weight
• Increased damage tolerance
• Increased impact resistance
• Reduced maintenance
• Incredible strength to weight ratio
• Hydrophobic (doesn’t absorb moisture)
• Dampens vibration
• Disperses energy
Nex-gen researchers threw out the conventional design book and came up with a unique and proprietary blend of different composites which have resulted in a low weight rim which is able to withstand an ISO 4210 industry standard impact strength 4x over what is the minimum requirement (>150j).
Using a proprietary mix of polyolefin Innegra fibres knitted with carbon fibres has yielded a composite fabric which has significantly enhanced ability to absorb and disperse impact energy throughout the rim. When structural limits are exceeded, the rim will crack but not dissociate
Vertical stiffness (compliance) comparing carbon and Innegra/carbon rims of the same profile is reduced by a marginal 2%.
Combined with class-leading Sapim spokes and an Industry 9 Hydra Classic Boost hub set has resulted in the world’s premier off-road enduro wheelset.
FEA SIMULATION DATA
Development snapshot courtesy of Stefan Dalberg / Simon Bainbridge CEng MiMechE, PES (UK) Ltd.