Half Frame Bag - How much will it slow me?

wondering how much a half frame bag will slow me down. let’s say on a 30km ride where I normally average 30 km/hour if I go 225 watts. (riding for fun, not racing)

if I keep the same wattage am I looking at 29.8 km/hour? or 29?

I use my bike mostly for commuting to work and I train along the way. this would make life much more convenient.

I currently have a top tube bag and a seat bag…I could consolidate both of those into the half frame bag and have room for extra gloves / jackets / snacks etc. right now I use a fanny pack but i’d be able to ditch that.

I have a Tailfin aeropack for when I need to carry heavier stuff (lunch / tools, whatever)…but I usually leave that off the bike. I’d just prefer for comfort to have my stuff in the half frame bag over stuffed in my shirt or a fanny pack.

I am guessing I’ll be slowed mostly during heavy cross winds…in which case I’ll be slowed anyway.

I know no one knows the exact answer. just wondering what your best guess is.

I’m riding a Trek Emonda. I think my main hold-up to doing this is looks or becoming a sail in cross-winds - but it’ll be super convenient.

Doesnt that save a watt. Ridley did some test on stuff and so did dylan johnson

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It matches my grip tape and water bottles. Nice choice.

Yes, some do. It depends if it transitions seamlessly into the frame.

Given OP’s uses it’s probably not enough to worry about. However, if you care or just enjoy the discussion for fun, there’s a Marginal Gains episode on the aerodynamics of commuting.

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@ABG If it closes the frame it could gain you a few watts or it might cost you a few watts depending how it integrates with the frame, its all just a guess without your exact set up in a wind tunnel, even then that still a guess of the real world. The thing that’s more certain, running out of supplies will cause you to run out of energy maybe shipping 75-100watts or more.