Stan’s MK4 and S2 alloy rims roll out with new M-Pulse and E-Sync hubsets

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Stan’s have introduced new MK4 and S2 asymmetrical and symmetrical aluminium rims across their popular Crest, Arch and Flow models. This collection of welded and sleeved rims with 25mm, 28mm and 30mm internal widths offer gravel, cross-country, enduro and downhill riders a reasonable choice of price points to suit most budgets.

Here we discuss the main differences between the more expensive MK4 and cheaper S2 options. First… Reed Boggs riding the new Flow MK4 rims in Virgin, Utah.

Stan’s MK4 and S2 Rims

stans flow mk4 wheelset with 2021 m-pulse hub
The Stan’s Flow MK4 asymmetric alloy rim laced to the as-of-yet unreleased 2021 M-Pulse hub

Stan’s have released six new wheelsets for off-road riding; Crest MK4, Crest S2, Arch MK4, Arch S2, Flow MK4 and Flow S2. The Crest model caters to the gravel and XC contingent, with a 25mm internal width rim seating gravel tires from 40mm to 2.3″ MTB tires. Arch are wider at 28mm, catering to trail riders running 2.2″ to 2.5″ tires. Flow have a 30mm internal width rim, able to accommodate tires from 2.3″ to 2.6″, pleasing the enduro and downhill crowd.

Each of these models are available in the MK4 or S2 rim design. Both are aluminium, but the MK4 is almost twice the price of the S2. So, what are the differences here?

stans flow s2 symmetric rim
Stan’s Flow S2 aluminium rim with a symmetrical rim bed and 30mm internal width

It’s all down to the rim’s fabrication process, and the shape of the rim bed itself. The S2 rims are Stan’s symmetrical aluminium rims. The spokes aren’t offset of centre, and there is equal space on either side of the rim valley to the edge. They are manufactured with 6061 aluminum using a durable sleeved joint and stainless steel rim eyelets.

stans flow mk4 alloy rim
Stan’s Flow MK4 rim with asymmetrical rim bed and 3mm offset spoke hole drilling

The MK4 rim, on the other hand, is manufactured from 6069 aluminium, which has a higher tensile and fatigue strength than 6061. They are fabricated with a welded seam, and have a reinforced spoke bed and walls with a matte-blasted finish. These rims feature an asymmetric profile said to result in a more dent-resistant rim.

The spoke hole drilling is offset of centre, too. The distance of offset is dependent on the rim in question; for Crest it is 1.5mm, for Arch it is 2.5mm and for Flow it is 3mm. The asymmetry of these rims mean that Stan’s can improve the spoke bracing angle and achieve an almost equal spoke tension between the drive- and non drive-sides. 

Stan's Crest MK4 Gravel XC rim
Stan’s Crest MK4 asymmetric rim for Gravel and XC has a 25mm internal width and 1.5mm offset spoke hole drilling

The Crest MK4 asymmetric rim, for instance, has a 92% balance between the drive side and non-drive side spoke tension, versus the 58% spoke tension balance of previous symmetric Crest MK3 rims. This is said to give rise to a stronger overall wheel build.

The MK4 rims are Stan’s first-ever asymmetric aluminium rims, developed from their proprietary asymmetric-Bead Socket Technology we saw previously on their Flow and Baron CB7 carbon rims.

What about the wheelsets?

stans arch mk4 wheelset
The Stan’s Arch MK4 alloy wheelset with a 28mm internal width for trail riding

These aren’t standalone rims that customers will need to lace themselves. The Stan’s MK4 rims and Stan’s S2 rims will be available as complete wheelsets, laced to new M-Pulse and E-Sync hubsets, respectively.

stans arch s2 wheel e-sync hub

The new E-Sync hub is Stan’s eMTB-specific hub, designed to withstand the greater torque associated with a motor-assisted drivetrain. In fact, they have a 47% increase in max torque load capacity over Stan’s previous Neo hubs. Reinforced pawls that distribute stress away from bearings, chromoly axles, Enduro bearings, including a double row bearing in the freehub, are all said to contribute to the increased durability.

stans crest s2 alloy wheelset e-gravel riding e-sync hubset
The Stan’s Crest S2 is an aluminium e-gravel bike wheelset suitable for 40mm tires

Freehub engagement is fairly middle-of-the-road for the E-Sync, at 8.18° with all pawls engaging simultaneously for reliable engagement under high loads. No close-up photos of it just yet.

stans 2021 m-pulse hub
A poor quality close-up of the 2021 M-Pulse hub from Stan’s No Tubes…

The higher-end MK4 rims will be laced to a new M-Pulse design that will be shared with all of Stan’s high-performance aluminum and carbon wheels. Details are non-existent at this point in time. Stan’s website tells us this:

“The M-pulse is an entirely new hub design unlike anything we’ve done before. It’s currently busy exceeding every test we can throw at it and blowing us away with how quick and positive it engages and how smooth it rolls” – Stan’s No Tubes.

Claimed Weights

The other factor contributing to the significant price difference between these two aluminium rim designs is the weight. While the MK4 rims are made from a higher-quality aluminium with the asymmetric rim profile resulting in a stronger overall wheel build, the rims themselves are also significantly lighter than the S2 counterparts.

29″ Rims Crest Arch Flow
S2 457g 520g 583g
MK4 399g 481g 521g

Pricing & Availability

stans crest s2 gravek wheelset 40mm tires

While you will see the Stan’s S2 wheelsets spec’d on complete bikes, they will also be available aftermarket at $595 USD with a three-year warranty on the E-Sync hubs and a two-year warranty on the S2 rims. These will be available with Shimano Micro Spline, HG, or SRAM XDR freehubs, and 6-bolt or Center-lock brake style, with options to fit all popular axle configurations.

stans flow mk4 alloy wheel front

The Stan’s MK4 rims retail at $129 USD. Complete wheelsets with the new M-Pulse hubs will retail at $925 USD. These aren’t available just now, as the M-Pulse hubs won’t be released until late 2021. They will be available for Shimano Micro Spline and HG as well as SRAM XDR cassettes and offered in all common axle sizes.

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