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Aerodynamics of Gravel Bikes

renehersecycles.com

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Re: Aerodynamics of Gravel Bikes

#91

Post by 762236 »

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)

Re: Aerodynamics of Gravel Bikes

#92

Post by gergely »

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…

You are correct on the watt, weight computes but I think the aerodynamic saving is worthless on a gravel race. People are not going that fast on gravel to gain anything from aerodynamical optimisations. You need to keep going at least 40 km/h to have any advancement without up-down movement which is obviously not something that you can achieve on gravel.

Re: Aerodynamics of Gravel Bikes

#93

Post by cycomanic »

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…

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.

Re: Aerodynamics of Gravel Bikes

#94

Post by prmoustache »

gergely wrote: post #92
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 are correct on the watt, weight computes but I think the aerodynamic saving is worthless on a gravel race. People are not going that fast on gravel to gain anything from aerodynamical optimisations. You need to keep going at least 40 km/h to have any advancement without up-down movement which is obviously not something that you can achieve on gravel.

Aero also helps at 25 or 30kph.

It is quite easy to check out actually on a road bike. Ride at a steady pace without pushing hard, hands on top, then put your hands in the hoods of the brake lever, elbows at 90° without pushing more, you will gain easily 1kph just by changing position. More if it is windy.

Re: Aerodynamics of Gravel Bikes

#95

Post by prmoustache »

gergely wrote: post #78
jackmott42 wrote: post #73

Earlier quoted context omitted.

And you can do fine in a road race with a gravel or cyclocross bike! Just gotta put appropriate tires on.

You have just proved you haven't rode a cyclocross bike. Since those bikes' center of mass is higher than the road bikes it is really "nervous" on high speeds for example long descents.

I won a criterium once on a cyclocross bike while waiting for my team supplied road race bike.

That so called nervousness is greatly overstated. I think this is a US thing actually.

Re: Aerodynamics of Gravel Bikes

#96

Post by prmoustache »

dc-programmer wrote: post #84
prmoustache wrote: post #67

Earlier quoted context omitted.

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.

Cyclocross bikes also have higher bottom brackets

That is what I mentionned by "Slightly lower BB" for the gravel bike, just stated in the opposite direction.

It doesn't matter much anyway and CX bikes from US brands had already started lowering the BB of the CX bikes because US courses designers are usually less keen on putting off cambers section than euro courses designers.

Re: Aerodynamics of Gravel Bikes

#97

Post by antihero »

Steltek wrote: post #19
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 expectin…

Modern drop bar shifters have an upright position though?

Re: Aerodynamics of Gravel Bikes

#98

Post by TrueGeek »

Doctor_Fegg wrote: post #83
lukah wrote: post #24

Earlier quoted context omitted.

If anything, you might be thankful of a full suspension mountain bike on some of our "gravel" trails in the UK. There's such a wide range from US-style back county roads all the way to bridleways with baby-head sized rocks that you probably wouldn't want to be riding on something typically sold as a gravel bike.

Yes, this. There's actually not that much US-style "gravel" in England and Wales: basically a few Forestry Commission tracks in mid-Wales, Northumberland and places like that. Elsewhere it's single-track bridleways that dominate. Routes like King Alfred's Way, the Pennine Bridleway, the Great North Trail and West Kernow Way are sometimes marketed as gravel routes but they're probably more MTB than anything.

I spent a month in the UK and was glad to have brought my CX bike instead of my road bike. Several of the routes (in Kent) that I had thought were going to be road routes suddenly turned into paths that we would classify as gravel here in the states. It was wonderful! So little traffic and not one F350.

Re: Aerodynamics of Gravel Bikes

#99

Post by gergely »

prmoustache wrote: post #95
gergely wrote: post #78

Earlier quoted context omitted.

You have just proved you haven't rode a cyclocross bike. Since those bikes' center of mass is higher than the road bikes it is really "nervous" on high speeds for example long descents.

I won a criterium once on a cyclocross bike while waiting for my team supplied road race bike. That so called nervousness is greatly overstated. I think this is a US thing actually.

But crit races are not like coming down from Stelvio kind of speed where nervousness counts. Crit races are exactly like cx races but on asphalt or at least where I'm in Europe ;)

Re: Aerodynamics of Gravel Bikes

#100

Post by prmoustache »

chitowneats wrote: post #66
qwertox wrote: post #58

I started biking around three years ago. Lots of biking, like 5000-8000+ km a year. As long as I don't weigh my ideal weight and aren't planning on becoming a machine myself, I have zero interest in spending anything in optimizations which will make my bike a better one. I don't care if it could go faster or be more lightweight, spending 600€ for the bike was enough. The cheapest 30€ Schwalbe tires are good enough; I…

I appreciate your approach but the reason people like optimizations is for speed. The thrill of riding fast is what keeps a lot of us coming back.

There is riding fast and there is riding fast but just a tiny bit slower.

I have a modern race bike, less than 3y old with some but not all of the latest aero features. I also still own my 30y old racing bike that I used to race until 20years ago (it was already old bike then). It stays at my parents place and I ride it maybe twice a year. If you ask any bike reviewer he will tell that old bike is obsolete, feel much slower and make me lose 45s over the course of a 50km ride according to the data given by the manufacturer. If you ask me, sure I feel a difference, mostly in feeling, when I start riding the bike. But after 5 minutes all this is forgotten and I enjoy the ride as much as on my more modern bike. And that bike is perfectly fine surrounded by superbikes in a group ride. Actually I did one this summer with a group that tend to stay together but ride at a fast steady pace until the last 20k where the wait "policy" disappear and people start to attack the climbs at max pace. I ended up in the 5 rider leading group out of maybe 40 and I was totally out of shape.

That old bike would sell for 300-400€ in the second hand market right now. The difference with a 2k and 8k modern bike is much lower.

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