How to Get Fat this Spring

Until the early 1980’s, road bikes were made to ride on roads.  Not perfectly groomed asphalt, with no cracks, broken pavement, or glass.  Real roads, asphalt and chip seal to cobbles to dirt to gravel.  And they were designed to be ridden in all seasons, not just dry summer days.  Road bikes, even pro level road bikes, bikes that Eddy Merckx would win tours with, bikes the Jaques Anquetil would dominate time trails on, had the ability to be used for all sorts of roads, in all sorts of weather. These weren’t touring bikes, or cross bikes, but died in the the wool road racing bikes, with the highest end Campagnolo Record bits, and drilled out chainrings, and super light modified saddles. They were able to achieve this amazing versatility because of one thing: tire clearance.

PX-10 _ Weinmann rear brake

A 1970s race bike with clearance for fat tires and a fender. Note the centerpull brakes, which were long derided as paupers brakes, are coming back into vogue on the highest end time trial bikes.

If you have clearance for big tires, your bike suddenly goes from being a one trick pony, to a versatile, year round machine built for exploring the world we live in.  Some of the very best roads in our area are not smooth or groomed tarmac but chopped up pavement or just straight dirt and gravel.

The concept of riding a normal road bike on dirt is basically a non starter for most road cyclists.  They have tiny tires pumped to over 100 psi.  The thinking is; tiny tires have no grip on that terrain, and the ride quality will be atrocious.  The prevailing philosophy of tire size is that narrower is faster.  Narrower tires have to be faster, because they have less of a foot print.  A smaller contact patch means lower rolling resistance, right?  Wrong.  The size of a contact patch at a given pressure does not change depending on the tire size.  If you have a 100 pound weight on a 23mm wide tire at 100 psi, there will be a 1 square inch contact patch.  If you have a 100 pound weight on a 32 mm wide tire, at 100 psi, there will be a…. wait for it….. 1 square inch contact patch.

Image stolen from Velonews

Here’s the kicker though: narrower tires have longer contact patches than wide tires, which means that even though the contact with the ground remains the same size, the shape changes.  The shorter, wider contact patch of the wider tire means that when you are pedaling there is less sidewall of the tire flexing.  Sidewall flex is caused by friction, and friction is bad.  If you doubt that sidewall flex is a major cause of friction, touch the side of your car tire after a road trip.  It’s hot, from the flexy friction action.  All lost energy.  So not only does a wider tire have the same contact with the ground, but it also rolls more efficiently.  The added size adds safety: resistance to pinch flats, protection of the valuable wheelset.  The larger air volume allows you to drop pressure on crappy road surfaces or when its raining or snowing out.  Major classics races are raced on fat tires at pressures that would make the average american road rider flinch.   80 psi, 60 psi…  Way lower than the 120 psi that many people ride.  And these are the fastest riders in the world, riding over real roads of varying surface quality.  Tom Boonen won Paris Roubaix on 29mm wide tires at 60 psi.

Boonen went chubby this spring and won.

Is there a limit to how fat you can go before it starts to negatively affect the speed at which you can ride?  Yes, but no.  Yes, if you are riding at the highest level of the field and maintain an average speed in excess of 20 mph on your rides.  You’d probably want to top out at a 25mm tire if that is the case.  The slight added weight will be out weighed by the contact patch shape change.  Any bigger, and the tire starts to have aerodynamic consequences.  BUT: only if you ride really fast, everywhere.  If you are a typical enthusiast rider, your average speed is under 20, and in that speed range, aerodynamics are basically worthless.  You could ride a 28mm tire, and the only thing holding you back would be your psychological resistance to such a fat tire.  The slight added weight gain can easily be offset by a lighter rim strip and or lighter tubes, if you care about such things.

Personally, the smallest tire I ride on the road is a 28mm tire.  I like to be able to go out and ride whatever I come across, be it a grassy path into the woods or a big hill like Coxey Brown road.  I’d run bigger, but my frame won’t allow it. 28’s reach their limits in really really rough terrain, like a newly graded gravel road, but otherwise can take anything Washington, Frederick or Carroll counties can throw at them.



Shop rides:
Sunday evenings, at 5.30, meet at the shop for a group road ride.  We’ll head out and explore some less traveled roads in the Frederick area.  You’ll need: a spare tube and something to pump it with, a tail light and possibly a headlight, and a road bike you aren’t afraid to get dirty on.  Almost all of these rides have at least one dirt road on them.  It goes till around dark, sometimes a little after… Casual pace but hard roads…

Tuesday mornings: Meet at the 7th street Starbucks at 8am for a mixed surface road ride.  We’ll go from between 40 and 70 miles, depending on various variables.  Not a fast ride, a chugging ride.  Climbing, dirt, some place to eat something, even if it’s a gas station…

Wednesday evening shop ride with Brian.  This is THE CLIMBING RIDE, pretty quick pace.  The route is up Hamburg road, a real corker of a climb, and then decisions are made from the top of the climb as to the route. Back to the shop at dusk.  A tail light isn’t a bad idea.

Thursday evening mountain ride at the Frederick Watershed with Brian and Team Flying Dog.  Meet at the maintenance shed at the foot of mountain dale road, right where it goes from paved to gravel.  Call at the shop if its been raining: we don’t like to ride on wet trails because it leads to damage.  5.30pm.   Lots of climbing and tech rock sections.  Experienced mountain riders…


Do we stock fat tires? Yes.

Thanks for reading this week,

-The Bike Doctor Crew of Sublime Subliminal Subterranean Sorcery

One thought on “How to Get Fat this Spring

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