most aerodynamic/fairingiest handlebar bag or basket?

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mjr
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most aerodynamic/fairingiest handlebar bag or basket?

Postby mjr » 19 Sep 2019, 5:31pm

Reading about velomobiles got me on to upright bike fairings and then someone on another forum mentioned some now-discontinued handlebar bag which was sufficiently big and rigid with a map pocket with a curved rigid water-deflector that they thought acted as a mini-fairing, while others opined that fairing even just the handlebars and top headtube cluster should produce significant results...

Anyway, that led to this question: what's the most aerodynamic/fairingiest handlebar bag or basket that you've seen (or got!) that's currently on sale?
MJR, mostly pedalling 3-speed roadsters. KL+West Norfolk BUG incl social easy rides http://www.klwnbug.co.uk
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Re: most aerodynamic/fairingiest handlebar bag or basket?

Postby Brucey » 19 Sep 2019, 10:51pm

if you want a fairing, its probably best to get a fairing. You can put whatever bag you like behind it. Bar bags can give a benefit, but much as per the racks in another thread, they are not optimised for aero performance. Probably you could quite easily make something that is better than anything you can currently buy; it still won't be a very good fairing but it would surely be better than a poke in the eye with a sharp stick...

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Re: most aerodynamic/fairingiest handlebar bag or basket?

Postby mjr » 19 Sep 2019, 11:18pm

I'm not sure. Reading around it, the weakest link in fairings often seems to be the brackets: noisy, weighty and fiddly. It just seems like an obvious opportunity to use a bag (or its rigidity inserts) to hold the shaping instead.
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Re: most aerodynamic/fairingiest handlebar bag or basket?

Postby kylecycler » 20 Sep 2019, 2:08am

This might help:

Image

A handlebar bag was more aerodynamic than a Carradice saddlebag that extended just slightly beyond the hips of the rider (see photo above). Front panniers (on low-rider racks) were more aerodynamic than rear panniers.

Image

Fairings actually increased the wind resistance in most positions. We tested many different fairings, and the photo above shows the “best” setup, and even that decreased the wind resistance only if the rider assumed a full aero tuck. It’s obvious that fairings only work if they form one body with the rider. Otherwise, you are just pushing one extra object through the air.

https://janheine.wordpress.com/2012/05/ ... -bicycles/

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Re: most aerodynamic/fairingiest handlebar bag or basket?

Postby eileithyia » 20 Sep 2019, 8:34am

Interesting windtunnel testing, I was just thinking whatever fairing or bag you have on, the wind still hits the least aero part of the bike at some stage; the rider and unless you are well tucked down behind the fairing.... it is going to slam into you at some stage.
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Re: most aerodynamic/fairingiest handlebar bag or basket?

Postby reohn2 » 20 Sep 2019, 8:41am

Fairings are OK until therw's a cross wind,something that don't affect faster heavier vehicles such as motorcycles,bicycles are slow,light and feel side winds more,it's the same with deep rim or disc wheels.Fast into a wind unpredictable in the same side wind.
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Re: most aerodynamic/fairingiest handlebar bag or basket?

Postby Tigerbiten » 20 Sep 2019, 11:41am

I gather that a lot of air resistance is caused by vortex drag.
From my reading a good tail box is about twice as effective as a front fairing.
A good front fairing smooths the air flowing over the body but still generates a vortex behind it.
While a good tailbox which fills in the vortex behind your body, which is why it's more effective.
That's why you see more tail boxes that front fairing in recumbent racing.
But trying to fit anything that's effective to a bike is much more difficult due to a much bigger and more complex shape.

YMMV ......... :D

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Re: most aerodynamic/fairingiest handlebar bag or basket?

Postby Brucey » 20 Sep 2019, 12:06pm

if you mount a saddlebag on an uplift, it is out of the breeze and may even act as a tail fairing. Only dangling down like they tested it is a daft idea, aerodynamically speaking.

The contention that 'pushing an extra object through the air is bound to cause extra drag' is false. It very much depends on the shape of that object and the nature of the gap between that object and the one following.

Front fairings can and do work to lower drag, but some aspects of using them would be regarded as downsides by most folk. Especially in recumbents, a tail fairing is liable to be more effective than a front fairing, but both together is of course more effective than either by itself.

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Re: most aerodynamic/fairingiest handlebar bag or basket?

Postby mjr » 20 Sep 2019, 12:08pm

@kylecycler: thanks. It's interesting. I'd seen some of their tests before but not that.

@Tigerbiten: how does that reconcile with the tested saddlebag being less effective than a bar bag? That said, I don't think the choice is often saddlebag versus bar bag, it's more often saddlebag+trunk versus rear panniers and I already choose saddlebag+trunk for touring because it feels less tiring. Edit: I see Brucey offered a comment on positioning of the saddlebag while I wrote this.

I don't think crosswinds on a front-facing fairing are going to be significant compared to the effect on panniers or coatguards.

I also don't mind needing to tuck to get the benefit. I'm well used to praying my way across the fens into headwinds - bend right forwards and keep saying "ohhhh gawwwwwd"! :lol:
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Re: most aerodynamic/fairingiest handlebar bag or basket?

Postby Brucey » 20 Sep 2019, 12:23pm

FWIW front fairings can either be mounted on the steered part of the assembly or on the frame. The torque then exerted on the steering in a crosswind varies with steering geometry too. For any given position/amount of side windage (w.r.t. the steerer axis);


Lowest steering torque = frame mounted fairing, low trail steering
Moderate steering torque = frame mounted fairing, higher trail steering
Highest steering torque = handlebar mounted fairing (almost regardless of steering geometry)

handlebar mounted fairings can be set closer to the steering axis which can help to mitigate the torque on the steering. I'd describe the effects of running with a typical bar bag as being 'absolutely diabolical' in any kind of a crosswind. The saving grace is that if they are filled with stuff, the steered assembly is then slower to move and this helps to control the bike.

FWIW the fork offset means that the majority of the front wheel is ahead of the steering axis. This means that forks with a lot of offset can result in a bad steering reaction in a crosswind; however this can be offset by the presence of a mudguard, which increases the windage behind the steering axis. Of my bikes, the one that is most predictable in a crosswind is one with not that much trail, a fair amount of fork offset and a mudguard.

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Re: most aerodynamic/fairingiest handlebar bag or basket?

Postby Vorpal » 20 Sep 2019, 12:32pm

mjr wrote:@Tigerbiten: how does that reconcile with the tested saddlebag being less effective than a bar bag? That said, I don't think the choice is often saddlebag versus bar bag, it's more often saddlebag+trunk versus rear panniers and I already choose saddlebag+trunk for touring because it feels less tiring. Edit: I see Brucey offered a comment on positioning of the saddlebag while I wrote this.

I did aerodynamics as elective courses in engineering school, and it is generally true that vortex drag is often quite significant. However the shape and position of a saddle bag is not ideal for reducing vortex drag. I think it would take a whole other study to determine the best size, shape, and position for a saddle bag designed to reduced vortex drag. I think Brucey has part of it, in that a saddle bag on an uplift will be better than hanging down.

All that said, cyclists don't typically go fast enough that aerodynamics from stuff attached to the bike are likely make a noticeable difference. Jan Heine did all of the testing at 20 mph. My typical speed is a little more than half that. And in aerodynamics, speed is at the base of everything, and for drag it is the square of the speed, so a 5% difference at 20 mph may not even be significant at 10 mph. A pro would notice it, but that is largely because of a higher sustained speed.

It would also be a significant advantage to the folks willing to take Alpine descents at 70 mph. For me, the 1% or whatever extra momentum that I can retain on my descent from work (I won't go any faster than I already do!) disappears pretty quickly, anyway. As the linked article rightly points out, the biggest differences are in the rider position & clothing.
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Re: most aerodynamic/fairingiest handlebar bag or basket?

Postby mjr » 20 Sep 2019, 12:40pm

Vorpal wrote:All that said, cyclists don't typically go fast enough that aerodynamics from stuff attached to the bike are likely make a noticeable difference. Jan Heine did all of the testing at 20 mph. My typical speed is a little more than half that. And in aerodynamics, speed is at the base of everything, and for drag it is the square of the speed, so a 5% difference at 20 mph may not even be significant at 10 mph. A pro would notice it, but that is largely because of a higher sustained speed.

Is it only the speed of the cyclist that matters? Or does the speed of the headwind matter?
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Re: most aerodynamic/fairingiest handlebar bag or basket?

Postby Vorpal » 20 Sep 2019, 12:44pm

mjr wrote:
Vorpal wrote:All that said, cyclists don't typically go fast enough that aerodynamics from stuff attached to the bike are likely make a noticeable difference. Jan Heine did all of the testing at 20 mph. My typical speed is a little more than half that. And in aerodynamics, speed is at the base of everything, and for drag it is the square of the speed, so a 5% difference at 20 mph may not even be significant at 10 mph. A pro would notice it, but that is largely because of a higher sustained speed.

Is it only the speed of the cyclist that matters? Or does the speed of the headwind matter?

The headwind matters; at least the portion that is exactly opposite the movement of the cyclist.
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Re: most aerodynamic/fairingiest handlebar bag or basket?

Postby Tigerbiten » 20 Sep 2019, 12:56pm

mjr wrote:Tigerbiten: how does that reconcile with the tested saddlebag being less effective than a bar bag?

Completely the wrong shape ...... :D
For it to work then it needs to fill in the bodies trailing vortex better.
So a tailbox needs to be as long as a rear rack and tapered from the width of your body to almost a rear point.
If this shape was tested then it would show a better efficiency.

Luck ...... :D

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Re: most aerodynamic/fairingiest handlebar bag or basket?

Postby Brucey » 20 Sep 2019, 1:04pm

Tigerbiten wrote:
mjr wrote:Tigerbiten: how does that reconcile with the tested saddlebag being less effective than a bar bag?

Completely the wrong shape ...... :D
For it to work then it needs to fill in the bodies trailing vortex better.


hence my comment about a saddlebag on an uplift being a better idea than one that dangles in the breeze.

An idealised tail fairing is as described, but an appreciable improvement can be made by a cruder, shorter shape than this; if not then Kamm tails wouldn't work, for example.

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