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:

Aerodynamics

Bicycle Quarterly did extensive wind tunnel research on the aerodynamics of real-world bicycles. Among things like riding position, clothing and bags, we tested the aerodynamics of fenders. We made a telescoping front fender, which allowed us to test various configurations. Here is what we found:

  • The portion of the fender in front of the fork crown reduces the drag. This is because the tire rotates at twice the speed of the bike, and the fender acts as a fairing that shields it. This works only if the fender extends beyond the top of the tire and drops down in front. (We found that it’s not necessary to extend the fender as far as shown in the photo above.)
  • The portion behind the fork crown adds a little drag. So does a mudflap.
  • The overall effect of the full fender and (small) mudflap neither increases nor decreases the wind resistance of the bike.

If this comes as a surprise, check out modern Moto GP racing motorcycles (below). They all have fenders covering the forward-facing portions of their tires to improve their aerodynamics. Bicycle racing specifically prohibits fairings, otherwise we might see similar fenders in the Tour de France

Weight

What about the added weight of the fenders? The best fenders don’t weigh much: Honjo aluminum fenders provide generous coverage, yet they weigh between 423 and 540 g, depending on the width, including all the hardware to attach them. That is roughly the weight of half a bottle of water. The increased versatility of having fenders on your bike is well worth the extra weight – just like a water bottle will slow you down, but you still carry one.

Plastic fenders weigh more – they are more flexible, so they need heavier stays made from steel, whereas the stiffer Honjo fenders use lightweight aluminum stays. Weight-wise, the worst are aluminum fenders with heavy stays designed for plastic fenders – the Planet Bike Cascadia ALX fenders weigh 50% more than their Honjo equivalents, despite offering less coverage.

Reasons not to Use Fenders

There were other reasons why I used to take my fenders off the bike every spring. The plastic fenders I used back then resonated on rough roads. They tended to rub on the tires. The gaps around the tires were uneven, making the fenders look like an afterthought. And every few thousand miles, the rear fender broke and needed replacement. During the summer months, I wanted to enjoy a quiet, smooth and sleek-looking bike. And if that meant getting soaked during the occasional downpour, it seemed worth the trade-off.

With a bike that is designed from the get-go for fenders, like the J. P. Weigle from the Concours de Machines (above), those drawbacks no longer exist. The metal fenders are stiff, so they are quiet. The bike is designed with sufficient clearances, so the tire never rubs on the fender. The fenders follow the outlines of the tires, so they enhance the appearance of the bike. And since the fenders are securely mounted without stresses, they will last as long as the bike. (And the whole bike weighs just 9.1 kg/20.0 lb, so the weight isn’t an issue, either.)

There are some conditions where bikes without fenders work better: deep mud and snow – the same conditions that call for knobby tires. For all other rides, I prefer a bike with fenders, because it gives me the option of heading out even when the weather forecast is uncertain. And I am glad to know now that the fenders won’t slow me down.

Further reading:

Photo credits: Maindru (Photo 1), Alex Wetmore (Photo 2), Motoracereports (Photo 3), Nicolas Joly (Photo 4), Mariposa Bicycles/Walter Lai (@onlywalt, Photo 5).

About Jan Heine, Editor, Bicycle Quarterly

Spirited rides that zig-zag across mountain ranges. Bicycle Quarterly magazine and its sister company, Compass Cycles, that turns our research into high-performance components for real-world riders.
This entry was posted in Bicycle Quarterly Back Issues, Testing and Tech. Bookmark the permalink.

64 Responses to Myth 3: Fenders Slow You Down

  1. sisyphus says:

    What did your testing reveal about rear fender aerodynamics?

    • We didn’t test rear fenders due to time constraints. Wind tunnel time is very precious – it usually costs $ 500/hour – and testing multiple times to weed out errors takes time. (We spent two full days in the wind tunnel.)

      It is likely that a rear fenders acts like a front one: The front portion shields the tire, the rear adds a little drag, the result is probably slightly positive or neutral. Look at the photo of the racing motorbike – it has a rear ‘fender’ shielding the front part of the wheel.

  2. Rui says:

    How much cleareance do you have on the Weigle?

  3. Steve says:

    Hi

    I think you have mentioned previously that you prefer riding out of the saddle on a bike without fenders? Is that right?

    Steve

    • This applies only to a racing bike without any bags on it – then it feels subtly different, because it’s easier to rock from side to side. On a fast-paced ride where I sprint out of the saddle, I prefer a fender-less bike.

      When I am riding long distances, it makes little difference. And when there is any chance of rain, it’ll be my bike with fenders! And on a bikepacking bike that is loaded with gear placed high up on the frame, you won’t notice the fenders at all.

  4. Preston R Grant says:

    Since 2010, my wife and I have been doing rides in the Pyrenees, Alps, Dolomites, and Corsica, a total of nine rides, ranging from five to nine days. It always rains at least one day, no exceptions. Other riders in our group all ride fenderless, and have been highly upset when it rains, even panic stricken, but my wife and I have remained comfortable and content. One very rainy day in the French Alps, my wife rode 40 miles in heavy rain on a bike with fenders and a mud flap. Her comment afterward: “Honey, my feet did not even get wet”. And that was without rain boots.

    • I don’t use rain booties any longer, either, because with good fenders, there is close to zero spray reaching my feet. I need to get another lightweight pair, though, to block the wind during night-time mountain descents in sub-freezing weather.

  5. larryatcycleitalia says:

    Your myth-busting is great! I’ve never been much of a fan of non-ferrous frames, rode on wide tires before they were fashionable and never noticed any speed difference riding a bike with fenders. But of course all that was just my subjective opinion – until you began to bust these myths via real research and testing. Grazie!

  6. Jacob Musha says:

    Properly mounted, plastic fenders can work as well as aluminum. The cheapest Planet Bike fenders are actually the best – they use a single set of steel stays that make them just as stiff as my aluminum fenders. I’ve ridden them for many years and many thousands of miles without ever breaking one. They don’t rattle or cause any problems. The only downside is that two pairs must be purchased, so a rear fender can be used on both ends to provide proper coverage. But at $30 a pair they are still less expensive than most other fenders.

    The major advantage of plastic fenders is that they can be easily cut, trimmed, and modified to fit most bikes. I wish all my bikes could be built around custom frames that are designed for mounting aluminum fenders, but that’s simply not realistic for me or most people.

    • I’m glad those single-stay plastic fenders work for you. My experience: I think it was one of those fenders that I had on a bike I borrowed once. I took off the front fender because it oscillated so much that it touched the tire when riding at high speeds. It was raining, but I prefer to get wet over having an accident…

      • Jacob Musha says:

        Jan, I suspect you’re referring to Alex Wetmore’s “Travel Gifford” as shown here: https://janheine.wordpress.com/2015/04/04/the-enduro-allroad-bike/

        That’s how most plastic fenders are setup: two sets of stays with clamps at the fender. It’s a poor design because they are heavier (twice as many stays!) yet not as stiff, because the stays end at the clamps. (Plus, they look cluttered and the pointy ends of the stays tend to snag on things.)

        The Planet Bike fenders I use have a single stay that wraps around the fender in one continuous loop, the same as any good aluminum fender. They function much better than the fenders you experienced.

        Quality aluminum fenders are certainly lighter and better, but the basic single-stay plastic ones are an acceptable substitution if cost or unusual frame/fork mounting is an issue.

      • I don’t recall which model was on the front of the bike… I appreciate that more and more builders now use a second fender stay in front of the fork crown to stabilize the fender when not using a rack equipped with a braze-on for that purpose. Mounting the fender well eliminates 95% of fender noise and trouble.

    • Rick Thompson says:

      If cost is the issue but you need two pair of the Planet Bike fenders at $30/pair then Velo Orange aluminum fenders at $65 – $67 are not much more. (Just don’t use their leather washers….)

    • Francesco Nardone says:

      Came here to say this. Never had durability or noise problems with SKS even after years of abuse in city racks. Plastic just bounces back even after rather severe whacks.
      They do not make long enough front fenders thou.

      • I am glad your fenders work well for you! When I used SKS fenders, they lasted at most two winters. It seems that the faster you ride, the more they vibrate. And of course, every bike is different. On some, you can install them without inbuilt stresses, and they last a long time. On others, you have to pull them into shape, and then they won’t last. I thought about heating the fenders after installation to stress-relieve them, but instead went to aluminum fenders that are easy to shape, keep the water inside better and don’t resonate even on rough roads.

  7. Dr J says:

    One more situation where bike fenders generally suck is when you have to disassemble your bike for transport. I know you have your Rinko solution but it still isn’t pretty and not best for all situations (e.g. you don’t remove front fender or wheel – you rely on removing the entire fork).

    Ideally, for transport (not just on train but also on top of you car’s roof) you would want to pop fenders out and then later put them back in without using any tools. I haven’t seen such system yet.

    In general, I think the reason we don’t see fenders being better integrated with modern bikes is that it’s hard to do to make them look like a native part of the bike. Bikes have lots of empty spaces so you can’t hide fenders in any way. Unless fairings become more common, I don’t see easy way around it.

    • You raise an interesting point. Cyfac presented a bike at the Concours de Machines with carbon fenders that came off without tools. Regarding the Rinko solution, it’s almost invisible – the rear fender of the J. P. Weigle above splits in two for transport, and at the front, it’s far easier to remove the fork to reduce the size of the bike than to remove fender and rack. Below is my Mule, which disassembles the same way.
      Rinko bike disassembled for travel

      • Kirt says:

        From a size perspective, would this fit into the S and S (coupler) suitcase?

      • Probably not. It’s a little bigger than that. Easy to check – if the bare frame fits in the box with a little room to spare, then it will work. The neat thing about Rinko is that the bike is reduced to the size of the frame, yet there is only very little disassembly necessary. The whole process takes under 10 minutes.

  8. Scott Bontz says:

    You say, “We found that it’s not necessary to extend the fender as far as shown in the photo above.” But you don’t say at what point the fairing effect ceases. That would be helpful. Can you give it to us, in, say, degrees from vertical? Also, the fenders in the wind tunnel photo appear nicely matched to tire width. But fenders come in cruder width increments that do tires. If the gap between fender and tire width were greater than in your test, I wonder if you’d find greater drag with the fender. Did you try this? If not, I’d be skeptical about generalizing that fenders don’t increase wind resistance. Can you tell us the width of the tires and fenders in the photo or test(s)? Thanks.

    • You are right, poorly mounted fenders that stick high into the air in front of the fork crown don’t act as fairings. We tested just the front section of a plastic fender that did this, rather than come down in front of the ‘top’ of the tire. The aero benefit went away, but even then, it didn’t add drag, probably since the fender remained within the outline of the bike. (Frontal area, more than anything else, determines the wind resistance of the bike.)

      I suspect that for best aero, you want the closest clearance between fender and tire, but you have to weigh very minor aero benefits with the risk of debris going into the fender and causing an accident. The fender on our test bike was about 15 above the tire.

      Fenders generally should be about 35-40% wider than the tires to provide good coverage and prevent spray from exiting on the sides. The wind tunnel tests were done with 31 mm tires and 43 mm fenders. Honjo fenders come in multiple widths to match a variety of tires. For more details about the testing, check out the original data in the Bicycle Quarterly back issue mentioned under ‘Further reading’ above.

  9. Rick Thompson says:

    The Fitz is my first bike with full fenders, and I’m convinced. The fenders and wide tires do not slow the bike any perceptible amount.
    Even on mostly dry pavement it’s really nice keeping road grime off the bike, the brake mechanisms stay clean.
    Compass does not offer a Honjo fender to fit the Snoqualmie Pass tires, so I have VO Zeppelins. I have to say these are well made, nice fenders.
    Leather washers are trad mounting, but I found the VO ones crushed if screws were tightened much, did not seem very secure. I tried some washers I’ve used in boatbuilding called sealing washers, they are cupped stainless with bonded neoprene. One on each side of the fender holds it between 1/2″ diameter rubber support, very low stress on the thin aluminum and very quiet while riding. Picture here: https://www.flickr.com/photos/ricks_boats/39227281931/in/dateposted-public/

    • I recall a set of those VO leather washers – the leather was much too soft. You need a relatively hard leather to make these washers – check out the ones we sell. Of course, your solutions works as well – it’s basically an updated version of the leather washers that were used in this application not just on bikes, but also cars.

  10. morlamweb says:

    I last rode a fenderless bike about 5 years ago, on the occasion of my first rainy ride home after committing to bike-to-work on a daily basis. Soaked to my bones, I stopped at the bike shop even before going home, and they fitted my bike with it’s first set of fenders. I didn’t know of BQ at the time, and the thought of losing some top speed due to the fenders never even crossed my mind. I just wanted to stay dry on my commutes.

    The first set was a set of plastic fenders, and they were better than nothing, but I wasn’t satisfied with their performance. They didn’t extend far enough past the crown to prevent sprayback, and the fender attachments – which were designed to detach in the event of a logjam, eventually worked themselves so loose that running over a pothole would cause them to break free and flap against the tires. They would also twist themselves laterally, so they would follow the line of the bike. The bottom of the front fender, for example, would be lined up with the tire, but the top would be pointing off to the side.

    I saw the same twisting issue with the other sets of plastic fenders that I tried. I worked through three sets in total, increasing in width along with my tires, and my knowledge of tires (aided by BQ). I have now a set of aluminu(i)m fenders and they’ve been on the bike 24/7 for a couple of years. I haven’t seen that twisting issue with them. I’m considering an upgrade to Honjo fenders for the greater coverage.

    Nowadays, I can’t imagine riding my bike without fenders. Sure, they could rattle – that happens for me a couple of times a year when the bolts work loose – but they stay on because the weather is unpredictable. I’ve had many days that started off dry but turned into a thunderstorm for the evening ride home. I’d have been soaked if I had taken off the fenders on those days. That’s more than enough reason for me to keep them on all the time. It is great to know that they don’t hold me back. Thanks, Jan.

  11. marmotte27 says:

    Another reason to ride with fenders always is leather saddles. You can’t really use them on bikes without fenders.

  12. Smithy says:

    In the past 48hrs I have had 2 stay and mudguard-bending interactions with sticks, one of them cataclysmic (destroyed the rear alum. mudguard) . Plenty of clearance ( >20mm). Small twigs & grass stalks are commonly getting caught in the gap but I put up with them for the utility and aesthetics . Bad karma? perhaps but I’ll be going back to my former practice -riding without mudguards until winter.

    • That sounds like either really bad luck or you ride through stuff where fenders really are a hazard. I’ve yet to have a problem with my fenders, despite riding more than 100,000 miles on bikes with fenders… Generally, the wider and deeper the fender, the stiffer and thus less likely to collapse.

    • Francesco Nardone says:

      You may want to try safety stay mounts (oddly found only on plastics). They disengage the stay before the fender is forced onto the tyre. There’s unfortunately a lot of bad ones out there that come out if one rides on bumpy roads.

  13. Francisco says:

    A datapoint regarding fender weight: a pair of long carbon 40mm Swarf fenders /700c) with Gilles Bertoud aluminium stays ended up at 310 g including all hardware.This type of fender does not have rolled edges, however, and is thus a bit less effective regarding spray.

  14. john hawrylak says:

    You stated:
    “This works only if the fender extends beyond the top of the tire and drops down in front. (We found that it’s not necessary to extend the fender as far as shown in the photo above.)”

    How far down is required to reach this point??? Degrees from vertical would help.

    This was asked earlier, along with multiple questions

  15. Fenders are desirable even on dry days or a very simple reason: there’s always the chance of a small pond of filthy water, especially in the city.

    • morlamweb says:

      Fenders also protect the rider and the frame from dirt, dust, sand, etc. kicked up by the tires on dry days. I’m reminded of this advantage whenever I ride on the stone-dust paths near me in warm weather.

  16. Rick Harker says:

    I remember reading UCI rules from the past that fenders were banned as they were an aerodynamic advantage.

  17. Pete says:

    Hope you tested those pants in the wind tunnel!

    • 😉 My normal tights wore out the day before the wind tunnel test. I grabbed these, which I had made during the days when fade paintjobs were still fashionable. I thought I’d need them only for warmups, but the wind tunnel is cold. I am glad they amused you!

  18. I’ve been a bit put off with the performance of my Berthoud 60mm fenders, my feet get wet when it rains, there’s a lot of spray coming out of the edges. I’m using Rat Trap Pass tires on this bike, but on relatively narrow rims (Mavic XM719) so they must be on the 50mm range.
    Do you think that the shallow profile of the Berthouds contributes to the lack of coverage? I’ve seen that all your bikes have quite deep “domed” profile.
    Taking into account the limits of the clearances in a road bike, 650bx42 has proven to be the perfect wheel size for a randonneur bike.

    • It’s hard to do fenders for 54 mm-wide tires, at least with road cranks, because the chain will touch a fender wider than 62 mm when it’s in the smallest gear. So it’ll always be a compromise. Yes, the domed shape keeps more water inside, but width is as important. The Specialized Diverge had narrow fenders (compared to the tires), and when we rode over some wet gravel roads, the bike was covered in mud, where my riding partners’ bikes remained clean.

      Taking into account the limits of the clearances in a road bike, 650bx42 has proven to be the perfect wheel size for a randonneur bike.

      I agree.

      • Rick Thompson says:

        700cx44 is pretty good too, better match to a big frame in appearance at least. Now that supple tires are available from Compass I’m not sure that 700c is not just as viable as 650b. Your last test showed that light rims might actually be better in the bigger diameter.

      • Agreed – with carbon rims, disc brakes and lightweight tires, 700C is a better choice up to 44 mm – except for the difficulty to fit the big wheels into a frame that also accepts fenders. And if you are running discs anyhow (and no fenders), why not go to 48 mm – at which point 650B is better to keep the handling nimble.

      • Conrad says:

        For that reason I decided to put SKS fenders on my bike with Rat Traps. They come with a cutout where the the chain otherwise rub the fender. The terrain where that bike is ridden (roads that may devolve into a rough neglected trail) pose increased hazards to the fender in the way of crashing or debris caught in the fender. One hates to wreck Honjo fenders. I wont lose any sleep if I wreck the SKS fenders but so far it hasnt happened. Also, my biggest problem with SKS fenders is the sliding bracket that mounts to the seatstay bridge. Always loosens and breaks. If there is a threaded boss perpendicular to the tire (as there should be!) and you can properly mount the fender- even plastic fenders last a long time.

  19. William says:

    Could you please explain the statement that the tyre rotates at twice the speed of the bike as I’m obviously missing something.If a tyre rotates 50 cm the bike moves 50 cm in the same time no?

    • It may work best to look at the wheel as a lever. The bottom of the tire touches the ground. It doesn’t move at all, otherwise, you’d be skidding. The hub moves at the speed of the bike, since it’s connected to the frame. The top of the tire is at twice the distance from the ground compared to the hub, so it rotates at twice the speed. So if you roll at 50 km/h, the bottom of the tire moves at 0 compared to the surrounding air, while the top moves at 100 km/h.

      To visualize this more, think about rubbing your tire to clear off debris. You are moving, yet the tire moves under your hand. Clearly, it’s faster than you and the bike.

  20. Piaw Na says:

    My biggest issue with fenders for mixed riding is stones/gravel/etc getting thrown up and scraping between the tire and fender. It’s an annoying noise. Good thing I live in California and get away with not needing fenders most of the time.

    • Yes – that ‘scrrrrtch’ sound is annoying and potentially dangerous (fender collapse). The solution is not something you can retrofit – you need about 20 mm of clearance between tire and fender. Only small stones stick to the tire enough to go up into the fender – if the clearance is enough, then they will go through without you ever noticing. These days, I hear the scraping sounds once every few hundred miles. I wish every builder/maker would space their bridges to provide sufficient clearance on bikes intended for fenders.

      • Rick Thompson says:

        My bike has 17 mm clearance, but the fender stay eyebolts take up 5-6 mm of that. It’s not happened, but I’m concerned that something could jam on the internal exposed stud and nut. Sure would like to see a stay design that only has a low profile, rounded screw head as internal mounting.

      • We made our own, shorter “classic” eyebolts for the fender stays, which come with locknuts that also don’t build tall. So you gain a few millimeters. (We also sell the eyebolts separately.) The alternative is to use a set of Berthoud stays and rivet them to the fender. We’ll offer Berthoud stays soon.

        It seems that the biggest issue is at the top of the tire, not so much on the shoulders. That is one more reason to use two eyebolts to attach the fender stays (the other being that this makes for a stiffer connection, which prevents the fender from vibrating or breaking).

  21. Mark c. says:

    Zip ties can be used on some fenders to attach fender to frame. I did that when I misplaced the mounting hardware.

    • Sam Atkinson says:

      Some fenders actually come with zip ties, and I think it’s for geometry reasons. In particular, there are some bikes where the chainstay bridge is positioned such that a fender will interfere with the front derailleur if it is bolted to the bridge. But if you zip-tie the fender to the bridge so that it sits a little away from it, you can sometimes get things to “fit”, and without needing to mess around with spacers; just use the zip tie to set the distance between fender and bridge!

      It’s definitely a bodge, but it can work.

      • It’s definitely a bodge

        When riding fast on rough roads, I’ve found that the zip ties don’t last long, and a fender that is flopping around is a big safety risk. (Never attach the fender to the fork crown with a zip tie!) So I wouldn’t recommend using zip ties for mounting fenders. They are fine for lighting wires and other non-stressed parts that you just want to hold in place.

  22. Mark c. says:

    If you look at old photos of the Tour de France or other racers, you rarely see fenders, but I do see a really small front fender used by some riders around the 1920’s from what I can see. The tire clearance was really tight too. Racers probably wanted to save weight, so fenders got associated with slow commuter bikes? I know when I raced, fenders were considered heavy and not cool.

  23. “Sure would like to see a stay design that only has a low profile, rounded screw head as internal mounting.”

    There are a couple of easy solutions for this:

    The first is that you can use the Gilles Berthoud stays and reverse the mounting screws, so instead of putting the nut on the inside you put it on the outside, and just have a small button headed screw on the inside.

    It doesn’t look as nice for sure but it does gain you a few mm and the dome heads are less likely to snag things. I guess you could also use button headed nuts on the outside, might look a bit neater!

    The second is using R-clips instead of eyebolts. The same kind of R-clips you use at the frame/fork end to anchor stays. You can slide one (or two) up the stays and use them as the mounting on the fender, as above, small button head screw from the inside and bolt on the outside.

    The second option is a bit cheaper as R-clips are chap, you can use your existing stays, and probably re-use the existing holes too. using the GB stays you obviously have to buy them, and then normally drill a couple of new holes in your fender.

    • marmotte27 says:

      I shortened the screws and filed down stainless steel nuts for the inside. For the other screws I replaced the Allen screws with normal bolts (changing to stainless steel at the same time and filed their heads to 2.5mms.

  24. Julio C. says:

    I have used both metal and SKS chromoplastic mudguards. As you surely know, Chromoplastics are made of aluminium sandwiched between plastic. To me the Chromoplastic are far better. They are cheaper, easier to set up, quieter, and safer (they have safety clips on the front wich I have not seen in any of the metal mudguards). They do not move or rattle at all and have lasted for several thousand kms on- and off-road. What I find most annoying of the metal ones is the noise, the sheet metal is, in effect, like a drum sounding with every little stone thrown by the tyre.
    As for your claim that plastic ones do not follow the contour of the tyre, being plastic, metal or whatever is no reason for that. Being cheap and nasty surely is. This statement and the claim that they rattled and did not last makes me think you had “el cheapo” plastic mudguards. I dare to suggest you try the Chromoplastics, they are excellent.

    • When I used plastic fenders in the past, they were SKS. They were the best ones we could get back then!

      Metal fenders come in all kinds of qualities, too. The biggest issue with metal fenders is that to mount them securely, the bike needs to be set up for fenders with bridges spaced correctly and threaded for direct mounting. The installation also takes more time, but then the fenders last as long as the bike.

      As to reshaping the fender to follow the outline of the wheel, that actually is quite easy with aluminum fenders. You squeeze them to make the radius larger, or pull the edges apart to make the radius smaller. Plastic fenders tend to spring back to their original shape, for better or worse.

  25. Samuli says:

    Here’s a computer model comparison someone called Richard Smith made of the same subject, that says fenders do add some drag. Though that’s without a fork or frame or handlebar bag. http://www.symscape.com/blog/bicycle-wheel-and-fender-aerodynamics

    • Interesting! However, all models must be validated in the real world. Since the model doesn’t match the wind tunnel tests, we have to reject the model (unless we can find some major flaw with the wind tunnel tests). I am fairly confident in the wind tunnel data, since we did so many runs with different fender configurations, even testing two different tire widths (25 and 31 mm).

      • Samuli says:

        Indeed.
        Did you use the handlebar bag on all of the runs? Might not really matter, but it might be directing more air towards the top of the tire/fender. Which could mean that the bag and fender even out the air flow together, but only one of them would be less aero than having no fenders or bag.

        There’s also been this aero fender/fairing prototype, https://www.bikerumor.com/2015/09/02/eb15-birzman-guards-against-spray-with-worlds-most-aero-fender/

      • Initially, we didn’t use a handlebar bag when we tested the fenders, as we tried to isolate the factors. Then we tested the ‘most aero’ setup, including the bag. As you mention, the interplay between the various elements is important.

        As to the fender/fairing, it’s an interesting idea – but I wonder whether it’s really more efficient than just a standard fender. I had to laugh at the introduction of the bikerumor article that says: “As soon as you slap a fender onto your bike, the aerodynamics take a huge hit.” It’s one of those myths we all used to believe – in bikerumor’s case, they apparently still believe it.

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