Myth 10: Stiffer Forks Steer Better

To celebrate Bicycle Quarterly‘s 15th anniversary, we are looking at myths in cycling: things we used to believe, but which we’ve since found out not to be true. This week, we have a ‘double feature’ that looks at fork blades. In the first post, we looked at whether they flex enough to improve comfort. Here we examine the belief that stiffer fork blades make the bike steer better.

Looking at Hahn cornering hard on the comparatively flexible Kaisei ‘TOEI Special’ fork blades (above), you can see that the wheels are perfectly aligned as he scythes around this fast downhill corner. His bike steers no differently from a bike with ultra-stiff fork blades. This goes against the widely held belief that a stiff fork offers more ‘precise’ steering.

Stiffer setups improve the steering response in cars and tricycles, where the forces of cornering flex the suspension components. On a two-wheeler, those forces are aligned with the centerline of the bike, otherwise, the rider would fall over (above, from Bicycle Quarterly‘s article on balancing and steering). Even when you corner hard, the centrifugal forces don’t cause the fork to flex.

At low speeds, the front wheel turns at a greater angle, which puts small lateral loads on the fork, but since you aren’t going fast, you won’t notice the little flex this causes. The one exception is tandems: Due to their long wheelbase, you can feel the flex of the front wheel when cornering very hard on tight mountain hairpin turns.

At high speeds, as in the top photo, the fork turns very little even when you corner hard, so the flex is insignificant – even on a tandem.

The only time you put significant side loads on the bike is when you ride out of the saddle. What you realize then is that the lateral flex of the front wheel is far greater than that of the fork.

Climbing out of the saddle on the same bike with two different front wheels confirmed this: On a wheel with a ‘narrow’ SONdelux generator hub (right), the rim rubbed on the brake pad. With the ‘Wide-Body’ model (left), the rim never touched the brake pads, because the wider flanges make the wheel laterally stiffer. The difference in the flex of the wheels was very noticeable.

By comparison, the fork blades flex only very little: Riding the same ‘Wide-Body’ wheel on bikes with different fork blades (standard vs. flexible Kaisei ‘TOEI Special’), we never had the rim rub on the brake pads – even flexible fork blades are plenty stiff for riding out of the saddle. You can easily test that by pulling sideways on your front rim while holding the handlebars steady. You’ll see the wheel flexing, but there won’t be any visible flex in the fork blades.

Even a flexible wheel corners just fine – I haven’t heard anybody talk about the poor handling of aerodynamic wheels with few spokes (and low lateral stiffness). Still, there is no benefit to a laterally flexible wheel… We asked Schmidt to make the ‘Wide-Body’ hubs for us, because they don’t just reduce brake rub – they also make a much stronger wheel. That allows you to use fewer, thinner spokes, which improves the wheel’s shock absorption, weight and aerodynamics.

The one time when you don’t want your fork blades to flex is when you are braking hard. The longer the lever, the greater the force – so fork blades taper as they move away from the hub. The tops of fork blades are ovalized for the same reason – they have to resist the loads of braking, rather than side-to-side flex. Thanks to these features, the flexible ‘TOEI Special’ fork blades are more than stiff enough for hard braking. Their flex is concentrated at the bottom of the blade, where the forces of braking are small.

Disc brakes are a different matter, as the forces of braking are fed into the fork blade where the caliper attaches. That changes the requirements on fork blades. Using flexible forks with disc brakes will require some more thought and testing.

Contrasting with the myth, slender fork blades actually improve the cornering, because they absorb bumps that would otherwise unsettle the bike. If your bike skips over bumps, the tires lose traction…

If you are a powerful sprinter, the suspension of the fork blades can be a disadvantage: When you work the bike extremely hard while out of the saddle, slender fork blades can feel a bit like a suspension fork that bobs with your pedal strokes, albeit to a much smaller degree. Even track sprinters don’t need ultra-stiff fork blades; they might choose something like the Kaisei ‘Standard’ fork blades. In fact, since they also rock the bike much more from side-to-side and don’t have brakes, they often use round fork blades.

For the rest of us, we’ve found that the Kaisei ‘TOEI Special’ fork blades (above) take the edge off large bumps to improve comfort, tracking in corners and speed. Steel is a great material for fork blades, because it can flex without affecting its durability: our ‘TOEI Special’ fork blades have been 100% reliable over tens of thousands of miles. I consider them a key component of our bikes, making them faster and more enjoyable at the same time.

More information:

Posted in Framebuilding supplies | 39 Comments

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?

We designed a simple test to measure the flex of fork blades. By combining a small bag-support rack with the hoop of a low-rider, we could easily visualize (and measure) the flex of the lower fork blades: The two racks will move against each other only if the fork flexes between their attachments – in the lower 2/3 of the legs. (If the flex occurs higher on the fork, both racks will move in unison.)

The video above shows the same test on my ‘Mule’ with its flexible Kaisei ‘TOEI Special’ blades. As the camera zooms in, you can see how much the fork blades actually flex. That is what takes the edge off bumps that are too large for the tires to absorb.

And since more comfort equals more speed, flexible fork blades make your bike faster, too – even on smooth roads. We quantified that when we ran a stiff fork, a suspension fork and a fork with flexible blades both on rumble strips and on the brand-new, ultra-smooth pavement next to them (above).

It didn’t come as a great surprise that compared to our stiff fork (Trek unpadded), the suspension fork (RockShox) and the flexible steel fork (Singer) each saved about 50 Watts on the rough surface of the rumble strips (left graph).

What we didn’t expect was that both flexible forks saved somewhere between 20 and 35 Watts on the smooth pavement (right graph). That is a very significant difference in power output – in fact, it was large enough to pass the all-important test of statistical significance.

In the graphs above, you notice a fourth bar: Trek (bar padding). We also tested thick foam on the handlebars to simulate the maximum padding you could put on your bars, but we found that the effect was much smaller than that of the forks’ suspension. It was not statistically significant, and neither were the small differences between the RockShox and Singer forks.

So it’s clear that the Kaisei ‘TOEI Special’ fork blades make a bike more comfortable and faster. That brings us to the next question: Do flexible fork blades negatively affect the handling of the bike? Check back tomorrow to find the answer!

Further information:

  • Bicycle Quarterly 23 with our original experiment measuring the flex of fork blades
  • Bicycle Quarterly 29 with our rumble strip tests of suspension losses that included forks, tires and other equipment
  • Compass framebuilding parts, including Kaisei ‘TOEI Special’ fork blades
  • The Alex Singer fork in the original test used old Reynolds 531 ‘Super Resilient’ fork blades that are no longer made. The Kaisei ‘TOEI Special’ blades have the same diameter and profile with slightly thinner walls, making them yet a bit more flexible.
  • The RockShox fork was a brand-new Ruby. With age, the performance of the suspension fork will probably deteriorate.
Posted in Testing and Tech | 60 Comments

New Compass Web Site

If you have visited the Compass Cycles web site in the last few days, you’ll have noticed that it has a new look. On the home page, you’ll see a slide show with the three parts of the Compass story.

The first slide links to the story of the ‘Wide Tire Revolution’ – how we realized that wide tires could be as fast as narrow ones, and how we developed our pioneering allroad tires.

The second slide talks about the philosophy behind our components: classic in appearance, but 100% up-to-date in their performance. And compatible with modern bikes.

Much of what we do at Compass Cycles draws on the experience of René Herse. Read how we became the successor of the great constructeur.

We’ve also updated our menu to make it easier to use. ‘Shop’ and ‘Support’ put all the information you need in one place. ‘About’ gives you direct links to the slides with our story. There are links to our Instagram and YouTube contents, and the flags give you access to the translations of our web site into French and Japanese. (The translations are works in progress…)

When you click on a product category (like ‘Bags’ above), you see an overview of the parts we offer. The pull-down ‘Read the Back Story’ explains why we use (and sell) these parts. For example, on the ‘Bags’ page, we explain why we prefer handlebar bags, and why we feel that leather and canvas outperform synthetic materials.

Go to to start exploring the new site.

Posted in Uncategorized | 4 Comments

Back in Stock / Expected Soon

At Compass Cycles, we try to keep our entire program in stock all the time, but some items are so popular that it can be difficult to keep up. Our cyclotouring knickers continue to be one of our best-sellers, as riders appreciate their comfort and light weight. One reviewer wrote: “I am practically living in them.”

The knickers are sewn right here in Seattle. We just received a new batch, and all sizes are in stock again.

I wish we could say the same about our 11-speed cranks. They’ve been exceedingly popular, and the first run of chainrings sold out quickly. New ones are in production, and we hope to have them by early June.

The MKS Allways pedals are also popular, as they combine MKS premium bearings with a large platform. The platform is slightly concave, so your foot has better grip. They are available in standard and Rinko versions (above). A new shipment from MKS is on the way. We expect them in early June as well.

We appreciate your patience when popular items are temporarilyout of stock. Click on the images to find out more about these products.

Posted in Clothing | 6 Comments

Being Interviewed by the Quoc Pedaler

Recently, The Pedaler interviewed me for the blog of Quoc Pham’s eponymous cycling shoe company. We chatted about the origins of allroad bikes, the inspiration of the mid-century randonneurs, and what makes Compass Cycles different from other companies.

Click here to enjoy the full story.

Posted in Uncategorized | 3 Comments

How to Test Tire Performance

In the 15 years of Bicycle Quarterly, one of our discoveries has been that testing bicycle performance isn’t easy, and that taking shortcuts often has led to erroneous conclusions.

Carefully designed tests that replicate what happens when real cyclists ride on real roads have allowed Bicycle Quarterly to debunk several myths. Certainly, the biggest change in our understanding of bicycles has been about tires.

Tires, more than anything else, change the performance, feel and comfort of your bike. We now know that fast tires can increase your on-the-road speed by 10% or more. But how do we know which tires are fast?


Lab testing is the most common way to test tire performance, usually on a steel drum (above). In the past, these steel drums were smooth. Now the testers have added some texture to simulate the roughness of the road surface. Unfortunately, that doesn’t address the fundamental flaws of drum testing:

1. The curved drum pushes deep into the tire

Since the drum is convex, it pushes deep into the tire, unlike a real road, which is flat. The more supple the tire, the deeper the drum pushes. This makes the tire flex more, which absorbs more energy. That is why a stiff tire performs well on the drum, and a supple tire does not. We know that the opposite is the case on real roads.


Increasing the tire pressure also makes the tire harder, and so the drum won’t push as far into the tire. That is one reason why drum tests show higher pressures rolling much faster (above). According to this data, increasing your tire pressure from 60 to 120 psi (4.1 to 8.3 bar) reduces the resistance by 30%!

Bicycle Quarterly‘s real-road testing (above) has shown that the opposite is true, especially for supple tires: They roll slower at 100-120 psi than at lower pressures. (Higher power = slower.)

This problem with drum tests has been recognized for a long time. There is a way around this problem, but it’s very expensive: Make the drum so large that it’s barely convex. One of the best drum testing rigs is in Japan, and from what I’ve heard, it measures about 7 feet in diameter. That means it’ll push into the tire much less, and thus it won’t make stiff tires seem faster than they really are.

On the other end of the spectrum, you have efforts to measure tire performance on small-diameter rollers,  like those used for training. That will always be futile: Anybody who has ridden on rollers knows how high the resistance is, because the rollers push so deep into the tires. And if you want to increase the resistance further, you just let some air out of the tires…

Not surprisingly, tests on small-diameter rollers show the ultra-supple Compass ‘Extralight’ casing rolling not much faster than the ‘Standard’ version. On real roads, the performance difference between the two is quite noticeable.

TOUR magazine in Germany has designed a test rig that eliminates the problems associated with the convex drums: Two wheels carry weights that are off-center, so they rock the wheels like a pendulum. This test rig rolls back and forth on a flat surface. You could even use it to test on real roads. The longer the test rig rocks from side to side, the lower the tires’ rolling resistance.

This test showed the Compass Bon Jon Pass as the fourth-fastest tire they’ve ever tested. (‘Rollwiderstand’ means ‘rolling resistance;’ the dark bars are for ‘rough asphalt;’ the light ones for ‘smooth asphalt;’ to convert the pressure from bar to psi, multiply by 14.5)

It’s interesting to compare the same tires – Compass Bon Jon Pass 700C x 35 mm tires (standard casing) vs. Continental 4000 S II in two tests:

  • tested on a steel drum:
    • Compass (6 bar / 90 psi): 15.8 W
    • Continental (7 bar / 100 psi): 12.9 W
    • Conti has 18% lower rolling resistance.
  • TOUR magazine used their rocking test rig:
    • Compass: 17 W
    • Continental: 17.5 W
    • Conti has 3% higher rolling resistance.
    • Compass is fourth-fastest of all tires TOUR tested (graphic above).

It’s clear that the drum test disadvantages a supple tire – the stiffer Conti performs much better. Adding to the confusion, gets lower resistance values than TOUR – it should be the other way around with the drum pushing into the tire.

There is another odd thing: TOUR shows the wider Compass tire in 4th place on the smooth road surface, but in 5th place on the rough surface, where it gets beaten by the narrower Conti rolling at higher pressure. That isn’t how it works in the real world, where the advantages of wider tires and lower pressures are greatest on rougher roads. That brings us to the second problem of these lab tests:

2. No rider on the bike


Without a rider, you have no significant suspension losses. Suspension losses are the energy that is absorbed when vibrations cause friction between the tissues of the rider’s body. Without a rider, there is nowhere to absorb the energy – steel weights don’t behave like human tissue.

Without suspension losses:

  • vibrations wouldn’t slow you down.
  • wider tires would be slower than narrow ones.
  • higher tire pressure would make your bike faster.

On the road, with a rider on board, all these statements are false – because suspension losses absorb energy, and reducing suspension losses is key to making a bike go faster. Understanding suspension losses has revolutionized our understanding of tire performance. It’s the underpinning of the ‘wide tire revolution.’

The lab tests described above are like a return to the last century, when we all ‘knew’ that narrow tires rolled faster because they could run at higher pressures. So we ran 19 mm tires (above) and inflated them rock-hard for optimum performance. That was long ago – when did you last see a short-reach racing brake with so much tire clearance?

Today, even professional racers run 25 mm tire at 80 psi. They have found that this is faster, no matter what the steel drum tests say. Racers have concluded: When tests don’t replicate the real world, they aren’t of much use.

At least TOUR‘s test rig gives us some indication about the energy absorption in the casing. It neglects one half of the equation – the suspension losses – but it’s useful if we understand its limitations. On the other hand, tests on small-diameter drums are just misleading – because if you design a tire to perform well in these drum tests, it’ll have a stiff casing and ultra-high pressures. And that means it won’t perform well on real roads.

A better lab test?

Is there a way to design a realistic lab test for tire performance? After all, Bicycle Quarterly‘s test procedures – testing only on totally calm days; when temperatures are constant; with a rider who has trained to keep the same position for lap after lap – are fine if you are doing scientific research. But they are not feasible for commercial applications, where you need to be able to just mount a tire on a wheel, take it to the lab, and get an immediate reading of its performance – without having to wait until the weather is right, the wind has died down, and the temperature is constant.

At Bicycle Quarterly, we’ve been thinking about this. Current drum tests load the tire with metal weights that don’t absorb much energy as they vibrate. Is there another material that behaves similar to a human body? ‘Ballistic gelatin’ is used to simulate gunshot wounds in human tissue. It closely simulates the density and viscosity of human tissue. Using a material like that to weigh down the wheel might simulate the suspension losses.

Suspension losses vary with speed (higher/lower vibration frequency), so TOUR‘s rocking rig probably would not work – it simply moves too slowly to replicate suspension losses at normal cycling speeds.

That brings us back to the steel drums. You’d have to make the drum huge to reduce the problems with the convex surface. The drum surface itself would have to be a true replica of actual pavement, not just a diamond tread. You’d probably want to map a bunch of road surfaces with a laser and then use EDM (electrical discharge machining) to engrave an ‘average’ road surface into the steel drum surface. You could make interchangeable plates covering the drum with several road surfaces that feature different roughnesses. And why not a gravel road, too?


To validate your test rig, you’d take a fast, a middling and a slow tire, and test them on the road, just like Bicycle Quarterly has done. If your drum test results match those on the real road, then you can be confident that they replicate real-world conditions.

Back to Real-Road Testing


As you can see, making a useful test rig is a huge undertaking, which is probably why nobody has done it yet. For now, tire companies continue to develop their tires with the help of simple steel drum tests. That may be the reason why they don’t offer their supple high-performance models in truly wide versions: The steel drum tests indicate that you lose performance quickly as you run tires at lower pressures. And since supple, wide tires cannot support high pressures, steel drum tests suggest that wider tires should strong and not supple.

At Bicycle Quarterly, we’ll continue to test tires on real roads. To get good results, we can’t just put a power meter on a bike and go for a ride, then change the tires and repeat. We must keep the conditions the same for all tests. First, this means testing in a controlled setting, like a track. Second, we must control the variables tightly: test only on days with no wind and constant temperature, test each tire multiple times, and do a rigorous statistical analysis of the results.

The statistics are important, because there always will be some ‘noise’ – even in a lab test, because the tire warms up the longer you run it on the machines. The statistical analysis shows where you are recording real differences between tires and where you just see ‘noise.’

After more than a decade of testing tires under real-world conditions, we can say with certainty:

  • Supple casings, more than anything else, determine the performance of your tires.
  • Wider tires roll as fast as narrow ones on smooth surfaces, and faster on rough ones.
  • Higher tire pressures don’t make the bike faster.

There is little doubt about these findings any longer – they’ve become widely accepted, even though the lab tests still haven’t caught up to the new science. But for us as riders, what matters is how well our tires perform on real roads, not on a steel drum.

Further reading:

Posted in Testing and Tech, Tires | 80 Comments

Compass and BQ in the News

During the last week, Bicycle Quarterly and Compass Cycles have been mentioned in several news stories. The popular web site featured an article about converting a 700C bike to 650B. They wrote: “The benefits are fairly obvious. Wider tires offer more floatation, a more supple ride, and are all around better suited to dirt and gravel surfaces. They can also be just as fast as road tires.”

They equipped their bike with Compass Switchback Hill 650B x 48 mm tires, and we talked about some of the things to consider in these conversions: clearances, bottom bracket height, gearing, etc. The article is a great introduction if you’ve looking into running 650B wheels on your disc-brake bike.

It’s not every day that you get a call from Matt Wiebe, the editor of Bicycle Retailer and Industry News“We’re working on a cover story about big car tire brands like Pirelli and Goodyear entering the bicycle tire market. We’d like to talk to Compass as one of the established smaller brands in the high-end tire market.”

In the article, Wiebe explains how Goodyear is proud to offer 100 SKUs (Stock Keeping Units), while Pirelli plans to expand into gravel tires, quoting their head of sales: “Gravel is growing in Europe, and I think it will quickly be a big part of the road market.”

Matt Wiebe contrasts this with Compass, explaining how our program “grew out of the tires we needed to do the type of riding we liked — long rides in the mountains on road and dirt surfaces.” The article shows how the industry is trying to catch up with the trend toward high-performance tires – a trend that caught them by surprise because it originated with riders and not with the industry.

Global Cycling Network has brought the latest research about tires into the mainstream. In a recent segment, they looked at why you need lower pressures to make wider tires perform better. They talk about suspension losses – crediting Bicycle Quarterly (Thank you!) – and test different tire pressures on cobbles. No surprise: When the going gets really rough, the lowest pressures roll fastest.

Earlier, GCN took three bikes to the same cobbles: a racing, a cyclocross and a mountain bike (below).

Again, readers of BQ and of this blog will not be surprised: The bike with the widest tires was fastest. In GCN‘s test, it was the mountain bike, even though the data showed a lower power output when the riders were on the mountain bike. The explanation is simple: The lower suspension losses more than made up for the mtb’s wider Q factor, lack of ‘planing,’ etc., that limited the tester’s power output.

Now imagine if GCN had tested a true allroad bike instead of the mountain bike! A bike like my Firefly (above), which enables the rider to put out the same power as on their racing bike and which has tires as wide as their mountain bike, plus its more supple tires reduce rolling resistance and suspension losses even further. From our own on-the-road experiences, we know that it would easily outperform the mountain bike. Perhaps we’ll see that test in a future episode – for now, GCN already is pushing the limits of what a mainstream cycling audience finds believable…

With all this exposure, it’s nice to see that many of the ideas we’ve championed over the last 15 years are getting widely accepted. Click on the images above to read the full stories!

Posted in Uncategorized | 22 Comments