Comparing 700c & 650b Wheel Sizes for Gravel Riding

Dual wheel size bikes have continued to gain popularity.  Honey first offered dual wheel sized bikes in 2011, so we've collected a lot of real world data about the pros and cons of both wheel sizes.  The bike we first offered dual wheel sizes on was our Allroads for 700c x 40mm and 650b x 47mm.  We're doing more and more Allroads with two wheel sets -- and some other models with dual wheel size options.  People tend to have questions about what works and when it makes sense to ride one wheels size over the other.

We're agnostic about which wheel size and tire size to use.  Unfortunately, there is a lot of misinformation out there, sometimes biased by bike companies with a horse in this race.  We're not trying to sell any specific technology.  Honey doesn't get paid to sell one wheel over another.  Honey is agnostic about wheel size because we build with all wheel sizes.  We like both 650 and 700 but neither is perfect for everything.  Here are our thoughts on the benefits and shortcomings of 700c and 650b wheel choices.

Assumptions for the wheel comparison:  There are many ways to specify 700c wheels and tires along with 605b wheels and tires.  So, to simplify the comparison a bit we're focusing on Honey Allroads type riding.

  • Tire diameter within about 1cm so they're fairly similar rider center of gravity.  The idea being that riders want to swap back and forth with both wheel set without much trouble.
  • Tires with minimal tread, file tread, or similar.  Tires that are focused on gravel riding or mixed-terrain riding, not aggressive mountain bike trails.
  • Riding terrain:  We assume an even spread of the common surfaces for about 1/3 dirt road, 1/3 fun singletrack, and 1/3 pavement.
  • Wheel set price of about $1,000 to $1,500.  These are high quality, durable, and light wheels.

Some benefits of 650b x 47 mm tires versus 700c x 40 mm tires

  • Smoother ride.  The bigger air volume of the 650 allows for lower tire pressure.  This provides a plusher ride.
  • Faster on technical trails.  This is because you can roll over obstacles more easily because of the larger air volume at lower pressure and you can hit stuff harder without flatting.
  • Better for technical riding.  The bigger tire provides a larger, more surefooted contact patch to the ground.
  • Better traction and control.  The bigger tire has a larger tread surface area on the ground.  The lower pressure provides improved traction, too.
  • Stronger wheels.  Because the diameter of the rim is smaller, the rims tend to be wider, and the tires have more air volume, the wheel is more durable in tough conditions.
  • Stiffer laterally.  All things equal, a smaller diameter wheel will be stiffer side to side.  Also, because the rims are usually wider than a 700c rim this augments the lateral stiffness.  The benefit of this is crisper handling.  However, this crispness is more than offset by the larger, and usually softer feeling, tire choice.
  • Funner on trails.  A wider tire is more fun to ride on technical trails.  The bike rides more like a hardtail mountain bike.
  • Fewer flats.  We qualify that this is not always the case.  It really depends on the tire pressure and how you ride.  Lower tire pressure may mean more flats.  Also, a bigger tire allows you to get over your head in technical riding more easily so this can lead to getting more flats.
  • Traveling.  We think of this benefit in two ways:
    • Having two wheelset options make your bike more tailor-able to the area of the world to which you're traveling.  It's nice to have two distinct wheelsets from which to choose.  it's kind of like having two travel bikes in one.
    • 650b wheels, with partially deflated tires, pack more easily in an S&S case or just about any travel case.

Some considerations with 650b x 47 mm tires versus 700c x 40 mm tires

  • Slower rolling on pavement.  And, technically slower rolling on dirt roads for the same reason but some of the slowness is offset by the tires' surefootedness.  The wheels are slower for three reasons:
    • Higher inertia due to weight. 
    • Significantly larger contact patch.
    • Frontal area penalty of about 7 watts.  Many mortals don't want to pay that power price.
  • Higher inertia overall because 650b wheels are very likely to be heavier.  Read the counter-intuitive reasons below.  Higher inertia is good for going downhill but not great for any other purpose such as accelerating, climbing, and maintaining speed in a headwind.  All of these aspects of riding benefit from lower inertia wheels.
  • Limited tire choices.  Specific for gravel riding and mixed-terrain riding 700c tire options are about 5 fold more varied than 650b tire options.  This disparity recedes every season but there's still a long way to go.
  • Slower steering.  Some literature will tell you the bike will handle more quickly but that's not the case.  The handling is slower for three reasons:  The tire contact patch is larger, typically you'll ride at lower tire pressure, and the wheels are heavier.  These factors slow down the steering noticeably.
  • Braking is not as good.  Inertia is the cause.  higher inertia means more effort to stop the bike.  This is a small difference when compared to a lighter 700c setup but over a long day of riding, like many small influencers, this deficit adds up.
  • Harsher ride because the wheels are stiffer.  All things equal, a smaller diameter wheel will be stiffer and harsher in the vertical vertical.  However, this harshness typically more than offset by the larger, and usually softer feeling, tire choice.
  • Tire clearance is a bit worse because the tire is wider.  A 47 mm tire fits in a Honey Allroads but it shaves some of the clearance away.  Not great if you break a spoke.

Additional Comments

  • Frame material plays a tremendous role in bike feel.  We find that the typical higherrchy looks something like this:  Tires are number one, frame & fork are number two, and wheels are number three.  If you're riding a carbon bike you'll appreciate the benefits of 650b wheels more than if you have a high quality steel or titanium frame.  These two materials, and particularly titanium, excel at absorbing shock so these materials are not asking as much of the tires and wheels to be shock absorbers.  Carbon has to be stiff in order to keep the resin from failing so softer tires can make a big difference in a riders enjoyment of a carbon bike.  The benefits of 650b at mitigated in some ways when matched to a good titanium or steel frame.
  • 650b big tires will tend to have a smaller diameter and therefore your center of gravity will be lower.  This can be good or bad depending on how you like your 700c setup.  Lower is more stable and that's good.  Too low means you'll be digging your pedals into rocks and that's not good.  Determine the expected change in bottom bracket height before finalizing your tire choice so you can decide if the change is good or too much.
  • 650b tire volume pressure tends to be run lower so the rider's center of gravity will sit a bit lower than the pure math would indicate.
  • 650b wheels are smaller when using similar tire sizes, 38mm to 38mm for example, so you may want to run slightly higher gearing if your wheels are not the exact same diameter as 700c.

Heavier:  650b x 47 mm wheels are almost always heavier than 700c x 40 mm wheels

We're not very interested in building the lightest bikes because there are a lot of issues when you start chasing light weight.  However, if there's anywhere on the bike to focus on reducing weight, its wheels and tires.  Pulling grams out of the wheels can make a noticeable difference by reducing their rolling inertia.

Most articles you'll read promise that 650 wheels are lighter and that's intuitively logical because the wheel is smaller.  However, that's not true in almost all cases.  In fact, the typical weight difference between a performance 650b and 700c wheel set is about 200 to 300 grams or about 7 to 10 ounces.  Why?

  • 650b rims are almost always wider because they tend to be paired with wider tires.  Also, many 650b rims are actually 27.5" mountain bike rims so the rim is much wider than needed for 650b tires.  A wider rim is significantly heavier than a narrower rim.  There are some companies making 700 and 650 rims from the same extrusion so the 700 version is heavier.  However, it's not logical to use a 700c rim that's as wide as a 650b rim because the tires aren't the same width.  So, if your rims are optimized for the tire width, a 700c rim will most likely be lighter than its 650b brethren.
  • 650b tires are heavier than 700c tires.  There are a few reasons for this but one of the primaries is that there is simply more material needed to make a large volume 650b tire.  More material means more weight.  A secondary and still relevant weight issue is that there are simply a lot more 700c tire options so you can optimize for tire weight.  We find that the average weight difference between 700 and 650 tires is about 50 to 150 grams, sometimes more.  That's a wide range but there are a lot of tire options out there.  Double that for two tires and you see the grams piling up.
  • Tubeless.  If you choose to ride tubeless the weight difference challenges are about the same even though most literature says the opposite.  In addition, you'll use more sealant because of the larger air volume.  This weight difference alone will likely be about 70 grams or about 3 ounces depending on what sealant system you use.

One more thought:  We find that a lot of riders and reviewers that prefer 650b wheels with big tires are strong riders.  We don't think this is a coincidence.  Most or the downsides of the 650b wheels relate to speed.  If you're the strongest rider in your group, you don't have a speed problem.  If you're that rider, 650b are great.  If you need every watt going to forward momentum, 650b may not be the ideal solution.

The Bottom Line:  Don't believe everything you read, hear, or watch on video.  Have two sets of wheels so you don't have to choose the middle ground.  Have a 700c x ~40mm set for fast performance and all out speed, and a 650b x ~47mm wheelset for fun, technical, all day adventure rides.  Easy for us to say.

We hope this information is helpful.  We know some of our research contradicts popular myths but we have no investment in propagating myths.  Whatever system you choose, make sure it's right for the kind of riding you want to do.  Enjoy the trails!