Nothing too earth-shattering here, IMO…wider tires have more drag, as do tires with more knobs.
Based on these numbers, I’d say that traction and comfort are more important considerations for gravel than aero…again, not exactly earth shattering.
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I don’t know if they’re well suited for gravel, but I do know if you take a gp5k 32mm tires & put them on a FLO G700 gravel wheelset it’s very, very aerodynamic. If you are looking at a long day on chipseal that’s a good setup. For a day of bad tarmac there probably isn’t a better setup.
Also fast on the gravel but maybe not durable enough to be a true gravel wheelset. But super fast among wide wheels.
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This test looks like it’s comparing the aero drag differences between gravel tires, which to me is borderline useless. What I want to see is the difference between running a shallow gravel wheel vs a deeper aero wheel. Even if it doesn’t match the 105% rule. This is where I believe the aero gains matter. This test doesn’t seem to take rolling resistance between tires into account, correct?
Dont try that tire on a long gravel day. I learned my lesson
I would like liked them to compared numbers with
- see images attached below, deeper is better
- Wider wheel like 40mm external width and seen if it was more aero
If were all running a 25ID by 28EID whats its like with 30ID 40Eid. It should be a flush mount
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This video is pretty cool regarding deeper wheels and wider tires.
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2-5W in a 200mile race is worth it in my opinion
No, that is what they did…go to the report itself, not the articel and you can see where they compared the 28mm rim vs the 42mm rim.
ETA- @cwiggum beat me to it!
Depends on a lot of other factors…the type of gravel, course, etc.
Some interesting data in that WinTunnel video…but the stinted dialogue is cringeworthy. 
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But…I feel better about sticking 32mm tires on my 31mm external 50mm rims 
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Ted King’s average when he won DK in 2018 was 19.2mph. So you’re much closer to the published 1.8w than you are to the 2-5 watts. 1.8w would hardly register especially since the margin of error for your power meter might be 1%, so at 200w your margin of error would be…higher than your “watts savings” between the Gravon 420 and Gravon 250
Lol, they tested these things at 45kph…how long do people average almost 28mph during a 200 mile gravel race? That seems awfully fast in the dirt.
How the hell did I miss that 
? I guess I didn’t click on the test and just quickly read the article. Not as much aero difference as I expected.
They don’t.
Maybe that’s the only way they can get measurable difference
Yeah, measured width is part of the bicyclerollingresistance protocol. All that data is valid but honestly in all conditions except Gravel101 conditions (or lots of tarmac with gravel segments) I’d pick the gravel king over the terra speed. Terra Speed has more tendency to flat and one flat equals at least 10W. 
For chunky, typical gravel I’d pick the Bontrager GR1 or GR2. I really like those tires.
I’ll say that I’ve ridden at least 100 miles in anger with each of these excep the terreno zero. That’s probably just about exactly how I would have ranked them except I would have swapped the g-one speed and the riddler. But durability matters and t he terra speed is probably at the bottom of this list in that regard (except for the terreno zero…I don’t know about that one)
That’s been my experience. If anybody else has a different experience do share!
Also the gravel king is a little bit like having a tail gunner on your bike. So there is that if you’re a rider who can’t stand wheel suckers.
Tom Anhalt has some good rolling resistance info for gravel tires on his site:
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I’ve got two criticisms of this
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(minor) They used the most aero of aero of aero setups rather than a more common one. There’s never a day you’re ever going to be flipping a coin there. A semi-aero bike would have been a better data point (Tarmac or something). It’s a nice measure for OVERALL penalty for best to realistic…except for the complete lack of water bottles (major). Why not use a full TT bike?
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(major) Looks like they used the tire rolling resistance #s off BRR. This makes sense, except the tests are different. As shown in the GP5K tests, the CX tube yields a number about 4-5w higher. You’re going to running that TL, so consistent with BRR’s own data you can subtract about 4w from their number per end - so 8w with their math (which is again flawed because of weight dist). They used a TL w/ 20ml sealant v thick tubed tire; in BRR’s own test that’s worth 2w there too.
Doing some maths…
The difference is about 7w rolling at 30kph. This is consistent with BRRs test between the GP5k TL 32 (tubed), GP5k TL TL, and the Terra Speed 38. That puts you at 24W @ 30kph. This seems about right, because a Terraspeed is basically a GP5K with mini knobs.
We can then infer…
it’s about 1.5w per tire increment (roughly in agreement with SS), 1.5w for mini knobs (same agreement), so they’ve got 15w aero difference between the 25c and 40c tire/bike - I can find about a 6w aero penalty for the tire, leaving 13w for the frame/wheel/bars, which is about right.
Anyway, the penalty for slapping 38c tires on your Aspero is about 3-4w(aero) & ~5w(rolling) ; the penalty for taking your 32c tire Aspero on a road ride is about 17w at 30kph (1.5w rolling; 3w aero + 13w for the rest of the setup) - as long as youre not on the bike and you dont have water bottles. This about the same difference any light-road bike would have .
back to positive…
I think the lesson here is that the gravel frame isn’t any less aero than a TCR/Emonda/Aethos or AL road bike. The tire aero / wheel differences seem plausible. The road bike setup as a reference is a data point from “full optimized”. Good to know what the cost of knobs are. Good to see what the difference in wheels are.