Touring - Wind resistance vs. tire resistance
Bikeforums.net is a forum about nothing but bikes. Our community can help you find information about hard-to-find and localized information like bicycle tours, specialties like where in your area to have your recumbent bike serviced, or what are the best bicycle tires and seats for the activities you use your bike for.
01-19-07, 11:19 PM
I would like to have a civil discussion on this subject and I value everyones opinion. I would like to discuss the wind resistance of touring with four panniers vs. a one and two wheel trailer. I have toured using a one wheel trailer (BOB), using four panniers, and using a two wheel trailer (Burley Nomad). It seems that there is a fair amount of wind resistance when using four panniers because of their width. And then there is the drag of another wheel when using a BOB but the BOB is narrower than when using the panniers. The Nomad has both wind resistance and the drag of an extra two wheels. I have heard of and read a lot of journals where some of those that tow a BOB break lots of spokes. This also is the case of some when using panniers. It does not seem to be the case when using a two wheeled trailer. I will have to say that I have never broke a spoke, period. I have strong, hand built wheels and maybe I have just been lucky. There seems to be a lot of twisting at the rear triangle when using a one wheeled trailer. I don't notice this when using panniers or a two wheel trailer. The issue of having to carry another tire/tube when towing a trailer does not make much of a difference to me since it is not that much more weight when fully loaded touring, but it has been mentioned by others as a reason for not using a trailer.
But, is there a noticeable difference in the wind resistance of panniers vs. the single tire resistance of a BOB? Please lets keep this discussion civil!
Old Hammer Boy
01-20-07, 12:12 AM
I've never toured with panniers, but allow me to point out that which tire is used on my BoB makes a considerable difference. Since I switched to a Schwalbe Marathon, BoB rolls quite a bit easier. Not only is the Marathon a higher pressure tire, it's quite a bit smoother and narrower than the OEM (POS) tire supplied with the trailer. Just one observation...
I have about 4000 miles with the BOB... pull it using a ti race bike; works great.
the bob sits in the wind shadow of the bike, and drafts you (it's about as wide as you), rather than adding to the air drag of you, as panniers do.
Wind resistance is always a bigger threat cycling than rolling resistance, assuming reasonable tires. I'm not clear on the terms here, but I beleive RR is just the energy lost in deforming the tire as it forms a contact patch over the gorund, as the wheel turns. Does it also include bearings, and the resistance of the wheel (small) lifting itself over roughnesses in the road. There is also the resistance of accelerating the rotating parts of the wheel and so forth. Not sure what all that is called.
In addition there are a bunch of vibrations when pulling a trailer deformations in the trailer structure itself, though the BOB looks very resistant in this regard. Suspension activation.
On the other side, paniers can be large or small and a lot could be done to smooth them, make them aerodynamic, or even fairing like. In the old days, when Zipper fairings were popular on touring bikes, I can also remember reading copy about how low riders and the right paniers could reduce the drag on a touring cyclist, operating as fairings. This may have been balderdash, though it might be possible if it was actually studied and pushed forward. What is certainly possible is to increase the air risistance of bags from behind to allow them to contribute to sailing the bike downwind if the wind should ever change from dead on the nose.
Just because the bob is about the same width as the rider, does not mean that it is drafting the rider, afterall it is low to the ground. If the rider does not rear bags, as in this example, I am not sure the bob is escaping drag though it is low in any headwind that may be present. Any wind that is off the nose a little will pick up the bob, and whatever else the BOB may be it is not very streamlined. Directly aft the wind will find less of the BOB to push. Again, it's low to the road, sloping upward, and narrow. What is more drafting is not as effective at low speeds around roughly shaped objects where vortices form...I am not suggesting that the BOB is as wind resistant as the largest paniers. It might be as wind resistant as some of the smaller ones.
In the real world there can be a number of alternative systems like front paniers and BOB before rear paniers are mounted; Front paniers and a box mounted only on the top of the rear rack, Machka style; Paniers and BOB. etc... These all have their benefits and different drag profiles.
I prefer, where a light to medium load is concerned, to drive a mini van rather than a small sports car towing a trailer. It's mostly the feel of the ride. But I would use a BOB if I needed to carry more supplies.
The Human Car
01-21-07, 04:50 AM
I started touring with a two wheel kid trailer with two wheels and then moved to a Yakama trailer with one wheel (near identical to a BOB) then to an Xtracycle. My impression is the fewer wheels the faster the ride. At touring speeds of 10-15mph I don’t think wind resistance plays that much of a factor, but if you are faster then that then wind resistance does come into play. Personally I don’t see much aero advantage to a trailer or rear panniers as they both are in your draft. Having toured with a couple people with front and rear panniers they both made the argument that front panniers make the bike more stable in windy conditions.
But personally I think an over looked factor in touring efficiency is do not over pack your setup. Whatever you decided on is designed to work well within the volume and weight limits specified.
I used a BOB trailer on my 5100 mile cross country tour. I rode with several different folks using the classic 4 pannier set-up and we did some non-scientific coasting tests to compare the wind resistance you described. In all cases, both frontal and side winds the BOB rig was better and that was me on a jumbo sized Cannondale frame, the largest they make with a mountain bike seat post so that I can get the seat high enough for me. The BOB packs more compactly and therefore presents a smaller frontal and side area for wind resistance. From the front, you bike has already begun cutting the wind which helps the trailer. Wind resistance is a tourists number one enemy.
If you have strong wheels you won't have a spoke problem with either set-up.
The down side to a BOB trailer, which is significant to many cyclist is the transport of the trailer to and from tour start /end points. Additionally dealing with an awkward 15 foot long (?) bike on a day to day basis can be a pain, especially for someone without the upper body strength to maneuver the heavy trailer. Every time you stop for a photo or at a store you have to deal with this trailer that never seems to be in the right position, try backing one up. I put a handle right on the BOB fender and have no problem lifting and moving it while loaded, but I'm sure that many would. I also put a second kickstand on the trailer which really helps in the parking department.
So pick which ever floats your boat and get out and ride.
01-21-07, 09:42 AM
But, is there a noticeable difference in the wind resistance of panniers vs. the single tire resistance of a BOB?
Perhaps, but... is it really important?
Speed is simply not an issue for most people who are touring. The primary criteria for deciding between panniers and trailers (or, for the ultralight, a stuff-sack and a backpack ;) ) are other issues, like capacity, reliability, repairability, handling, weight, access to equipment, ease of transport and (of course) personal preference. All of these issues typically outweigh the issues of wind vs rolling resistance, AFAIK.
And any plausible advantages could be negated by sitting upright, which is fairly common with cycle-tourists, as it is more comfortable for some, and provides a better view.
Originally Posted by SupertickBut, is there a noticeable difference in the wind resistance of panniers vs. the single tire resistance of a BOB?
"Perhaps, but... is it really important?"
For me, yes! Ask any tourist about their day on the road and wind will be a main topic. A tailwind can make an average day great and a headwind can have the opposite effect. Wind resistance is important, not that other considerations can't override that factor, but it's high on my list.
01-21-07, 11:22 AM
In side by side tests with BOB versus panniers (what else is there to do on a long tour?) it was clear that the BOB rig is much faster coasting downhill - maybe by 5 mph on steep hills. "High speeds" is where aerodynamics are important.
However, I think while touring, you spend far far more time going slowly uphill when "rolling resistance" is much more important than aerodynamics. This testing was of course more subjective, but my opinion is that while going uphill the four pannier system is much more efficient than the BOB.
In headwind situations BOB wins, just like going down hill. But in cross wind situations (most of the time) panniers win and in tail wind situations (never that I remember) panniers win.
Conclusion, after 6000 miles of touring on a BOB, I have switched back to panniers.
Powered by vBulletin® Version 4.1.12 Copyright © 2013 vBulletin Solutions, Inc. All rights reserved.