Back in the day I found some vintage "aero" bars that were designed to bolt on to any bicycle made before larger diameter drop bars became the norm. I did not want them, however, specifically for the "aero tuck" - I wanted them to give me more hand positions for long term comfort. While I eventually got rid of them because they took too much space on the flats of the bars due to the way they clamped I always wondered if we could design something like an aero bar but specifically for comfort. It could bolt on to the stem or in a way that still allowed multiple hand positions on the flats. The elbow pads were also a very nice way to get some lower back stretches in and I even ended up mounting a small cyclocross brake at the end of one of the aero handles so I could comfortable adjust speed (rear brake only - front brake in this position might be suicide) while going downhill and tucked. Or hell - maybe even something that had a small fold mechanism so that you could fold away the forearm / elbow pads when not in use!
Aerodynamics of Gravel Bikes
181–190 of 211 posts
Re: Aerodynamics of Gravel Bikes
#182Earlier quoted context omitted.
To quote someone I met thru-hiking: "Food is lighter once you eat it." Or in other words, subjectively, weight on your body doesn't cost as much as weight you're hauling whether on your back or on your bike. Nope, I can't explain it either, but I've got over 3000 miles hiking/backpacking and it holds true. Can't measure it, didn't try, but I can assure you that feeling worn down is roughly equivalent to being worn do…
That’s been tested and it’s objectively not true from a physics perspective. That said, weight isn’t as big a factor until you go uphill, which is why you’re seeing the trend to more aero instead of lighter weight bikes. What you’re describing, however, is the simple effect of eating food replenishing your energy.
The parent did say "subjectively", but I think there's a case to be made that this is even objectively true:
A pound of food carried inside your stomach is located very close to your body's unloaded center of mass. That same pound of food carried in a backpack is placed further away, creating a torque that your muscles need to work to counteract. So it very well may be the case that carrying the food on your back has a slightly higher energy cost.
It's possible that the additional energy is negligible, or at least low compared to the "subjective" increase in perceived exertion. But I don't think the idea is entirely unfounded.
Re: Aerodynamics of Gravel Bikes
#183Earlier quoted context omitted.
Why don't you actually do some math, or experiments, rather than just telling us you have doubts? This is all really easy stuff to answer. For instance. 75kg rider + bike. Make the bike 1kg lighter. Go up a 8% grade for 1 kilometers at 300 watts Time saved by 1kg weight reduction? 30 seconds out of 40 minutes. Or suppose we add 300grams to the frame to make it aero, which is typical. If that reduces the CdA by .02 ou…
I'm a former racer too and this constant equipment arms race and arguing is just so fatiguing. People can argue about analytics around equipment till pigs fly. It's all still just an order of magnitude smaller than the differences between being fit and not fit and a stronger rider versus a weaker rider or a coached rider versus un-coached rider. The sport has separated into riding enthusiasts and equipment enthusiast…
Its always easier to try to buy your way up the chain than putting in the work. And when you are not actually a pro it often becomes a social novelty of its own (and within reason one I often enjoy myself). The end game for me in all things like this is that when I actually become a sort of expert in the gear choices I realize that often the middle ground items are sometimes the best - pricier things are often better but there are huge diminishing returns and sometimes the simplest item of decent quality is actually the most functional.
Re: Aerodynamics of Gravel Bikes
#184Earlier quoted context omitted.
Why don't you actually do some math, or experiments, rather than just telling us you have doubts? This is all really easy stuff to answer. For instance. 75kg rider + bike. Make the bike 1kg lighter. Go up a 8% grade for 1 kilometers at 300 watts Time saved by 1kg weight reduction? 30 seconds out of 40 minutes. Or suppose we add 300grams to the frame to make it aero, which is typical. If that reduces the CdA by .02 ou…
I'm a former racer too and this constant equipment arms race and arguing is just so fatiguing. People can argue about analytics around equipment till pigs fly. It's all still just an order of magnitude smaller than the differences between being fit and not fit and a stronger rider versus a weaker rider or a coached rider versus un-coached rider. The sport has separated into riding enthusiasts and equipment enthusiast…
> The sport has separated into riding enthusiasts and equipment enthusiasts and the bike companies have completely brainwashed equipment enthusiasts.
I'm NOT a former racer but I've cycled recreationally (probably an average of about 30 miles a week, give or take) for over 20 years.
When I first got into road cycling I nerded out on gear. Back then that meant skinny tires, carbon fiber, big bucks. I felt reallllly cool.
As I've gotten older I stopped caring about what's cool. Like, in cycling, but in pretty much everything else too.
I had to move recently, and ditched my road bike but kept my "cyclocross" (as it was called at the time I bought it) bike, since I wanted something more flexible and comfortable. It ways weigh more, and I ride on big honking tires with hefty tread.
I tracked my (solo, non-drafting) rides and I'm slower... by like, .5 mph.
I have no doubt that all the gear nerds out there know what they're talking about, and these data driven fads are real improvements, but the margins have gotta be smaller than most of us weekend warriors should realistically ever care about.
At a certain point you gotta ask yourself why you're even into the sport - either you think you're gonna win something, and then this is your life (and every advantage is worth it), or you're in it to ride with buddies and enjoy the feeling of moving through space. If you're in the latter category, and you aren't getting dropped, obsessively optimizing gear isn't actually gonna make your experience any more fulfilling.
Re: Aerodynamics of Gravel Bikes
#185I am an out of shape former racer who has ridden his bike 10 times in the last two years. I have a dad belly and rarely work out at all. I recently did The Rift this summer - a 200km gravel race here in Iceland that people come from all over the world to race. I did it on a carbon cyclocross bike from my racing days with file treads. I felt like the light weight of my bike outweighed just about every gravel fad that'…
There is actually very little difference between a cyclocross bike and a lightweight gravel bike. Slightly lower BB, slightly longer wheelbase, sometimes slightly different headtube angle, flared handlebars. Actually the first gravel bikes were rebadged cx bikes. You can race cx with a gravel bike and race gravel with a cx bike. The rider makes most of the difference.
Geometry is actually probably the big difference - cyclocross bikes are designed for small repeatable courses often with tight turns and the need to carry the bike on your shoulder. A slightly lower or higher BB height would probably work well for either - it is the ratio of total height vs top tube (so height vs length of the frame) that really defines cross vs gravel. Cross bikes will be taller and shorter (length wise) to have shorter turning radiuses and slightly lower weight at the expense of long term rider comfort and stability at speed. Gravel bikes will be longer and have worse turning radiuses but slightly better stability at speed. You can see the same thing with cars. A shorter bike (just like a short wheelbase vehicle) will also have better approach angles relative to its height.
That being said depending on your leg length to upper body torso length you can of course size a cyclocross bike up or a gravel bike down and achieve sort of the same effect. In my opinion these types of geometry questions do not come up nearly enough in relation to the rider, however, as someone with a very long torso is going to be quite uncomfortable with a bike with a short top tube even if the "size" of the bike is correct for their leg length / height. And of course the opposite can also be true. Ideally we should be sizing and matching frame geometry to the persons geometry regardless of the intended use case of the bike.
Re: Aerodynamics of Gravel Bikes
#186Earlier quoted context omitted.
They’re not- 300W of effort is 300W of effort, it doesn’t have a bigger impact if the bike is heavier or not.
I wonder if that's really true on hills. Most people ride hills with more effort, pushing down on one pedal at a time. The bike speeds up and slows down much more with each pedal stroke. Compare to the flats where you have a smooth stroke and very consistent output. I could see all the mini accelerations adding up to a much larger energy expenditure than would be indicated by a spherical cow in a vacuum.
Eh, it's really quite small, unless you have stupid heavy wheels (meaning, that the wheels are a significant percentage of the mass of the entire system).
If the mass of the wheel is 100% located at the rim, the energy goes 1/2 into straight line energy and half into rotational. But -- if you slow down, you don't lose that energy, it just redistributes to gravitational potential. The flywheel effect from heavy wheels may actually help, as it tends to smooth out pedal strokes.
The energy to go up a hill is just mgh - friction. Some cadences are less efficient than others (e.g. for me, standing is more power but lower efficiency), and bikes that are too stiff may not help you get the best rhythm.
In a totally unscientific test -- I've got a 12kg Aluminum gravel bike, wide tires, rack, fenders. I've also got an 8kg carbon racing bike, skinny tires, aero rims, etc. They have similar riding positions (reach/drop), though the gravel bike has a wider seat, which is better for one climbing cadence. I usually ride the gravel bike these days, because comfort.
Two weekends in a row, I did a 12x rep climbing workout (2.5 hours), one on each bike. First weekend, Road bike. It felt _fast_. Quick, lively, accelerated from the stoplights on the way to the hill. Second week, back on the gravel bike, grinding up the hill. Total ET difference: 5 seconds.
Sure there are differences.
Re: Aerodynamics of Gravel Bikes
#187Earlier quoted context omitted.
I cut my stem long and run my bars high due to a back injury. It does mean that I essentially had to learn how to build my entire bike from scratch since noone builds a bike that way, but I'm happy I did.
For what its worth there are custom builders that do bikes in any geometry. There are also a number of small bicycles companies that may not have a shop in every city but that provide bikes with various kind of geometries.
Eventually I may do that, but for now keeping the stem long has been a good fit for me.
Re: Aerodynamics of Gravel Bikes
#188Earlier quoted context omitted.
That’s been tested and it’s objectively not true from a physics perspective. That said, weight isn’t as big a factor until you go uphill, which is why you’re seeing the trend to more aero instead of lighter weight bikes. What you’re describing, however, is the simple effect of eating food replenishing your energy.
The parent did say "subjectively", but I think there's a case to be made that this is even objectively true: A pound of food carried inside your stomach is located very close to your body's unloaded center of mass. That same pound of food carried in a backpack is placed further away, creating a torque that your muscles need to work to counteract. So it very well may be the case that carrying the food on your back has…
This has been tested and, no, the location doesn’t make a difference to the necessary power output on a bike. Weight is weight as far as the system is concerned.
Another thing that might come into play is simply holding the backpack on your back. If you put that same weight on a saddle bag or frame bag, your power output won’t need to change but you’re not constantly carrying it physically on your back.
Re: Aerodynamics of Gravel Bikes
#189Earlier quoted context omitted.
I agree the tyres are expensive, but their findings on tyre width and pressure are largely bourne out by more controlled tests. In addition, their rolling distance tests include one factor which most standardised rigs didn’t: the losses from hysteresis when uneven surfaces have to lift/return your mass over a bump. I think soft wide tyres would be even more advantageous than most people realise once real losses on re…
The tire width definitely has a break even point where wider tires are significantly less efficient than narrower ones unless you run them at unsafe pressures. More volume in the tire means that at the same pressure, there is more deflection, and deflection hysteresis in the tread, notably the rebounding of the tread behind the contact patch is what causes the rolling resistance in the first place.
RH 48mm tires at 25psi are pretty damn good on a single. Likewise my tandem uses 44's at 45psi (front, heavy captain) and the rear 53mm at 40 (light stoker).
Re: Aerodynamics of Gravel Bikes
#190The article mentions the upper back fairing of a motoGP racer but then blows off the idea for a cyclist because they might get too hot? I've always wondered why road cyclists don't ditch their frame mounted (and drag inducing) water bottles for a camelback. The original camelback was slim and I can't imagine it added any drag seeing as it sits on the back of the cyclist. Plus it has the advantage of allowing the cyclist to maintain a better cylcing position without having to reach down for a bottle.
But then again if roadies were really all that concerned about aero and efficiency they'd switch to recumbent bikes...