Author Topic: Carradice saddlebags less aerodynamic than handlebar bags (Read 6304 times)

mrkwr · « **on:** 17 May, 2012, 11:56:21 am »

An interesting post on the Aerodynamics of Real-World Bicycles:
http://janheine.wordpress.com/2012/05/02/aerodynamics-of-real-world-bicycles/

Basically you need to have a tight jersey and do up the zip, get low over the bars, and switch from a saddlebag to a handlebar bag. And using mudguards makes no difference!

vorsprung · « **Reply #1 on:** 17 May, 2012, 11:59:54 am »

Quote from: mrkwr on 17 May, 2012, 11:56:21 am

An interesting post on the Aerodynamics of Real-World Bicycles:
http://janheine.wordpress.com/2012/05/02/aerodynamics-of-real-world-bicycles/

.. switch from a saddlebag to a handlebar bag. And using mudguards makes no difference!

Jan Heine would say that though

LittleWheelsandBig · « **Reply #2 on:** 17 May, 2012, 12:37:04 pm »

Mr Heine has strong preferences that are not always felt by all.

He ignores that some saddlebags don't have side pockets. My main saddlebag is noticeably narrower than my hips, so I doubt that aerodynamics are being adversely affected.

I've done quite a few miles on low-trail bikes with handlebar bags and don't like how they steer.

Andrew · « **Reply #3 on:** 17 May, 2012, 12:50:13 pm »

Tbh, I've never really concerned myself with being aerodynamic so it's not really a subject that overly interests me. I think more of comfort than anything else. So I found it a thought provoking article.

I can see why the teardrop shape is both aerodynamically advantageous and be disrupted by a saddle bag. I do have a preference for closer fitting jackets but that's because I hate flapping noises rather than for any aerodynamic reasons.

mrcharly-YHT · « **Reply #4 on:** 17 May, 2012, 12:51:45 pm »

Quote from: mrkwr on 17 May, 2012, 11:56:21 am

And using mudguards makes no difference!

Obviously they haven't seen my mudguards.

Cudzoziemiec · « **Reply #5 on:** 17 May, 2012, 01:10:08 pm »

If we're talking real world effects, surely a lot is going to depend on the shape of the handlebar bag versus the saddlebag and how they interact with the shape of the bike plus rider. My handlebar bag is shaped like a brick (but I like it a lot!) whereas some are much more rounded.

LittleWheelsandBig · « **Reply #6 on:** 17 May, 2012, 01:11:50 pm »

Shape of handlebar bag makes little difference.

Kim · « **Reply #7 on:** 17 May, 2012, 01:29:06 pm »

Interesting point about lowrider panniers, presumably because they're down in the boundary layer.

I'd guess that a handlebar bag does more to guide the airflow around the bike and rider in an aerodynamic manner than a saddlebag.

As for mudguards, well, I certainly go faster when I'm not covered in poo

Andrew · « **Reply #8 on:** 17 May, 2012, 01:36:34 pm »

Quote from: LittleWheelsandBig on 17 May, 2012, 01:11:50 pm

Shape of handlebar bag makes little difference.

Yep, I think it says that in the article, or maybe the comments that follow.

I guess because it's between the drops and behind the front of the wheel that it is actually kind of hidden and out the way - enclosed within the teardrop. There's maybe a bit of 'noise' around it but little in the way of disruption.

On a related note, it was interesting what they found out about fairings. Basically, one would make sod all difference. I like having to deal with the counter intuitive!

mrcharly-YHT · « **Reply #9 on:** 17 May, 2012, 01:43:38 pm »

His statement about mudguards I can believe, when the guards are a similar width to the tyres and fitted close to the tyres.
My mercian came with 90mm-wide mudguards, mounted nearly 25mm from 50mm tyres. They are absurdly over the top and I'm sure they create a lot of turbulance - in a strong wind or when going fast, the front guard 'flutters'.

It would be interesting to find out how much difference the gap between guards and tyre makes. Intuition says it would be alot.

citoyen · « **Reply #10 on:** 17 May, 2012, 01:48:06 pm »

Quote from: Andrew on 17 May, 2012, 12:50:13 pm

I do have a preference for closer fitting jackets but that's because I hate flapping noises rather than for any aerodynamic reasons.

My formerly close-fitting jackets are no longer so close-fitting since I lost the spare tyre and I do find the difference in wind resistance quite noticeable. And the flapping noises are bloody annoying too!

d.

LittleWheelsandBig · « **Reply #11 on:** 17 May, 2012, 01:48:25 pm »

Gaps between rotating wheels and 'fixed' objects are non-intuitive. There are interactions that vary with Reynolds number and other factors e.g. 'sausages' of air pumped by the wheel. Sometimes more clearance reduces drag despite increasing the effective frontal area.

Cudzoziemiec · « **Reply #12 on:** 17 May, 2012, 02:05:15 pm »

Quote from: Andrew on 17 May, 2012, 01:36:34 pm

Quote from: LittleWheelsandBig on 17 May, 2012, 01:11:50 pm
Shape of handlebar bag makes little difference.

Yep, I think it says that in the article, or maybe the comments that follow.

I guess because it's between the drops and behind the front of the wheel that it is actually kind of hidden and out the way - enclosed within the teardrop. There's maybe a bit of 'noise' around it but little in the way of disruption.

On a related note, it was interesting what they found out about fairings. Basically, one would make sod all difference. I like having to deal with the counter intuitive!

There's nothing about shape of handlebar bag in the article and I can't see it in the comments either. What he does say is that the most important factor is frontal area and then the teardrop shape. The difference between bar bag and saddlebag must be pretty small. He does say in the comments that they'd previously found reducing rolling resistance makes more difference than aerodynamics, because there's much more variation between tyres. So in the real world I doubt you'd notice the drag difference between saddlebag and barbag - unless you're racing of course, in which case you won't have either anyway so it doesn't matter!

LittleWheelsandBig · « **Reply #13 on:** 17 May, 2012, 02:14:25 pm »

Mr Heine is a snake-hipped type and the side pockets of a saddlebag add noticeably to his frontal area. Handlebar bags don't add to frontal area at all.

Some of us have child-bearing hips (despite being male, I blame my mother) and use saddlebags that are narrower than or the same width as their hips = frontal area unchanged.

Kim · « **Reply #14 on:** 17 May, 2012, 02:17:17 pm »

Yes, would be interesting to repeat the experiments with alternatively-shaped riders...

Andrew · « **Reply #15 on:** 17 May, 2012, 02:18:24 pm »

I think I must have read it as implied by

Quote

They pointed out that the ideal aerodynamic shape, a teardrop, is wider at the front and thinner at the rear. So any rear bag sort of messes up that ideal airflow, whereas a front bag fits nicely into the profile of the teardrop.

So I guess any bar bag that extended outside of the teardrop would present an issue!

Cudzoziemiec · « **Reply #16 on:** 17 May, 2012, 02:24:50 pm »

It would have to be a pretty enormous bar bag to do that, though!

Cudzoziemiec · « **Reply #17 on:** 17 May, 2012, 02:26:13 pm »

Quote from: Kim on 17 May, 2012, 02:17:17 pm

Yes, would be interesting to repeat the experiments with alternatively-shaped riders...

I imagine that in addition to width (of hips, shoulders, or anywhere else) height would also be a significant factor.

Andrew · « **Reply #18 on:** 17 May, 2012, 02:31:41 pm »

Quote from: Cudzoziemiec on 17 May, 2012, 02:24:50 pm

It would have to be a pretty enormous bar bag to do that, though!

Yep!

That was what I was meaning to imply!

jogler · « **Reply #19 on:** 17 May, 2012, 03:15:00 pm »

Aerodynamics!
I'll concern myself with aerowhatever when I've shed at least 10kg of ugly blubber.*

*standby for the "remove yer face" type comments

mattc · « **Reply #20 on:** 17 May, 2012, 03:21:31 pm »

Quote from: LittleWheelsandBig on 17 May, 2012, 02:14:25 pm

Mr Heine is a snake-hipped type and the side pockets of a saddlebag add noticeably to his frontal area. Handlebar bags don't add to frontal area at all.

Some of us have child-bearing hips (despite being male, I blame my mother) and use saddlebags that are narrower than or the same width as their hips = frontal area unchanged.

You would still be closer to a teardrop with the bag at the front of the bike. Your current setup is crayon-shaped

LittleWheelsandBig · « **Reply #21 on:** 17 May, 2012, 03:25:59 pm »

I have no doubt that I descend faster than Mr Heine. I was no faster descending on a bike with a handlebar bag than on one with a saddlebag. YMMV.

GrahamG · « **Reply #22 on:** 17 May, 2012, 03:49:27 pm »

I interpret 'well mounted metal fenders' as 'dangerously close clearance, so pray nothing gets thrown up by your wheels'. My audax bike has been ridden without guards and I can tell the difference. Bar bags are crap for anything but touring - you can't ride no-hands with 'em and handling changes too much.

zigzag · « **Reply #23 on:** 17 May, 2012, 04:04:17 pm »

i agree that handlebar bags are not only superior to saddle bags aerodynamically, but also very convenient to store and access food/snacks. sadly, most bar bags mount with a clamp which puts them too far forward off the steering axle - the handling then is similar as if you would strap a sledge hammer to your stem..

mrcharly-YHT · « **Reply #24 on:** 17 May, 2012, 04:20:27 pm »

Quote from: GrahamG on 17 May, 2012, 03:49:27 pm

I interpret 'well mounted metal fenders' as 'dangerously close clearance, so pray nothing gets thrown up by your wheels'.

I thought the same.

Quote from: GrahamG on 17 May, 2012, 03:49:27 pm

Bar bags are crap for anything but touring - you can't ride no-hands with 'em and handling changes too much.

Funny you think that. Now I've done a bit of riding with a bar bag, I wouldn't do a long ride without one. They are just so convenient. They might muck up the handling of a racing bike, but aren't an issue on something with stable steering.