Touring - Air drag from rack+trunk vs Carradice saddlebag
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06-23-06, 09:40 AM
In the February issue of the Randonneuring magazine, there was a brief article that said that there is significant air drag from transverse-mounted saddlebags like the Carradice Nelson Longflap, and that the faster British randonneurs use a Carradice rackbag and rack.
I'd been planning to get a Nelson to increase carrying capacity and save weight relative to my current rig (Arkel tailrider and Blackburn rack), but now I'm reconsidering, in light of the wind resistance argument. Has anyone out there tried both and would like to comment?
How much does a Nelson Longflap weigh (it doesn't say on Carradice's or any other web page I've found ...)?
06-23-06, 09:44 AM
I can't comment on the Carradice, but use a Tubus Fly rack and a waterproof stuffsack bungied on the rack for both of your concerns. It's light weight and I think there is zero additional cost due to airdrag because it is neatly tucked in behind me.
06-23-06, 10:08 AM
I have done a number of coast-down-the-hill tests over the years in different body positions, with/without baggage, and loose/tight clothing. At touring speeds 12/15 MPH nothing makes too much difference. A few percent at most. Air drag is a cubed function of power (see the Fan laws) so if you want to cruise at 30 MPH any bags, loose clothing, and bad body position can really hurt. I have hit 45 MPH with front and rear panniers going down Loveland Pass at high altitude in a full tuck with full spandex. The thinner air helps, not something the Brits need to worry about even on Ben Nevis.
06-23-06, 11:59 AM
How fast are you planning on riding?
Air resistance is only significant above about 15mph/24 kph, which is pretty fast average speed for touring.
06-23-06, 01:50 PM
I'm talking about randonneuring, so rides are typically long and require sustained hard effort to complete in the given amount of time, e.g., 375 miles in 38 hours. My average on-bike speed is around 14 mph, but that includes a lot of hill climbing (last ride had 22,000 feet), so I'm typically going 18 to 20 on the flats and as fast as I can or dare on the downhills. A percent more drag or weight makes a big difference on these rides. For instance, when you've already ridden 300 miles and are grinding your way up five miles of steep hill, you can very readily tell how much easier it is to pedal if you dump a waterbottle. When you've been riding for the last three hours into a 10 mile an hour head wind, you can very readily tell the difference in drag between riding on the hoods versus dropping onto the aerobars. I'm not sure how drag trades off against weight, but the combination of rack (1.5 pounds) and rack trunk (1.4 pounds) is (I'm told) about a pound heavier than the combination of a Nelson Longflap (??? pounds) and a Bagman seat-rail-mounted rack (1 pound). But if the Nelson is lighter and doesn't have appreciably more drag, then you'd think that combination dominates.
So, that's why I thought it'd be useful to ask if anyone has tried both combinations.
06-23-06, 09:06 PM
I was using my touring bike to ride with a group of DF and recumbents. Rides were about 25 to 35 miles each. I could stay with them for the first 20 miles but then would get tired and slow down a bit. I took off my racks, fenders and panniers and gained 2.5 MPH and was able to stay with the fastest riders for the entire ride. Made a lot of difference for my particular use. I can put the stuff back on when I tour. That has been my experience. Rich
06-24-06, 01:57 AM
If your fighting a stiff headwind the air drag can really make a difference even if your not going very fast.
A wide bag across the bicycle has more air resistance than a long bag inline with the bicycle even if the two bags have the same volume. For touring where the effort is measured out over a daily distance the issue is not usually significant. When doing a brevet where the effort is more or less continuous over the total distance I would think the extra drag would become more noticable.
I use a Nelson long flap for commuting, and I would be suprised if it added much in the way of drag. The majority of the bag sits behind the saddle, thus, behind my rear and thighs. I have no tests to support this however, just a user's guess. I don't know what it weighs, it is heavier than my nylon rack bag, but I doubt it is as heavy as my rack bag and rack together and holds much more than my rack bag. I did a google image search of Paris Brest Paris and found many pics, but few that accurately showed the bags riders were using. A few that did showed rack bags. The website http://www.ultracycling.com/equipment/gear_bags.html says you can tell the rider's nationality by what kind of bag they use, Brits use bags like Carradice and Americans use rack bags, with the French using handle bar bags, so maybe it's not much of a consideration? I can get into my Carradice, at least the side pockets, while riding without killing myself and I couldn't do that with a rack bag, but my saddle is high. A Carradice bag needs a saddle with bag loops, like a Brooks, if that's a consideration. I think they make an adapter for a plastic saddles without loops. I'm interested in your progress through this, especially your equipment picks. I hope you keep the forum posted.
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