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Quite a lot of the design inspiration comes from top riders and their coaches - the level of technical knowledge they have is astonishing. We work with bikes like these, covering them with sensors and loadcells (we've had something like 20 ARM processors on a bike at a time, communicating wirelessly), and while the bike is part of the equation most of the drag comes from the rider's body. So a lot of effort also goes into comfort and fit, in order to get the rider into an aero position that they can hold for a period of time (the most aero position may not be possible to hold for very long) so it rapidly becomes an area-under-the-curve thing. We spend a lot of time in the lab, in wind tunnels and in velodromes sorting it all out (now with AI, vision systems, rider position tracking - it's getting really complicated).

Also these bikes are not generally roadworthy - every so often we hear a multi-thousand-dollar 'crack!' indicating another frame has had enough.

Thanks for this comment. For anyone interested in hearing more -- from road/track cyclists who can't use non-UCI compliant equipment -- I highly recommend searching Youtube for content featuring Dan Bigham. He owned the hour record briefly (about a year) until it was broken by Filippo Ganna (late 2022). They're two very different body types and because Dan is the aero & performance engineer working for INEOS (Ganna's pro team), he helped design and optimize the same frame (Pinarello Bolide) to work with a far different rider in a different position. As zh3 notes, the rider & their position has more to do with aero optimization than the frame, and it's interesting to hear someone like Dan talk about how the setup he used for his hour record attempt was so different from Ganna's.

Here are a few links to get started:

https://www.youtube.com/watch?v=YOLlyKnMz3Y

https://www.youtube.com/watch?v=QweOJXRcb0g

https://www.youtube.com/watch?v=WHc52cGz4AA

https://www.youtube.com/watch?v=cgpywSW6t0M

https://www.youtube.com/watch?v=qKT9DsRtuCc

Lionel Sanders (Canadian Triathlete) doing aero testing on the road and the velodrome:

https://www.youtube.com/watch?v=6u_Tw3S8KWA

https://www.youtube.com/watch?v=O6sqOX1nUIU

On the road, he was able to reduce his drag coefficient by lowering his hands/arms - (0.23 to just under 0.20), but on the velodrome, he wasn't able to reproduce the improvement despite several variations in hand/body position.

In the first video, the testing expert mentions that cycling pros would be in the range 0.16 to 0.18 (smaller/lighter cyclists had the lower coefficients).

Dan's name does indeed come up a lot in our circles :) Thanks for the links, even being in the biz there's always more to learn.

Funny, the last time I read an article about bicycles here, a writer was getting dragged for trying to explain that same point. https://news.ycombinator.com/item?id=39181473

The bikes this post is talking about and the bikes that post is talking about have basically nothing in common. Mass market carbon bikes aren't designed to be used for exactly one race and then thrown away in the way that tri bikes sometimes are.

No tri bike is designed to be used just once in a race. Not even the GOAT ever used single-use frames. A frame is ridden for a season - unless it breaks.

The point that the racing bike is more likely to have a failure during use? The difference seems to be suggesting people not have a toy they want vs. only explaining that there is a serious drawback.

Occasionally something happens that makes the attitude really stand out. I once saw an actual electrician tell someone their 3D printed light switch cover was an accelerant. He suggested they re-do one to attach on top of a standard flame-retardant cover. There were like half a dozen "nuh-uh" comments from people who felt attacked by that.

There's a pretty big gap between the bikes in this post and the kind of carbon road bike most people ride eg, a Giant Defy

> while the bike is part of the equation most of the drag comes from the rider's body

So the real solution is to mod the rider?

To a large extent, yes. Head position (varies with helmet), back curve, hand and arm positions etc. We measure the number of watts saved by various combinations of rider position/rider equipment (helmets/skinsuits etc) in real time and pop the number up on the on-bike screen in real time. Currently moving to doing this out on the road (following validation on indoor velodromes and wind tunnels), kind of fun being able to see this position saves 10 watts, that one saves 15 watts but is too uncomfortable to hold for long etc.

There are been a lot of fuss about that in the UK time trial scene with rider mounting 3d printed parts behind their arms and calves to lower their drag.

It's a great time for experimentation (outside the UCI straitjacket) to see what works; there's scope for lone inventors (harking back to Obree) to figure out what works, perhaps not so equally there are people designing stuff on intuition ("looks fast") but unable to practically measure the difference. Sounds like you're up on this, stuff like VE, Chung, DFDM etc as ways to meaningfully measure the effect of the many ways to improve bike aero.

The biggest gain of TT/Triathlon bikes is moving your position from an upright seated position to a lower and narrower position, so "modding" the rider ;-)

After that, skinsuits, helmets and overshoes are usually the best bang-for-your-buck (in no particular order) in terms of aero gains.

I love blowing past other riders who have spent ridiculous sums on their bikes optimizing for weight with carbon and titanium setups when they could have had better performance by just eating better and losing a few more pounds. Beyond a minimal threshold, it's not the machine, it's the motor that counts.

And someone who rides professionally would blow past you on a rusty huffy.

And someome who rides professionally AND is on a proper well fit TT bike will blow past all of you.

Sure, somebody did 28mph on a dollar store bike in a recent Ironman. I don't think this is an arguable point.

Yes but there are lots of rules about that too, and lots of workarounds to those rules, of varying ethical dubiousness.

...hence aero helmets, socks, leg shaving....so, yes.

Oh I was more thinking of surgical modding. Guess leg shaving is the first step :)

If racing frames didn't break from extended use, then they could be lighter. You want them to be just barely strong/stiff enough.

Anybody can build a bridge that works - it takes an engineer to build a bridge that barely works.

So you're saying real engineers are all playing polybridge. Sounds about right.

The racing frames here don't break as a rule as OP suggests, if one does there was a manufacturing flaw or a crash/impact of some kind.

A few grams of weight does not have enough impact TT bike performance enough to make it worth shaving 100 grams if it risks reliability.

The immediate question is: if they are more efficient, why aren't all disciplines using these?

The article doesn't say! It suggests in passing that Triathlon has different rules because it doesn't allow "drafting" (Which I'm guessing is something related to team-riding to reduce air resistance, but the article doesn't explain what it is). Are there any rules prescribing (say) that a tour de France bike must use a normal (double triangle) design? Or is that just used because a traditional frame is optimal for weight rather than aerodynamics?

>Are there any rules prescribing (say) that a tour de France bike must use a normal (double triangle) design?

Yes. The UCI is the international governing body for most forms of cycle sport. UCI regulation 1.3.020 states:

For road, track and for cyclo-cross competitions, the frame of the bicycle shall be of a traditional pattern, i.e. built around a main triangle.

A complex set of rules govern the permissible shape and construction of a bicycle used in UCI-sanctioned competition, similar to the rules governing Formula 1 or NASCAR. These rules are shaped by competing and often contrary aims of many stakeholders - to ensure safety, to maintain the traditional aesthetics of cycling, to allow fair competition for less well-funded nations and teams, to allow equipment manufacturers to showcase innovative new products etc. The design of a modern racing bicycle is guided as much by politics as engineering.

https://assets.ctfassets.net/761l7gh5x5an/wQympSG6EWlKq6o6HK...

https://assets.ctfassets.net/761l7gh5x5an/7s1ma6mVAVlFwi8rRg...

The article explicitly says that UCI banned NDD bikes. Given that the Tour de France is a UCI event the answer seems obvious.

The question I guess is: are UCI-governed events not using "NDD" bikes only because of regulations on what shape can be used, or is triathlon special in that it favors aerodynamics more than other events?

That is: if regulation was dropped, would pro cycling be filled with weird looking CF monocoque designs, or is the traditional design still optimal for some use cases (e.g. for weight and events with team ridning and lots of climbing)?

UCI has strict regulations on the geometry, weight and even ancillary equipment (think brakes, gear shifts) of bikes. I vaguely recall the minimum weight being something like 14.9 lbs, but this is likely incorrect. Point is, it's quite possible to make a bike that is lighter than this while still remaining safe for racing. I've heard of some using lead ballast to make weight. One advantage of this, though, is you can choose where to place the weight, such as in the bottom of the frame, near the crank, lowering center of gravity and helping stability a bit.

The regs do make for some funny situations though. Take a look at a pro peloton and look for the shortest rider, preferably someone close to 5 feet tall. Their bike will be comically oversized for them.

The UCI tends to be a fairly conservative organization that favors tradition over accepting the latest technology and design trends, especially with road racing. You're more likely to see new technology in non road disciplines such as cyclocross or mountain biking. Just see disc brakes only just getting into road racing in the past several years (I've not been following racing closely anymore, so not sure when).

> That is: if regulation was dropped, would pro cycling be filled with weird looking CF monocoque designs, or is the traditional design still optimal for some use cases (e.g. for weight and events with team ridning and lots of climbing)?

The original Lotus bike mentionned above was introduced and used in olympic events. Chris Boardman held for a long time the speed record in a grand tour time trial that he set with the original road Lotus Bike (the track version he used at Barcelona olympics predates it):

https://www.youtube.com/watch?v=OjJ60Kx2j8I

Also Miguel Indurain in the 90's used the "Espada" time trial pinarello bike and some of his rivals used also non diamond shaped carbon bikes.

If regulations were dropped they would race with egg shaped bicycles, because of aerodynamics. They are very fast. Google that term, lots of funny pictures. On climbs, I don't know how they perform. On descents, I have no idea about their safety.

Even without going to those extremes, they need a tradeoff bike between going fast on level roads, climbing, descending, replacing flat tires, overall weight, etc. So something like those NDD bikes with maybe a switch to more extreme shapes on long flat courses.

Really depends on what regulations remain. If you drop too many regulations,you could end up with recumbent bikes with aero fairings.

Beside the UCI ruining everything for almost every cycling sport, you can't even do a superman these days, there's also the NJS in Japan who do the same for track cycling in Japan. Which is a massive sport and betting market.

Btw, Graeme Obree is/was one of the most innovative cyclists, he came up with ideas the UCI didn't like at all. But he's such an outstanding personality and inspiration.

+1 for Obree - more people should know the history.

For those into cycling who don't already know them, the Obree book [0] and film [1] are worth the time.

[0] https://www.goodreads.com/book/show/231993.Flying_Scotsman_

[1] https://www.imdb.com/title/tt0472268/

NJS is intentionally heavily prescriptive since people bet on the outcomes of the keirin races. The racers even announce what tactics they'll use during the race so that gamblers can decide who to bet on.

I don't know anything about UCI but keirin is intentionally a very narrow and heavily restricted slice of sport cycling. I've never heard anyone who is into it have anything negative to say about NJS's equipment restrictions. It is like how even though riflery is a sport, archery still is too. The governing body of archery isn't doing something profane by restricting the technology of the sport, that restriction is the sport.

Agreed, Keirin (in my limited knowledge) aims to keep things pure in their particular area (making competition a level playing field). By comparison, the UCI wants to have control over a much wider part of cycling (and so want to rule over what innovations we can and can't have).

> Or is that just used because a traditional frame is optimal for weight rather than aerodynamics?

It's exactly this tradeoff.

Time trial bikes are generally optimized for aerodynamic efficiency since there generally isn't a lot of climbing they do.

Climbing bikes are generally optimized for weight - typically with more basic looking tubes.

And for many sections, riders pick a hybrid bicycle with some aero features, but also with an emphasis on light weight.

The tucked aero position is only allowed in time trials since it's unsafe when riding in a pack, so UCI compliant time trials bikes look pretty similar to triathlon bikes, just with the traditional double diamond frame design.

Basically there are a lot of reasons, but it all comes down to a small aerodynamic efficiency gain is no where near the sacrifice required in the other disciplines.

in other cycling disciplines the efficiency of a rider on a flat smooth road, in the wind (no drafting) without significant corners or descents (no technicality) matters far less, and/or how you get efficiency is different. In fact in other disciplines that situation basically doesn’t exist.

Keep in mind that for a lot of people, for a long time, the pinnacle of triathlon, and primarily how these bikes are marketed and designed, is around the Ironman World Championships in Kona. The 112 mile course only has 4500ft of elevation gain. That is very flat.

Additionally some top triathlon pros consider even themselves to be basically beginner level bike handlers compared to road bikers. Which is basically beginner level bike handling compared to mountain biking. Why can you win races and compete for world championships if you have such poor skills? Because in that discipline courses are designed such that one needs virtually no skill, and the bikes are thus not designed at all for handling.

Meanwhile in road bike racing, such as the Tour de France, riders can win races or stages due to their descending skills despite bike handling not being a top priority of the discipline (look at Tom Pidcocks performance vs Chris Froome on Alpe d’Huez in 2022). Also in road bike racing, protected riders are protected from the wind 99% of the time or more. It’s more important to be able to get close to the rider in front of you, and to still have control of your bike, than to be extremely aerodynamic yourself as most of those gains are lost in the draft. Especially true in the peloton, where riders frequently talk about the feeling of being “sucked along” and not having to pedal basically at all. It’s almost hard to believe, but it’s wild when you actually experience it.

In mountain biking for instance, control, grip, flexibility of body position etc is much more important than just outright aerodynamic efficiency. Rolling resistance too is a much bigger proportion of the energy lost than on smooth roads. Speeds are also naturally slower due to the fact that courses are not only off road, but often much steeper than what is typically found on road. Additionally aerodynamics matter little if you can’t complete the course without crashing/blowing up your bike. (See Peter Sagan at the Olympics where he DNFd.)

It does say the UCI banned NDD bikes in 1999.

Trick question, all tri bikes look weird.

First off, while the UCI specs don't apply to triathlon bikes, they still roughly have to. A lot of these bikes have aspects that once were legal by UCI rules at some point (although not sure about the "boom" bikes with no seat tube, but bikes like that were made by trek in the 1990s).

The UCI is kind of like the Navy: there's a right way to design a racing bike, a wrong way, and then there's the UCI way. It has conservatism and history to be concerned about (bike racing is pretty old in Europe), keeping costs down for the lower run of even UCI pro teams (the female UCI teams can't even field a TT bike for all their teammates in TTTs), and there are durability concerns so bikes don't break and cause crashes in pelotons and the like, because there are already plenty of crashes.

Triathlon isn't a big enough sport to have its own weird cogsets, wheel standards, etc, so they generally have to piggyback off what Shimano/SRAM/Campy make for the protour and general bike public.

Now, I will say that my P3C with a disc and a trispoke front looks like an amazingly awesome back back when I did serious triathlons. Before children.

Also, CFD will be what CFD is, the wind/fluid dynamics doesn't care about your superficial proclivities.

"NDD bikes were designed to be more aerodynamic by completely eliminating surface area."

Not sure nut they do not look like they are eliminating surface area. Not saying they are less aerodynamic.

Also, I raced road bikes in the late 80s. I am wondering how much these bikes weigh. Then light weight was what was sought after.

I used to do tri's 10 years ago. Was sorta into it. Friend was super into it.

Tri athletes are super into aerodynamics over weight (weight is still important but aerodynamics are more so IE disk wheel inserts etc etc). The reason being because the more effort you spend on the bike the more gassed you are on the run coming up after. (also see below there's no pelotons in tris/TT)

Because of the square law of wind resistance basically bike times haven't gotten faster but run times have because riders are conserving more energy while riding at the same speed because of efficiencies in the bike designs.

Also you are never allowed to draft in triathlons and must maintain a certain distance behind the rider in front of you unless you are passing on the side unlike

>Also, I raced road bikes in the late 80s. I am wondering how much these bikes weigh. Then light weight was what was sought after.

The focus on reducing weight has largely stopped in favour of optimizing for aerodynamics, which matters more in all instances except for climbing, essentially.

In fact, none of the bicycles in the world tour this year are at the weight limit specified by the UCI - they are all a bit above it for the sake of aerodynamics.

I imagine we're also at the point with these kinds of bikes where whatever marginal weight shaving you might achieve is lost in the noise of variation in rider weight?

I'm just speculating really though, I ride a Dawes tourer that's older than I am.

As I understand it, the major competitions all have a minimum allowable weight for the bike - 6.8 kilograms in UCI competitions - to avoid a costly arms race, or dangerously flimsy bikes.

And yes, a recreational rider doing a serious distance will often carry 1.5kg of water, so saving 150g with special lightweight paint or whatever is lost in the noise.

> And yes, a recreational rider doing a serious distance will often carry 1.5kg of water, so saving 150g with special lightweight paint or whatever is lost in the noise.

But a lighter bike is still a lighter bike. If everyone is carrying 1.5kg of water, then a 150g lighter bike still has as much of an advantage[1] as it always had.

[1] Likely unmeasurable. Yes, there's some sarcasm in my comment, but I hear this type of reasoning all the time, e.g. "people say they want thin phones, then put a case on them anyway, so what's the point?" The point is a thin phone plus a case is still thinner than a thick phone plus a case. Similarly, a light bike plus 1.5kg of water is still lighter than a heavy bike plus 1.5kg of water.

But it's deep in the noise, 150g is a tiny amount of difference in how much water you drank before you left that morning.

It's like when people say they 'lost half a pound', no, you just went to the loo. Or you had one less coffee today. It's not significant.

I made my bike as light as possible because I had to carry it up several flights of stairs to my apartment. Being lighter makes that easier and applies less friction to deciding whether or not to go out for a ride. (I live on the 1st floor now. So less of an issue.)

Most recreational riders should lose 10kg or more according to their doctor. However they will instead pay thousands of $$$ to save 150g.

To a point, weight is less of a concern in the modern era because aerodynamics dominate at almost all speeds.

I’ve always found NDD bikes interesting but I suspect the advantages are overstated given the top pros are moving away from them. LCB and Sam Laidlow both rode “classic” TT-style bikes to win the Ironman WC last year.

Yeah at the pro-ish level of triathlon, I think you need stiffness even in 112 mile bike legs. These aliens are doing 25-27mph, if you have the inevitable sway from the lack of the triangle, you'll lose power to the drivetrain.

The Pros might get to piggyback on some of the wind tunnel testers here or there for reasonable amounts, and the "NDD" bikes might not really stack up much in the "total system" aero testing.

One might think that ultraskinny 18mm tires would be more aero, but 1) they have bad rolling resistance and 2) they actually aren't, at least for a while the pro teams were using 25mm tires because aero testing said it was better + lower rolling resistance. Point is, aero is weird.

But I haven't followed the state of the art of the last three or four years.

Finally, modern tri bikes shape themselves for onboard nutrition transport and integrated fluids, sometimes in the tubes. They also have storage boxes for the flat kit. Ironman triathletes care a lot about that.

The article makes it seem like these are all fresh off the design board, but these have been around for, what 5-7 years now? I was kind of hoping for more designs in the article, but these are basically what was the cutting edge back then. I would hope the 10,000$ price tags would have come down, but I doubt it.

And the other laughable thing is the wheels in those bikes. Where are the disc wheels? A disc wheel is often more important than the frame and helmet.

It's funny. You spend 200$ for an aero helmet, that's 1/3 of the gain, another $2000 for aero wheels, that's 1/3 of the gain, and then 10,000$ for a frame, and that's the last 1/3 of the gain.

BTW. The lotus was my favorite bike ever. https://www.theproscloset.com/blogs/road-bikes/colby-pearces...

Totally agree on the Lotus. Although I prefer the original 108 design to the 110.

Seeing Chris Boardman win on it at the Barcelona Olympics was like seeing something arrive from another planet. It left quite an impression on a young me.

I know a bike shop owner with one of the road versions in his private collection. Seeing it up close is... like being near a religious relic. Yep I am a cycling nerd! :D

https://en.wikipedia.org/wiki/Lotus_108

Pro teams are going 28 mm or even 30 mm at the front and 32 mm at the back. Some measurements from Tour de France 2023 at [1]

One of the reasons why larger tires are better is that the size of the contact patch to the road depends only on the internal pressure of the tire. A 20 mm tire and a 40 mm tire have the same contact patch but their shape is different. The one of narrower tire is aligned back to front so the wheel is less round. The contact patch of the wider tire is aligned right to left, so the wheel is more round and it rolls more easily without dissipating energy in elastic deformations. You'd have to inflate the narrower tire to double pressure to compensate, but then the ride is less comfortable and you can double the pressure only up to a point.

That was about rolling resistance, then there is aero. Wind tunnel tests discovered that tires should connect smoothly to the profile of the rim without making the classic shape of everyday bike's wheel: a wide tire in narrow rim. They must have the same width instead and a fatter rim is more aerodynamic than a skinny one. Hence the drive to wider tires.

However there is catch. A wider tire adds more mass to wheels and they are the worst place to add mass to because it works against you every time you have to make that wheel spin faster. You add mass to the frame and all the static parts of the bicycle if you really have to. And finally a very large tire (100 mm or 4 inches) is obviously too wide to have a reasonable front surface at high speeds. The sweet spot nowadays seems to be around 30 mm. Note that UCI mandates cyclocross tires to be 33 mm max, and they must work in muddy conditions. Road bikes are at almost those widths.

[1] https://escapecollective.com/what-we-learned-by-measuring-ty...

> A wider tire adds more mass to wheels and they are the worst place to add mass to because it works against you every time you have to make that wheel spin faster.

If I recall correctly, this isn't a big deal because accelerating the rotating mass is assisted by the (equal) mass on the other side of the wheel, so adding weight doesn't really make any difference vs adding that same weight on the frame.

Where it can hurt is cornering. GCN did a video that suggested increasing width increases grip and cornering... to a point. Once you exceed that point, you spend more time moving the bike "over the tyre" and have a hard time cornering.

For the idealized mass entirely at the rim of a hoop, the effect is exactly 2x.

Kinetic energy is 1/2 mv^2, rotational is 1/2 Iw^2, where I = mr^2 and w=v/r. Make the substitutions and it reduces to mv^2

However, while it takes more energy to spin up the wheel, you get that back when slowing down (unless you hit the brakes).

It's also a pretty small effect, since the rim masses are only ~10% of a bike's mass, and 1% of the bike+rider mass.

> However, while it takes more energy to spin up the wheel, you get that back when slowing down (unless you hit the brakes).

That energy doesn't get back into the legs of the cyclist. So the bicycle with more mass in the rims might coast for a longer time but the cyclist gets tired sooner than the one with lighter rims.

You do get that energy back though, because you don’t slow down as much between pedal strokes with the same input power. Or you get a bit more up the next rise, or it burns off against the wind. But either way, it’s energy that is stored and returned, not lost.

You're right about the smaller slow down between strokes, I didn't think about it.

Anecdotally, I have a gravel bike with two different sets of wheels, 28 mm and 42 mm. I use the 28 mm for asphalt only rides, especially uphills, and the 42 mm for mixed terrain flat rides. The 28 mm feels immediately faster, it's like 3 or 4 km/h for free. On the same training circuit the average speed is higher. The only differences between the two sets are: 1) the weight of the tire and the inner tube because the rim and the rotors of the brakes are the same and 2) the 28 mm tire is smoother but the 42 mm is relatively smooth too.

BTW, I know that should use a wider rim for the 42 mm but the previous one broke right before one of the announced covid lockdowns and I got what I could find. We could cycle alone during the last lockdown and I didn't want to go asphalt only for a couple of months or so. I'll buy a wider rim next time.

So, I believe that the only difference between the wheels is the tires, but I'd say that there's probably more difference than the weight, and that would be rolling resistance.

I've got 3 bikes I ride -- a tandem w. 26"xwide supple road tires, a 12kg gravel bike running supple 650x48 (now, but have done 650x42 and 700x35, and the stock tires), and a 8kg carbon road bike running fair 700cx25.

I'm sold on big tires, because narrow/high pressure is too tiring.

Some anecdotal evidence:

The gravel bike shipped with the most horrible tires I've ever used, 38mm, 800g (each), felt like riding through deep sand. I used them for maybe 10 miles total till the good tires were delivered. It wasn't the weight, it was the super stiff sidewalls that just _sucked_ the energy out. I haven't noticed a major difference between the other three different tire sizes I've run on it, but they've all been running the same casing, Rene Herse ExtraLights (but the point of the light is that it's a super supple casing, so low rolling resistance. The 650x48mms are about a 400g tire).

Last summer, the gravel bike was out of commission for a week, so I did my hill workout (6x5 minute reps, + there and back) on it. Went back to the gravel bike the next week. ET difference between the two rides -- 10 seconds over 1.5 hours. Much less than the usual week to week variation on the same bike.

The tandem used to be on Schwable city 40mm tires, which are tough and durable. Went to RH 44mm in front and 53 in back, and average speeds over the next 6 rides went up by 1.5 mph (from ~16 to 17.5).

In short, I don't think weight is a predictor, but tire quality and rolling resistance is. High pressure leads to suspension losses as your body bounces and absorbs energy, stiff tires lead to hysterisis losses when rolling, low pressure, supple is both comfortable and low resistance.

That's probably the gyroscopic effect. The more massive the wheel is, the more it wants to keep going straight on. So the rim deforms the tire and the rim plus the tire and even the hub and the spokes resist cornering.

About the issue of mass on frame vs mass on wheels (most often on the rims) I found this article [1] where an engineer from Lotus states that "In the case of a wheel, because you have a lot of mass distributed around the rim, some distance from the centre of the wheel, that gives it inertia. [...] We can see that reducing the wheel inertia has a beneficial effect over reducing non-rotating mass, but it is very small. In reality, mass saved from the rims of wheels is likely to be less than 10% more beneficial than the same mass saved from the rest of the bike."

[1] https://www.cyclist.co.uk/in-depth/do-light-wheels-beat-a-li...

The weight-at-the-wheels is apparently the most apparent in the mountain climbs.

Lots of pros had specific clauses in their contracts to use certain ultralight rims regardless of the official team kit of the proteam.

Anecdotally, I think this is related to the inevitable far lower rpms climbing a hill and that highlights the uneven power output as a rider (even heavily trained pros don't output perfectly distributed power as they turn a crank). At the low RPMs and variant power highlighted combined with the unending pull of gravity, I guess there's lots of micro-accelerations of the wheel rims.

It is a big deal. Rotational inertia depends on the distribution of weight around the point of rotation (i.e. the wheel hub). The further the weight is from the hub, the more force is needed to accelerate the wheel.

> These aliens are doing 25-27mph, if you have the inevitable sway from the lack of the triangle, you'll lose power to the drivetrain.

I suspect they're actually really stiff because of the amount of carbon fibre in the construction. What I also suspect is the aerodynamic gains are being overstated in the real-world, which would explain why the pros are going for more standard bikes. The current brands (Canyon, Specialized, Argon-18, Cube) are probably close enough (or faster) in practice that the sponsor money is a better trade-off.

> And the other laughable thing is the wheels in those bikes. Where are the disc wheels? A disc wheel is often more important than the frame and helmet.

For performance, I 100% agree. That said, disc wheels from the big brands are expensive enough that $10,000 still doesn't cover it. And they probably don't want to put cheaper Chinese wheels on for image purposes (though owning an Elitewheels disc, I'd suspect they're in the same ballpark for aero performance).

> then 10,000$ for a frame, and that's the last 1/3 of the gain.

It's probably even less than that (going from one TT frame to another) but, hey, if it looks fast, isn't that the real victory? ;-)

> Yeah at the pro-ish level of triathlon, I think you need stiffness even in 112 mile bike legs.

meh it is not that simple.

Vibration loss and fatigue is something that is more and more studied these days in cycling. What is fastest in the first 10km might not be the fastest setup 3 hours later.

I would suggest they mean to say front-facing surface area, which this bikes would indeed achieve over a standard design bicycle. One post in front of another will likely have a bigger impact on aero than a single deeper post. Could be phrased for better clarity I guess, but in an aerodynamic mindset, I think it's sufficient.

I was also confused about the talk about surface area, its not clear what they mean by that here, nor how reducing it improves aero. Cross-section maybe? My expectation would be that true surface-area minimization would not result optimal aero, as it would be closer to just having circular tube construction?

Surface area, and cross section are different variables. They are not independent variables, but they refer to different parts of aerodynamics.

Surface area is a problem because of fiction of air rubbing on the surface. Cross section is a problem because you push the air aside.

You would use solid bar, and it would be exceptionally heavy.

Yeah my guess would also be that weight is the reason they fell out of favour. Aerodynamics are important, but weight is also, especially if you are outside and the route isn't perfectly flat.

They fell out of favour because the UCI doesn’t allow them in road TTs.

Now that doesn’t matter to pure triathlon bikes (as they’re not governed by the UCI) but it matters to the manufacturers accessing a much smaller sub-market.

It also matters to the customers who might want to also race UCI events or resell a bike.

Essentially double diamond designs are competitive enough now to make non-double diamond unviable.

These frames have to be exceptionally well engineered and built not to be death traps. Some people will be dumb enough to use these for touring, commuting and whatnot. Imagine you're coming down a long mountain road, hit some crack in the road, and the frame goes crack.

Carbon fiber is extremely durable when it is designed to be stressed in the directions it's designed for.

For instance if you eat shit and fall laterally the frame is likely to crack :).

When you invest in these kinds of bikes you end up having to get them x-rayed after accidents to verify they aren't having sub-surface cracks and are safe to ride.

Aluminum will also stress crack and just fracture.

Steel is dramatically more ductile and will most likely deform instead of catastrophically failing.

Steel also has lower embodied energy than aluminum, it's rather underrated.

That is true but aluminium requires less energy to recycle when you're finished with it.

I have bikes made of steel, aluminium and carbon fibre. I don't worry about the longevity of any of them.

Hydro-formed aluminium is cheap, relatively light and easy to live with IMHO. Horses for courses.

I also think geometry of a frame is far more important than frame material for things like comfort but that's a different story. i.e. how much can the seat post flex.

Steel is real!

Steel has a bad rap because cheap, bicycle-shaped objects sold in the consumer mass market are usually made of steel: both frame and often wheel rims too.

Like "Ozark Trail" bikes sold by Walmart, bikes for toddlers and what not.

These bikes are massively heavy and susceptible to rust.

> end up having to get them x-rayed

Maybe if you can find an X-ray lab that offers 2 for 1 coupons, you can get the bike imaged for free.

took me a second but that was hilarious.

Friend fell over at a red light from a stop (was clipped in on the pedal on the wrong side and fell over). Had to get frame x-rayed and it was cracked inside. He was fine of course...

Speaking of pedal contact, I learned to countersteer once upon a time and came to habitually use it all the time. I rarely take a turn without countersteering and often take sharp corners at speed. There have been a few times when I forgot to stop pedaling, just muscling my way through the curve because I'm so confident I can take it without slowing down, and ended up scraping the pedal crank on the pavement. I've not fallen down, luckily.

The good thing with carbon is it is relatively easy and cheap to repair compared to alu and steel.

If you you think that some cloth and resin patch is a good and safe repair for a bike frame, you can easily apply that technique to aluminum and steel too.

Carbon fiber weave and resins don't stick to aluminum and steel very well. It was an issue in the earlier days where frames using both metal and carbon fiber would come apart when the glue failed.

With aluminium you risk galvanic corrosion but yes I was contemplating using that technique to bond steel tubes and build a tall bike.

> Some people will be dumb enough to use these for touring, commuting and whatnot.

Pro tri bikes? I haven't been close to that world in 15 years, but even then the high end started somewhere around $10-15k and looked little more approachable to a less specialized cyclist than these do. You're not wrong they are poorly suited for general-purpose riding, but it would also surprise me quite a lot to see one used that way.

Never underestimate the ability of rich folks in sport to spend money with gear.

Oh, I'm a photographer, I get it. But I also feel like there's a reverse-GAS - Gear Disappearance Syndrome? - after rich folks overspend and discover "way more than I need" is also "way more than I want to learn how to use".

I got my D500 that way, actually. Used, but in perfect condition and with a shutter count below 5000 - per the fellow at the used counter, the former owner had said it was 'too much camera for him.' Considering his error got me an effectively new body at 2/3 the new price, I hope rich folks go on making such mistakes for a long time to come!

Oh, don't misunderstand me. I am totally in favor of obscenely rich people buying expensive gear, even if doesn't end up in the used market, they are creating jobs.

I am small so I always wanted a 650c bike to be 2 inches closer to the ground.

That alone has to be faster for wind resistance given everything else the same.

If 650c is still legal in races I am surprised even large riders haven't adapted frames to sit lower to the ground.

You can only lower the bottomo bracket so much. At some point you start having pedal clearance issues. I've put the end of the crank on my Brompton into the ground pedaling around a corner, and it wasn't like I was deeply leaned into it.

> The tubes of a traditional bike essentially form two diamond shapes.

Huh? I only see one diamond shape. There are two triangle shapes; one from the steering column to the seat post, and one from the seat post to the rear-wheel axle. They make up one diamond, not two.

What am I missing?

I think double refers to the tubes making up the frame being double lined for strength.

It took me a bit of searching but it does appear "diamond frame" bikes are a concept which then makes sense. Apparently some mountain biking applications or uses with more stress require a "double diamond frame".

That's what I could figure out though.

I also don't think they need to be exactly triangles, just as long as the nodes are generally connected via the same edges. Also sometimes the top and bottom bar don't meet at a single point on the steering post so that shape ends with with 4 sides.

I'm not sure, either, but the double could also refer to having the two triangular arms to secure the rear wheel instead of a single one.

I thought that might be it too but found literally 0 references for it.

edit:

Also, don't all of the designs have two arms in the back? Even the original "diamond frame" has the same rear tire attachment.

Consider the possibility that one diamond goes from the steering tube to the right rear axle mount and the second diamond goes from the steering tube to the left rear axle mount.

Because triathletes have extraordinary bad taste. Thank God for UCI keeping real bicycle racing proper.

Bring back the steel bikes, downtube shifters, no helmets, and the smoking in the peloton!

Wooden wheels and no pedally bits?

Easier to hide the secret electric engines when the frames are thick /s