Prepare for Gravel Riding

un_meeting_2014

Gravel riding is becoming increasingly popular, and we are very happy about it! It was natural for Bicycle Quarterly to become a co-sponsor of the Eroica California ride in April, since it combines two things we love: gravel roads and classic bikes. But gravel riding isn’t limited to riders trying to recreate the glory days of mid-century racing – almost any bike shop in North America will have a selection of carbon fiber “gravel bikes”.

There are many reasons why cyclists have discovered gravel: Gravel roads see much less traffic than paved ones. Gravel roads often traverse magnificent scenery. And riding on gravel enhances the simple experience of cycling, as your bike slides a bit – whereas on pavement, a slide usually results in a crash. On gravel, you can play with the limits of adhesion. It’s fun.

corner_gravel

For more than a decade, Bicycle Quarterly has featured cycling on unpaved roads: dirt roads, gravel roads, even mountain paths. As people have become interested, they often ask us: “What do we need to ride on gravel?” 

Here are some thoughts based on our experience of testing many different bikes on many different gravel roads.

hahn_enduro_allroad

Bike

Almost any bike can be ridden on gravel. When I was a college student, my friends and I rode our racing bikes through the forest – on 20 mm tires! Today, we call that “underbiking” – riding a bike that is only marginally suited to the environment where we ride. That can be fun for a short while, and it hones your skills, but in the long run, you’ll want a bike that is better suited to the task.

A good gravel bike combines the performance of a racing bike with the ability to use wide tires. If you have a choice, stay away from touring bikes and hybrids! Their stiff and heavy frames limit their performance. You’ll have more fun on a bike that offers a spirited ride and encourages you to go faster and further. Cyclocross bikes are great for gravel, as are the increasingly popular gravel bikes. A good randonneur bike with wide tires is an excellent choice as well. Classic racing bikes often have clearance for wider tires, too. On these bikes, you fly over the gravel, rather than grind through it.

gravel_road

Knobs vs. Smooth Tires

Tires are the most important choice of your gravel bike. Contrary to what many cyclists expect, you don’t need knobs to ride on gravel. When you slide, it’s because the gravel layers slide against each other, not because your tires slide on top of the gravel. Knobbies don’t improve your traction. (Knobbies mostly give you an advantage on mud.) Most gravel rides include a fair amount of pavement, where knobbies roll slowly and corner unpredictably. That is why most gravel riders choose “road” tires with relatively smooth tread patterns.

rough_gravel

Tire Width

You want the widest tire you can fit on your bike. At Bicycle Quarterly, we’ve ridden tires between 20 and 54 mm wide on gravel. The verdict is clear: The widest tires are by far the fastest and most fun. Three reasons:

  1. When your bike bounces on the gravel, that energy is lost from the forward motion. (The technical term is called “suspension losses”.) The more your bike bounces and vibrates, the slower it is. With wider tires, you can run lower pressure, so your tires bounce much less. You get more speed and more comfort.
  2. The more rubber you have on the “road”, the more sure-footed your bike becomes. Your bike slides sideways in corners when the stones under your tires roll or slide. A wider tire spreads the cornering forces over more stones, so it’s less likely to slide.
  3. On soft surfaces, a narrow tire sinks into the gravel. Displacing gravel takes energy. (Imagine walking on a soft sandy beach or in deep snow. It’s hard!) The ideal tire leaves almost no track in the gravel, but just floats over it. (Imagine snowshoes. They distribute your weight, making hiking through deep snow easier.)

Your tire width is limited by the clearances of your bike’s frame and fork. Read this post about determining how wide a tire you can fit on your bike. And then use the widest tires that safely clear your frame.

compass_babyshoe

Tire Choice

Many riders imagine that you need a reinforced tire for gravel, but that isn’t necessarily the case. On gravel, you are much less likely to get flats. Here is why: As you roll over debris, your tires push it into the ground. It’s the opposite of unyielding pavement, which pushes the debris into your tires – they puncture.

For some riders, sidewall cuts can be a problem when riding over sharp rocks. We don’t really know why some riders cut their sidewalls and others don’t. Many experienced cyclocross racers use hand-made tubular tires with thin cotton casings. Others tend to slash the sidewalls even if they use reinforced tires. Experiment and see what works for you.

There is a good reason to ride high-end tires with thin, flexible sidewalls: Supple tires are especially fast and comfortable on gravel. (That is why ‘cross racers use those expensive tubulars.) Supple tires reduce vibrations, so less energy is lost to the bike bouncing. You go faster. Less bouncing also means that your body doesn’t suffer as much. It’s a win-win situation.

diverge2

Brakes

On gravel, your braking power is limited by the lack of friction between tire and road. You can only brake until your tires start sliding. This means that absolute brake power is less important, but modulation is key.

On gravel, you often need to keep your wheels right at the lockup point to slow down for a corner. You need brakes that provide good feel and feedback. Many modern disc brakes are still lacking in that respect. At Bicycle Quarterly, we have found classic centerpull brakes to be so excellent that we re-introduced them through our sister company, Compass Bicycles.

no_fender_gravel

Fenders

Most gravel bikes don’t come with fenders. It’s really a shame! Fenders will keep you and your bike much cleaner than Hahn in the photo above. Gravel roads remain muddy long after paved roads have dried out. And even the most beautiful ride can be miserable, if you are getting coated with mud.

Why don’t bike makers install fenders on their gravel bikes? Unfortunately, most commonly available fenders will not withstand the vibrations of gravel roads for long. There are alternatives: Well-mounted, high-quality aluminum fenders, like the Honjos on our bikes, will last as long as the bikes they are mounted on.

Make sure that your fenders have adequate clearances around your tires. Ideally, you want 20 mm on top of the tire, so that gravel picked up by the tires doesn’t grind against the fender. If you hear constant “Scrrrshh” sounds, your fenders are too tight. This isn’t just a cosmetic problem: Debris can collapse your front fender, jam it into the fork crown, and send you over the bars. Don’t use fenders that are sub-optimal! When in doubt, it’s better to get muddy than to risk injury.

walking

Pedals/Shoes

Walkable shoes are useful. On gravel roads, you may have to carry your bike across small washouts or landslides. Sometimes, it’s easier and more efficient to hike up very steep passages. Use a pedal system with cleats that don’t get mashed up when you walk across gravel. SPD pedals have proven themselves in this environment. Others use touring shoes or even light hiking boots with traditional pedals and toeclips.

Prevent Mechanicals

On gravel, your bike inevitably vibrates more than it does on pavement. Make sure that all your bolts are tight. Check that straps and other parts don’t rub through. During the 360-mile Oregon Outback, the spare spokes that I had taped to my fender stays rubbed through two layers cloth tape until they fell off! The faster you go, the higher the vibration frequencies, and the more you demand of your bike.

It is possible to design and build a bike that can withstand thousands of miles of gravel riding without requiring maintenance or tightening of bolts. The lost spokes were the only problem I encountered during that epic trek across Oregon. (Below is my bike after the race.)

herse_outback

What to Carry?

Gravel riding takes you into remote places. Don’t count on getting outside help – you’ll often be out of cell phone range. Make sure your bike is reliable, and carry a few essentials.

Be prepared for flat tires. Carry two spare tubes and also a patch kit, in the unlikely case that you have more than two flats. Bring a pump, and not a CO2 inflator. (You may need to inflate multiple tires.) A spare tire is useful if you slice your tire. (Or bring a piece of tire casing that makes an excellent boot – much better than the stuff you can buy for this purpose.) When I carry a spare, I bring a narrower, lighter tire than I usually use – it’s only intended to get me home…

Obviously, a few wrenches, for the bolts that are most likely to loosen, should be in your tool kit. If you ride with friends on similar bikes, you can pool your spares. For example, one spare tire will suffice for the group if all use the same wheel size…

Bring water and food, plus clothing for all expected weather conditions: Be prepared for hot climbs, cold descents, and everything in between. Use a layering system that packs small. Your bike should have the capacity to carry that luggage. Backpacks are a last resort: They tend to be uncomfortable during long rides.

A good gravel bike will have lights, so you aren’t stranded if you get lost and have to ride after dark. Bring a small emergency blanket and a small first aid kit, just in case.

With these precautions, you’ll be able to enjoy gravel roads with little worry. Riding off the beaten path is quite safe. The biggest danger for cyclists, drunk drivers, are rarely found on  twisting gravel roads in the mountains. In the unlikely event that your bike breaks and you cannot continue, you’ll hike back to civilization. That might be uncomfortable, but not dangerous. And on many gravel roads, you’ll still encounter a car or truck every few hours.

And during events like the Eroica, you can experience gravel riding without the need to be self-sufficient. It’s a great way to get a taste of gravel riding, before heading out on your own or with friends.

GravelHelens

If you don’t have a perfect bike, don’t let that keep you from enjoying riding on those unpaved roads. If all you have is a hybrid, make sure it’s in good shape, maybe put on new tires, pack your gear in a backpack, and head out. It’s good to be prepared, but once you are out there, don’t worry and enjoy the ride!

More information:

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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42 Responses to Prepare for Gravel Riding

  1. Jon Vara says:

    “Underbiking” is a useful term–thanks!

  2. I think I’m speaking on behalf of all the readers when I say that I want to see a good photo of Hahn’s enduro allroad bike.

  3. jsallen1 says:

    Yes! And even on a $39.95 Columbia 3-speed, on gravel roads around Middlebury, Vermont, when I was a student in the 1960s. There are still plenty of gravel roads in Vermont, and the scenery is great too.

  4. Larry T. says:

    Excellent advice!!! And thanks for helping with EROICA CA 2016! These bici d’epoca events are not just gravel rides, for us the atmosphere reminds us why we took up cycling in the first place. And of course eyeballing all the beautiful bikes from the golden age of cycling doesn’t hurt either.

  5. 47hasbegun says:

    I’m still a big fan of 26″ wheels because of the wide tires they allow without too much rotational inertia. They still handle quickly (unlike fat 700C tires), yet don’t dig into stuff (unlike skinny 700C tires). Get something like Compass’s Rat Trap Pass or Schwalbe’s various 26″ slick options and riding gravel is almost easier than riding on pavement!

  6. adam says:

    Gravel riding is another way to breath life in to an older high quality 26″ hard tail. I was trying to figure out what to do with my old Ti Ibis Mojo after I got a 29er and the 26″ wasn’t seeing much use. The OD of a 26×2.25 tire is approximately the same as a 650bx45. If you have discs this conversion is easy, if not Paul Motolites have enough adjust ability that they can fix the rim reach issue. I left the relatively lightweight suspension fork on mine as it is nice for the wash board high speed descents that I come across out West, and I have a remote lock out for the climbs. Just another idea to throw out there, and another reason I’m glad to see the proliferation of more high quality 650b tires in the 35-50 range.

  7. Tony says:

    Right on Adam. I find my 1992 Kona Explosif hardtail with a Project 2 fork, and 26 x 1.75″ tires to be excellent on gravel. The frame is strong but just as light as a gravel specific frame and the geometry is very similar as well.

  8. Useful article…thanks!

    I’m curious about the relationship between tire width, wheel size, frame size and handling. For example, I equipped a 50cm Surly Cross Check with 38mm on 700c wheels and the handling seemed to suffer. As an experiment, I threw on a 26″ front wheel and the handling seemed much better. Of course, with my front brakes rendered useless I couldn’t give it a serious test.

    Conclusion: fat tires may cause the handling to suffer in the case of large diameter wheels and a small frame. Thoughts?

    • The rotational inertia of the front wheel determines how easy it is to turn the handlebars. Wider tires are heavier, so they make the bike more stable to the point where it feels sluggish. Smaller wheels compensate for this, so if you want nimble handling and wide tires, you need to go to smaller wheels. We tested three bikes that were identical except for the wheel size with different tire widths for Bicycle Quarterly. The 700C bike handled best with 30-32 mm tires, the 650B with 38-42 mm tires, and for wider tires, 26″ was the best wheel size. That is why our widest Compass tire comes in 26″.

  9. Michael says:

    Is it wise to ride carbon fiber for gravel biking?
    I’ve heard that getting knicks on a carbon frame is bad. I’ve heard that even benign scratches on carbon can later develop into failure points.
    I do limited gravelling on my fendered steel and with all the clanging around that goes on I can’t imagine rocks flying up at a carbon frame being good.

  10. It’s utterly preposterous to suggest that disc brakes don’t have the modulation required for fine braking control. Disc brakes by virtue of their design, especially hydraulic, completely outclass rim brakes of any sort in terms of fine control/ modulation.

    • I am glad you have found disc brakes that work well for you. I find some hydraulic “road” discs to be a bit grabby, especially at lower speeds. Others require only very light hand pressure, which makes them hard to modulate when going over bumps where your body moves around a lot in relation to the bike. This probably is less of a problem on mountain bikes with suspension forks, but the carbon forks of many gravel bikes are very stiff and don’t absorb shocks well.

      • 47hasbegun says:

        I have to agree with your findings. The only time I’ve test-ridden a bike with hydraulic brakes—a Ritchey build with big rotors—I had to be very careful to not do an endo. I’ve previously had similar experiences with linear-pull brakes. Considering how I tend to grab the levers very hard during an emergency stop, I’d more than likely either do an endo or skid to the ground with such brakes.

        I’ve come to appreciate how cantilever brakes modulate when set up properly.

    • adam says:

      Rotor size will certainly effect modulation and power. Also Shimano has two different hoses (one stiffer than the other) that allows you to fine tune this with their brakes, and the option between resin and sintered pads will also change things. I find the modulation on Shimano hydros to be fantastic, they are what I have used primarily for the last few years. Mechanical discs have generally been too grabby for my taste.

      • emem1956 says:

        I use a TRP HY/RD mechanical / hydraulic disc brake (reservoir at the hub operated by cable from normal shift lever) at the front with a Paul Minimoto rear brake. If I could fit a disc at the rear, I would. I ride on lots of rough & deeply graveled roads: the control, modulation & power of the disc brake is far greater than any rim brake I’ve used. Despite their power, I’ve never come close to doing an endo in any conditions. Being able to reliably stop in the wet is a (big) bonus! The Paul brake is very good, and I used to have one on the front that I was very happy with, but I would never choose to go back to it. On wet gravel I can hear and feel the rear brake grinding tiny pieces of rock into the rim. The front brake just works, always, and allows precise control. I’ve never used a modern dual-pivot sidepull, but I can’t imagine they’d be anywhere near as good as the disc brake in the wet, lat alone offer the wheel clearance. I’ve only ridden Shimano road discs for a short time, but see no reason why they’d be any “worse” than the TRP. I used MAFAC cantilevers for a long time, and don’t think they’re anywhere in the same league as the TRP. I’ve also used modern Avid Ultimate cantilevers and IME they’re an expensive, over-complicated, fiddly, under-powered joke. Tektro cantilevers stopped better but are still largely woeful, It’s too long ago to remember what centrepulls were like, tho I remember they were much better than 1970s & 1980s sidepulls. Disc brakes for me! (BTW zero issues using them on travel bikes.)

      • The TRP HY/RD are among the best disc brakes we’ve used. I wish the new hydraulic Shimano road discs worked nearly as well.

        I agree that cantis aren’t ideal. We are just a bit spoiled by the centerpulls on our Allroad bikes. It’shard to improve upon their sweet modulation, while their absolute power also is more than adequate.

  11. Ray Ogilvie says:

    I’m anxious to put a set of 26″ Rat Trap Pass on my Rigid Serota “Mt. Bike” . When will the Standard casing be available again?

  12. Andrew Gemmell says:

    Here in Iowa we ride plenty of gravel, simply because there are thousands of miles more of gravel roads with little to no traffic. The group I ride with is a variety of different bikes. 26″ mountain bikes, 29ers, fat bikes, cross bikes, a few 26″ mountain/touring bike conversions, and then me on my 650b randonneuring bike, complete with mudguards and dyno hub. Often our route includes B level maintenance roads and single track, and asphalt, but the majority of the route is on gravel roads. I never feel like I am really “under biking”. I feel my bike is an excellent balance.Despite the commentary I often receive from fellow riders about having a proper gravel bike and all the unnecessary and inappropriate accessories on my rig, I find I am generally the one out front and fastest. This is not because I am a stronger rider. The equipment plays a major role. Most people’s notion of a proper gravel bike is akin to needing a monster truck to drive down a gravel road. The reality of the majority of our riding is that is on roads, they just happen to be gravel. Logic tells me a road bike with a few changes made to accommodate the different surface is all that is necessary.
    I can attest to all the recommendations you made in this post and past. They are are in my opinion absolutely spot on to a good “gravel” bike.

  13. Michael says:

    I’m not very experienced with gravel riding but once, on the DC Randonneurs’ Belle Haven Boogie PermPop, there was a section on the Georgetown Branch Trail. That trail was great! Hard pack fine gravel through forested area and we flew along there so fast and easily. It was fun flying so fast over the shady, cool, gravelly trail. And, visually, it seemed the trail tilted upward slightly the whole way we went but we just flew along effortlessly. We even commented on how it was we were blasting along so easily even with the uphill tilt. A head scratcher there.

    I was on steel with Loups. My fellow Randonneur was on Alu/Carbon with some sort of narrow tires but we both felt the effortlessness of floating over the trail so easily. Quite exhilerating.

  14. Jacob Musha says:

    Jan, I have read with great interest your “Journey of Discovery” when you switched from skinny tire 700c bikes to wider tire 650b bikes (along with fenders, handlebar bags, lights, etc.)

    With gravel riding in particular, do you expect to take this a step further and go down another wheel size to settle on 559-54 as your preferred tire size instead of 650b?

  15. Jack says:

    Jan, really insightful piece. As a Brit I don’t really have the same sort of gravel roads that you have in the US.

    Slightly related, I have been wondering for a while what you think the most suitable type of bike would be to ride the Great Divide? Obviously the mainstream opinion tends be front/full suspension mountain bike, but is that really the case? (Also I don’t have a mountain bike and don’t really want one). Do you think a fully equipped 650B randonneur bike with 42mm tires could handle it or maybe 48mm (sacrificing fenders)?

    The description on wiki (that seems to match what I’ve seen in videos) is ‘The unpaved portions of the route range from high quality dirt or gravel roads to a few short sections of unmaintained trails which may not be possible for most people to ride at all’. That makes it sound like it would be fine.

    It may be that a fellow commenter on here has done it and can add their opinion!

    • I have been wondering about the Great Divide as well. I read a report by a rider on a traditional touring bike with front and rear panniers, and he was fine.

      If you were racing, you’d probably give up a little speed on the maybe 5% that are really rough, but gain a lot on the 75% that are relatively smooth…

      • Jack says:

        That was my thinking. I currently only have a Condor bike that is semi-touring/audax with 700c wheels. It weighs in at just under 12kg including pedals, Honjo fenders etc and I use your 32mm tires however it has very large clearances and could easily run 45-50mm tires without fenders. I suspect the handling might go out the window though running tires that big with that size wheel. as the trail is alreay 62mm.

        Currently saving for a 650B bike so maybe come 2017 I can report back with a verdict..

    • gregachtem says:

      Jack, perhaps your Condor is suitable for a 650B conversion. You could try before you buy so to speak. Relatively inexpensive and reversible if you don’t like it or if you take the plunge for a new 650B frame or bike.

      • Jack says:

        Interesting idea. The exact bike I have is a Condor Heritage with cantilever brakes (probably should have got the disc braked version). Loads of clearance but what brakes would I use considering the rim would be 19mm lower? The other issue I suppose is unless I get a new fork made then I still have a relatively high 60+mm trail.

    • vankempf says:

      Jack, I have a Condor Fratello. It has more or less the same geometry as your Heritage and it works fine for me on long distance touring holidays. I currently use 28mm tires and a rack that carries two panniers. Although I have not ridden the Great Divide (yet…), I have used it on gravel roads in Colorado (including the Engineering Pass, dirt roads in the Western Cape and macadam roads in Scotland. It all worked well and punctures were rare (say one every 5,000k or so, probably less). I have sacrificed fenders to keep the weight down for air travel (assuming you travel back of the bus the bike and box together has to be less than 23kg if you want to avoid excess luggage charges). On gravel roads, as noted in the main article, you do want fenders and afternoon showers in the Rocky Mountains are a common occurrence in the summer months.

      • Jack Whorton says:

        Really useful feedback, thanks. I originally planned to get a Fratello but in the end settled for the bigger clearances of the Heritage, lovely bikes though. I am now thinking sod it, just get the 38mm Compass tires, change the fenders over to some wider ones and give it a go. As Jan says ‘We all ride the bikes we have, not the ones we wish we had or plan to have’. As I can’t currently get 2 months off of work my plan is to do 3 weeks and ride from Helena to Denver.

  16. Ford Kanzler says:

    Your post on gravel riding is perhaps one of your most informative ones yet.
    Thank you!

  17. B. Carfree says:

    While I agree that most modern touring bikes are heavy and dead feeling, I have been riding gravel and mud on my ’81 Trek 720 touring bike since, well, 1981. I would definitely include fine older touring bikes in the mix of appropriate rigs for gravel riding.

  18. Sukho Goff says:

    Timely post as I’m about to commission my first ever custom frame. Basically a lightweight rando but with room for Switchback Hills and fenders. 42’s just don’t seem fat enough anymore LOL. And I don’t even ride that much gravel (yet). I just love the way fat, supple tires feel on EVERY surface. For a lightweight frame like the one I’m contemplating, do you think (for 650b) that 48mm is the limit as far as performance (for both road and gravel) or would handling/ride quality start to feel wonky for an even larger size, say 650bx52? Maybe imagine how your Herse would feel or handle with tires that size.

  19. Wileydog says:

    i guess i’ve doing it wrong – gravel/dirt riding on a Salsa Vaya touring bike with 700 x 40 tires and mechanical BB7 disc brakes. Still lots of fun! don’t have problems braking or handling.

    • We all ride the bikes we have, not the ones we wish we had or plan to have. The important thing is to go out there and have fun!

    • Tony says:

      Bike Snob warns folks like you that you are risking serious injury and perhaps an untimely end if you insist on riding gravel on anything less than a gravel specific bike! Lol!

    • Tony says:

      I guess I am with you Wileydog…ride a Van Dessel WTF, 700×45 Panaracer Firecross tires with TRP disc brakes..tires are not what one would call low profile…I think the real appeal to gravel riding/grinding….run what you brung and you fit in and still have fun like everyone else.

  20. nic says:

    I suggest you bring a chain tool also. A broken chain really makes you walk. Into the wild it can be long.

  21. michael says:

    And a power link.
    And napkins/tp of some kind, if you are doing a long ride.

  22. Bill Wood says:

    Hi Jan, does putting 650b wheels on a Diverge sound like a good idea? It would reduce trail, and give more room for bigger tires / fenders. I’d like to try it but it’s a substantial investment of time/money.

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