REASONS TO BUY
Nice levels of mobility on the pedals
Lightweight
Sensible stiffness
REASONS TO AVOID
Lacks grip
Quirky fit
Bontrager Flatline Review
A lightweight and functional mountain bike shoe with passable levels of grip
Our Verdict
The Bontrager Flatline are functional flat pedal shoes best suited for riders who enjoy the freedom of easily repositioning their feet. We found the Flatline's Vibram outsole paired with the understated tread pattern to be comparatively lacking in terms of grip and pedal hold. They offer a good level of comfort, although we found they run a touch small and recommend sizing up if you are in-between sizes. These shoes provide solid power transfer and strike a nice balance of sole stiffness and walkability. They are also impressively lightweight which could be a consideration for the gram-counting crowd.
Our Analysis and Test Results
Bontrager recently updated the Flatline with a new upper that features increased ventilation and foot protection. The model we tested may still be available, and we hope to test the new version in the near future. -May 2022
The Flatline is a flat pedal shoe made by Trek's house brand, Bontrager. Grip/pedal traction are of critical importance when evaluating a mountain bike shoe. Unfortunately, we found the Flatlines to be lacking in this realm compared to other models in this test. It is difficult to recommend this shoe when there are other options that cost significantly less that deliver superior performance. Still, this shoe gets the job done on the trail and could still be worth considering if you're looking for a lightweight and relatively stiff shoe and you prefer a less grippy sole.
Performance Comparison
These shoes offer passable levels of grip, but if grip is of critical importance, we suggest looking elsewhere.
Credit: Laura Casner
Grip
The Flatline shoes have an outsole made of Vibram rubber. We found this rubber to be on the firmer side of the spectrum, as opposed to the soft and supple soles found on some other shoes in this test. When handling the shoes, the harder compound is immediately apparent. The majority of the sole's tread is quite simple, with large, square, smooth lugs with shallow channels in between. The toe and heel of the shoe have a zig-zag pattern for enhanced traction while walking.
When perched upon the pedals, the Flatline shoes have a decent platform feel. The sole isn't overly stiff or rigid, and you can feel the shape of the pedal platform quite easily. While testing, we found that the pedal pins don't engage the sole of this shoe as well as other models. The harder Vibram rubber sole simply doesn't accept the pedal pins as readily as other, softer compounds, but we feel the tread pattern is also part of the issue. The square tread knobs are quite large and the shallow channels between them don't provide much for the pins to settle into. That said, when fully weighted on a descent, our feet felt generally secure on the pedals, although the grip didn't inspire tons of confidence.
The less aggressive tread pattern paired with a harder rubber makes it easy to reposition your foot on the fly.
Credit: Jeremy Benson
If you are a rider who likes the peace of mind of being able to quickly reposition your foot, this shoe could be a viable option. Since your foot doesn't feel totally locked into the pedal pins, it is easier to make quick adjustments. The slightest unweighting of the foot allows you to adjust your foot position. This mobility can also be important for bailing off the pedals on those awkward slow-speed tech sections.
Off the bike, the Flatline shoes provide decent traction. The zig-zag pattern in the toe and heel help deliver some traction when pushing your bike up a hill or scooting over a downed tree. Walking traction is fine, but it can be a little questionable in damp conditions thanks to the big, smooth, square lugs that comprise much of the sole.
The Flatline shoes are reasonably comfortable, although we found them to fit about a half size small.
Credit: Laura Casner
Fit and Comfort
We found the Flatline shoes to be reasonably comfortable. They have a padded, skate-style feel to them, although we observed a couple of quirks about the fit. Since every foot is different, we have a hard time dinging the Bontrager shoes too much on fit.
When you strap these shoes on, the fit is generally quite comfortable. They have a medium volume fit with a little extra wiggle room in the forefoot, and we feel this shoe should work for the majority of foot shapes. The upper portion hugs your foot effectively and feels cushioned and padded while avoiding an overly bulky, hot feel. The toe box feels firm from within but remains pleasant around the toes. The insole is nothing special, but it gets the job done. The tongue stood out as particularly enjoyable. It sits flat on the top of your foot and has a plush, padded feel under the laces.
We found the Flatline to run a bit small in terms of their length. It should be noted that we don't knock a shoe for quirky fits in terms of a final score. That said, we do believe it is our duty to mention any fit quirks as it could be extremely helpful for a potential buyer. These shoes fit small, plain and simple, and our size 11 test pair fit more like a 10.5. If you are on the cusp between sizes, we definitely recommend sizing up. Our size 11 tester's toes were pressed up against the front of the toe box and he had to wear extra-thin socks to make this shoe work. Additionally, and probably related to the smaller fit, it felt like this shoe was squeezing our arch. Again, we do feel that if we ordered a slightly larger size, these issues would likely be resolved.
The Flatline shoes aren't overly stiff or rigid. That said, they do offer a nice balance of on-bike performance with easy walking abilities.
Credit: Laura Casner
Rigidity and Power Transfer
The Flatline shoes strike a pretty good balance of rigidity and pleasant off-bike feel. These are not some bruising, ultra-stiff, shoe, nor are they some flimsy, wet noodle. Bontrager struck a nice balance here that works well in most applications save for full-on downhill riding.
Giving this shoe the old hand flex test, they are relatively easy to flex from the ball of the foot forward. Moving further back, the sole stiffens up considerably from the ball of the foot to the heel. They are rigid enough to deaden most forces of the trail while still retaining a nice walking motion. When you are hammering on the pedals, there is no unwanted slop or flex in the sole and we feel they translate virtually all of your power into the pedals.
These shoes breathe well enough to be worn on days when the temperatures soar.
Credit: Laura Casner
Breathability
The uppers of the Flatline are made from a synthetic leather-like material. There are small perforations on both sides of the midfoot section of the uppers, as well as a few more on top of the upper toe box. These vent holes are quite small and resemble pinholes. It is hard to really ascertain how effective these vent ports are, but they allow more heat to escape the shoe than none at all.
While the Flatline shoes don't breathe particularly well, we did find that they were far from the least breathable shoes we tested. They are lightweight and not particularly bulky, and we found them to feel cooler on the feet than heavier, burlier shoes. On high-output days, these shoes can get a little warm, but it is not egregious, and they seem to dry relatively quickly.
After heavy mileage, these shoes are still in excellent shape. The harder Vibram rubber resisted wear more effectively than softer rubber compounds.
Credit: Jeremy Benson
Durability
The Flatline shoes appear to be quite durable. We have ridden our test pair off and on for over a year and aside from some cosmetic discoloration of the laces, they look pretty much brand new.
The synthetic upper is still in great shape and the harder Vibram rubber sole has resisted premature wear. The tread pattern is still in excellent shape and there is little visible pin-scarring. All of the stitching on the uppers is still intact and the lace holes show no signs of stretching or tearing. The reinforced toe and the outsole are still perfectly bonded and have not separated from the shoe at all. We are confident these shoes will have a long and happy life.
These shoes are quite light. Still, we don't think they can stand up to the competition in other, more important, metrics.
Credit: Jeremy Benson
Weight
Our size 11 Flatline shoes hit the scales at an average of 372-grams per shoe. This makes them one of the lightest shoes in our review. We find this to be particularly impressive as the shoe offers some of the pillowy and padded feel of our skate-inspired shoes while managing to keep the weight low.
On the bike, the low weight is noticeable. We don't find shoe weight to be a critical ride characteristic for the majority of riders save for the light trail/xc crowd who tends to prefer clipless pedals anyway. That said, weight can be a deciding factor if you are stuck between two similar products.
Value
At their retail price, we feel the Flatline are an average value. While these shoes are totally functional and have some nice characteristics such as low weight and good power transfer, they are far from the grippiest model we tested. If pedal grip is high on your list of performance attributes, we recommend looking towards other options in our test class. Some of these other shoes cost less and deliver significantly better grip performance.
These shoes are certainly functional. Unfortunately, it is hard to recommend them over other shoes in this test class.
Credit: Laura Casner
Conclusion
The Bontrager Flatline are serviceable mountain bike shoes that get the job done out on the trail. They are functional and they do their job dutifully, albeit with less pedal grip than most of the competition. Yes, these shoes are lightweight and provide good power transfer, and they may be a good option for the rider who prefers a less grippy sole and more foot mobility.
—
Pat Donahue
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