These days, much of the innovation in the gravel scene is in the form of rubber. Fast-rolling, wide tires are the order of the day and the Challenge Gravel Grinder TLR’s are quickly showing their age. They roll fast, but have some shortcomings when pushed and those sidewalls aren’t supposed to bubble, are they?

Challenge Gravel Grinder TLR 42 Tire Features:

  • Center file tread with knobbed shoulders
  • 120 TPI casing
  • Available in black wall only
  • Aramid folding TLR bead
  • 33, 38, 42 and 45mm widths
  • Weight: 430 grams (42mm, actual)
  • MSRP: $67.99
Challenge Gravel Grinder TLR 42 Tire Tread

The center file tread works wonders on the road and fast gravel.

Roll fast, but sadly, they weep

The Argon 18 Dark Matter GRX came equipped with these tires out of the box. Mounted on a set of 21mm wide HED Ardennes GP Plus tubeless wheels, these measure out to a respectable 43.3mm, so keep that in mind as you mount these up on wider rims, like the Bontrager Aeolus Pro 3V or gravel-specific wheelsets.

No matter whether you ride on tarmac, gravel or singletrack, you want to reduce rolling resistance. That’s always the name of the game and Challenge is taking aim at that square in the face with the tread pattern of the Gravel Grinder TLR’s. Down the center, you’ll find what we affectionately call a “file tread.” This one mimics a diamond-shaped wood rasp, which results in roughly a billion (give or take) little triangles that can adapt and grip to all the surfaces, while the large outer knobs can help with cornering and traction on rough terrain.

The file tread down the center works awesome for pavement. Traction remains superb and rolling resistance is outstanding on rough and smooth tarmac. I can consistently get up-to-speed and maintain momentum without much of a fuss on the local road routes. Even long climbs aren’t terribly difficult and are only slowed down a touch with these tires.

Challenge Gravel Grinder TLR 42 Tire Review - Tubeless Setup

These tires weep… a lot. Not something I see from TLR’s these days.

Tubeless woes

From Argon 18, the Dark Matter arrived with tubes — even though these are TLR tires and clearly HED makes great tubeless wheelsets. After rocking higher-than-normal pressures with tubes, I set them up tubeless. That process was very straightforward as I was able to seat them up without any soapy water or anything. I just made sure both the rim surfaces and tires were clean, then inflated them with the Blackburn Chamber Tubeless Floor Pump, left them seated up for a bit, then added Bontrager tubeless sealant (the last of their old formula I had).

This is where things got interesting. I typically add about 40ml of sealant to gravel tires of this size. Yes, that may be a little less than others might recommend, but that’s how much I usually insert. Very quickly, the sidewalls started bubbling in massive amounts. I shook the sealant around to be sure it would start to seal. I inflated them a little on the high side (~36-38 psi), just for good measure, then went for a ride. During the course of the ride, the sidewall bubbles continued and you can see that the sealant made its way from the sidewalls to the downtube in the above photo.

As a result, throughout the course of a 1 hour ride, I could expect upwards of 8-10 psi loss. Because I’m stubborn, I kept riding with that amount of sealant just to see if they would improve over time. I shook them and kept inflating them before every ride. With that amount of sealant, they went completely flat in a matter of 2-3 days.

Challenge Gravel Grinder TLR's Weeping Sidewalls

Weeping all over the place — not just in one spot.

After a few weeks of this process, I finally decided to add double the amount of sealant, so I added another 40 ml or so and tested things out some more. The results were improved, but not perfect. At that volume of sealant, they continued to weep, but less so. I found I would only lose 2-5 psi on a long ride, so that was much more acceptable (but still frustrating). When I boxed the Dark Matter up to ship it back to Argon 18, I inflated the tires to about 50 psi and the sidewalls continued to bubble pretty extensively. Again, this was not just in one section of the tire, but multiple areas on both sides of the tire.

Singletrack on the Challenge Gravel Grinder TLR

Rolling some fine singletrack on the Gravel Grinder TLR’s.

Gravel and dirt

When the gravel or singletrack is smooth, these tires roll fast and handle superbly. The side knobs add a dose of confidence when things get more technical. I’ve been able to corner and ride with confidence on the best gravel and dirt around. But, once things get steep, loose or rocky, that speed breaks down a bit. I’d say this tread pattern is awesome for the endless, smooth gravel roads of Colorado or the upper Midwest. And, they’d be a great choice for SBT GRVL, for example. But, on rougher gravel, I’d opt for something a little more capable.

You’ll notice the rear tire loses traction on steep climbs and the treads to tend to gather with mud and become slicks on wet singletrack. On loose climbs, the rear tire has a tendency to spin out. Again, a mixture of road and smooth gravel is the ticket with these tires.

The Good

  • Fast-rolling and smooth on tarmac
  • Devours the best gravel terrain around
  • Easily-mounted and seat up for tubeless
  • Light for a 42mm tire

The Bad

  • Sidewalls weep… a lot!
  • Take double the amount of sealant and they still weep
  • Rear tire quickly loses traction on steep climbs

The Bottom Line: Challenge Gravel Grinder TLR 42 Tires

While the Challenge Gravel Grinder TLR 42’s do offer a nice width and excellent performance on the road and smooth gravel/dirt, they fall short when things get rough or steep. And, their tubeless performance has been questionable at best. If I had time, I would have tested a variety of sealants to see if one works better than another to seal these weeping sidewalls, but I didn’t have the time to do that. Frankly, the sidewalls shouldn’t weep at all if they are TLR tires. Did I get a bad batch? Perhaps I did because no other reviews are mentioning this, but, this kind of thing just shouldn’t happen. There are better and less expensive tires out there, like the Specialized Pathfinder Pro, that I’d definitely recommend over these.

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About Author

A native of the Pacific Northwest, Jason quickly developed a love for the outdoors and a thing for mountains. That infatuation continues as he founded this site in 1999 -- sharing his love of road biking, mountain biking, trail running and skiing. That passion is channeled into every article or gear review he writes. Utah's Wasatch Mountains are his playground.


  1. Weeping starts because there is a thinner layer of rubber on sidewalls. I had some weeping tyres too. In general after small research what I found – it’s usually lack of sealant. In weeping ones I started to add around 90ml of Effetto Mariposa Caffelatex and this solved problems. Weeping usually stops in a day or two and when sealant starts to dry out in the tyre, on some areas weeping starts again. Basically it’s a good indicator for me to add it up.

  2. Definitely a good point and certainly a way to fix what was going on with these tires. However, with today’s latest crop of outstanding TLR tires, compensating for porous sidewalls with egregious amounts of sealant seems unnecessary. I run tubeless pretty much exclusively and these sidewalls are terrible compared to the competition.

    That said, dropping 90ml of sealant in these to seal up the sidewalls would be a smart choice from the get-go. Kind of crazy though, since that’s as much as you’d want with an oversized MTB tire.

  3. I installed those tires three weeks ago and the weeping and reassure losses are driving me insane especially considering the pretty high price tag.

    • Such a bummer, right? I saw that the WorldTour teams experimenting with tubeless are brushing sealant inside the entire inner lining of the tires and letting that dry before installing. Perhaps that would help these tires?

      I know, it’s a pain to uninstall and re-install, but it may be worth a shot.

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