A few months ago I spent a day testing different weights in my panniers to determine how those differences would affect my travelling speed. On one test run I decided to use front instead of rear panniers, and realised there was a speed difference. It worked out to be around five minutes on a hilly 100km ride, or the equivalent of carrying five less kilograms.
That experience spurred on the idea to determine the aerodynamic differences between front panniers, rear panniers, both panniers and bikepacking bags on a velodrome. I decided to go around in circles until I’d gathered enough data, using a power meter to ensure that my effort was consistent from start to finish. This isn’t an exact science, I know, but it’s the best I can do without having access to a wind tunnel!
I used an outside velodrome in Melbourne (AUS) as my testing ground. The velodrome is precisely 320.622m long and actually has one metre of up and down for every lap. There was a slight breeze coming from the south but it didn’t seem to change throughout the day.
The bike I used was my Surly Long Haul Trucker touring bike. It weighs precisely 15kg and has Schwalbe Marathon Mondial 40mm tyres installed. I fitted a Stages power meter crank arm to keep my effort of 200w in check. I wore casual clothes, as that is generally my preference on a bike tour.
I tested four different bag configurations on the velodrome. I used Ortlieb Backroller Plus 21L panniers for both the front and rear pannier testing. When testing both front and rear sets, I used the Backrollers on the rear rack and added some Frontrollers to the front. My bikepacking kit consisted of a Revelate 12L saddle bag, half frame bag, top tube bag and handlebar sling with drybag. The overall weight for all setups was identical.
All of my tests runs had a rolling start and were conducted in the same gear from start to finish. My power fluctuated up a little on one side of the velodrome, and down on the other, presumably due to the elevation changes.
I initially completed 10 laps (~3.2km/2mi) with each bag setup. I then re-tested for another 10 laps with each setup to ensure that my times were consistent. The average speeds and times below are based on all 20 laps for each bag setup.
What about fatigue?
Here’s the deal; I got fatigued, but that didn’t affect the results. How? I picked a power that I knew I could push all day long, so even as I was getting gradually more tired after each test run, the pressure I put through the pedals remained the same from start to finish.
Bikepacking Bags – 20 laps @ 200.5w Average Power
38.262 seconds av per lap
119.34 seconds av per kilometre
30.17km/h average speed
Extrapolated Time for a 100km (62mi) Ride: 3:18:54
Rear Pannier Bags Only – 20 laps @ 199.5w Average Power
40.931 seconds av per lap
127.66 seconds av per kilometre
28.20km/h average speed
Extrapolated Time for a 100km (62mi) Ride: +12 minutes (6.5% slower)
Front Pannier Bags Only – 20 laps @ 199w Average Power
40.89 seconds av per lap
127.54 seconds av per kilometre
28.23km/h average speed
Extrapolated Time for a 100km (62mi) Ride: +12 minutes (6.4% slower)
Both F+R Pannier Bags – 20 laps @ 200w Average Power
41.542 seconds av per lap
129.57 seconds av per kilometre
Extrapolated Time for a 100km (62mi) Ride: +17 minutes (7.9% slower)
The effects of aerodynamic drag turned out to be quite significant. Using two panniers on either the front or rear slowed my speed by about 6.5%, while running both sets at the same time stretched that out to 7.9%.
It’s reasonable to extrapolate this data because the number of laps I completed on the velodrome should balance out many external influences. It was reassuring that after completing 10 laps, and re-testing for another 10 laps, that I was within a couple of seconds each time. Should I have completed more laps on the velodrome, there would have been the risk of greater changes in the weather, which wouldn’t have provided a fair comparison between each of the loads that I was carrying.
It’s interesting that there’s very little difference between using front vs rear panniers. While you’d assume that having the front panniers lower to the ground would reduce the effects of aerodynamic drag, my testing demonstrated that the difference is negligible.
As expected, adding a second set of panniers to my bike slowed it down a further 0.5km/h.
Are Aerodynamics Significant?
Aerodynamics have a very significant impact on your speed, especially when compared to my weight testing. On my hilly test course when carrying 20 extra kilograms it worked out to be 18 minutes slower over 100km. To put that into perspective, that time difference is essentially the same as the difference between bikepacking bags or four panniers with equal weight (17 minutes). That’s a lot!
A Few Thoughts on Aerodynamics
The more distance you’re looking to travel per day, the more aerodynamics matter.
If you’re planning on completing some big days on the bike, then your time savings will become greater and greater with bikepacking bags. For example, if you were riding 200km on a flat route, you could expect a 24 minute saving for the day given the same amount of effort.
The flatter your tour route – the more aerodynamics matter.
You move faster on flatter surfaces, so the effects of aerodynamic drag are greater. For a trip that traverses flat land, it makes even more sense to use bikepacking bags.
The hillier your tour route, or the more weight you have – the less aerodynamics matter.
Aerodynamics play a bigger role the faster you’re moving. As your average speed is reduced in the hills (or with more weight) the effects of aerodynamic drag will reduce too, and the overall time savings have less of an effect.
If you’re carrying bikepacking bags, you’re probably not on a touring bike and you probably have a lighter load.
If you’re using bikepacking bags on the road, you’re probably on a lighter weight bike, with slicker/narrower tyres, and in a more aerodynamic position. The time savings from you bag setup choice are just the beginning, really.
While this test is an interesting comparison between travelling speeds with different bag setups, you should ideally choose your bags based on the type of trip you’re doing. If you like carrying comfort items, or if you’re travelling for a long time – then panniers are going to be the most practical solution for you. But if you’re travelling light, you’ll have the option for either setup.
Alee, the aero savings are huge! Should I sell all my panniers?
Don’t do it! Panniers are are awesome for bike travel as they’re:
– Quick to take on/off the bike
– Easy to carry off the bike
– Able to fit all kinds of objects
– Twice the capacity as a complete bikepacking kit (four panniers)
For those tours where you don’t need to carry as much gear, it’s hard to look past using a set of bikepacking bags. They’re light, fit to any bike and force you to pack light – the aero savings are really just the cream on top.