This winter, we expanded the M Series mountain line even further – or wider – 85 millimeters wide, to be exact. For years we’ve been working on ideas for our fat bikes, and have heard the many requests from our most faithful fat bike friends. A rim that followed our mountain wheel ethos, but provided specific fat-bike benefits, was a big undertaking.

So, what goes into the making of a fat bike rim? Quite a bit more than what would meet the eye. As with any project, we had some design and engineering targets to hit:

1. Incorporate Pinch Flat Protection
2. Maintain M6 Series Mountain Wheel Impact Performance Metrics
3. Improve the Fat Biking Experience

Incorporate Pinch Flat Protection

During the development of the latest M Series wheel line, we created technology within the rim that can eliminate pinch-flatting. This patented technology, known now as Wide-Hookless Bead, has proven itself across the spectrum of mountain bike world-cup racing from cross country to downhill. We knew fat bikes weren’t limited to ‘Snow-only’ riding, and their use case spread across a wide variety of terrain. Incorporating the Wide-Hookless Bead Technology, and creating a wheel that was far more durable than the current available products was a necessity.

By following the same rim shape design exercises we’d created during the M Series development, we landed on a rim width of 85mm. This width provides an optimal balance of support and flotation for tires between 3.8 and 4.5 inches wide. Finally, we incorporated the Wide-Hookless Bead technology to provide the same anti pinch-flat promise as the other M6 Series wheels for a fat bike wheel that is truly all-terrain.

Maintain M6 M Series Mountain Wheel Performance Metrics

To take this rim shape and have it match the ride characteristics we’d defined with the existing M6 lineup (M630, M635,M640) took careful structuring and articulation of the carbon in the rim’s lay-up. This set of performance metrics is specific and demanding of a rim. These metrics include: Impact strength, pinch flat resistance, stiffness, control, and compliance. Finding the right lay-up to meet these metrics, while keeping weight as low as possible, can require countless iterations.

The M6 Series of wheels are ‘trail rated’, and cover the widest spectrum of varied riding. To earn this ‘trail rated’ credibility at ENVE, a rim structure and lay-up are put through tests that not only gauge the durability, but also ride and trail feel to give the rider confidence in every condition and over any surface.

Improve the Fat Biking Experience

All ENVE product development projects are viewed through the lens of creating a better ride experience. This may include improvements over the current market offering, or incorporating a new technological benefit that makes you a better rider. With the M685, we set out to create a trail-rated rim that worked well with the fat-bike tire offerings available.

Snow in particular, has a way of bonding and accumulating on a bike that’s unlike dirt or mud. While fat bikes are used for anything from racing to multi-day bike-packing, eliminating unnecessary rotational weight is a benefit shared by all. Our rim shape features steep sidewalls that are designed to shed any snow or dirt that might otherwise stick to a flat rim shelf without this feature.

Finally, in looking at the wheel as a whole, we were challenged to find a way to incorporate our patented molded spoke hole technology (Read more about it here) with a wide rim, and the wide hub set spacing required for fat bikes. The hub diameters stretch to 150mm for the front, and 197mm in the rear for optimum chain-lines around fat-bike tires. Asymmetric spoke holes – a first for us – along with our molded spoke hole technology, together allowed for the best bracing angles to keep the M685 and its hubset in line with the stiffness metrics required of all M6 Series wheels.

Ultimately, we believe we answered – and delivered an ENVE worthy fat bike wheel to those devout fat-bikers and their many product requests over the years. The M685 provides equally great ride enhancing features on both the snow and dirt in keeping with the M6 line and M Series mountain wheel ethos.

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