In my gavel aero data gathering experience having a frame bag in the upper part of the front diamond is a measurable aero benefit. But the difference between that and two UCI-legal compensation triangles in the same place is not measurable outside a wind tunnel. And since it’s gravel, if you stretch the envelope to 100mm you’re probably better off with the compensation triangles.
That’s strictly from an aero/weight point of view. I’d still opt for that super-well-conceived frame bag design because it has a lot of practical advantages! I can’t carry anything in my compensation triangles (yet).
What really makes the frame bag probably a net aero negative in this case is the large section of drinking tube that’s hanging out in the wind. Just 18" of drinking tube out in the wind is horribly UN-aero. This I know for sure! You have to get that tube up against another surface, for sure. I know that part of the tube is hidden by the race number and part of it is behind the comfort bars…but there is enough of it hanging out in the wind to undue whatever aero advantage you’ll get from the frame bag in my estimation.
My very educated guess is that the frame bag setup is a net aero disadvantage vs a clean water bladder on the back with a tube that’s just long enough to reach…held next to your body with velcro/magnets.
But it would be fun to take some data on a setup like that.
One interesting thing re: compensation triangles…they perform really well at large yaw angles. I would be interested to see if a frame bag would also perform well at large yaw angles. I’m gonna try to test that if the opportunity presents.
In such a long and difficult race, aero is definitely NOT everything. Comfort will matter a whole lot to maintain ability to put out watts late in the race. Bike handling also suffers when fatigued and can cause you to DNF or lose tons of time.
Even if a hydration pack were more aero (I’m not so sure it is), the added weight on my back would certainly fatigue me much more over such a long race. So hands down I would run the frame bag.
I think keeping the weight off your back and allowing your body to keep you cool matters more then aero. The hydration pack is a heat sink and doesnt allow a large part of your body to cool its self.
Oh yeah, I agree…well, depending on the individual. I’ve done DK both ways…with a hydration pack and with a frame bag. I prefer the hydration pack but it is also true that I’m just more durable on the bike than pretty much any other rider. It doesn’t bother me if my stem is an inch longer or if my saddle is 20mm lower or if my hips are half an inch further from the bottom bracket.
So it definitely doesn’t bother me to have a hydration pack on my back for just a 14 hour ride. No prob. Unless it’s hour 12 and the hydration pack is empty. Then I’m bothered. But if you’ve got back trouble or some other chronic problem caused by the hydration pack you gotta find another solution regardless of how aerodynamic it is.
I’m just limiting my observations to whether or not the setup is more aero. Collin’s frame bag setup on my bike would be demonstrably less aero than a hydration pack. 100% sure.
But just the same I’d take that design. It’s a clever approach & I could make it aerodynamically superior over the course of an afternoon.
@hoffman900 that’s my opinion as well. Plus, you can freeze your bladder. How many people who can’t stand having a water bladder on their back love having an ice sock between their shoulder blades?
I’ve raced DK both ways. There are advantages to both.
This may be true when the water in the pack is at ~body temp, but until then it is actually absorbing a ton of heat off your back. You can actually see this on a really hot day, especially running, that when the pack heats up the water in the tube is actually cooler than what’s in the bladder.
I am an ultra runner and have to run with a pack pretty often (and occasionally do big fun rides with limited access to water). I know myself and know that I don’t like wearing a pack unless it is necessary. I RAN a 50 mile race with two 10 ounce water bottles vs carrying my pack.
Here is a different idea but similar approach from Dylan Johnson (yes that one). Having a frame bag to just store extra water bottles in. This would cut down on the aero drag from the exposed hose from a hydration pack.
If you knew how much difference in drag the alternatives presented, then you could evaluate it in terms of comfort and weigh the importance of one vs. the other.
In the absence of measurement then all you’ve got is people making guesses.
Im talking about an added layer of material that keeps air from getting to your back to keep you cool.
The 85degree heat and direct sun at unbound is rough, wearing a backpack made it worse. If I could have made the bike carry my 2.5L i would have. I also ran ice socks at all stops.
This I know for sure! You have to get that tube up against another surface, for sure. I know that part of the tube is hidden by the race number and part of it is behind the comfort bars…but there is enough of it hanging out in the wind to undue whatever aero advantage you’ll get from the frame bag in my estimation.
