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-   -   Aero seatpost bag vs. saddle bag (http://www.bikeforums.net/long-distance-competition-ultracycling-randonneuring-endurance-cycling/915434-aero-seatpost-bag-vs-saddle-bag.html)

joewein 09-29-13 06:37 AM

Aero seatpost bag vs. saddle bag
 
I've used a large Carradice bag on centuries and brevets, but it feels a little too big and I'm wondering how much air resistance it adds at higher speeds:

https://lh6.googleusercontent.com/-Y...0/IMG_4906.JPG

https://lh4.googleusercontent.com/-b...0/IMG_5287.JPG

On a recent 600 km brevet I decided to try it without the bag and instead put my stuff into a soft bag with drawstrings that I can also wear like a back pack. I wrapped that into a plastic bag against rain and then attached it to the seat rails and seatpost using rubber bands (from cut up bicycle tubes). I used the same setup again for a 180 km mountain ride with a friend.

https://lh4.googleusercontent.com/-_...0/IMG_5857.JPG

https://lh4.googleusercontent.com/-b...0/IMG_5856.JPG

This solution was very light weight though unsightly and not that easy to use, as I needed to unpack and repack the complete set every time I needed anything from inside: No side pockets for frequently accessed items. I mostly used it for clothes (wind breaker, leg armers, winter gloves, winter tights, winter jacket). I have a separate handlebar bag for tools, camera, USB battery, spare tube.

The advantages of the DIY bag were: low cost, relatively narrow profile, light weight, flexibility regarding packing volume.

At the same brevet I also saw some seatpost-mounted bags by Ortlieb and by Rixen & Kaul.

https://lh6.googleusercontent.com/-K...0/IMG_5754.JPG

https://lh6.googleusercontent.com/-V...0/IMG_5755.JPG

These bags are longer than wide, which should make them more aerodynamic than the Carradice. Intuitively I worry about the mechanical load on the mounting clamp on those bags, as they are not supported off the saddle or the seat stays. That seems like a lot of leverage for vibration on a bumpy road. Do such seatpost-clamped saddle bags really last?

What kind of rear bags do you use for brevets?

ijsbrand 09-29-13 07:16 AM

It mainly depends on the weather predicted -- how much clothing I have to take along or to store after it has done its duty.

Often, in summer, the large Ortlieb saddle bag is big enough. Mind you, its standard plastic mounting system can not be used with Brooks saddles. So instead I use some long old fashioned toe clip straps -- but those enable me to use the bag loops on the Brooks as well. This is a very stable solution. Though it does look odd.

https://lh6.googleusercontent.com/-W...ieb-saddle.jpg

However, when I use my Carradice, and its bagman, to schlepp more stuff along, I do not notice that bag a lot either.

Aerodynamics do not play a large role either between the two. Also, air resistance only begin to play a role at speeds > 32 km/h [20 m/h]

StephenH 09-29-13 07:54 AM

I was riding yesterday with a couple of friends, it was reasonably warm, and started raining. I didn't put on rain gear, since I'd just stay sweaty under it, they both stopped and put on rain gear. It took them about 15 miles to catch up with me, even though they're faster riders. So one moral there is a couple of minutes of fumbling around with awkward baggage will counteract any minor savings on the aerodynamics.

I notice on the original photo, you have the Carradice bag, plus a small bag up front, plus a plastic bag, and consolidating some of that might help.

I notice on local rides, there's a big difference in how much people bring along. When you start carrying stuff "in case you need it", you can wind up carrying an awful lot of junk and it's hard to know where to draw the line. But just traveling lighter in the first place might have more benefits than swapping bags around.

Bandera 09-29-13 08:30 AM

Quote:

Originally Posted by StephenH (Post 16114390)
I notice on local rides, there's a big difference in how much people bring along. When you start carrying stuff "in case you need it", you can wind up carrying an awful lot of junk and it's hard to know where to draw the line. But just traveling lighter in the first place might have more benefits than swapping bags around.

StephenH,

Would you have pics of how you set-up for a local ride as well as a longer Brevet?

-Bandera

Bacciagalupe 09-29-13 08:35 AM

You can't really determine aerodynamic effects without literally going into a wind tunnel. E.g. there is probably so much turbulence in that area, that you really can't know how the shape of the bag will have an effect.

The only study I've seen that is oriented towards LD was done by (who else) Bicycle Quarterly. They found that position has the biggest impact, and that handlebar bags reduce drag more than saddle bags. http://janheine.wordpress.com/2012/0...orld-bicycles/

In a separate study, they interviewed PBP participants and found that time spent at the stops has a significant impact on overall finishing times. I've seen this effect even on rides as short as 60 miles.

So, I for one am currently more concerned about making the ride more comfortable and convenient, minimizing stops, and training rather than worry about very small performance effects.

StephenH 09-29-13 08:40 AM

Try this link, which was pictures of bikes on a 600k brevet.
http://s192.photobucket.com/user/ste...doBikes?sort=3
Note in particular the contrast from carrying "a lot" to "a little". This was on a brevet in Texas. And if I remember right, it was spring, and not especially hot or cold at the time. And it was on a 600k that has about 350-375k on the first day then loops back to the start place.
This will obviously vary by region, as the amount of clothing and rain gear you need to carry depends on where you're at.

Personally, I tend to be on the "carry it all" end of the spectrum, so it's a challenge for me to leave stuff behind.

Homeyba 09-29-13 09:23 AM

My personal opinion is that people carry way more stuff than the need to. The general rule is: the more space you have to carry stuff, the more stuff you will carry. Especially some of the slower riders. Riding at the back of a 1200k like PBP is quite enlightening. The faster the riders are/go the less they carry (speaking generally). I don't even use a seat post mounted rack on rides less than 600k and only use the rack on 600k's to get used to using it on 1200ks.
I don't think the carradice bag is going to give you that great of a performance disadvantage over a seatpost rack/bag combo. You'd really need a wind tunnel to know for sure. I do know that at 20+ mph the bicycle is responsible for 25-35% of your drag, things like loose clothing and flapping bags can increase your drag by 30%. To give some numbers, the drag coefficient of a rider on bike with no bags in a touring position is 1.0, the same rider in the drops with no flapping clothing is .88
If you get a bag shaped like this it's good for a 50% decrease in drag. :)
http://i224.photobucket.com/albums/d...ps68ece83a.png

cdat12 09-29-13 09:35 AM

I'm not particularly knowledgeable and am throwing this out more as a question then an answer. I've read several articles that say keep your rear bag narrower than your hip width, any thoughts from those of you with experience?
thanks

Homeyba 09-29-13 10:24 AM

Quote:

Originally Posted by cdat12 (Post 16114589)
I'm not particularly knowledgeable and am throwing this out more as a question then an answer. I've read several articles that say keep your rear bag narrower than your hip width, any thoughts from those of you with experience?
thanks

That would make sense. Anything that is sticking out into the wind is going to have a negative effect on your aerodynamics.

njkayaker 09-29-13 10:54 AM

There are also things like this, used for "bikepacking":

https://www.revelatedesigns.com/index.cfm?fuseaction=store.catalog&CategoryID=4&ProductID=7


(Similar to some of the earlier pictures.)

Carbonfiberboy 09-29-13 12:04 PM

The Arkel randonneur setup is very good. The rack addresses your concerns. The Tailrider bag is large enough and very convenient.
http://www.arkel-od.com/us/arkel-randonneur-rack.html

joewein 09-30-13 01:13 AM

Thank you, guys! This has been very helpful input.

Quote:

Originally Posted by StephenH (Post 16114390)
I notice on the original photo, you have the Carradice bag, plus a small bag up front, plus a plastic bag, and consolidating some of that might help.

The plastic bag holds some food that I eat and then put the bag away, so it's not there all the time. In recent rides I moved more towards keeping food in jersey pockets.

The small handlebar bag holds my camera and USB battery that I need to have upfront. I've looked for bigger handlebar bags to do away with the need for a rear bag, but many interfere with the shifter cable coming sideways out of the hoods. I use Tiagra 9 speed shifters where the cables are not run under the bar tape. With hidden shifter cables as in current 105 and up it becomes impossible to pack the Bike Friday into a suitcase as there is not enough cable slack to remove the handlebar for packing.

Quote:

Originally Posted by cdat12 (Post 16114589)
I've read several articles that say keep your rear bag narrower than your hip width, any thoughts from those of you with experience?

Holding the Carradice bag behind my bottom while standing in front of the mirror, it only seems to protrude by about 2-3 cm on either side, which is less than I expected. However, because it hangs off the back of the saddle, it actually sits more behind my knees and thighs than my bottom, which rests on top of the saddle. Looking at a ride-by shot of me taken by brevet staff, I think the air flowing around my thighs will still hit the bag pretty much head-on, so its width is an issue. I think especially on the longer brevets that energy expenditure will accumulate.

Quote:

Originally Posted by Carbonfiberboy (Post 16114916)
The Arkel randonneur setup is very good. The rack addresses your concerns. The Tailrider bag is large enough and very convenient.
http://www.arkel-od.com/us/arkel-randonneur-rack.html

With something like the Arkel Randonneur Rack the luggage should sit significantly higher up, at least partially behind the saddle than all below it. I like the looks of behind-the-saddle bottle holders used by many triathletes. That should be a great place to hide luggage from the wind. I will definitely investigate the Arkel Randonneur Rack and bags for it.

znomit 09-30-13 05:37 AM

Quote:

Originally Posted by njkayaker (Post 16114763)
There are also things like this, used for "bikepacking":

https://www.revelatedesigns.com/index.cfm?fuseaction=store.catalog&CategoryID=4&ProductID=7


(Similar to some of the earlier pictures.)

I have the revelate pika bag, I use it for credit card touring (no handlebar bag), it holds everything I need with space left over. Note its not 100% waterproof.
There is a small add on bag that attaches to the top, usually put my gilet and flat kit in there.

The ortlieb seat bag is perhaps a better size for rando rides (and waterproof). Note there is a brooks friendly strap setup you can add.
http://www.ortlieb.de/_anleit/saddlebag.pdf

I have a carridace nelson too, the side pockets are handy. Apart from being a bit of a sail my real gripe with it is it sways around a bit. Seems to make quite a difference to the bike handling.

jlafitte 09-30-13 06:40 AM

If you don't carry an excessive amount of stuff, Topeak makes a large wedge pack -

http://topeak.com/products/bags/mondopack_hydro

http://topeak.com/mediafiles/products/3317/?show=1


The other side has a flap that opens into a tool compartment, very convenient. Be sure to have 11" of clearance from saddle to tire or you may burn a hole through the water bottle.

mander 09-30-13 08:13 AM

In this sport we all have our own values but getting more aero makes sense for a randonneur IMO.

Znomit do you think the pika is a bit big? It looked to me like a good sized bag for especially long rides, but maybe overkill for shorter stuff and rides where you won't need much extra clothes? How is the compaction on it if you aren't stuffing it completely full?

njkayaker 09-30-13 09:18 AM

Quote:

Originally Posted by mander (Post 16117016)
In this sport we all have our own values but getting more aero makes sense for a randonneur IMO.

Znomit do you think the pika is a bit big? It looked to me like a good sized bag for especially long rides, but maybe overkill for shorter stuff and rides where you won't need much extra clothes? How is the compaction on it if you aren't stuffing it completely full?

I'd say it's pretty good. It won't be a small bag. My opinion is that you want to reserve "completely full" less-common situations. It would be bit "over kill" if you don't need a medium-to-large pack. It looks like you can roll it down smaller than 6 liters.

The Carradice and, (as far as I can tell), the Ortlieb, are always the size they are.

========================

* The old-style Carradice saddle bags run from 9, 15, 18, 24 (!!) liters.

http://www.carradice.co.uk/index.php...&product_id=56

* The SQR Carradice saddle bags are 16 liters.

http://www.carradice.co.uk/index.php?page_id=category&category_id=13


* The Relevate Pika is 6-12 liters. The Viscacha is 6-14 liters.

https://www.revelatedesigns.com/inde...=4&ProductID=1

* This Ortlieb seatbag (S and M) is 1.5 and 4 liters.

http://www.ortlieb.com/_pdf_en/seatpostbag.pdf

* This Ortlieb saddle bag (S, M, L) is 0.8, 1.3, 2.7 liters.

http://www.ortlieb.com/_pdf_en/saddlebag.pdf

* The Topeak bag (mentioned above) is 1.7 liters but you could stuff more things in the water bottle pocket. It requires a lot of exposed seat post.

http://topeak.com/products/bags/mondopack_hydro

========================

If we can say that around 6 liters is a "medium" saddle bag, then the Relevate is a medium bag that can be pressed into service as a large bag.

The other bags (except marginally, the Ortlieb) are mostly stuck being the size they are. (You can overfill the Carradice "Long Flaps".)

MileHighMark 09-30-13 09:22 AM

I found that I prefer the Carradice SQR models over their traditional saddlebags. Zero issues with the mounting system (even off-road).

StephenH 09-30-13 12:01 PM

If you look at some of the futuristic cars and planes from long long ago, one of the mistakes they made was assuming that things that looked more aerodynamic were more aerodynamic (like big roundy fenders), and that can be deceptive. For example, for cyclists, the drag coefficient is related to projected frontal area, but that isn't all it depends on. So if everything else is held constant, then reducing the frontal area reduces drag. But when you also change the shape of things, who knows what is really going on unless there's some kind of testing involved?

The carradice bag is a good example. So it sticks out an inch on either side of your body, is that extra drag? Could be, but if you have a quartering headwind, then a long narrow bag on a seatpost rack may effectively be sticking out a foot into the wind. And it's being blocked by your body, only it's a part of your body that's churning around, so what does that do to it? The result is you can guess at what looks more aero, but you don't always know, and it's probably not worth a lot of time or money to make changes based on assumed minor improvements.

Homey's picture up there is a great example. Common sense tells you that it'd be way more aero if that cone pointed forward instead of backward, but reality doesn't always agree with common sense.

StephenH 09-30-13 06:30 PM

1 Attachment(s)
Quote:

Originally Posted by Bandera (Post 16114463)
StephenH,

Would you have pics of how you set-up for a local ride as well as a longer Brevet?

-Bandera



Attached pictures shows what I was carrying Saturday, with one or two additions and deletions. I packed for a 300k, but we only did the 200k, and I could have left a couple of items out. The stuff "on bike" fits in a seatbag. Not shown is a Road Morph pump which is on the top tube. Remaining stuff was in a Camelbak. In the last 16 months, most of my rando rides have been on the tandem, with different setup, so this is not my normal run. I'm not suggesting that this is what anyone else should carry, just what I had that particular day. I think Gary had more junk than I did, and Dan had less.

In bike bag:
Tire tools
Spare tube(s)- I should have a patch kit, too, it wasn't in there
4" vise grips
Park chain tool
Quick links
Extra chain links
Small knife
Small backup light for maps
Spare shift cable (carry tandem length, it'll fit tandems and recumbents)
Hand cleaner
Roll of small wire- should have zip ties, too, but didn't
Small allen wrenches (not sure why those are still in there, they fit the fenders which are not currently on the bike)
Spoke wrench
Emergency AA batteries
Car key
House key
Cleat screws and washers
Multitool- in going through my stuff, I discovered I did NOT have this on last Saturday's ride!
Extra cash- for local rides, normally, cash is in my walled
Fiber spoke kit

In Camelbak:
Spare headlight
Emergency toilet paper
Baseball cap- adjustable strap and button on top removed, worn in the rain to keep rain off glasses
Reflective vest
Reflective ankle strips
Wallet
Brevet card (not shown) & pen

I forgot my helmet lamp, which would normally be on my helmet, not in the bag. And all this stuff was in baggies, with the small items all thrown in a couple of baggies.
http://bikeforums.net/attachment.php...hmentid=343501

Homeyba 09-30-13 08:20 PM

Quote:

Originally Posted by StephenH (Post 16119096)
Attached pictures shows what I was carrying Saturday, with one or two additions and deletions...

Wow, I need to ride with you. That way if something breaks on my bike you can fix it! :) :)

On a 1200k I bring:
A Tire tool
Spare tubes (2) and a patch kit
CO2 cartridges and pump
Small backup headlight/bulb
AA batteries
cash and a credit card
Brevet card
Extra clothes if needed
food
I wear my reflective stuff.

In Camelbak(I only use a camelbak if there are extended sections between controls with no support) :
water and rarely extra clothes.

unterhausen 09-30-13 09:09 PM

hydration packs are evil as far as picking up worthless junk, I wear mine when it's hot because I really, really hate running out of water. I also carry a spare set of shorts when it's really hot because I've found that can be a ride saver. I have a collection of small things that would have made previous rides a lot easier, such as zip ties, spare cables, spare taillights, food. The bulky things are a spare tire, 2 spare tubes, patch kit and a rain jacket. On longer rides I usually carry arm and leg or knee warmers. It all fits in the large Ortlieb saddle bag.

Carbonfiberboy 09-30-13 10:16 PM

I use an Ortlieb for shorter rides and an old Detours rack bag that's not made anymore for longer. I carry in the bag, for 3 season, in no particular order:

Reflective ankle bands.
Reflective Sam Brown belt
Wind vest
Rain jacket
Arm warmers
Leg warmers
Spare gloves, sometimes different weights
2 tubes
Patch kit
Spoke wrench
Multi-tool
Chain tool (I hate the spoke and chain tools in multi-tools)
Leatherman Juice C2
Spare brake and derailleur cables
Minimalist first aid kit with ibuprofen and a couple of codeines in case of the worst
Zip ties
Spare batteries (no spare lights - they're all on the bike or my helmet)
Spare socks in a baggie if it's going to be wet and cold
Malto/whey powder mix in Ziplocs, amount depending somewhat on distance.
Endurolytes
Small chamois for cleaning glasses and lenses
Boot material
Accident reporting forms and a pen
1 oz. of allergy medicine, eye drops, chain oil, butt cream
Glasses lenses for different light conditions, including clear
Spare headband/skull cap
Spare cue sheets in a Ziploc
Car key
Plastic case with cc, driver's license, Starbucks card, health insurance card, and some cash
Brevet card is in a Ziploc in a jersey pocket
RoadID dog tag around my neck

I've used or wished I'd had everything I carry. That's why I carry it. The record among my riding buddies is 9 flats on a 600. He finished.

Homeyba 09-30-13 11:00 PM

Quote:

Originally Posted by Carbonfiberboy (Post 16119789)
...The record among my riding buddies is 9 flats on a 600. He finished.

I had 8 on my very first 200k. ;) I think I've had only a couple on the half dozen 1200ks I've done. I had two on one RAAM and three on another, the other two zero. Flat's are really not that common but it sucks when you get them in clusters which seems to happen every once in a while.

joewein 10-01-13 01:22 AM

Quote:

Originally Posted by ijsbrand (Post 16114333)
Also, air resistance only begin to play a role at speeds > 32 km/h [20 m/h]

Not strictly true. It plays an increasingly larger role at higher speeds, but on a flat road without head wind energy expenditure for overcoming air resistance dominates over other sources of friction at any speed you're likely to find a randonneur riding under such conditions (i.e. even at 20 km/h).

Play around with a cycling power calculator such as this one, it gives some interesting data. If we assume air resistance to be negligible at 5 km/h, without any air resistance your power output at 20, 25 and 30 km/h should 4, 5 and 6 times greater. In fact it is 9.2, 16.5 and 24.4 times greater. This suggests that air resistance accounts for roughly 57%, 70% and 75% of power output at 20, 25 and 30 km/h respectively (12.5, 15.5 and 18.6 mls/h), if my math is correct (riding on the hoods, box rim 32 spoke wheels, training tyre, 10 kg bike weight).

RChung 10-06-13 09:18 AM

Quote:

Originally Posted by joewein (Post 16120067)
Not strictly true. It plays an increasingly larger role at higher speeds, but on a flat road without head wind energy expenditure for overcoming air resistance dominates over other sources of friction at any speed you're likely to find a randonneur riding under such conditions (i.e. even at 20 km/h).

Play around with a cycling power calculator such as this one, it gives some interesting data. If we assume air resistance to be negligible at 5 km/h, without any air resistance your power output at 20, 25 and 30 km/h should 4, 5 and 6 times greater. In fact it is 9.2, 16.5 and 24.4 times greater.

I get slightly worse ratios than you: more like 12x, 21x, and 35x greater.

The eyeball is a poor wind tunnel so if you want to know how big an effect a bag, or clothing, or a change in position, has on aero drag the best thing to do is measure it. Many people seem to think that it's impossible to measure so you may as well not worry about it. I think it can be tedious to measure but it's not hard and there are ways that can get you a quick estimate of total drag so you can pop that value into that online calculator you're using. Then if you decide the effect is negligible at least you're making an informed decision.


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