The Specialized Rhombus Pro Tire is a Mountain Bike Tire for Gravel Bikes [Review]

I love dispelling common misconceptions. “Gravel biking is just what mountain biking was 20 years ago!” That’s a loaded phrase with a whole lot of room for debate. For someone who spends too much time thinking and writing about all of the differences in off-road bicycling, I’m not sure the Specialized Rhombus Pro tire does me any favors trying to dispel the mis/conception. I’m positive though that I don’t care because it’s my favorite gravel bike tire I have tried yet, even if it might not be my primary gravel bike tire.

To make matters more complicated, Specialized describes the Rhombus Pro as a gravel tire made for “aggressive riding on aggressive trails.” Damnit. This gives too much fuel to people who insist that gravel biking would be awesome if the bikes had dropper posts, suspension forks, and flat handlebars.

Also Specialized: “With more tire clearance and more capability, today’s gravel bikes can take on tougher trails than ever before.”

Also gravel bike haters: “Just get a mountain bike!”

Now there is a proper use case for the Rhombus Pros that differs from proper trail bike riding, but before we get there, let’s go over the specs for the Rhombus.

Specialized Rhombus Pro tire specs

The casing has 60 threads per inch and it’s a folding bead tire which uses the Gripton tire compound with and Endurant flat protection. The recommended tire pressure range for the Rhombus is 35-65psi and the tires weigh a claimed 575g for a size 42. I’ve been testing the 700x47s.

For a while there, bike brands tried to convince us is that 27.5 is the “fun size” wheel, like it’s a bag Snickers destined for the Halloween bucket and that 29ers are the “race” size. The terminology is kitschy to say the least, but I’m going to use it anyway and say that 700×47 is the “fun” tire size for gravel bikes.

If you’re into underbiking, this is a great tire to for it.

The width has is drawbacks. It’s heavier and unnecessary if you find yourself on real smooth gravel or pavement. The tire might not feel as firm or responsive as a narrower tire, but the added volume adds some damping when you’re on chunk, which is where you want to be on the Specialized Rhombus.

I mounted the 47s up ahead of a bikepacking/touring trip from Boulder to Denver to Winter Park and back to Boulder. Since then, they’ve seen about every surface you can imagine except for snow. Being a narrower tire, these mounted up rather easily with a shot from a compressor and I haven’t had any issues with air leakage.

The Rhombus looks like a compact mountain bike tire. The center tread is made of ramped, clustered knobs with open pockets for added traction. There are well-spaced transition knobs with siping for consistent traction as you lean the bike over and then blocky side knobs, more sipes, and some give for more traction.

Specialized Rhombus in action

The Rhombus tires spin up well but there is some noticeable drag and buzzing on smoother surfaces. And even though it may be draggy for a gravel tire, it’s not much different from an XC tire.

I haven’t had any issues with expected traction on the tires. They excel on buff singletrack, but even in looser, rockier conditions, the knobs dig in and grab the ground. The only times I have had issues with slippage is in deep, loose dirt, which is to be expected. A narrower tire like this isn’t going to match a 2.3-2.5″ tire.

Leaning the tire over, there aren’t any lapses in coverage and they move from the center to the side knobs easily. On a gravel bike, I never quite feel like I’m leaning the same as on a mountain bike, but the tires hold a line on the corner knobs.

I’ve also been pleasantly surprised with how the tires hold up. I’ve been running lower pressure, somewhere around 35psi, and the tires experienced a lot of rock smashing on the cruise down Rollins Pass.