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Aerodynamics of Gravel Bikes

renehersecycles.com

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Re: Aerodynamics of Gravel Bikes

#11

Post by usrusr »

cdot2 wrote: post #2

"Some readers have suggested that the boxy shape of the bag could be improved. However, since the bag sits between the handlebars, a rounded shape was actually less aero when we tested it in the wind tunnel." I would not have guessed that. Could a more efficient shape be made?

The boxy shape would likely still be less aero in isolation, but certain parts that in its slipstream might be so un-aerodynamic that the see less drag through more turbulent air than through clean air, and the boxy one provides more turbulence. Or it's the reverse, total drag benefits from the boxy rear and the rounded one was round on the rear as well (or not round at all, just some knotty wrap that approximates "round" very roughly, contrasting with a clean box)

Re: Aerodynamics of Gravel Bikes

#12

Post by matsemann »

nedludd wrote: post #6

These in-depth scientific studies always seem to neglect the weight and aerodynamics of the RIDER. That is surely the biggest factor when it comes to speed and efficiency.

It's always funny with people having paid $10k extra to save a kilogram on their bike, and then show up on the Sunday group ride with a beer belly. But I think these articles and study are mostly written for / paid by professionals, and they don't have that much more weight to lose.

But reading "The secret race" by Hamilton (one of Armstrong's team mates), they do focus obsessively on it. They would often ride for hours, then take sleeping medication and go to bed without eating.

Re: Aerodynamics of Gravel Bikes

#13

Post by hi »

> the fastest riders in the 200-mile Unbound average 20 mph (32 km/h) across the Flint Hills of Kansas.

Let’s not forget that the most important aspect of averaging 20mph on grave roads: drafting, low body weight and high fitness.

If you watch footage of the unbound gravel race they mention, the winners are with a group of riders until the very end.

The fastest riders are professionals sponsored by the companies trying to sell you this aero gear.

If you want to ride faster ride in a group, find your ideal body weight and spend money on a coach. Only then spend money on bike parts beyond the basic lubricated chain, correct tire psi, etc.

Re: Aerodynamics of Gravel Bikes

#15

Post by Lio »

WA wrote: post #4

Related, this fascinating video, which covers different bag positions, clothings etc.: https://www.youtube.com/watch?v=Ue_Tz7e0DmE

I'd also suggest this Francis Cade video1[1] where they tested various bike packing bags in a wind tunnel.

Bar bags of any size or shape are really slow.

A much better solution is something like a Tailfin aeropack[2].

1. https://www.youtube.com/watch?v=WcXh_oqs_Bs

2. https://www.tailfin.cc/

Re: Aerodynamics of Gravel Bikes

#16

Post by nradov »

jrf6 wrote: post #10
nedludd wrote: post #6

These in-depth scientific studies always seem to neglect the weight and aerodynamics of the RIDER. That is surely the biggest factor when it comes to speed and efficiency.

The rider is a much bigger factor, of course. But that’s not the problem being addressed here. You’re not suggesting the bike should not be optimized are you?

It makes no sense to optimize the bike in isolation. There is complex airflow interaction between the bike and rider. There are changes that aerodynamicists could do to reduce bike drag that would actually increase drag on the complete bike plus rider system.

The problem is that there are so many variables with riders. For example, just a slight change in head position can increase drag more than any improvement in frame tube shape could save.

Re: Aerodynamics of Gravel Bikes

#17

Post by [deleted] »

matsemann wrote: post #5

A gravel bike is the perfect commuter bike! At least if you're not going electric. Almost as light and fast as a road bike. But a bit more upright riding so it's more comfortable. Wider and more treaded tires means tram lines, pot holes, curbs etc. are less of a problem and can handle rough surfaces and not just asphalt. Mounting points and wider forks allow for mudguards / fenders so rain is no problem. The wider sp…

[deleted]

Re: Aerodynamics of Gravel Bikes

#18

Post by benjaminwootton »

I bought a cool book yesterday which is all about gravel trails in the UK. I had never heard the term gravel bike until reading it.

Silly question but can I do these trails on my full suspension mountain bike, or will I be mercilessly mocked and possibly chased out of town?

I already have a mountain bike and a road bike so not keen to add a third!

Re: Aerodynamics of Gravel Bikes

#19

Post by Steltek »

matsemann wrote: post #5

A gravel bike is the perfect commuter bike! At least if you're not going electric. Almost as light and fast as a road bike. But a bit more upright riding so it's more comfortable. Wider and more treaded tires means tram lines, pot holes, curbs etc. are less of a problem and can handle rough surfaces and not just asphalt. Mounting points and wider forks allow for mudguards / fenders so rain is no problem. The wider sp…

Gravel bikes are good commuters, if you like drop bars. Many commuters prefer flat bars for the more upright riding position, which allows for a better field of view for misbehaving drivers.

You still also have the classic problem that higher end bikes lose all the commuter friendly features. Carbon forks and frames often lose mounting points for fenders+rack. The marketing vision of a gravel bike is someone expecting to get muddy and who isn't trying to stuff a laptop into a saddle bag. Durable, maintenance friendly choices like threaded BBs and easy cable routing go away. You're stuck with heavy bikes with poor gear ranges, super low end components, cable brakes, etc.

Re: Aerodynamics of Gravel Bikes

#20

Post by Lio »

wffurr wrote: post #7
nedludd wrote: post #6

These in-depth scientific studies always seem to neglect the weight and aerodynamics of the RIDER. That is surely the biggest factor when it comes to speed and efficiency.

Harder to spend money to improve the rider. Fancy clothing, I guess.

A skinsuit or roadsuit will definitely make you faster on the bike. It's pretty easy to measure the effect with a power meter.

Weirdly "aero socks" are both a thing and make a big difference to the point that they are heavily regulated by the UCI.

Any cylindrical part of the bike or rider is going to perform badly so if you can encourage the airflow to stay attached around it you reduce the amount of effort required to move you forward, hence aero clothing being a big deal.

If you're a serious cyclist then it's pretty easy to spend money on good quality clothing.

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