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Aerodynamics of Gravel Bikes

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Re: Aerodynamics of Gravel Bikes

#151

Post by dc-programmer »

prmoustache wrote: post #96
dc-programmer wrote: post #84

Earlier quoted context omitted.

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.

Sorry somehow missed that.

The explanation I heard for the traditionally higher brackets is that it facilitates quicker turning. Is there truth to this or is this more of a marketing thing?

Re: Aerodynamics of Gravel Bikes

#152

Post by ActorNightly »

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 assuming that rider can output X watts continuously. This is not how humans work. Riders have different profiles in terms of torque vs rpm from their legs. A lighter bike means that a rider is outputing less torque, which he/she can sustain without downshifting to a lower gear, leading to overall increase in time not only during the climb, but also how much energy the rider has left in the tank after the climb for the rest of the course.

Re: Aerodynamics of Gravel Bikes

#153

Post by ActorNightly »

bigfudge wrote: post #34
pharmakom wrote: post #28

I’m sorry but Jan Heine has unscientific methods and his products are of questionable reliability. You can drop 200usd on his tyres. It’s like hifi nerdy but for rubber.

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.

Re: Aerodynamics of Gravel Bikes

#154

Post by mariusor »

lm28469 wrote: post #68
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…

Reminds me of this bicycle subreddit where they spend thousands on bikes and cosplay attires to get smoked by 60+ years old dudes on 40 years old bikes As a casual rider you'll be the bottleneck for years before your gear matters even the slightest

> As a casual rider you'll be the bottleneck for years before your gear matters even the slightest

For absolute performance, maybe, but for enjoyment of riding the gear definitely matters. For a beginner it's important that the ride is enjoyable so they don't get discouraged and call it quits.

For relative performance against yourself, and in all honesty that's most of us really get out of it in the end, it's good to see times drop and speed increase just because you bought a better bike.

For me it was the other way around, I moved from a very aero cheap fixed gear to a boxy (but with a plentiful cassette) midlevel gravel bike. I was expecting that the gears I had extra would make me have faster times, however the fat tires and less aero profile makes me about half a minute slower for a 6km round. The power I'm pushing however, has increased, maybe because I can keep it more uniform by shifting to lower gears when I get into windier sections. Shrug.

All I want to say is that good gear is beneficial, maybe not for performance, but definitely for enjoyment of a ride. And at the beginning that's pretty important for someone to build a habit out of riding.

Re: Aerodynamics of Gravel Bikes

#155

Post by rich_sasha »

sorenjan wrote: post #114
rich_sasha wrote: post #41

Earlier quoted context omitted.

Yeah but carbon gives you cred, and basically _buys_ you speed. Losing weight is effort. Sarcasm over, one of the funniest cycling stories i ever encountered. My work had a little low-key "bike club", a few guys cycling on warm evenings. One of the partners was a key member so over time non-bike guys started wiggling in for networking purposes. One guy, with no clue how to ride, drops 2k++ on a full carbon bike, high…

The sad thing is that $2k barely gets you a carbon frame with low end components now. A mid tier bike is maybe $5k, and high end can easily be more than $10k. Personally I really don't get why anyone would pay $10k for a bike. Amateurs won't benefit nearly enough to make it worth it, and pros are of course sponsored.

It was 2k GBP so more like 3k USD but point stands. It wasn't a good bike.

I think semi pros are possibly the main audience. A friend is into endurance events and he just dropped something like 2k on a titanium frame.

Re: Aerodynamics of Gravel Bikes

#156

Post by NegativeLatency »

The aerodynamics of upright bikes compared to recumbents remind me very much of stock car racing compared to f1. Where one is actively pushing forward in terms of speed and performance and the other is stuck with one type because of how it "should" conform to previous ideas of what a bike looks like.

Re: Aerodynamics of Gravel Bikes

#157

Post by r00fus »

ehnto wrote: post #31
Fradow wrote: post #26

Earlier quoted context omitted.

I'm in agreement with almost everything except the tires. Unless your commute has a significant portion of rough surfaces, you definitely want to use some road tires. Not the super skinny ones used on road bikes, so you don't have an issue with tram lines/pot holes/curbs, but good reinforced road tires (so you don't have flats when going over glass/nails/whatever). I've been commuting daily on a mountain-bike (chosen…

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…

Have you considered tubeless? I hear that gives the RR benefits of high pressure but at lower pressures.

Re: Aerodynamics of Gravel Bikes

#158

Post by r00fus »

matsemann wrote: post #60
Steltek wrote: post #19

Earlier quoted context omitted.

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…

> You're stuck with heavy bikes with poor gear ranges, super low end components, cable brakes, etc. Hmm, not my experience at all. At least the market here there are no "cheap" gravels. For around $1k-$1.5k (which is the cheapest gravels available here) I've gotten hydraulic breaks, Shimano GRX groupset, an OK weight etc.

Those prices seem low these days if you want any availability. All I'm seeing around me is $2-2.5k minimum for the same specs (higher end = carbon frame).

Re: Aerodynamics of Gravel Bikes

#159

Post by toss1 »

vikingerik wrote: post #139
toss1 wrote: post #137

Earlier quoted context omitted.

One racecourse I know about that has both running and bicycle races is the Mt Washington Auto Road in New Hampshire USA. It is the tallest mountain east of the continent. The top is at 6288ft/1917m above sea level. The road is 7.6 miles / 12.2 km long and the climb is 4650 vertical feet / 1420m. The footrace has been run since 1936 and the bicycle race since 1973. The road used to be paved only half way and gravel th…

Very interesting information, thanks. The sibling comment pointed out that the parent probably meant 40 minutes for 1km of elevation gain, not linear distance, which makes sense too. Maybe I'm just trying to justify my own struggles where it's faster to walk the bike up any significant grade :)

YW. You might be using too high a gear, so pushing too hard, which will definitely slow you down going uphills.

In general for reasonably flat riding, you want to be spinning at 80-90RPM. Most cyclists I see are spinning much slower, so pushing much harder. Think in terms of lifting a weight. You might be able to lift 10kg only six times on some motion, but you can likely lift 1kg far more than 60 times with the same motion.

I also have a lesson from Mt Washington. I was an unranked teenage amateur bicycle racer doing ok, but only using bicycle racing as training for ski racing. I'd won a couple regional-level hillclimbs and was looking for another race and someone said "call this guy". I did, and got told about the first Mt Washington bike race. I had no idea what gearing to use, so got the lowest granny-geal cluster I could find in a day. I got to the race and among the small crowd were four guys from the US Cycling Team. I wound up finishing 3rd, only 4min behind John Allis (3-time Olympian) 1h:15m time and 4sec behind 2nd place. I had by mostly dumb luck out-guessed everyone on the gears (neither my conditioning nor my bike was close to their class). The next year Allis came back and won again knocking 14min off his time, presumably with a lower gear cluster.

So, I'd definitely take a look and see about using lower gears...

Re: Aerodynamics of Gravel Bikes

#160

Post by Melatonic »

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'…

Are gravel bikes heavy now? From what I remember (admittedly 10 years ago) "gravel" bikes were pretty much cyclocross bikes to begin with just with slick tires.

I sold my fancy lightweight cyclocross bike around this time and built myself a fully custom bike with a hodgepodge of parts - I wanted something that looked a bit vintage cool and also not as stealable so I went with the pinnacle of late 1980s touring frames (steel) which is obviously not light but not all that heavy either. Bought lightweight 29er rims + 35C quality touring tires, wide flared dirt drop bars, nice 9sp bar end shifters with a triple crank up front (9sp being my favourite in that you can still friction shift it easily if needed and the bar ends can easily switch from indexed to friction at the flick of a switch). The thing absolutely flys on gravel, pavement, dirt roads, shitty sidewalks - basically is my do everything bike for general use from groceries to exercise.

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