The most obvious changes are to the upper, which has a more tightly-closed mesh to keep out debris, a 360-degree protective synthetic overlay, and a reinforced toe cap for added protection from stubbing your toes on rocks or roots. These features work quite well, and the upper remains fairly breathable despite the closed mesh, but I never really felt any debris or impact limitations with the Sir Isaac, either.
Other specs of the Terra Momentus upper include a more stable, stretch-resistant webbing to improve foot stability, and features such as slip-proof laces and a gusseted tongue that stays nicely in place - but again, these aren’t hugely noticeable improvements from the Sir Isaac. In fact, I found the fit of the Terra Momentus upper to be somewhat tighter through the toebox, with a slightly constricting feel by comparison.
Midsole actuator lugs
The midsole of the Terra Momentus is generally identical to the Sir Isaac, and this is where most of Newton’s remarkable technology features are packed. I’ll assume that you’re familiar with the tech aspects – and if you’re not, check out my original Gravity review – and they’re all here on the Terra Momentus: high-rebound EVA, midfoot and rearfoot support chassis, and half-inch actuator lugs that extend beyond the outsole and create the action/reaction biomechanics that Newton users have come to love.
My trail-running experience with the Sir Isaac has been that the actuator lugs are highly effective at reproducing barefoot biomechanics on fire-roads or well-groomed trails, but their protrusion can be a potential liability on highly technical trails. The Terra Momentus has a similar feel, although I’d say there’s a bit less flexibility, likely due to a protective metatarsal plate that was added to the midsole. As a result, the actuators sometimes have a tough time conforming to irregularities in the trail, which can be tricky if you’re not paying attention to foot placement.
Midsole heights for the Terra Momentus are quite similar to the Sir Isaac, with a 26mm heel and 5mm drop to the forefoot. Perhaps it’s my minimalist bias at play here, but I was hopeful that Newton could somehow figure out a way to make the entire midsole and actuator lugs ride closer to the ground for improved ground feel and stability with its dedicated trail shoe. I know that’s asking a lot, but I feel like I give up a bit of agility when switching to the Terra Momentus from my VivoBarefoot Evos or similar flat, flexible shoes.
High-durability runner outsole with traction grip
The underside of the Terra Momentus is – are you sensing a theme here? – very similar to the Sir Isaac as well. It features a super durable, high traction rubber that grips the trail very nicely in all conditions. The overall durability issue may be the primary improvement in this model over the Sir Isaac, because from top to bottom, the Terra Momentus seems like a shoe that can take a beating for hundreds of miles and still keep you running comfortably.
I suppose that’s probably my best recommendation for who should buy these shoes. If you’re a Newton user who enjoys the Gravity or Sir Isaac, and are looking for a highly durable version to beat up on the trails, the Terra Momentus is your shoe. If you’re just starting with Newtons, or looking for a good transitional shoe from traditional trail runners to minimalist footwear, you’ll do just as well with the Sir Isaac.
(Of course, it's entirely possible that I'm missing something major here. If there are Newton users out there who note more significant differences between the Terra Momentus and Sir Isaac, please drop me a comment below.)
Newton’s Terra Momentus retails for $139 from the company website as well as other online vendors.
*Product provided by Newton Running
**See other product reviews on sidebar at right. If you have a product you’d like reviewed, contact me at firstname.lastname@example.org
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