Aerodynamics of Gravel Bikes • Hacker News Board

Re: Aerodynamics of Gravel Bikes

#121

Post by jackmott42 » Tue, Sep 20, 2022, 4:09 PM UTC

cycomanic wrote: post #93

jackmott42 wrote: post #61

Earlier 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…

The issue is that a lot of the aerodynamic frame advances only work in ideal laminar conditions. However wind is gusty, there are trees and other obstacles next to the course etc. In those cases the advantages largely disappear as Hambini has shown.

I'm not sure what testing Hambini has been up to, last I saw him he was calling for the death of Damon Rinard (who is a really nice guy, by the way! and great cycling engineer)

However I have plenty of first hand field testing data showing that this is very obviously not true, as do hundreds of other people. We ride in the real world with power meters and timers and we can detect these things even in gusty real world conditions.

Just two examples:

http://www.trainingandracingwithapowermeter.com/2010/10/chal...

and

https://betterbicycles.org/science/speed/validation-of-bicyc...

Re: Aerodynamics of Gravel Bikes

#122

Post by fnbr » Tue, Sep 20, 2022, 4:10 PM UTC

bbarn wrote: post #120

jackmott42 wrote: post #61

Earlier 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…

You're forgetting the effect of exertion on the rider under heavy loads like climbing. I've ridden heavy bikes, and I've ridden light bikes. Light bikes feel better, rotational weight mattering more than anything else.

They’re not- 300W of effort is 300W of effort, it doesn’t have a bigger impact if the bike is heavier or not.

Re: Aerodynamics of Gravel Bikes

#123

Post by elektronaut » Tue, Sep 20, 2022, 4:12 PM UTC

vikingerik wrote: post #115

jackmott42 wrote: post #61

Earlier 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 know nothing about typical bike timings, but I was struck by that. Does it really take 40 minutes to go 1 km at an 8% grade? Would it be faster to get off the bike and walk? When you're not rolling, you don't have to output power to fight your own weight trying to roll back - the friction between your shoes and the ground counteracts that. (I assume a real race doesn't allow you to walk, just batting around thought…

I suspect the parent is referring to elevation, not distance. 1km in distance would only take a few minutes.

Re: Aerodynamics of Gravel Bikes

#124

Post by ben7799 » Tue, Sep 20, 2022, 4:22 PM UTC

jackmott42 wrote: post #61

bbarn wrote: post #50

I 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'…

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 enthusiasts and the bike companies have completely brainwashed equipment enthusiasts.

Your times don't make any sense either... 8% for 1km takes vastly less time than you're talking about at the power levels you're talking about. You're probably off an order of magnitude there. A rider with an FTP of around 300 will probably climb closer to 10km @ 8% in 40 minutes.

Nothing is more tiring than being at the start of a race and there's someone with a $10k+ bike and a gut talking smack about bikes to someone everyone else knows is going to win the race and the guy with the $10k bike is getting dropped & pulled from the race. One person spent all their time on training and the other spent all their time researching & buying equipment.

Re: Aerodynamics of Gravel Bikes

#125

Post by [deleted] » Tue, Sep 20, 2022, 4:23 PM UTC

fnbr wrote: post #122

bbarn wrote: post #120

Earlier quoted context omitted.

You're forgetting the effect of exertion on the rider under heavy loads like climbing. I've ridden heavy bikes, and I've ridden light bikes. Light bikes feel better, rotational weight mattering more than anything else.

They’re not- 300W of effort is 300W of effort, it doesn’t have a bigger impact if the bike is heavier or not.

[deleted]

Re: Aerodynamics of Gravel Bikes

#126

Post by intrasight » Tue, Sep 20, 2022, 4:27 PM UTC

benjaminwootton wrote: post #18

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!

Any bike you ride on gravel is a gravel bike. All my bikes have been on gravel so they are all gravel bikes.

Re: Aerodynamics of Gravel Bikes

#127

Post by bckygldstn » Tue, Sep 20, 2022, 4:30 PM UTC

Fradow wrote: post #36

ehnto wrote: post #31

Earlier quoted context omitted.

I've commuted on a roady, a steel big tire bikepacking bike (basically a hardtail MTB) and now a gravel bike. I'd say the tires on gravel bikes tend to be the best compromise between comfort you get from a big volume tire, and the speed of a road or commute tire. They can run pretty high pressures, which is the biggest factor for rolling resistance, and they're pretty skinny relative to MTB tires. For me, the minute…

Thanks for the feedback! I've not had the occasion to try gravel tires. For me, the main reason to use road tires is grip on asphalt, not rolling resistance improvment. On your commute, you may need to stop in an instant, and more grip = quicker stop = safer (I've had a few close calls, especially downhill under rain). Obviously, that's also dependent on your regular commute road condition.

Braking is the main reason I love gravel tyres for commuting: their increased size means a larger contact patch which directly translates into a shorter stop (as stopping on skinny tyres with disc brakes is typically traction-limited).

The tyres on my gravel bike look just like fat road tyres: no knobs.

Re: Aerodynamics of Gravel Bikes

#128

Post by jackmott42 » Tue, Sep 20, 2022, 4:31 PM UTC

ben7799 wrote: post #124

jackmott42 wrote: post #61

Earlier 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…

You are right I had the gradient off by 10x, sorry that should have been obvious, it has been a while

Actual time savings of 1kg of weight reduction: 1 second

And personally I've used aeroweenieing to podium in a cat 3 road race, and my wife has set state records and won pro races. You can make fun of fat guys doing a professional job if you like but it isn't just them.

Re: Aerodynamics of Gravel Bikes

#129

Post by mauvehaus » Tue, Sep 20, 2022, 4:32 PM UTC

762236 wrote: post #91

bbarn wrote: post #50

I 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'…

Their "giant heavy gravel bikes" were probably a few pounds heavier than your CX bike, but your dad belly made you like 10 or 15 pounds heavier. Heavier people go faster down hills. I'm unconvinced that their bikes slowed them down, unless they were also super un-aerodynamic (wide handlebars, attaching water bottles to the forks, upright positions, flappy wind jackets)

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 down. Getting a pound of weight off your back and into your belly (or the reverse when you fill up with water) is noticeable.

Re: Aerodynamics of Gravel Bikes

#130

Post by dev_tty01 » Tue, Sep 20, 2022, 4:32 PM UTC

benjaminwootton wrote: post #18

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!

Yes! First, if you haven't spent much time on gravel, you will be more confident and sure-footed on the MTB. Second, you will have a much more comfortable ride. As others have said, it will be a bit more effort, but the improved confidence will probably do more for your overall speed than a skinny tire.

I would however lock out the rear suspension, and probably the front too. The high volume tires at the right pressure will likely provide all the suspension you need for gravel and your pedaling will be more efficient.

As far as being mercilessly mocked, that reminds me of an old adage. We spend our youth worrying about what other people think. In middle age we decide we don't care what other people think. As we get older, we finally realize no one was thinking about us.