Roadie physics article

[jameso]

I thought this was interesting, some smart people discussing aero vs weight in bike design. It's roadie-biased of course but interesting since adding a bag to your bike is weight plus drag and where we put bags can make a real difference in drag. Also bringing it back from the realm of shaved legs into the touring world, some of the savings mentioned equate to the power my dynamo pulls at ~25kph so that's easy to relate to.

https://bikerumor.com/aerodynamics-vs-w ... -cyclists/

I'm not into aero kit or weight-saving gains in particular but I do recognise that there's no point adding weight or drag needlessly. What I take from examples like this is that the differences are small overall and once we've refined kit or bike down to a fairly sensible efficient point, after that the weenie-ism over weight or aero isn't important.

Generally once weight and drag is reasonably low I think the most to be gained is in rider comfort and confidence. They're the things that keep you riding well for longer, maintaining flow and holding the speed you've worked for. Motivated to keep going, even. Conveniently for me as someone not gifted in mathematics those things are subjective and almost impossible to quantify across individuals and test for reliably - but we know it when we feel it. And where we put those heavy/bulky bags and how well they attach makes a big difference there too.

[RIP]

An interesting read that James. Good to remind us about the mental side of things making a difference to the feeling of how much 'weight' we're carrying. It's possibly a relief that we can't measure that to a minute (gramme) degree or we'd obsess even more over it . Or maybe there is an exact measurement.... calling the Boner psychology department....

[fatbikephil]

Cheers for that Jameso, interesting! I'd always figured that adding a kilo or two doesn't make a huge difference on anything more than the steepest of climbs and this article shows even then it isn't as significant as you might think. Hasn't stopped my shelling out on weight savings though...

That said, when I lost 5kgs from my belly a few years ago you could definitely feel the difference! We also have to figure in the hike-a-bike through tussocks / rocks factor. Then the kilo or two bike weight difference does become important.

[Boab]

I'll save that for reading later. As for the shaved legs, I thought the current "fastest" was shaved back of legs, hairy front. Hence why the Danes team pursuit all had the exact same physio issue, which the solution for tape down the shins.

[jameso]

As for the shaved legs, I thought the current "fastest" was shaved back of legs, hairy front.

Laminar flow and detachment or something like that. Like those aero-optimised socks with the fluffier front, thought they were taking the p155 with those but no, they'd suggested there was a wattage saving on offer

[Bearbonesnorm]

I tend to think that bikepacking of the type I do* becomes much harder with the addition of weight - as Phil says, it'll be all those tussocks. The only time I really noticed an 'aero' effect (or lack of) was when I first used fork mounted cages as they acted as a considerable air brake when at speed - the effect was very noticeable when descending long hills in the company of others and without pedal assist.

I also think that perception and conditions play a significant part in how we do. Even the company you're in and frame of mind can make you feel super-human or like you're towing a barge and all with absolutely no alterations to bike or kit. It's something you can't 'science' nor factor but it's very real and for most, it likely plays a much bigger role than other factors.


*should get out more really.

[jameso]

Fork mount bag/cage systems have to be a contender for greatest gain to be had from removing them, if you can TLS - weight loss of weight (weight that's also on the steering) and a decent amount of aero drag saved. I used them for one trip and took them off when I got back, as you say, the air brake effect is fairly obvious I think.

https://www.cyclingabout.com/fascinatin ... e-touring/ - pretty sure this article was discussed here a while bac, it's another good one.

[GregMay]

Thanks James, I'll fire that at some of my Y12 students!

[PaulE]

Thanks James, I'll fire that at some of my Y12 students!

I was thinking pretty much the same thing... Now I just need to find a CFD add-in for Autodesk Inventor so they can do some modelling of the airflow...

EDIT... Ooooh, there's a 2023 package that does just that! Now for some high-end geekery (or professional development as I believe it is sometimes called) to go alongside my FEA lessons in Y10,11&12!

[rudedog]

“Weight is not as significant as most riders probably believe. Even with no aerodynamic improvement, a 1 kg difference has a relatively small impact on road speed.”

Hmm I think there is a fairly big flaw in the calculations used in this article as they completely fail to take into account the effect that mass has on acceleration (Mass is inversely proportional to acceleration).

Cycling off road on uneven ground, I would imagine the effects of the acceleration/mass ratio will be even more pronounced.

[PaulE]

They are talking about road riding though, and there are some valid points made about percentage changes of weigh... That 1kg isn't much more than 1% of the combined rider/bike/kit system. Given that F=ma is a linear relationship that's roughly a linear change in the force required and thus work needing to be done.

A 1% reduction of frontal area (or some other measure of a cause of aerodynamic drag) would make roughly a 2% change to the required power as the drag force is proportional to velocity squared...

Probably the worst bit of maths I've done, but hopefully makes the point.

For bikepacking, where the bike is being lifted, then that 1kg is a proportion of just the load & bike so much more significant... And when you are going over lots of bumps requiring many accelerations then the foxes caused by these add up much more than on a smooth surface (the same reason why larger softer tyres are faster on the road, just at a much larger scale of bump)

[rudedog]

Yeah I get that they are taking about road riding, you still need to accelerate frequently on a road bike though.

Every pedal stroke provides an acceleration to the wheels which is instantly followed by a deceleration from the combined effects of tyre resistance, aero resistance and gravity (when going up hill). On a more pronounced scale, usually on a hill climb you will lose some velocity on the face of the climb and then start accelerating as you get to the crest.

To not acknowledge the effects of mass on acceleration seems like a pretty big omission.

[jameso]

Yeah I get that they are taking about road riding, you still need to accelerate frequently on a road bike though.

Every pedal stroke provides an acceleration to the wheels which is instantly followed by a deceleration from the combined effects of tyre resistance, aero resistance and gravity (when going up hill). On a more pronounced scale, usually on a hill climb you will lose some velocity on the face of the climb and then start accelerating as you get to the crest.

To not acknowledge the effects of mass on acceleration seems like a pretty big omission.

I could be wrong here but as pointed out F=MA so it's linear, the affect on acceleration is proportional to the effect on climbing pace overall and it's a simpler model to look at constant speed and power in this example. So it's an omission but not one that changes the gist of the outcome (I think).

I was thinking about this in general RE wheels / wheel size a while back. I decided that the more load I have on the bike the less 'acceleration-ability' of the wheels, and the bike in general to an extent, really matters. I'm far more interested in conserving momentum which is backed up by finding bigger tyres and larger OD wheels more efficient despite being heavier (and I get that in acceleration all I'm looking at is wheel weight, since the radius part of the calc is cancelled out / a bigger wheel spins slower. The idea that wheel weight is worth more than frame weight only really counts for maybe the first pedal stoke or 2 of a hard acceleration). When on an unloaded road bike in a group there's a lot of small accelerations and that's where the light bike feels rewarding and easier.

[jameso]

Thanks James, I'll fire that at some of my Y12 students!

I was thinking pretty much the same thing... Now I just need to find a CFD add-in for Autodesk Inventor so they can do some modelling of the airflow...

EDIT... Ooooh, there's a 2023 package that does just that! Now for some high-end geekery (or professional development as I believe it is sometimes called) to go alongside my FEA lessons in Y10,11&12!

I wish I was a student these days.. We barely got into AutoCAd when I was at college + uni. Markers for renderings, jumpers for goalposts etc

[GregMay]

*old man moment*

You had computers at school? I remember in first year at university having to explain how to use a mouse to several fellow students... I was quite lucky to have grown up with basic computers at home thanks to my dad.

[PaulE]

Thanks James, I'll fire that at some of my Y12 students!

I was thinking pretty much the same thing... Now I just need to find a CFD add-in for Autodesk Inventor so they can do some modelling of the airflow...

EDIT... Ooooh, there's a 2023 package that does just that! Now for some high-end geekery (or professional development as I believe it is sometimes called) to go alongside my FEA lessons in Y10,11&12!

I wish I was a student these days.. We barely got into AutoCAd when I was at college + uni. Markers for renderings, jumpers for goalposts etc

Sadly I think I'm pretty unusual for teaching basic FEA at y10, shame really as it does a great job of getting kids enthusiastic about engineering design and making their ideas more efficiently... and given the potential for F1 style aerodynamics I can only see CFD being another excellent tool for enthusing future engineers (or at least keeping them out of trouble for an hour a week!)

[jameso]

*old man moment*

You had computers at school? I remember in first year at university having to explain how to use a mouse to several fellow students... I was quite lucky to have grown up with basic computers at home thanks to my dad.

University in 93> so common by then. A Sinclair then C64 at home before that, Dad was into them. I was learning basic/Basic programming around that time (and I wish I'd stuck with it!).

[jameso]

Sadly I think I'm pretty unusual for teaching basic FEA at y10, shame really as it does a great job of getting kids enthusiastic about engineering design and making their ideas more efficiently... and given the potential for F1 style aerodynamics I can only see CFD being another excellent tool for enthusing future engineers (or at least keeping them out of trouble for an hour a week!)

This is so important, they're lucky to have you as a teacher. Being able (or just seeing the potential) to visualise ideas has never been easier or more inspiring, and that's the step that gets others inspired by an idea and it goes from there. I had a brief intro to VR design with Oculus a couple of weeks ago, looking at a friend's automotive design work.. just incredible.

[Bearbonesnorm]

It was all clay tablets when I was a girl.

[whitestone]

*old man moment*

You had computers at school? I remember in first year at university having to explain how to use a mouse to several fellow students... I was quite lucky to have grown up with basic computers at home thanks to my dad.

*older man moment*

My secondary school built their own "computer" back around 1969/70 - it was the size of a large suitcase, used valves rather than transistors, and could do basic maths. The first year I was there the school bought one of the first four function calculators, it cost around £250! Five years later they bought another calculator, this time a programmable Hewlett Packard model, for about the same amount.

Where's those four Yorkshiremen when you need them?

[jameso]

Stuart's (I think?) point on here about giving a teenager a rotary dial phone now and asking them to make a call on it

[Cheeky Monkey]

I remember a Uni module on basic word processing. We had to type the codes, none of this WYSIWYG nonsense.

[voodoo_simon]

Suddenly feel very young (and privileged) having my own laptop at uni…

[Boab]

Suddenly feel very young (and privileged) having my own laptop at uni…

I took my IBM PS2/50, it could just about play DOOM. It also had a whopping 20MB HDD...