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Why Are Road Bikes Faster Than Gravel Bikes? A Comical Look at Speed and Conspiracy Theories

I read a post yesterday that had me laughing.  Now that wider tires have been proven to roll as fast, or close enough for government work, as their skinnier bretheren, say 25 to 28 mm, contrasted against a 23 mm tire, there’s all sorts of craziness coming out trying to make the leap that, if 25’s or 28’s are good, then 54’s are even better!  Uh, no.

The concept with the 25’s, 26’s and 28’s is sound; in real world situations, we’re not riding on perfectly smooth asphalt (if we were, the 23 mm tires would win, hands down) so the wider tires, while slightly less aerodynamic, smooth out the imperfections which improve the performance of the motor (us) to a greater degree than the loss of aerodynamics in going from a 23 mm tire to a 25, 26, or 28 mm tire.  Add in gains from today’s wider 23 mm rims, which make the leading edge of those wider tires more aerodynamic than the older 19.5 mm rims, and you’ve really got something – a smoother ride, with no aerodynamic disadvantage.  Now we’re talking!

What happens when we start looking at wider tires, though?

Enter Jan Heine, the Don Quixote of bike tire width and speed.  Here’s my favorite quote from his “Are gravel bikes slower than road bikes” post (click here):

Is it true? Are gravel bikes slower than racing bikes? The answer is: ‘It depends.’

Now, he’s right, even though he’s making the leap from tire width to gravel bikes which messes everything up, anyway, but let’s stick with it. It does depend, it depends a great deal on what you’re riding.  First, gravel tires are meant to grip the road better, especially dirt, so they will naturally be slower than road slicks on asphalt.  Also, most dirt road riders are going to set their dirt steed up so they ride a little more upright for pothole avoidance.  That’s slower.  Then, as in my case, my Specialized Diverge AL Sport, at 24 pounds, is more than eight pounds heavier than my Specialized Venge aero race bike.  So let’s see, slower, slower, slower…. that’s slower, not “it depends”.

20190914_164921  This….

Is faster than this… is faster very much faster than…


But why?  Why all of this mess, anyway?  It’s all about the Benjamin’s and an industry conspiracy to get you to buy more bikes…

I suspect the reason is simple: The industry wants to sell more bikes. The thinking seems to go like this: Now that many riders have bought a gravel bike, let’s convince them that they need a new road bike.  Of course, most already have a road bike, but that one has outdated rim brakes. It’ll be easy to convince them that they need a disc road bike with tubeless tires.

Um, no.  I disagree entirely with that conclusion, especially if you know what you’re doing.  Disc brakes are nice – they really are – but not nice enough to necessitate at new road bike.  The brakes are only there to slow you down, anyway.  Especially with advances in carbon fiber brake pads.  Second, gravel riding shot up in popularity for one reason; less traffic… well, two, better scenery.  We used to have to ride a 28 pound mountain bike (I have two) to ride on dirt roads.  Now we can ride 17 pound road bikes with tires wide enough for some decent stability, so people added the gravel bike (not the other way around).  Some of us just opted for the heavier, less expensive version, as I did.

Look folks, if you absolutely have to have a bike that does everything, you can get a nice 17-18 pound carbon fiber gravel bike, with an extra set of wheels (one 50 mm carbon set for road tires, one [carbon or alloy] for gravel).  You’ll lose a pound or two and a little in aerodynamics to someone who’s got a full aero race bike or a climbing bike, but that’s about all – and that can be made up for with some extra “want to”.

At the same time, if you think your entry-level gravel bike with some cheap dirt tires will keep up with you on a 15-pound racing missile on asphalt, you’re frickin’ nuts.  Those entry-level gravel bikes are a lot of extra work!

To wrap this up, gravel bikes are slower than aero road bikes on asphalt.  They are, and no amount of fuzzy science is going to change this.  On the other hand, hold your breath now, gravel bikes are faster than aero road bikes on dirt roads.  They are.  On anything but perfect dirt roads, I’m going to be faster on my gravel bike than I would on my Venge.  First, because the increased stability of the dirt tires make riding on gravel and rocks a lot more enjoyable, second, because 105 pounds of air in a 25 mm tire sucks on bumps next to 50 psi in a 32 mm tire on the same bumpy dirt roads.

If you don’t want to fall into the N+1 bicycle trap, where you always need another bicycle, get yourself a really nice gravel bike with a 50/34 double crankset (maybe a 48/31, but don’t go any smaller), some hydraulic disc brakes, and an extra set of 50 mm carbon fiber disc wheels for asphalt tires.  You’ll spend around $6,000 when it’s all done, but you’ll have everything you need in one bike.  You can’t go the other way, though; you can’t get the aero race bike and hope to ride that on dirt.  Even a disc aero race bike… there won’t be enough clearance for the dirt tires on a road bike.

Also, and this will be another source of contention, if you want a “one bike does it all” solution, I’d go with a double crankset, not one of those 1x drivetrains.  Whilst riding on dirt, finding the right gear isn’t such a big deal.  Riding on pavement, you’ll want to match gears to your cadence and speed a little more.  The 2x drivetrain will be better for group rides on asphalt.

Conspiracy theory debunked.  Drops mic, goes for a ride.