What Makes a Bike Fast?

What Makes a Bike Fast?

It used to be easy: If you wanted a fast bike, you chose a racing bike. End of story. And what made a racing bike special were first and foremost the narrow tires. Light weight was a plus, too, and so was the lower, more aero riding position.

Then came the ‘All-Road Bike Revolution,’ and suddenly things aren’t so simple any longer. When we recently tested OPEN’s new MIN.D. racing bike (right), it was a great opportunity to look into what really makes a bike fast. So we tested the racer side-by-side and back-to-back with my Firefly all-road bike (left). Carbon vs titanium. 32 mm tires vs 54 mm. Superlight (7.7 kg) vs merely light (9.7 kg). (That’s 17.0 and 21.4 pounds.) Which is faster?

And then we changed the variables: We put narrow tires on the Firefly, added weight to the OPEN. How did this affect their performance? How do you make a bike faster?

Mark and I share the same build, same height, same weight and same power output. We are as close to identical clones as you can get. For this test, we rode (and sprinted) side by side, then switched bikes and repeated. Then switched bikes again… This method allows us to find out quickly if one bike is faster. Wind, temperature, fatigue, and other factors affect us both equally, so if one bike is always ahead, it’s faster. If one rider is always ahead, that rider has a really good day. Even then, we can see whether one bike gives a greater advantage than the other. It’s a very useful test made possible by the fluke of nature that created two riders who are so well-matched.

How much faster is a lighter bike?

Bike weight is easy to measure: Just hang your bike from a scale. The 7.7 kg bike on the left is 20% lighter than the 9.7 kg bike on the right. Simple physics tells us that the bike on the left will be faster uphill. The question is: How much faster? Can you feel the 20% difference on the road, as you ride with friends?

The answer is: No. Why? We need to look at bike and rider together. Mark and I each weigh 70 kg. With the rider on board, the OPEN tips the scales at a little over 80 kg. Now the 2 kg weight difference is just 2.5%. And since wind resistance goes up with the square of speed, a 2.5% weight difference translates into just a 1-2% difference in speed. We’ll later see that even if we make the OPEN heavier and the Firefly lighter, it won’t noticeably change their uphill speeds.

This doesn’t mean that weight doesn’t matter: A lighter bikes feel different. When you ride out of the saddle, how the bike rocks from side to side depends on how much the bike weighs and where the weight is placed. (Lower is better.) That is why it makes sense to lower the bike’s center of gravity, for example, by placing the water bottles low in the frame.

Do lighter wheels accelerate faster?

Physics tells us that lighter wheels ‘spin up’ faster. You sometimes hear that “an ounce saved on the wheels is worth a pound on the frame.” Does rotating weight really make such a big difference?

The OPEN has carbon rims and superlight tires (235 g). The 54 mm tires of the Firefly are very light for such big tires (418 g), but there’s a lot of rubber on a 54 mm tire. Add the aluminum rims, and the Firefly’s heavier wheels account for almost half of the weight difference between the two bikes.

In an uphill sprint, you’d expect the racing bike (OPEN) to leave the all-road bike (Firefly) for dead. To test this, we sprinted, racing up a steep ravine on Seattle’s Magnolia Hill. We repeated this time after time, swapping bikes, until the result was clear: In all-out sprints, the two bikes were evenly matched.

Of course, it could be that some hidden variable – maybe the ‘magic of titanium’ – gives the Firefly an advantage and compensates for its heavier weight and wider tires. How to make sure? Simple: Put narrow (and light) tires on the Firefly, too.

The Rene Herse Elk Pass tires are among the lightest bike tires in the world. They measure 30 mm wide and weigh just 165 g. That makes them 2 mm narrower and 70 g lighter than the OPEN’s tires. (The Firefly runs 26″ wheels, hence the big weight difference in the tires.)

Now the Firefly’s wheels are actually a little lighter than those of the OPEN. To equalize the weight further, we’re also putting two full water bottles on the OPEN and two empty ones on the Firefly. Now both bikes weigh the same, and the Firefly has the narrower tires and lighter wheels. Before, both bikes were evenly matched. Now, with so much weight and resistance removed, will the Firefly be faster than the OPEN?

The Firefly’s uphill speed is unchanged. It accelerates as fast on the slender 30 mm tires as it did on the big 54 mm rubber. Taking more than a pound off the wheels hasn’t made a noticeable difference.

Why? The simple fact is that cyclists don’t have a very high power-to-weight ratio. Even the cheapest economy cars have five times as much horsepower per kilogram (or pound) of weight as a pro bike racer. Cyclists don’t accelerate very quickly, and the weight of the rotating parts doesn’t make a huge difference. That is simple physics and easy to calculate. In fact, we did this for our book ‘The All-Road Bike Revolution.’ We ran a model with two top-level sprinters (think Peter Sagan and Sam Bennett), who put out 1600 Watts each. They sprint side-by-side, one on the superlight wheels (like the OPEN), the other on heavy wheels with wide tires (+530 g, think Firefly with 54 mm tires). After 200 meters, the sprinter on the light wheels will be 0.29 meters ahead on the lighter wheels. That’s just 0.1%. In cycling terms: half a wheel length.

For a pro sprinter, half a wheel can make the difference between winning or second place. For the rest of us, the difference isn’t noticeable even in all-out sprints.

So we’ve established that converting the Firefly from all-road to racing bike hasn’t made it any faster. Narrow tires and even a pound off the wheels and another off the frame (removing the full bottle) hasn’t really affect its speed. And yet we all know there are bikes that are faster than others. So what’s the secret? What makes a bike fast?

Aerodynamics

At high speeds, aerodynamics are the main resistance that a rider has to overcome. As with weight, the main component for aerodynamics is the rider. A lower and narrower position decreases the rider’s wind resistance significantly. Clothes that flap in the wind increase the wind resistance noticeably.

That’s why aerobars are so effective: They lower the rider and pull their arms inward, reducing the frontal area in two ways. Position is always a compromise, though: If you are too low and narrow to be comfortable, you put out less power and go slower than you would with a slightly less aero, but more comfortable, position.

For our Firefly vs. OPEN test, we set up both bikes with identical riding positions. The only difference was that the OPEN’s handlebars were a little wider (45.5 vs 42 cm). When both bikes were equipped with 30-32 mm tires, the Firefly coasted slightly faster on a moderate downhill, no matter whether Mark or I were riding it. With the wider 54 mm tires on the Firefly, both bikes coasted at the same speed. In other words, 24 mm wider tires had the same effect as 3.5 cm wider bars…

That doesn’t mean that wider tires are always less aero: In a different test, we found that wider tires increase the wind resistance only when they are wider than the bike’s down tube. We ran 28 mm and 44 mm wide tires in a carefully controlled roll-down test (zero wind, constant temperature, multiple repeats). The conclusion: On the bike we used in that test (Salsa Warbird), 44 mm tires are as aero as 28 mm rubber.

What about aero wheels?

Aero wheels are a popular upgrade to improve a bike’s performance. In wind tunnel tests, they improve the aerodynamics of the bike and rider by about 2-3%. Is the difference noticeable on the road?

The OPEN has 24 spokes and aerodynamic rims, while the Firefly has 28 spokes and rims that aren’t especially aero. Yet on the downhill, the OPEN coasted slower than the Firefly, when both were equipped with similar tires (30-32 mm wide). As mentioned before, that was probably due to the wider handlebars. If the aero wheels offered an advantage, it was small – too small to make up for the extra wind resistance caused by the slightly wider handlebars. As mentioned above, the rider is more important for aerodynamics than the bike.

Tire Casing

We’ve seen that wide tires roll as fast as narrow ones, but that doesn’t mean that all tires offer equal performance. What makes a tire fast is first and foremost the construction of its casing. A supple casing has fine threads and as little rubber coating on the fabric as possible. The tire deforms at the bottom of the wheel, where it touches the road. This takes energy (hysteretic loss). Supple tires are easier to flex, so they lose less energy and roll faster. That isn’t the only benefit of supple tires: They also reduce vibrations that absorb energy and slow you down (suspension loss). So you gain twice with supple tires. And thanks to the reduced vibrations, your bike is more comfortable, too.

The casing is far more important than rubber compound (which matters in the lab and on steel drums, but not on the road), pressure (which makes no real difference on real roads), or tread pattern (unless you have small knobs that flex and squirm).

After rider position and clothing, tires offer the biggest gains in performance. At moderately high speeds of 30 km/h (19 mph), the difference between a slow and a fast ‘racing’ tire can amount to 8% in the rider’s speed – on the fast tire, you’ll go 2.4 km/h (1.5 mph) faster with the same effort.

If you compare supple performance tires with heavy touring or ‘gravel’ tires, the speed difference can be up to 20%. Putting that into perspective, it’s 10x as much as the benefit of aero wheels.

Improve the rider’s power output

Everybody knows: The best way to make a bike faster is to increase the rider’s power output. A bigger engine makes any bike go faster. That is why we train… but there’s more to it. The rider’s power output isn’t constant – it depends on the bike.

Imagine jumping on a trampoline. Then jump on a concrete floor. Then in a foam pit. It’s obvious that you’ll jump higher on the trampoline, even though your legs aren’t any stronger. The trampoline has just the right amount of flex, whereas the concrete floor is too stiff to optimize your leg power, and the foam pit is too soft. The same principle applies to bike frames: Just the right amount of flex in just the right places allows the rider to put out more power. Years ago, Bicycle Quarterly did a double-blind test of three bikes that were identical, except the frame flex was different. The difference in power on the bike that worked best for our testers was a whopping 12%. That’s huge!

You may have heard that stiffer frames are more efficient in transmitting power. Or that frame flex loses energy. But that’ s not how it works. Despite many studies about bike performance and frame stiffness, none have shown that any power is lost when the frame flexes. Like a spring (or a trampoline), the frame stores energy and returns it to the drivetrain when the flex is released. The frame should be built to time the release so it helps the rider’s legs (like a trampoline), rather than work against them (like a foam pit).

The frames of racing bikes have been designed through trial-and-error to have just the right amount of flex. Superlight frames use less material, so they’re actually less stiff than cheaper bikes. Yet they seem to perform better for most riders – even on the flats, where the small weight difference matters even less than on the hills. Fine-tuning the frame individually for its rider can provide additional benefits. Japanese Keirin racers – some of the strongest sprinters in the world – firmly believe that the hardest part in making a good bike is to tune the flex to the rider’s power output and riding style.

In fact, our testing did show some performance differences between the Firefly and the OPEN during sustained climbing. That is why we did all this testing – we wanted to find out why one bike was faster under moderately high power outputs. We’ve established that it’s not the weight, nor the tires, nor the aerodynamics. The performance differences appear to be due to different frame flex characteristics of each frame.

What about ceramic bearings or other ‘marginal gains’?

The logic is simple: If you cut a little resistance in many places, it’ll add up. Ceramic bearings may save only a few Watts, but that’s better than nothing. A better chain lube might gain another Watt or two… I’m sure it works that way, and there’s no reason why parts should have more resistance than necessary. But don’t expect big gains, because the reality is that even cheap bearings have almost zero resistance. There’s nothing wrong with seeking these ‘marginal gains,’ but it makes sense to focus first on the areas where you can get much bigger results.

Summary

Racing bikes really are fast, but it isn’t because of their narrow tires. Real racing bikes are fast because they use supple high-performance tires. Their frames flex just the right amount for a powerful rider. Racing bikes are fast because the rider has little wind resistance thanks to the low riding position, narrow handlebars, and tight-fitting clothing.

All these features can be obtained from an all-road bike, too. As the Firefly shows, as long as the tires have supple casings – all tires in our test used the same Rene Herse Extralight casing – even 54 mm-wide tires roll and accelerate as fast as narrow rubber. If you set up the all-road bike with the same riding position as a racing bike, it’ll be as aerodynamic. (At least until the tires get wider than the frame.) As long as the frame flexes just right, the all-road bike will be as fast as the racer.

On the other hand, if you set up a gravel bike with wider handlebars, a more upright position and stiff, reinforced tires, it’ll be slower than a racing bike. It’s easy to blame the wide tires for that lack of speed, but just putting narrow tires on that bike won’t make it any faster. In the end, the fastest bikes use the elements of racing bikes – supple tires, aero riding position, a frame with flex in the right places – but their tires don’t need to be narrow any longer.

And that – the ability to run wide tires without giving up speed – has opened up a whole new world of riding, since we can now enjoy the performance of a ‘fast’ bike on rough backroads, on gravel and beyond.

One test alone isn’t really enough, and this isn’t the only test that has come to similar results. What we’ve found comparing the Firefly and the OPEN confirms more than a decade of research into bicycle performance, handling, comfort, reliability, etc. by the Bicycle Quarterly team.

If you’re curious about how bikes work, you’ll enjoy our new book ‘The All-Road Bike Revolution.’ In easy-to-understand terms, the book explains aerodynamics, tires, geometry, how your power output affects your position and much more. Find out what matters for speed, comfort and reliability, and enjoy the fun illustrations by Miyoshi.

For the full test of the OPEN MIN.D., as well as the roll-down tests of 28 and 44 mm-wide tires, check out the Winter 2020 Bicycle Quarterly.

Image credits: Miyoshi (No. 6, 7, 8); Rugile Kaladyte (No. 9).

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Comments (55)

  • Christoph Hornig

    I ordered the book in november. It came late. But it was here on christmas and what can I say, it was worth the wait and I read it very quickly.
    This book is almost a work of art!

    January 4, 2021 at 6:20 am
    • Jan Heine

      We’re sorry that international mail delivery is very unpredictable right now. Some packages arrive in days, others take weeks or months. Thank you for your patience! Most of all, we’re glad you enjoy the book so much.

      January 4, 2021 at 7:42 am
  • Erik H

    This is a great overview with just enough numbers to drive home the results.

    I am curious that you attribute the difference in roll down between the Firefly and the OPEN to specifically the handlebars. It could alternatively or also be the wider downtube. Yes, the rider contributes more than the components to aerodynamics, but I am not convinced that small of a movement of the hands explains it.

    January 4, 2021 at 7:41 am
    • Jan Heine

      You are right – it’s hard to tease out all the details. The wider down tube falls within the outline of the bike, so it doesn’t increase the frontal area. The wider bars do. When we tested aerobars in the wind tunnel years ago, the difference between narrow and wide arm settings were quite large. The next test could be to run the OPEN with narrower bars and confirm that it’s the reason it coasted (slightly) slower.

      January 4, 2021 at 7:46 am
    • Andrew H

      It isn’t just a small movement of the hands Erik. You are shaving a cm or more off each long side of your front “rectangle”. This is a quicker and arguably more comfortable way to lose frontal area than by lowering handlebars, which cuts cms only off the the short top of your “rectangle”.

      January 5, 2021 at 11:37 am
  • Richard Goldfinger

    One thing I wish you would discuss is tire flats. The Endurance casing flats less than the extralight casing, but is less supple. Is the tradeoff worth it? I hate flats because it is a bear to change tires on the modern tubeless compatible rims! What affects flats besides the casing? Tire width, and pressure are things I wish I knew how they affect getting flats. I’d go to 40mm tires over my 32s if I thought it would make a big difference in flat prevention. Jan: please comment.

    January 4, 2021 at 9:07 am
    • Jan Heine

      Generally, wide tires and lower pressures result in far fewer flats. Imagine somebody stepping on your foot with a stiletto heel (high pressure) or a running shoe (low pressure). A low-pressure tire rolls over stuff that would puncture a high-pressure tire. This is not just theoretical – since we’ve started to ride wide tires, flats are almost unheard of. (I had two in all of last year, and one in 2019). So going from 32 mm to 44 mm will make a big difference.

      Beyond that, it’s complex. If debris is relatively soft – thorns, glass – they can be stopped by a puncture-proof layer. They get pulverized before they work their way through the puncture-proof layer. Nails or the steel wires from exploded truck tires that litter highways shoulders will work their way through any puncture-proof layer. The only solution is to make the casing so thick that they get stuck before they reach the tube. But that makes the tires heavy and slow.

      What works for you depends on where you ride and how you ride. I’m having no problems on Extralight casings, even in the city. But I rarely ride on the shoulders of busy highways, since I prefer quiet backroads…

      January 4, 2021 at 2:47 pm
      • Jim E

        Jan, just like your “planing” principle of frame flex (great analogy btw), do you think supple casing tires ever exhibit this phenomenon? I believe I felt this when I switched from 25c Vittoria Diamante Pros to 25c Michelin Power Time Trials this summer. Their non-pedaling roll down test speed was only about 4% faster but in a timed milld climb at about 300 watts they were nearly 20% faster. For lack of a better term it felt like I was getting a much better return of energy, almost “springy”.

        January 5, 2021 at 6:59 pm
        • Jan Heine

          Totally – if the flex is in sync with the rider, it doesn’t matter where it happens. Alex Wetmore was the first to notice that, with wide tires, you could fine-tune the pressure to get just the right amount of flex. We’ve found that on a number of bikes now…

          January 5, 2021 at 10:34 pm
  • Karl Wilcox

    Thanks for such an intelligent, well-reasoned, and un-faddish article. I generally ride a 40 year old Mercian custom road bike (67cm) that is quite heavy by today’s standards at 27-28 pounds (it is a very compliant frame). I am 6’6″ tall and 200 pounds. The two bikes you reviewed are not as ‘heavy’ as my Mercian (nor are the riders, for that matter), and I am wondering if at 27-28 pounds, my bike has crossed some line where weight really does extract a serious speed penalty, or is a 27 pound bike not that heavy relative to my height and weight? Obviously, at some point, a heavier bike does dramatically slow down forward progress, but, given normal parameters where does that line lie?

    By the way, I use 39cm wide bars, and I find considerable aero benefit when pulling into a headwind, etc. But the narrow bars do not provide much arm leverage when climbing out of the saddle!

    January 4, 2021 at 9:27 am
  • Josh Greenfeld

    Jan – if tires are less aero when they are wider than the headtube, does that mean that on a bike intended for riding somewhat narrower tires like the 32s on the OPEN, the headtube is actually slowing the bike down or does the inverse not hold true? I’m wondering what this means for frame builders making decisions about narrower, tapered and “oversized” headtubes.

    Thanks! This is a great article!

    January 4, 2021 at 9:28 am
    • Jan Heine

      Airflow on bikes is very complex, because the air is so turbulent. The big differences come from changes in frontal area more than trying to manage airflow. That is why getting the rider lower and narrower has a much bigger effect than aero components…

      January 4, 2021 at 2:50 pm
  • Larry T

    Great stuff! FINALLY got the Rat Trap Pass rubber on my ancient 26″ wheeled MTB and feel a huge difference, at least as much as the switch from the heavy, stiff MTB tires to the Vittoria Saguaro folding bead rubber that opened my eyes to just how much difference a simple tire swap could make.
    I’m far from thinking this bike (despite it’s drop bars and similar position) is as fast and easy-to-pedal as my custom steel road bike with 25 mm Vittoria Pave tires but it’s great to take out when I want to not care much about whether the road is paved or even much of a road. Thanks for making these available – otherwise this old MTB would probably just be gathering dust as my days of wanting to bounce around MTB-style are long gone.

    January 4, 2021 at 9:31 am
  • mike greene

    I will be ordering the Antelope Hill tire this month for the rear wheel of a recumbent. I really want a black side wall, but given that as much as 70% of the weight distribution on a recumbent is at the rear, I am a little afraid to get the Extralight (planning on running them at lower pressure on the road for some passive suspension).

    So my question is this: how much performance is lost using the Endurance vs the Extralight? (I can live with dark tan – if I have to :0(

    January 4, 2021 at 9:37 am
    • Jan Heine

      Standard and Endurance have the same speed. Extralight is noticeably faster. See the previous comment on flats… If you only rarely get flats now, I’d say go with the Extralight. If your flat frequency is already high, Endurance is a great choice.

      January 4, 2021 at 2:52 pm
    • Terry Farrell

      I have a 2.3″ Rat Trap Pass with extralight casing on the rear of my recumbent Rans Stratus XP. The weight distribution on my bike is about 70/30. With my “Winnibego mindset” and my less-than-lightweight body type, that puts a bit over 200 lbs. on my rear wheel. I run the lightweight Schwalbe tubes (SV14) in my tires. (I wonder why Rene-Herse recommends the standard weight Schwalbe SV13 rather than the light weight SV14?) I have put 500 miles on my tire since installing. I had one flat early on when riding down a sidewalk. Most of my riding is on suburban residential streets and some rural roads, including some with a bit of traffic. Other than that one flat, it has been smooth sailing (and I DO mean SMOOTH – rides like my old Lincoln Towncar!). I did a bunch of roll-down tests down on a local half-mile long not-steep hill and found that speeds were constant with dropping test air pressures, but did start to drop and time increase when I let tire pressure down to about 35 psi or less. I run my rear tire between 40 and 45 psi. FWIW, I have the 1.8″ Naches Pass on the front of that bike and as there is only about 90 lbs on the front tire, I run between 20 and 25 lbs. in it with just a small bulge in the tire when I sit on the bike. Just curious, what kind of recumbent are you running a 29″ tire on?

      January 5, 2021 at 4:29 am
    • John Duval

      Passive suspension makes a huge difference on a recumbent, where road irregularities travel straight into your body. Much more so than an allroad bike. I too have built two recumbents around 650b Rene Herse extra light tires. One had a 70/30 weight distribution, the other 50/50. I am 6’-6” and weigh 220 lb. I run a 48mm in the rear and 38 in the front, with 35psi each. I have experienced no issues with the tires, or flats. I feel the smaller tire up front handles better because it has less of what I would call pneumatic wheel flop, where the tire self steers when leaned over. The tires have very little effect on frontal area on a recumbent, so there is much to gain and nothing lost. John Shlitter I believe is riding 38mm tires these days.

      January 5, 2021 at 10:11 pm
  • Ola Strandberg

    I enjoyed reading this chapter in the book, and the additional details here. I am eagerly awaiting my custom Firefly, which is being assembled as we speak. I ordered it as my ”forever bike”, but in the back of my mind, I have thought to myself that if I ever get an N+1, it would be like the Open MIN.D. I guess I won’t have to bother with this 🙂

    January 4, 2021 at 9:43 am
  • Joe Fleshman

    I can’t wait to get my copy! Has the Winter BQ already shipped?

    January 4, 2021 at 9:48 am
    • Jan Heine

      It has, but the US Postal Service has been terribly backed up over the holidays. Quite a few readers are still waiting for their copies. Thank you for your patience.

      January 4, 2021 at 2:52 pm
  • Ernie Meunier

    I’m starting to relize that reduced drag from being able to use the more stable center bends of CC’s TheWave handlebar with elbows more tucked on descents may be more important than swapping from a 44 to a 42c bar?

    January 4, 2021 at 9:54 am
  • Chris

    This is both affirming and problematic. I have had a small number of bikes that varied along so many dimensions that ranking them or pulling out the features that work best is tough. And, based on the article, it’s “tuning” that matters. I whole heartedly agree with this; my Torelli of lovely steel just works for me in a way that’s hard to describe. But this puts us in a position of finding what “tuning” is and what’s best for each of us. But, forever we’ve been like the drunk looking for his keys under the lamp post: we measure what’s measurable — grams.

    I’ve been a long fan of wider tires, squeezing 28mm tires into the Torelli while the mechanic was pushing for 21mm’s. This felt like progress. Now I’ve got the Juniper Ridge up front and Switchback on back of my turn-my-randonneur-into-gravel-bike bike. I go all sorts of places on it that it wasn’t “designed” for. But, the steel is good and the big tires make liking pavement through some gnarly trails fun to ride.

    I think both experiments are fully consistent with your article, but I’m wondering how I’ll go about finding the next bike when “tuning” is needed. When is your next book on “tuning” coming out? Soon I hope.

    January 4, 2021 at 9:58 am
  • Steve

    I greatly enjoyed ‘The All-Road Bike Revolution’ and this Journal entry. Frame flex is a really interesting subject, how would you optimise this to your own riding style? Do frame styles, e.g., traditional diamond or sloping top tube and dropped stays, make a difference? I guess this comes down to the relationship of resonant frequencies of frame oscillation and preferred cadence, with power and frame modulus feeding into flex amplitude. It will be interesting to see emerging studies on these dynamic processes.

    January 4, 2021 at 10:27 am
  • Monty Richardson

    Thank you Jan, I have learned so much from you over the last few years. Excellent explanations, in real world circumstances, again

    January 4, 2021 at 10:39 am
  • Jon Pope

    I always ride sew ups, never stopped. From back in the day on Wobler Neo-Pros to now on Tufos saving up for some FMBs!

    January 4, 2021 at 10:45 am
  • Tim Lo Monaco

    Very informative! I’m loving my Snoqualmie Pass tires and they feel super fast. I’d eventually move up to the Antelope Hills but my bike doesn’t have the clearance for them. Any future plans to make a slick 700 x 48 or 50 to bridge the gap between the two?

    January 4, 2021 at 10:52 am
  • Kenneth

    Any thoughts on how frame flex affects performance over long distance rides? I try to keep my power output low on brevets to try to save my legs for days 3-4 when power is very low due to fatigue. Will a frame that encourages me to ride faster fatigue me faster, or will I be riding with a higher speed at the same perceived effort even at low power outputs?

    January 4, 2021 at 11:10 am
    • Jan Heine

      I can only speak from my experience – I tend to prefer a more flexible frame for long rides. When I raced, I rode a Columbus SL frame (0.9-0.6-0.9 mm walls). Now I prefer much more flexible tubing (0.7-0.4-0.7 mm), and I find that I rarely have those “tough spots” where it’s hard to keep the pedals spinning.

      Of course, a bike that performs wonderfully is a temptation to go faster. On a long ride, it’s often good to hold back and not work too hard early on – no matter which bike you ride.

      January 4, 2021 at 2:57 pm
  • Paul Greenberg

    Jan:

    If some flexibility and good energy return (planing) is one of the big secrets of a fast bicycle, why is an extremely stiff frame with supple tires not the equivalent to the less stiff frame with similar tires? Air has less hysteresis than metal or carbon fiber. Additionally, the forces involved in deflecting a frame must be orders of magnitude greater than the forces to deflect a tire.

    Thanks!

    January 4, 2021 at 11:47 am
    • Jan Heine

      Absolutely! We’ve found that fine-tuning tire pressure can also improve the performance of stiff bikes. We’ve had two BQ test bikes that performed poorly (for us) with 50 psi in the tires, but were among the fastest bikes we’ve tested with 25-30 psi.

      January 4, 2021 at 12:07 pm
  • MSL

    Really interessting, but against all my experience i had in my life of cycling! You can immediately feel a lighter wheelset or a wider tire! And much more on a bike which is more than 2kg heavier, climbing up a hill!
    I don ‘t understand how you came to your result, maybe after reading your book which hopefully arrieve next time!
    Where i agree with you, are your great tires and i ll never ride smaller tires like 35 mm, because they re so fast, safe and comfortable.

    January 4, 2021 at 11:56 am
    • Jan Heine

      There’s no doubt that you can feel heavier wheels. The rotating inertia makes the bike react differently. What we measured was whether this affects speed and acceleration in a significant way – and it doesn’t. (Just like physics predicts.)

      The model is a bicycle acceleration model that takes the inputs of all variables (rider weight, bike weight, rim weight, spoke weight, drag coefficient, frontal area, slope, etc.) and calculates the speed in 1 second iterations.

      January 4, 2021 at 3:02 pm
  • Michael Johnson

    In 1970 I was working in a bike shop that sold Schwinn, Raleigh, and Peugeot bicycles. We had a customer with a Schwinn Varsity who had constant issues with thorn punctures. The owner had me install thorn proof tubes and fill the tubes with a liquid that was also used to stop small leaks. I can’t even guess how heavy those wheels were. I took the bike out into the parking lot for a quick spin and I can tell you that accelerating those two flywheels was an eye opening experience. This of course is an extreme example but the takeaway for me was that lighter was clearly more lively, the only difference was going to be the matter of degree. The extra weight was also easily noticed spinning those wheels up on the repair stand. Small differences may not be obvious going from bike to bike but personally I love the feel of a light wheel.

    January 4, 2021 at 12:07 pm
    • Jan Heine

      Your experiment is difficult to interpret, since you’ve changed so many variables. Your wheels aren’t just heavier, but you’ve also made them far less supple. And part of the weight is liquid (sealant), which reacts quite differently from solid weight (rubber, rim, spokes).

      Agreed that lighter wheels feel different – especially when rocking the bike from side to side as you sprint or climb out of the saddle. The side-to-side acceleration is actually quite large… but that’s a topic for a different post. (It’s also in our book.)

      January 4, 2021 at 3:05 pm
      • Rick Thompson

        Jan – You have often argued that low resistance to rocking side to side (less weight and less high) is a good thing for sprinting and climbing out of the saddle. I do not sprint much, but do climb standing often. It feels to me that some weight up high is not bad. When the bike resists rocking I do not have to put in as much upper body energy to oppose my weight on the pedal. Then the force on the pedal goes toward forward thrust, not pushing the bike over. I like some weight in the handlebar bag when climbing like that. I have made no measurements, this could be just a sensation and actually I am slower, but have you measured this effect to confirm what you are saying?

        January 5, 2021 at 4:04 pm
        • Jan Heine

          I think you may be onto something. In the book, I’ve refined this idea along the lines you suggest: There seems to be an optimal resistance for the side-to-side rocking, too. After all, the reason you’re rocking the bike is to put more power into the drivetrain by pushing against the resistance of the bike…

          January 5, 2021 at 10:31 pm
  • Owen

    After switching to Babyshoe Pass tires from Panaracer Gravelkings on my road bike, I concur fully with your findings on comfort and traction. I’m sure the increased speed is there too if I were inclined to measure it. The best comparison I’ve found is using a waxless cross-country touring ski vs. a racing ski kick-waxed correctly for the temperature and snow conditions–both work fine, but the latter glides with less effort, and you really feel like you’re flying. Thanks for the great tires, and best to the RH team for 2021.

    January 4, 2021 at 12:26 pm
  • marc baskin

    I am a road rider but have started to try out some gravel in central Massachusetts.

    I bought your 32 mm tires but not extra lights since I was concerend about flatting out in the middle of nowhere.

    Your review emphasized the importance of supple casing. When you go to buy a tire how can you determine if the casing is supple? Manufacturers usually tell you the weight but not much more.

    January 4, 2021 at 12:44 pm
    • Jan Heine

      Good question – it’s not something you can easily measure. Obviously, heavier tires usually have more rubber on the sidewalls and tend to be less supple. But if you just make the tread thinner, your tires wear out faster without gaining much speed… You can feel the sidewalls with your hands, but the only way to tell is ride them.

      It’s like all fabrics – how to figure out whether a Merino wool sweater is really soft or not? There are lot of things that aren’t easily expressed in simple specs.

      January 4, 2021 at 1:27 pm
    • Paul S Greenberg

      Marc:

      I do a ton of gravel riding in Litchfield County CT and in the area just south of Great Barrington. I typically run Bon Jon Pass 35mm or Snoqualmie Pass 44mm, both with extra light casings. I have not had a flat in thousands of miles running 30-45 lbs of pressure with latex inner tubes. My guess is that the rocks and gravel here in the east are pretty smooth, unlike the more jagged stuff out west.

      Paul

      January 4, 2021 at 1:42 pm
  • Al

    Jan, did you happen to have power meters on both bikes to note the differences in power output when you and Mark rode the Firefly or OPEN MIN.D?

    It seems like having that data would help rule out one of the many variables present in this experiment.

    January 4, 2021 at 1:33 pm
    • Jan Heine

      We have done the same experiments (different bikes, double-blind testing) with power meters in the past. Basically, when two bikes of equal weight and with the same tires climb at the same speed, we put out the same power. When one bike is faster, it’s because the rider puts out more power. That’s what the 12% figure came from.

      January 4, 2021 at 2:22 pm
  • Ian Hoffman

    Interesting findings regarding tire width, aero, and down tube size. I ride a high racer recumbent bike, the ‘frame tube’ is elevated mostly above the wheels and doesn’t angle down like a regular down tube. With that the front wheel basically stands on its own, along with the bottom ~60% of the rear wheel; no tubes, cranks, or legs in the way there. I’ve been using the 38mm Barlow Pass tires, and love them, definitely worth it for comfort (since I can’t lift off the seat). But I’ve been wondering about going all the way and riding the 55mm Antelope Hill. My body position is already much more aero than a regular bike, but also doesn’t change much either. I want to like the idea of going with the 55mm tire, but haven’t been able to accept that change yet (even though I love the 38s).

    January 4, 2021 at 1:50 pm
  • Alex

    This post makes me wonder whether you should do more testing of recumbents. If aerodynamics are far more important than weight and rider position is the most important factor in aerodynamics, then presumably a recumbent that offers an enormous aerodynamic advantage with no comfort penalty would be an extremely fast bike, especially with Rene Herse tires! I just finished building up such a bike with Babyshoe Pass Extralights and Honjo fenders. I won’t make any great claims about speed because I’m not very fast, but to me it’s a compelling choice, especially given what you’ve written here.

    January 4, 2021 at 2:14 pm
    • Jan Heine

      No doubt recumbents are fastest – just look at the speed records! However, for the roads we enjoy, not being able to unweigh the wheels or jump over small obstacles is a big drawback…

      January 4, 2021 at 2:19 pm
  • Joe Quinn

    Excellent article Jan, you clearly outline what matters in terms of speed on a road bike. How can one measure the correct amount of stiffness required when choosing a frame?

    January 4, 2021 at 2:59 pm
    • Jan Heine

      I don’t think there’s a simple formula. The Japanese Keirin framebuilders look at their riders, and then suggest the tubing for their bikes.

      January 4, 2021 at 3:07 pm
      • Paul

        Hi Jan, great article. So you would you say an all road bike/gravel bike with the same set up as a racing bike with the same riding positions would be equally as fast?
        Ie: A 3T Exploro and a Cervelo S5, same width bars, cockpit setup , wheels, tyres, etc

        January 5, 2021 at 5:00 am
        • Jan Heine

          It really depends on the frames. If the frames have the same flex characteristics, yes.

          January 5, 2021 at 9:16 am
    • Sam at Singular

      This is a big part of the art of bicycle frame design. Specifying the correct tubing to get the right amount of flex for a rider is a combination of years of experience and understanding of the feel of different tubesets. It’s even more challenging when designing production framesets which need to suit a wide range of riders – inevitably, the tube selection, frame design and resultant stiffness will not suit everyone. What is right for a lighter, less powerful rider, will be a noodle under someone heavier and stronger – though in terms of fit they might be riding the same size of bike. Well designed frames should use size specific tubing in consideration of this fact – but even then it won’t be perfect for everyone.

      January 5, 2021 at 3:50 am
  • R. Kent Stewart

    Jan,

    You once published information about the aero effect of having bags, cages, water bottles, fenders, etc. installed on your bike. As you continue to investigate the REAL performance of bikes, I’d ask that you consider reprising that information for those of us who ride ‘clothed” bikes. Current thinking seems to suggest tat bikeepacking rigs are more aero than traditional rando. handlebar bags, etc. Is that true?

    Thanks for all you do to elucidate us about real bike performance.

    Kent Stewart

    January 4, 2021 at 3:10 pm
    • Jan Heine

      The aerodynamics of bags is a complex subject that goes beyond this article. It’s covered in our book, though.😉

      January 5, 2021 at 7:41 am
  • Michael Cambronn

    I sure wish you’d consider a range of 24″ tires (and rims) for youth bikes. The current selection, that I’ve found, is crap. If you have a 24″ tire you recommend I’d love to know what it is.

    Thanks in advance,

    January 5, 2021 at 6:31 am
  • David Hopkin

    Wow. Crazy number of comments in a day! Hope you find time to reply to this. I have a pair of Switchback Hills on my custom built Kona Libre. They have been awesome on a variety of surfaces including hard pack trail, rough and smooth road, gravel roads and even a hard packed beach. However, I am pondering getting a pair Juniper Ridges to fully round out the bikes all-road capability. I have read your book (fantastic) and the fall Bicycle Quarterly looking for hints on how much less efficient the Juniper Ridges might be. Can you provide any insight? Cheers, Dave

    January 5, 2021 at 9:56 am
    • Jan Heine

      We’re still working on the final data on the resistance of our knobbies, which will be published in the Spring Bicycle Quarterly. What I can tell you already is that the difference between our smooth tires and the knobbies is surprisingly small. I doubt you’ll notice a difference unless you’re riding with a power meter or a closely matched friend – and even then, you might not.

      January 5, 2021 at 10:30 pm

Comments are closed.