Laughably Good Mud Traction with the Bontrager G-Spike Gravity Tire [Review]

The Bontrager G-Spike casing profile is someplace between rounded and square, and all those tall spikes dig deep for grip.
Bontrager G-Spike

If you haven’t seen the UCI Downhill World Championships race from 2020, do yourself a favor and peep the highlights. It was an adult-ish slip-n-slide. The root-strewn track in Leogang, Austria, made for one of the wettest that athletes had seen in several years, and tire tread selection was a make-or-break move for every last rider. Some of the fastest pilots in downhill were tripoding their way toward the bottom like children riding past their snow forts, while others mounted up tall spikey treads front and rear knowing that staying upright would matter more than rolling resistance. Reece Wilson earned a gold medal in the men’s elite field that soggy Sunday with a Bontrager G-Spike spinning up front, and we recently tested one out to feel how it might help mortals navigate the slop.

On a set of Evil Loophole rims with their 29mm, internal width the G-Spike tread measures 58.12mm, or 2.29 inches. I intentionally put this tire on the narrowest rim I had around to keep the tire as trim as possible. Traction in deep mud is largely dependent on the ability of those spikes to cut through the messy mucus on top to the sturdier grip below, and narrower tire profiles keep the traction patch from planing on top where it’s slickest.

The G-Spike snapped into my tubeless-ready rim without issue, and it has yet to weep or spray me with sealant. Some tires with sturdy two-ply casings are more difficult to set up tubeless, but this one didn’t pose any issues. I only mounted the spikes under my handlebar since I’m not racing downhill with it, and paired a Schwalbe Big Betty out back for solid braking grip and pedal-ability. This combo has proven ideal for steep riding when it’s actively raining, holding the line while some of my friends slide along it on their butts.

If you’re someone who gives off an audible squeal when the forest fun-meter hits eleven, your throat may be hoarse after a few G-Spiked descents. The cornering and off-camber capabilities these tires unlock are well worth a loud hoop-n-holler. The casing profile is someplace between rounded and square, and all those tall spikes dig deep for grip in the flattest corners and jankiest off-camber sections. With a slight lug trim, these tires should also work well for deep August dust conditions, much like a Maxxis Shorty or Schwalbe Magic Mary. Those spikes dig like fingers into the soil to catch your line and keep the bike upright when it otherwise feels like gravity is winning. If you’re looking outdoors and thinking “this is gonna be a slick pigsty,” a Bontrager G-Spike tire or two will find whatever grip exists.

Some tracks are steep enough that you can’t walk down them when you get spooked. Slopes so tilted that you can put a hand against the mountain to rest while standing upright. When gravity is in such an abundant supply this is a sweet tire to guide the front end toward that next catch-berm. A few of the trails here in Bellingham offer a unique brand of steep and awkward, wherein you are somewhat off balance and asking for all of the front tire traction in tandem. Few tires can pull those variables together like this one does, thanks in large part to the offset negative spaces that are slightly larger than the lugs they surround. The tread pattern clears mud quickly to open the lugs and grab hold anew. Slacker head tube angles, stronger brakes, and strength can save the day on vertical fall lines, and this tire has quickly added itself to that list.

Bontrager G-Spike

I entered those steep dips assuming this tire would squirm and glide at the first sniff of a root or rock. To my surprise, it hooks up just as well as my favorite Magic Mary on the shiny surfaces. No tire is truly stellar on wet wood and the sort of stones lodged in these hills, but the G-Spike does as well as the best of them. I can feel the spikes squirm a bit on dry rock rolls, but they maintain grip quite well and ultimately they aren’t designed for dry riding so it’s a somewhat moot point. If your favorite mud spike catches well enough on hard surfaces this one will likely perform similarly.

Bontrager G-Spike

My front tire plays second fiddle when it comes to testing puncture protection, but I did drop the pressure in this tire significantly to see how it holds up. I have yet to poke a hole through the dual-ply casing, which is exactly what I’d expect from legit DH race rubber. The tread does wear a little faster than some, which is a similar sacrifice for the high grip factor of any mud tire. Fortunately, you’ll only need it in the softest of conditions so it should make it through the season and could even be stored for the next one if you have a good dark place to keep tires cool and happy.

The G-Spike is only available in a 29 x 2.4″ size that compresses my scale to 1,421g, and it retails for $79.99 on the Bontrager website.

Pros and cons of the Bontrager G-Spike tire


  • Life-changing mud grip
  • Trimmable spikes
  • Sturdy sidewall support
  • Weather specific


  • Weather specific
  • Slow rolling with less trail incline
  • Wears quickly

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