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Archive | Testing and Tech

Ted King’s Tips for Choosing Gravel Tires

Editor’s Note: ‘Gravel’ means different things in different regions, from the smooth dirt roads of Vermont to the Flint Hills of Kansas. Few riders have as much experience riding and racing all over the world as two-times Dirty Kanza winner Ted King. Here is how the ‘King of Gravel’ chooses his tires.

It’s only in the relatively recent rearview mirror that we see cyclists steering their frankenbikes off the beaten path. “Gravel” as a name wasn’t a genre of riding yet; this was merely riding a bike on pavement and then riding a bike off pavement. Most riders were on two-wheeled amalgamated collections of misfit parts, trying to create what did not yet exist: Riders took the best parts of road and mountain bikes and combined them in a single bike. That was the start of “gravel” as we know it, and it’s quickly becoming something of a rarity in this day and age.

With the burgeoning support of the entire cycling industry behind gravel, and with a hyper-focus on components designed specifically for every style of gravel riding, my inbox is continually filled with questions about my choice for bike parts. Specifically, questions revolving around where the rubber meets the (off) road are the most common. So in an attempt to take a proactive approach, I’m excited to offer Ted’s Tips for Choosing Tires. Continuer →

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Enve and Zipp hookless rims and Rene Herse tires

Rene Herse tires are safe to use on hookless rims from Enve and Zipp – even when mounted tubeless. Over the last year, we’ve worked with the engineers from both companies to ensure the full compatibility of our tires with their rims.

Tubeless tires are an emerging technology. They’ve been around for decades on cars and motorcycles, and they’ve taken over mountain biking in a storm, too. These are all relatively stiff tires that run at relatively low pressures.

Adapting the technology to road, all-road and gravel bikes has posed special challenges. The supple high-performance tires we love have less casing stiffness, and they run at somewhat higher pressures. (Few cars, motorcycles and mountain bikes exceed 2.5 bar/35 psi.) Both factors combine to create much greater forces at the tire/rim interface than on other vehicles. Continuer →

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Myth 19: 700C Wheels Are Faster

When we started this series to celebrate Bicycle Quarterly’s 15th anniversary, we thought we’d eventually run out of myths. But it seems that new ones are created as fast as we can debunk old ones. The latest is “700C wheels roll faster than 650B.”

This is stated with the same certitude as the old “narrow tires are faster” – and it’s just as wrong. Simply put, there is no evidence that 700C wheels roll faster than 650B (or 26″), and much data to show that they all roll at essentially the same speed. Continuer →

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Are gravel bikes slower than road bikes?

The euphoria about gravel bikes is hitting a snag: Many riders feel that their gravel bikes are slower than their road bikes. For example, James Huang, the technical expert from CyclingTips.com, posted:

“I’ve been spending too much time on gravel and mountain bikes lately. Good to be reminded what real speed actually feels like.” Continuer →

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Myth 16: Higher Tire Pressure is Faster


This used to be one of the first things you learned as a cyclist: If you want to go fast, make sure your tires are pumped up to the maximum pressure. The harder your tires are inflated, the faster they roll.

We now know that this isn’t true. The realization that tire pressure does not affect performance is the key to the revolution that has swept through the cycling world in recent years. Without this new-found knowledge, all-road bikes and their supple, wide tires would make no sense at all. Here is how it works.

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Myth 15: Marginal Gains


‘Marginal gains’ are the latest buzzword in cycling. The idea is that many tiny improvements can add up to make a meaningful difference. Make 10 changes that each save 3 Watts, and you’ll have gained 30 Watts…

Think of Greg LeMond winning the 1989 Tour de France by eight seconds… If the second-placed rider, Laurent Fignon, had used ceramic bearings, he might have won that year.

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A knobby faster than most road tires?


At Compass, we see little point in replicating what you already can buy from others. When we made our first knobby tires, we wanted true dual-purpose tires. Could the new knobbies match the on-pavement of good road tires, yet grip as well in mud as true cyclocross tires. Impossible? You’ll never find out unless you try…

After a few seasons of cyclocross, there is no doubt that the Compass Steilacoom (700C x 38 mm) and Pumpkin Ridge (650B x 42 mm) offer plenty of grip and shed mud well – as you’d expect from their widely spaced knobs.
How about their on-pavement performance? I’ll let others speak on that. Matt Surch, the well-known Canadian gravel racer, wrote: “I don’t understand how the tread rolls so fast and quiet… these are wild!”

When BQ tester Mark tried them, he wrote: “Once the wind drowned out the tire roar at high speed, I was thinking about how unremarkable the Steilacoom tires had rolled on the paved descent. I had pretty much forgotten that I was riding on knobbies.” Yet he was glad to have them when a road closure detoured us via a muddy trail (above).

And now Mike Stead tested a set of Steilacooms for www.road.cc. Among other adventures, he set two Strava records on these tires. One was for a gravel descent. His comment: “I wasn’t even pushing that hard. […] The Steilacooms make you a better, faster descender than you deserve to be.”
The second KOM surprised not just him, but us as well: He set a new record for a flat-out 60-second sprint – on pavement. He wrote: “Averaging 45 kph, the Steilacooms made an awesome high-pitched noise as I fanged along the straight. Just to prove it wasn’t a fluke, I went back the next week and recorded exactly the same time to the second.”
Mike’s time on the Steilacooms was two seconds faster than the previous KOM record, which he had set on our Barlow Pass tires. Does that mean our knobbies are faster than our road tires? Not necessarily – there are too many variables – but it shows that they certainly aren’t much slower. And that is remarkable, considering that our road tires are among the fastest in the world.

In a future post, I’ll explain how we created a knobby that doesn’t ride like a knobby… until you hit mud or snow, when it behaves exactly like a knobby. But don’t take our word for it – read Mike Stead’s review.

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Myth 9: Fork Blades Don’t Flex


When we first started talking about shock absorption and fork blades, it was commonly believed that fork blades didn’t flex significantly. Experts told us: “All the flex in a fork is in the steerer tube, where the lever arm is longest.” And yet, when we rode bikes with flexible fork blades, they clearly took the edge of bumps. Was this another myth in need of debunking? Continuer →

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Myth 8: Modern Components are Lighter


To celebrate Bicycle Quarterly‘s 15th anniversary, we are looking at myths in cycling – things we all used to believe, but which we’ve since found out not to be true. During these 15 years we’ve learned a lot, and perhaps the most intriguing discovery is that modern parts aren’t as light as some classics. In some cases, there are functional reasons why modern parts are heavier. At other times, modern parts really could be lighter. Continuer →

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Myth 7: Tubeless Tires Roll Faster


When tubeless tires first became available, they were designed for mountain bikes and it was their resistance to pinch flats (above) that made them popular. Off-road, there are few nails or broken bottles that can cause punctures (and even those usually will be pushed into the soft ground rather than puncture the tire), but rims can bottom out on sharp rocks and other obstacles. So much so, in fact, that top mountain bike racers used to race on tubular tires – because tubular rims make pinch flats less likely. Eliminating tubes did the same, and while you still could ‘burp’ the tire, in general, tubeless allowed running lower pressures with fewer problems. Continuer →

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Myth 3: Fenders Slow You Down


To celebrate 15 years of Bicycle Quarterly, we are looking at ‘12 Myths in Cycling’ – things that aren’t quite what we (and most other cyclists) used to believe. Part 3 of the series is about fenders.

Many cyclists here in Seattle install fenders when the rainy season starts, and remove them for the dry summer months. British time trialists even had quick-release fenders that they used on the ride to the start; then they took off the fenders for the actual competition. Our research indicates that this isn’t necessary – fenders don’t slow you down. Here is why: Continuer →

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Myth 2: Titanium is Lighter than Steel


In part 2 of our series ’12 Myths in Cycling,’ we’ll look at why titanium isn’t always lighter than steel. I can hear you saying, “What? Everybody knows that titanium has half the density of steel.”

That much is true: The same part made from titanium will weigh half as much as the equivalent from steel. But titanium has only half the stiffness, so the part will be half as stiff. To make the parts of the same stiffness, you need to use twice as much material with titanium, and the weight will be equal. The same applies to aluminum, which is one-third as heavy and one-third as stiff. (These numbers are for the high-strength alloys; raw aluminum, titanium and iron are not strong enough to be used for cycling applications.) Continuer →

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Myths in Cycling (1): Wider Tires Are Slower


When we started to publish Bicycle Quarterly 15 years ago, it seemed that most of the technical aspects of bicycles were well-established. And yet, as we tested many different bikes, we started to question many of the things we had accepted as ‘facts.’ To celebrate our 15th anniversary, we’ll look at some of these myths. We’ll explain why we (and everybody else) used to believe them, and how things really work. Let’s start this series with the biggest one:

Myth 1: Wider Tires Are Slower Continuer →

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Minimum Tire Pressure

Hahn_Paso

Over the last few years, the idea that higher pressures don’t make your bike faster finally has become accepted. Many cyclists now run lower pressures to improve comfort and traction, without giving up anything in speed.

On gravel, lower pressures actually make you faster, since the bike bounces less. On soft gravel, like we encountered during our ride across the Paso de Cortés in Mexico (above), lower pressures (and wider tires) allow you to float on top of the surface, rather than sink in. Again, that makes you faster and more secure.

So lower pressure is better in many cases, but how low can you go?

contact_patch

Here is a detail from the photo of Hahn on the Paso de Cortés. You can see how long that contact patch is – there is a lot of tire on the ground, which spreads the rider’s weight over a larger surface area.

Yet the pressure is not too low. The tire still holds its shape: Seen from the side, the tire sidewalls form a nice circle. That is the reason why it still rolls as fast as it did at higher pressures: The flex in the tire is limited to a relatively small area.

Only when viewed from above, can you see the contact patch bulge outward – but even that should not be excessive.

paso_cortes_descent

What happens if your tire pressure is too low?

  1. The tire can collapse when cornering. During our Mexican adventure, we pumped up our tires when we reached pavement, so we could tackle the fast and twisty descent with confidence (above). Even on gravel, a tire can collapse under the forces of cornering, if it’s not inflated high enough.
  2. You can pinch-flat, if the tire bottoms out, and the tube gets crushed between rim and road surface.

BJPASS_result-750x481

3. The tire can get damaged. When the tire gets kneaded too much with each revolution, it’s not only slower. (Yes, lower pressures do get slower at some point.) It also puts very high stresses on individual threads of the casing, which then can break. The tire needs a certain pressure to hold its shape and distribute the stresses uniformly over all the threads in the casing.

In the photo above, you can see a cross-hatched pattern where the casing threads have broken. This tire was tested by a magazine, and they rode these 35 mm tires at extremly low presssures of just 35 psi (2.4 bar).

The tire probably is still fine to ride, but if you try to run it tubeless, air (and sealant) will seep out of the tiny holes caused by the broken threads. (The sealant colored the sidewall where it leaked.) If you see a single zigzagging line in the tire sidewall where one thread has broken, increase your air pressure slightly to prevent further damage.

What is the minimum pressure that is OK to ride?
This depends on many factors, including:

  • Rider weight. Obviously, heavier riders need to run higher pressures to prevent the tires from collapsing.
  • Surface grip: The more grip you have, the higher are the forces generated during cornering. To withstand those forces, your tire needs to be inflated harder.
  • Tire construction: A stiff tire is held up by its sidewalls as much as by the air pressure inside. A supple tire’s sidewalls do little to support the bike’s weight, so you need higher pressure. Thanks to the supple sidewalls, this tire still is more comfortable and faster, even at the higher pressure.
  • Riding style: A rider who has a round spin can run lower pressures. If your bike starts to bob up and down with each pedal stroke, your tire pressure is too low. Fast riders need to run slightly higher pressures, since they hit obstacles with more force. And riders who corner on the limit need higher pressures to prevent the tire sidewalls from collapsing.

I polled the riders on the Bicycle Quarterly team about the tire pressures they ride. I was surprised how consistent they are. Some riders are a bit heavier and use a bit more air, so we equalized the values for weight of 82 kg / 180 lb.
tire_pressure_chart_psi

Or if you prefer metric values:

tire_pressure_chart_bar
Of course, we’ll adjust these values if needed, for example, on rough gravel, we increase the pressure to prevent pinch flats… And remember that different pressure gauges can vary by up to 15%, so your 45 psi may be quite different from our 45 psi! Still, this provides a starting point for thinking about the right tire pressure.
For the majority of riders today, the advice “When in doubt, let out some air!” still holds true, but as we lower our tire pressures, we need to be aware that too little air also can cause problems.
Further reading:

Photo credit: Cyclocross magazine (damaged casing)

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The Missing Piece: Suspension Losses

old_road_to_mexico

How does it work that wide tires are as fast as narrow ones? It is really simple:

Comfort = Speed

When your bike vibrates, energy is dissipated as friction. That energy must come from somewhere – it no longer is available to propel the bike forward, so your bike slows down. That is why your bike rolls faster on smooth pavement than on rough chipseal.

At Bicycle Quarterly, we started testing tires on real roads, with a real rider, in 2006. We found that higher tire pressures don’t make your bike faster. Back then, that was pretty revolutionary. Previous tests on smooth drums had shown that the harder you pumped up your tires, the faster you went. But smooth steel drums aren’t a good model for what happens on real roads, and the results were misleading.

Over the last couple of years, our findings have become generally accepted. Most tech writers now talk about vibrations that slow down your bike. The missing piece is: How do vibrations slow you down? The most common explanation is that your bike goes up and down as it vibrates. All that climbing adds up and costs a lot of energy.

It’s true that vibrations slow you down, but it’s a bit more complicated. Energy cannot disappear. The only way to ‘lose’ energy is to convert it to heat through friction. When you climb a mountain pass, you put in energy as you gain elevation. As you descend on the other side, you get some of it back – you can coast downhill without pedaling – but most of it is converted to heat by your wind resistance. During the descent, your bike accelerates until you reach ‘terminal velocity,’ where the energy input from the elevation loss equals the energy consumed by wind resistance.

That explains where the energy goes when you cross a mountain pass. It cannot explain what happens when your bike vibrates on flat roads.

RumbleStrip

We tested various equipment on rumble strips to get a maximum value for the energy that is lost to vibrations. We found that riding on this “very rough” road can take up to 290 Watt more power than riding on smooth pavement at the same speed. So it’s true, vibrations can absorb a huge amount of energy. It was almost impossible to keep the bike moving at our testing speed on the “very rough” road. (Of course, in real life, you don’t ride on rumble strips, but the point was to see how much energy could be lost just by changing the surface roughness, and keeping everything else the same.)

Since we were going at the same speed as on the smooth pavement, the our wind resistance was the same, and yet we had to push the pedals with 290 Watts more. So where did all the energy go?

basketball

A little bit went into heating the tire as it flexes, but pneumatic tires don’t absorb much energy even when they bounce. Think of a basketball. When you drop it, it bounces back almost as high as before. Very little energy is lost, even though it deflects as it hits the ground. As the basketball hits the ground, it compresses and becomes an air spring. Then it stops, before it starts accelerating upward again. The ‘spring’ in the ball returns most of the energy, and the ball bounces almost as high as it did with the last bounce.

tire_push_off_2

Tires work the same way. When a tire hits a bump (left), it deforms (arrow). Energy is stored – the tire becomes a compressed spring. On the other side of the bump (right), the energy is released, pushing the tire off the bump. The net loss of energy is small.

If the energy isn’t lost in the tire, then where does it go?

rough_road

The answer is simple: As the rider’s body vibrates, the tissues (muscles, tendons, skin, etc.) rub against each other. This can convert an enormous amount of energy into heat. How much? In a study of vibrating tank seats, the U.S. Army found that up to 2000 Watt were absorbed by a human body before the vibrations became too painful to endure. The discomfort was directly proportional to the energy loss.

2000 Watt! That is more than the power output of a pro racer. Clearly, a lot of energy can be lost due to these vibrations. The technical term for this is “suspension loss”. It also occurs in shock absorbers of cars – rally cars’ shock absorbers absorb so much energy that they get hot – so hot that they need dedicated cooling.

rumble_smooth

We also tested different types of equipment on the new, super-smooth pavement next to the rumble strips. We were surprised that even on very smooth pavement, reducing vibrations through supple tires – and even, to a lesser degree, a suspension fork – resulted in significant performance gains.

What this means for cyclists is simple: If your bike’s vibrations are uncomfortable, it’s because energy is converted into heat, inside your body. This energy is lost from the forward motion of the bike. As far as vibrations are concerned, being uncomfortable slows you down. Or seen the other way around, the more comfortable your bike is, the less power goes to suspension losses, and the more power is available to drive it forward:

Comfort = Speed

It really is that simple. And it’s revolutionized how we think about bikes: Wide, supple tires are faster because they vibrate less. Fork blades that absorb road shocks – even suspension forks – are faster, not just on rough roads, but even on relatively smooth roads, because they reduce vibrations. On real roads and at the speeds most of us ride (<25 mph), the best gravel and all-road bikes actually are faster than their racing bike cousins.

diverge_skagit

This means that the biggest improvement in your bike’s performance comes from a set of wide, supple tires. “Supple” means that the casing is thin and easy to flex. This has two benefits:

  1. Supple tires are easy to flex, so they transmit fewer vibrations (lower suspension losses). That is Reason 1 why they are faster.
  2. Supple tires are easy to flex, so it takes less energy as they deform them as they rotate (lower hysteretic losses in the tire casing itself). Reason 2 why they are faster.

Wide tires also transmit fewer vibrations, which makes them faster than narrower ones.
Our testing shows that supple casings are more important than width. A supple 26 mm tire is much faster (and more comfortable) than a stiff 38 mm “touring” tire. Of course, ideally, you’ll get it all – a wide and supple tire.

This research led us to develop our Rene Herse tires. While quite a few makers offered supple racing tires in widths up to 25 mm, there weren’t (and still aren’t) many great high-performance tires in wider widths.

For our Extralight series, we use a casing that usually is reserved for high-end, hand-made racing tubulars. On top goes a layer of extra-grippy, yet long-wearing, rubber with our trademark tread pattern that interlocks with the road surface for extra grip. The result are our Rene Herse tires – available in widths from 26 mm to 55 mm.

tekne_gravel

Before releasing these tires in 2014, we tested them extensively on some of the roughest gravel roads to ensure they were durable enough for real-world riding. Since then, they’ve proven themselves in gravel races, but also on paved courses like Paris-Brest-Paris. They even took second place in the Washington State Road Racing Championships. The riders who use them are our best advertisers, recommending them to everybody who is willing to listen. We rarely advertise – instead, we focus on new research that will improve our products even further.

Further reading:

Photo credit (gravel racing): Chyla’s Race Photos.

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Tire Pressure Take-Home

un-meeting_uphill

What is the ‘correct’ tire pressure for your bike? The simple answer is: Whatever feels right to you. Confused? Here is how it works:
In the past, many riders inflated their tires to the maximum pressure rating. Now most cyclists now recognize that the optimum pressure often is much lower.

But what is the right tire pressure? At Bicycle Quarterly, we’ve done a lot of research into the rolling resistance of tires at various pressures, and on various road surfaces.

Frank Berto’s tire pressure chart (above), first published in Bicycle Quarterly many years ago, has received much attention. (Note that the weights are per wheel, not for the entire bike.)

Berto made the chart in the 1990s, when tires were much narrower. Hardly anybody today still rides on 20 mm tires, and even 23 mm are on their way out! At the other end, 37 mm no longer is huge, as many of us ride 42 mm tires on pavement, and even wider ones on gravel. How does it all translate into the modern world?
tire_drop
Much of it depends on the tires you run. Berto measured the tire drop (above; how much the tire deflects for a given load and pressure) for dozens of tires. He then averaged the values, and drew his chart for a tire drop of 15%.

The 15% as desirable tire drop was based on the recommendations of several tire manufacturers, but not on actual testing. So the chart shows how much you need to inflate an average 1990s tire to achieve a tire drop of 15% – nothing less and nothing more.

A few years ago, Berto sent me all his original data. Looking over his measurements, it’s clear that supple tires – back then pretty much only the Michelin Hi-Lite – deflect much more than stiff ones, at the same pressure. This means that specific tires can vary quite a bit from the averages shown in the chart.

golden_gardens

To get the same tire drop with supple tires, you would need to run them at higher pressures. But is 15% tire drop really what you want with supple tires?

The answer is “No.” The 15% tire drop is an arbitrary value. However, even if it’s only by coincidence, the values in Berto’s chart actually work quite well for Rene Herse tires. They’ll result in more than 15% tire drop, but that is OK: Comfort and speed are optimized. And that is what really matters.

track_tire_test

The biggest surprise of all our testing (above) was this: For supple tires, pressure makes little difference in performance. We tested three Vittoria tires (Rubino, CX clincher, CX tubular; all 25 mm wide) and found that the supple CX models roll as fast at 70 psi as they do at 130 psi. (For the rest of the world, that is 5 bar and 9 bar.)

The reason is simple: Higher pressure decreases the energy required to flex the tire. Less energy is lost due to internal deformation (hysteresis). But higher pressure increases the losses due to the vibrations of bike and rider. More energy goes to suspension losses. The two effects cancel each other. Whether you pump up your supple tires super-hard or ride them squishy-soft, they have the same resistance.

On the other hand, truly stiff tires feel sluggish at 15% tire drop. The stiff tire is much harder to flex, so it’s useful to minimize that flex by increasing the pressure. For stiff tires, the suspension losses do not vary as much with pressure – they’re always high – since the stiff casing transmits a lot of vibration at any pressure.

Recently, Velo-News confirmed our results: The performance of a hand-made tire with cotton casing did not change at different tire pressures. And a stiffer tire rolled slower at lower pressures than at higher ones. (It’s nice to see that our results, after having been highly controversial for years, now are becoming generally accepted.)

It can be hard to believe this, because higher pressure feels faster. Here is why: When you go faster, your bike hits more road irregularities per second: The road buzz increases in frequency. Most cyclists know: higher speed = higher frequency.

Higher tire pressure cheats you into thinking that you are going faster, because it also increases the frequency of the vibrations: higher pressure = higher frequency.

It’s natural to assume that this means: higher pressure = higher frequency = higher speed, but that is incorrect. Instead, you are looking at two different mechanisms that both increase the frequency of the road buzz.

Even after years of riding supple, wide tires, this ‘placebo’ effect sometimes plays tricks on me. A supple tire absorbs vibrations better, so it can feel slower – until you look at your speedometer.

hahn_un-meeting

What does it all mean? Here is the take-home summary:

  • Stiff casings always will be slow. They are even slower at lower pressures.
  • Supple casings are fast, and pressure doesn’t matter.
  • On smooth roads, tire pressure is a matter of personal preference (at least with supple tires). High and low pressures offer the same performance.
  • On rough roads, lower pressures are faster. So if you want to optimize your speed on all roads, including rough ones, go with a relatively low, but safe, pressure.
  • Your tire pressure needs to be high enough to avoid pinch flats. If you get pinch flats, increase your tire pressure, or better, choose wider tires. Pinch flats are rare with wide tires.
  • On pavement, your pressure needs to be high enough that the tire does not collapse during hard cornering.
  • The minimum safe pressure is higher for more supple casings. Stiff casings hold up the bike more, and thus require less air pressure.
  • On gravel, you can run lower pressures than on pavement. On loose surfaces, the tires don’t collapse as easily, because the cornering forces are much lower.
  • Don’t run your tires so low that the casing cords start to break. That happens only at very low pressures, but if you start seeing multiple lines across the casing where cords have broken, inflate the tires a bit more.
  • Berto’s chart still is a good starting point. Inflate your tires to the pressures it recommends, then experiment by adding or letting out some air.
  • See what feels best to you. That is the optimum tire pressure for you. Don’t worry about tire pressure any further! At least on paved roads, you won’t go faster or slower if you change your tire pressure.

Even simpler, here is a summary in two sentences:

  • Ride the tire pressure that feels good to you.
  • When in doubt, let out some air.

It’s really that simple!

Further reading:

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How to Brake on a Bicycle

lift_rear

Whether you ride fast or slow, being able to stop quickly is an important skill. Your ability to stop also depends on how well your brakes perform. In Bicycle Quarterly Vol. 10, No. 1, we tested brake performance to determine:

  • How do you brake most effectively?
  • Do brakes with different stopping power affect braking distances?
  • Do brake shoes and pads make a big difference?

brake_test

For this test, we coasted from a set point down a steep hill (always using the same riding position), and then braked at a predetermined point. Two testers performed the tests, to differentiate the “rider” factor in brake performance.

Why test on a downhill? The stopping distance on a hill is longer, and thus the differences between brakes and techniques are more pronounced. Afterward, we performed a statistical analysis to evaluate whether we were measuring real differences in braking performance and not just seeing noise in the data.

This test confirmed quite a few things about effective braking technique:

Front vs. Rear Brake

On dry pavement, the front brake alone halts the bike over the shortest distance.
Many riders think they need both brakes to stop effectively, if only because most bikes are outfitted with 2 brakes and that implies that one should use both. Here’s the way to think about it: the momentum of your body continues to move forward as your bike is slowing down, so your weight shifts forward. That’s why your rear wheel can come off the ground when braking hard. When your weight comes forward during hard braking, your rear wheel has close to zero traction. If you apply the rear brake under these conditions, the rear wheel will lock up without contributing significantly to the braking effort.

If you can apply the rear brake without locking up the rear wheel, then your weight isn’t shifting forward – a clear sign that you aren’t braking as hard as you should!

We tried braking with both brakes and with the front brake alone, and consistently found that if we focused all our attention on the front brake, we achieved much shorter stopping distances.

rear_brake

When we braked with the rear brake only, the stopping distance was more than three times as long. In fact, Hahn overshot the stop sign and went into the road at the bottom of the hill (above). This was despite Hahn modulating his rear brake carefully to keep it below the lockup point as much as possible. Skidding the wheel would have increased the stopping distance further.

While we couldn’t test this on dry pavement, the rear brake comes in handy when it is so slippery that even moderate braking will lock up your wheels – when you encounter ice, wet leaves, loose gravel, or other very slippery pavement during the first rain after a long dry spell.

Under these conditions, you cannot brake hard, and the forward weight transfer is much less pronounced. In that case, the rear brake provides added friction that will slow you more quickly. Rear brakes also are useful on tandems, where much more weight is on the rear wheel.

brake_line

How Hard Can You Brake?

Very, very hard. We found that to get the shortest stopping distance, we had to pull the front brake lever with all our might. Witness the tester’s bulging muscles on his right arm – which controlled the front brake on this bike!

This is despite using very powerful short-reach Dual-Pivot rim brakes. Some hydraulic disc brakes require less force at the lever, but with rim brakes, you really need to pull very hard on the lever.
When we came to a stop, the smell of burnt brake pads wafted through the air. After 21 full-on emergency braking maneuvers, the Aheadset of the test bike had developed play, because the stem had slipped on the fork steerer. Even the quick release of the front hub had loosened. Braking hard is a very violent affair. Not once did our front wheel lock up.

lift_rear

Going Over the Bars

Many riders are afraid of “going over the handlebars” when braking hard with the front brake. They fear that the braking force will cause the bike to rotate around the front wheel. In practice, we found that even on a steep hill, the rear wheel stayed planted for most of our braking. Wind resistance helps you here: It pushes the rider backward.

Once we had slowed to less than 6 mph, the rear wheel tended to rise. In the photo above, you can see how the front wheel has stopped, while the (unbraked) rear still is spinning. The wheel came up very slowly. This was far from dangerous: The rider simply opened the front brake slightly to make it come back down.

The shortest braking distances were obtained when we slightly decreased our braking power just before we came to a stop, so the rear wheel stayed on the ground.

Since few riders ever brake this hard, how come they still go over the bars? Here is what appears to happen to most riders who go over the bars: If riders don’t brace themselves against the handlebars, their momentum will push them forward over the handlebars as the bike slows. (Imagine being a passenger in a car without a seatbelt as the driver brakes hard.)

To avoid this, Hahn in the photo above braces himself against the handlebars and locks his elbows. He has shifted his weight as far back as possible. You can see his bicycle’s saddle underneath his belly. With this technique, he did not “go over the bars.” And if your bike’s rear wheel does lift, it happens slowly enough that you can counter it by slightly releasing the front brake lever.

Conclusion

We found that we could brake much harder than we thought. Car companies have found the same thing: Drivers tend to be too timid when braking in emergencies. Many modern cars are equipped with “brake assists” that apply the brakes with full force during emergency stops. (ABS makes sure the wheels don’t lock up.)

On bicycles, the “brake assist” and “ABS” are quite literally in our hands. Fortunately, instead of having to manage four brakes during an emergency stop, we can focus on the front brake alone.
Without electronics to assist us, we can benefit from practicing braking hard. (In fact, the same applies to your car, where practicing braking will make you a safer driver.) Practice on an empty road, preferably on a downhill where you can reach higher speeds. It takes a lot of confidence to pull on the brake levers with all your might, but it can make the difference between stopping safely and running into something in an emergency.

For the other parts of this research (differences between the two tested brakes and between brake pads), check out Bicycle Quarterly Vol. 10, No. 1.
Further reading:

Continuer

Why We Don’t Need Rain Bikes Any Longer

I moved from Texas to Seattle 20 years ago and continued to ride and train year-round. At first, I refused to use fenders. I did not want to spoil the beautiful lines of my racing bike. After one miserably wet winter, I gave in. Like most of my teammates, I got a rain bike.

For those from drier climates, a rain bike is a racing bike equipped with fenders. It usually is a less-valuable bike intended to take the wear and tear of riding in the rain, while your “good” bike remains pristine and ready for rides and events in better weather.

My rain bike was built with an old Celo Europa Columbus SL frame and parts sourced at various swap meets. The only brand-new parts were German SKS fenders (back then made by Esge), the best available in Seattle at the time.

As I wrote above, the “rain bike is intended to take the wear and tear of riding in the rain.” And wear and tear it took indeed, my poor rain bike. The drivetrain always felt gritty from the spray of the front wheel that went straight onto the chain. Lubricating the chain was a ritual after every long ride in the rain, because it squeaked terribly and turned a rusty orange as soon as it dried out. After each ride in the rain, my bike was covered in filth, and so was I. I overhauled my bottom bracket at least twice a year to remove the grit that had found its way into the bearings. I was glad to spare my “good” bike this ordeal. It always was a relief when the forecast had no rain, and I could take out my good bike, with its smooth drivetrain that seemed to run like clockwork.

Today, I don’t have a rain bike any longer. Neither do the people with whom I ride. We ride our “good” bikes all year round. It’s not that it rains less in Seattle than it did in previous decades. Nor have we resigned ourselves to riding ugly bikes with gritty drivetrains. It’s just that our good bikes now have aluminum fenders that don’t spoil the lines of the bike, and more importantly, keep the grit and spray off our bikes. We no longer oil our chains after a rainy ride, nor do we overhaul bottom brackets every year. How are our fenders today different from the SKS plastic fenders?

My rain bike never got photographed, so this bike will serve as a stand-in. The “spray zone” of the front wheel is shown, as well as the drip from the fender stays. Here are the characteristics of plastic fenders:

  • Front fender covers just 90°: Spray from the front wheel goes directly onto feet and drivetrain.
  • Fenders attach to stays with brackets that form dams on the inside of the fender: Water gets diverted and drips off the stays – onto your feet and chain.
  • Fenders are flexible: They resonate annoyingly on rough roads.
  • Fenders have to be pulled into shape for mounting: Inbuilt stresses cause them to break after 2-3 seasons.
  • Bike frame not designed for fenders means: Clearances are tight.  Fenders tend to rub on tires. Fenderlines aren’t perfect, so the bike’s appearance is compromised.

The spray zone of my current bikes’ front wheel is much reduced, and no longer reaches the pedals or the chain. Here are the characteristics of our aluminum fenders:

  • Front fender and mudflap reach within 5 cm (2 in) of the ground: No spray reaches feet or drivetrain.
  • Fenders have uninterrupted interior and rolled edges: All water stays inside. Most water exits at the bottom, where it drips off the mudflap straight back onto the road.
  • Stiff aluminum fenders bolts directly to the stays: Silent even on the roughest roads.
  • Metal fenders can be shaped to the desired profile: No inbuilt stresses, so fenders last for decades.
  • Bike frame designed for fenders: Perfect clearances everywhere and no rubbing ever. Fenders no longer detract from the appearance of the bike.

We never would have thought that better fenders would make such a difference. I discovered aluminum fenders almost by accident, attracted to the classic appearance of a set of hammered Honjo fenders that I put on my touring bike. It came as a surprise that my feet stayed so much drier.

Now we pity the riders we see riding in the rain with short plastic fenders. We have been there. Like most riders, we used to think that fenders were fenders, and spray and grit were an inevitable byproduct of riding in the rain. Now we know that it doesn’t have to be that way.

Continuer