When to Use Knobby Tires

hahn_tree_fb

Compass has long championed the use of “road” tires on gravel. More and more gravel racers agree: When gravel is sliding on gravel, knobbies are of little use.

So then why does Compass offer a knobby tire, the Steilacoom 700C x 38 mm? Knobs are useful in mud. They dig into the surface, and since the mud is viscous (gooey), it provides something for the knobs to push against. That is why cyclocross bikes use knobby tires.

700x38cx_mud

It’s important is to space the knobs widely, so the mud is ejected as the tire rotates. Otherwise, the tire just clogs up, and soon you are riding on slick tires again, except that their tread is made of mud instead of rubber. What you want is a muddy bike, but clean tires (above) – the tires pick up mud only briefly before it is flung off.

snow_walupt

Snow is a different story again. Depending on your speed, it behaves differently. At high speeds, you glide through the snow almost as if you were skiing, and tread patterns make little difference. At low speeds, you compact the snow and create the surface on which you ride. Knobs dig into that surface and give you extra grip. Even a herringbone tread works OK. Slick tires or longitudinal ribs act like the runners of a sled – they just slide and offer very little traction.

testing_ice

What about ice? Ice is too hard for rubber tread to dig into. You need metal studs that bore into the ice to find traction. Sometimes, snow compacts to ice (above). I prefer to walk rather than risk a fall when I see ice on the road. (Unfortunately, I don’t know of a good method to see “black ice” before it’s too late.)

fmb_super_mud

Back to mud, where knobbies make the biggest difference: Designing a good mud tire isn’t hard – space your knobs widely, and the tire will self-clean as it rotates. The downside is that it’ll be buzzy and slow on pavement. I love the FMB Super Mud tires (above) on my old ‘cross bike (our Steilacooms don’t fit!), but their secret isn’t in the tread pattern – the extra-supple casing makes them wonderfully fast and contributes to their great traction. The tread is incredibly buzzy on pavement. It’s good that most ‘cross courses include no more than a few meters on pavement.

The knob shape itself makes little difference. “It’s all about ‘design'” a Panaracer engineer confided.

dual_purpose_tireDesigning a knobby tire that rolls OK on pavement is not too hard, either. Space your knobs closely, and the tire will roll fine. But when it gets muddy, the tire will clog up, depriving you of the advantages of a knobby tire. You get only the disadvantages of knobbies, without many of the benefits.

steilacoom_testing

Designing a tire that rolls well on pavement and grips well in mud is much harder. If you also want the tire to corner well without knobs folding over and suddenly losing traction, it seems almost impossible. And yet… with the engineers at Panaracer, we spent a lot of time analyzing and testing knob designs during the development of our Compass Steilacoom 700C x 38 mm knobbies. We found a few things that can greatly improve a knobby’s performance on pavement, without detracting from its ability in mud. More about that in a future post…

Click here for more information about Compass tires.

Photo credit: Wade Schultz (bottom photo)

About Jan Heine, Editor, Bicycle Quarterly

Spirited rides that zig-zag across mountain ranges. Bicycle Quarterly magazine and its sister company, Compass Cycles, that turns our research into high-performance components for real-world riders.
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33 Responses to When to Use Knobby Tires

  1. Adamar says:

    What about sand? I know fatbikes use massive volume for traction, but do the knobblies dig into that?

  2. Gary Jacobson says:

    I and others would probably be interested in 26 inch version of the Steilacoom. If a 650b version would fit on a bike with fender clearances of 20mm with Hetres that might useful. My experiments using fenders in snow and mud haven’t uncovered any benefits yet.

  3. Rustilicus says:

    Another place for knobby tires is on loose over hardpack conditions. Many of our local roads get like this during the drier times and it’s good to have a tire with some bite – especially on the shoulders of the tread.

  4. Tim Nielsen says:

    Your knobby tire passes the ultimate tire test then…it ‘looks’ good! It reminds me of the tires I have favored over the years. One thing to note, is the amazing amount of ‘evidence’ riding in mud leaves on the trail. It’s a self-policing situation thus far in my local open spaces, and some do not police themselves. Huge deep gouges that exacerbate runoff, and ugly scars that last for months. Trail-widening is also a problem, as riders swoop around sticky obstacles. Wow sorry for the rant. Lovely season ahead for us all!

    • The Seattle-area cyclocross races do a lot of restoration after the race, and also, riders are asked to stay out of the parks afterward to allow the grounds to recover.

    • Conrad says:

      Cyclocross races are supposed to be muddy but you bring up a good point: if we are talking about trails, if it is muddy enough to make knobs truly worthwhile, you probably should not be riding on the trails. I use the rat trap pass tires for mountain biking now. They are faster on sand, gravel, hardback, and pavement (for riding to the trail)! You might slide around more on the odd patch of mud, but if you look at the sum total of the surfaces you ride on, the file tread is the fastest tire.

  5. Anne Paulson says:

    What about loose over hard? Where I live it doesn’t rain for six months. By the middle of the summer we have many fire roads that are hardpack covered with a thin layer of sand or gravel. I feel like my knobbies give me better traction, digging in to contact the dirt, whereas my smooth tires skid when I try to brake.

    • Anne Paulson says:

      It seems like this is the same as when I hike down a steep trail that’s loose over hard. If I hike with hiking boots with knobbed soles, I don’t fall, but if I try to hike with tennis shoes, I skid and fall. (I have made this experiment on trails where I live. Not hypothetical. I don’t wear tennis shoes on steep downhill fire roads any more, because I don’t like to fall down.)

  6. morlamweb says:

    I run studded knobbies all through winter: late December through March. The rest of the year I roll on wide slick tires (an aside: thanks to your advice on tire width and suppleness, I’ve switched over from relatively narrow 38-559s at ~70 psi to 50-559s at ~20 psi, and it’s made a world of difference). Yes, they’re a bit slow when riding on pavement, but with snow and ice a constant threat in my area during winter, I need studs in order to keep riding through these months. I have only one bike and swap the tires as winter approaches. I try to put them on as late as possible in the year and swap in my slick tires as soon as possible in spring.

    • Jacob Musha says:

      I live in Wisconsin and I bought a pair of studded tires for the first time this winter (Schwalbe Marathon Winter 26×2″, 1150 grams each.) They are great for the ice but I can’t stand riding them any other time. I wish someone would make a studded tire that isn’t obscenely heavy.

      Most of the time I run a separate wheelset sporting 26×2.1″ Bontrager XR0 Team Issue mountain bike tires. They have enough tread to provide traction in the snow and at 430g each, they feel like a Rat Trap Pass Extralight with tread tacked on. Switching them out for the studs saves over three pounds on my bike!

      • nickskaggs says:

        I imagine that the studded tires are extremely heavy for a reason. I imagine supple, thin studded tires would tear themselves apart, as the studs probably exert a lot of forces on the tire when they’re driven into the ice- especially when cornering, etc.

  7. M. Cambron says:

    FWIW, I cycle commute year round and have found the Continental TopContact Winter II tires to be a good choice for light snow and ice. They are certainly heavy and slow compared to the Stampede Pass tires I run the rest of the year but they provide grip and security when the roads are slick.

  8. Erick says:

    i only rides slicks tires on my bikes and do a lot of gravel, just make sense for my style of riding…
    but i ask my self for some one more agressive with lot of skiding (not eficient) maybe a knob tire suits better. im not confidence skidding in gravel with my slicks tires im feel they will destroy… but with knobs while im skidding in gravel feel like they get a lot mor gripp a not destroy so easy

    • Skidding with a locked rear brake isn’t good for the tires – it puts huge loads on the sidewalls. With supple, fine sidewalls, you can destroy a tire when skidding on pavement (where you have a lot of grip). On very loose ground, where skidding may make sense to round a downhill hairpin turn, you don’t have enough traction to damage the tire. Whether the tire has knobs or not has little influence on whether skidding will damage it.

  9. bonnev659 says:

    thank you for this great write up and also about rim vs disc brakes!

  10. Rod Holland says:

    Those of us who live in the Frozen North and spend the Winters riding studded tires often have irrational fantasies of a light, supple, studded tire, perhaps the result of a joint adventure between Jan Heine and Peter White. This fantasy has it that the initial prototype is a Steliacoom with carbide studs mounted in the knobbies. These counterfactual tires glide effortlessly y(and safely) over ice, mush confidently through a reasonable depths and conditions of snow, and buzz and crackle happily on pavement. It’s a lovely dream!

    rod

  11. Willem says:

    I do want to add to the praise for Conti Topcontact Winter II tyres. They may not run as well as slick Compass tyres, but they roll as well as most other touring tyres, and far far better than studded tyres. Grip on snow and ice patches is phenomenal. Of course, they are not suitable for really heavy snow and ice duty, but they are a remarkable intermediate option. They are also comfortable, because the compound remains more flexible in lower temperatures. They run rather narrow, so you may want to consider one size wider than you would choose otherwise. Not (yet) in 650B I am afraid.

  12. Rich Wolf says:

    What I can’t understand is why every major mountain bike tire manufacturer has tread on their tires. It can’t be just for “looks”.
    I am mostly a mountain biker and while I love my 44 c compass tires on my 29er mountain bike turned all road bike, there is not nearly the grip or confidence that I get with the compass tire vs. just about any mountain bike tire that I have tried. Even the pro mountain bike racers pretty much all use a treaded tire. You would think that if a smooth tire offered the same grip and rolled better why aren’t at least some of them using them?
    With that said the 44 c tires work much better than what you would expect and on the road they haul ass!

    • Mountain biking and gravel riding are quite different. For example, on single track, you have to climb out of ruts, but not on gravel roads. Mountain bikes use straight bars, gravel bikes have drop bars. Mountain bikes have suspension, gravel bikes (usually) don’t. Gravel bikes are much closer to road bikes than to mountain bikes as far as riding position and equipment is concerned. I think there are reasons for these differences, but I also don’t rule out that the new technology and findings from gravel riding might influence mountain bikes in the future. Perhaps we’ll see smoother tires on some mountain bike race courses in the future?

  13. kai says:

    Would like to flag for rubber quality. The adhesiveness of the rubber is in many situations more important than the tread. Examples are wet tarmac, wet rock and ice. Tyres may look good as new, but if the surface of the rubber is hard or dry you are easily in for a skid or fall in such situations. Natural rubber tends to be good when new but soon dries out, it can sometimes be a matter of just months. In my experience a good quality syntetic rubber offers the most lasting quality.

    Some manufactures have more problems with this than others. Schwalbe has given me good and lasting wet grip, have used ice spiker pro, marathon winter, thunder burt, rocket ron, and Stelvio road tyres. Continental X-King tend to dry out faster, loose their grip on wet roots, Mountain King seem better. Vittoria Bomboloni were very stiff start with, not much ice grip, however satisfactory on wet rocks. But not nearly as good as Thunder Burt there.

    With winter car tyres I have good experiences with Michelin, will usually remain pliable and adhesive for about 5 years, other makes I have tried have been unusable already the third winter in spite of test-winning abilities when new and good remaining tread.

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