Specialized did a win tunnel video on this idea:

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Alex Arman

Strava

Thanks. That is what I was after.

Whoa, that's pretty crazy. I never would have guessed that much of a benefit with a 42c tire. This makes me want to get an Exploro.

Yeah, I was shocked too. Kinda regret opting to lightweight Crests for my gravel tires, but meh, I’m not racing.

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Alex Arman

Strava

It would of been good if they also had shown the difference between the tires on the same rim.

Agreed. For everyone else I charted the results from the video below.



Roval SLX 24 vs CLX 50 (0 yaw, yaw)

• 26c - 20 seconds, 60 seconds
• 32c - 16 seconds, 48 seconds
• 42c - 12 seconds, 40 seconds

Consider that Ted King averaged 19.2mph at the Dirty Kanza last year. That's fast enough that aero matters but slow enough that the rider experiences higher yaws. Interesting.

trust me... Crr will kill everything and then some.

Everyone experiences high yaw. I did a TT at 29 MPH where Best Bike Split told me I never saw less than 10 degrees. Somewhat course specific, but the point is that fast speeds do not necessarily insulate one from high yaw.

Also if you believe the analysis done by Hambini, everyone sees really high yaw all over the damn place all the time. I don't know how much credence to place in that one analysis, but it does make me wonder if we've over-optimized to please CFD and win the wind tunnel. Not to win the real world.

¯\_(ツ)_/¯ It's hard to say.

Something that has me intrigued is how fast one could make something like the 3T Exploro with fast wheels (e.g. the CLX 50s) and fast tires (e.g. 25 CS or the new 25mm Hutchinson Fusion tires). I've fiddled with the geometry and I could hit my fit on an XL with a Sigma X stem and the MORF bars. Perhaps 5 watts slower than my Speed Concept with similar wheels and tires? 10w? What about with a bottle on the downtube? Perhaps a wash or a touch slower? It's so intriguing to me that I'm very tempted to pick one up and experiment.... just need to thin the herd a bit first.

As an aside, after fiddling with a lot of different hydration setups, I don't think it can be overstated how practical a bottle is on the down tube. I wish more bikes were designed to accommodate a bottle along the lines of the Velocite Syn, Pinarello Bolide ($10,000 for a frame??!!), and now the 3T Strada. I'd love to see someone make a tri bike with lower triangle integration along the lines of what BMC did with the new Time Machine Road.

How was this your conclusion to that video?

The point was that, tires held equal, deep / aero wheels still matter relative to shallow / non-aero wheels even when the tires basically balloon far bigger than the rim. But you now want an Exploro because the depth and shape of an aero wheel still matters with bigger tires? How does this video lead to that conclusion?

Fixed

First off, I can save you the money. I'll pay my way down to A2 if you pay for the tunnel time, because I have all these bikes. But the 3T Exploro is never going to come anywhere near 5 watts to your Speed Concept, aerodynamically speaking. That is just nuts. Not at any speed, at least not on the road. The bike (and the fork) of the Exploro is entirely (aerodynamically and in every other way) optimized to be fast with big tires, and to mate well with those bigger tires. The fork blades, the head tube, and the down tube are utterly massive. I have ridden this bike a lot, including in a pure road configuration with Enve 4.5 ARs and road tires that are an aero match for those ARs, and it's slow. Fast enough to hang with your buddies or in a good group ride, but out front, in the wind, you aren't going to come within striking distance -- I don't have data, really, but I have experience enough to feel strongly on this point.

The Exploro was built for a completely different terrain that cannot be easily tested for crr, per the poster above's point, but on the proper terrain it is absolutely faster due to the wider tire clearances and the ability to run those tires. I sometimes swear that when I'm running the Exploro with 47s and come off pavement onto some rougher gravel, the damn thing speeds up. You hit the rocks and you're like, WOOOO. The absorption of the lower pressure in the tires just takes all that turbulence and rolls right over it, not to mention the comfort involved with same. The 3T Strada, even with the 4.5s and tires (measuring) 30-31 down at 50ish PSI, feels like a ping pong ball over the same transition, bouncing around, hammering your arms, exhausting your wrists, and generally just plodding along. Note that this depends on "rougher gravel" as defined -- the smoother the gravel, well, there is an inflection point somewhere that the road bike is just going to be faster. Where that is I can't tell you, nor can anyone else.

If you were to tell me that the 3T Strada, if you could get steep enough on it and low enough on it to map to your current coordinates, could come within 10 watts of a Speed Concept aerodynamically speaking, on the road, I'd believe you for sure. But the Exploro, no way in hell. It's just not fast on the road/at speed relative to a pure aero bike. The tube shapes alone lend enough credence to this, as does 3T's own testing data on that bike.


Pictures should say a thousand words with respect to everything in your comment above. At least they do to me. Because this is a subject dear to my heart and wallet, I've uploaded them to an album.

My conclusions, just from looking at this, and from experience riding these bikes, are that round down tube and seat tube bottles make no sense ever on an aero bike, aerodynamically speaking, including on the 3T Strada (unless you are obsessed with the Morf aerobars); aero road forks/head tubes/down tubes are designed to mate exceptionally well with the tire and rim, while gravel bikes are...not; and, you should ride the best bicycles ever made as they are made to be ridden, because they will be fastest that way, unless you have reason to believe otherwise. And don't put a round bottle in between your triangle on a TT bike. Practical is between the arms and behind your asshole.

As to the original subject and where this thread went, well, I just don't fucking believe anything Specialized says on these lame videos. I think they are either irresponsible liars or their wind tunnel is complete shit -- and I am, by the way, increasingly inclined to agree with trentnix that this tunnel is neither repeatable nor reliable. Funny how we won't accept budget builds when it comes to product, but we accept budget builds when it comes to wind tunnels that test those products. These are the guys who / the tunnel which told us we would save 52 to 90 seconds in a 40K by shaving our legs! This is just nonsense. Chris Yu went to Stanford, fine, he's smart, but it's a Samford tunnel and these are Sampson Community College level analyses.

I honestly do not believe that the depth or aero shape of your wheels matters as much as they say (aerodynamically), when you are running tires that measure 42 or 47, especially on terrain that requires such widths. I just don't believe that there is not an inflection point -- with respect to a rim that is designed with a 20mm internal/24 mm external width (SLX 24), which widths are a critically important variable that they failed to normalize against -- where the depth basically does not matter as you expand the width of the tire. The damn tire is double the width of the rim! Think about the laminar flow off of that tire -- it has to be huge.

Should you have an aero rim on your gravel bike? This is not a simple question. It's like the guy who posted asking what the best setup would be for gravel tri -- the answer to that hinges on what the hell gravel tri is, and what its course will be, and what its surface will be, and, and...

At Dirty Kanza, which is essentially a road race on dirt, yeah, of course the aerodynamics and depth of your wheels matters -- it does not matter as much as the conditions of that particular year of DK, or your choice of tires for those conditions, or how those tires mate with the wheels, or the pressure you run in those tires and how it impacts the rolling resistance across a 200 mile day, or how your drafting that impacts all of the foregoing (including aero). On gravel courses or on courses where 19+ MPH speeds for 8+ hours are not possible but where the course is best and most quickly navigated by a tire that spans 42+ on which you run pressure of less than 30 PSI, then my gut says that deep rim won't matter a lick.

The transition to gravel tri is going to drive everyone nuts because none of this is readily testable, and the variables are only going to become greater than those on a smooth road with (arguably) quantifiable environmental conditions.

Because perhaps aero matters for gravel as well. I’d always written off aero and gravel because my gut instinct was “with a front tire that big the rest of the system doesn’t matter”. Perhaps that’s not the case. Btw you attributed the TT quote to me when you should be attributing it to Trail.

this is pretty much the opposite of the prevailing thinking. somebody's got some splainin to do.

i'm always all for more data. the more the better. i do have some issues with the hambini blog post. first is stylistic, the glib wiping away of all prior testing in one sentence, so that we can make way for the only one true expert.

second, i would like to know more about how the yaw data was generated. maybe i read it over too fast, but i didn't see anything about the equipment or methodology used, other than good amateur riders generated the data.

third, a rider in a straight line experiencing 5-6° yaw in a still wind (because of the dynamics of steering) doesn't meant he's constantly in a 5° yaw, it means he sees a 5° yaw twice in one steering cycle.

and finally, this is one thing i've asked for (for years) but hasn't been forthcoming in the testing (because of obviously tooling difficulties): a true sweep in a wind tunnel. a REAL sweep, as in, a rider actually riding those steering cycles, as in, riding on something like rollers in the tunnel.

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Dan Empfield
aka Slowman

It's tough to say if it's truly the opposite. Swiss Side, Flo et al. took all their data and compacted into nice, neat Guassian distributions and probability histograms with a few nice, neat angle bins.

It's possible that if someone took all of Hambini's 6 months of data and converted it into a Guassian distribution, it might end up looking like all the rest even though the one 10-minute chunk doesn't visually suggest that. Hambini would maybe just say, "What's the point in making a neat distribution of 1000 hours of data? You should care about every sample in a representative 60 seconds."

I think he would agree enthusiastically about your desire to include steering corrections, etc. He included "rider rocking from left to right" as one of the transient movements. I imagine that encompasses both rocking due to steering cycles as well as rocking due to power application (both of which seem to vary a lot between cyclists).

I agree about style and glibness, and more information about the test rig for real-world collection.

as to what hambini himself believes, i don't know (yet). i was referring to your redux of hambini, that "everyone sees really high yaw all over the damn place all the time." i think that's pretty much contrary to prevailing opinions industry-wide, tho i'm always happy to be proved wrong, esp if i exit the humiliation better informed.

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Dan Empfield
aka Slowman

I think there is benefit to aero rims and wide gravel tires, but it's NOT an aero benefit. Well . . . there MIGHT be an aero benefit, but I don't think it's enough to worry about.

The biggest and most pronounced benefit of aero rims on gravel is in the mud. The benefit of these rims in utterly nasty, peanut butter mud situations is far greater than any aero benefit they will ever generate. Box section rims gather mud and quickly amass a huge, heavy donut of earth that jams wheels and that must be cleaned out before the wheels will turn again. Sometimes, a box section rim will pick up enough muck to jam a wheel in less than a revolution of the wheel. In contrast, aero wheels tend to shed mud -- at least until you get to the full depth of the rim. It works for cyclocross, too. (You don't think people ride Zipp 404's in cyclocross for the 8 mph aero benefit do you?) On a really muddy course (think 2015 Dirty Kanza), aero rims are priceless. On a dry course, I would leave them at home.

Ah, gotcha. That was a poorly conceived sentence of mine. I'll clarify. What I meant was having read your page on Real World Yaw angles, but before having read Hambini's analysis, I'd assumed (maybe incorrectly) that the reason the prior studies only found yaw over ~10 deg. ~20% of the time was because situations with strong crosswinds were relatively rare. A special case. For example, the course I was talking about where I never saw yaw under 10 deg. is the TT course below your compound. A rectangle course with the a moderate wind at a diagonal to every leg of the course. That's not a common situation.

Hambini suggests that you can see those high numbers *all* the time. Even when there's not a strong crosswind.

So the total % may not change. Maybe it's still 20% over 10 degrees. But that 20% can happen *at any moment*. All the time, always fluctuating. Not just in special conditions. That was my "all damn place/time". It means even if you know your wheel is for a race with a dead-set headwind, you might still want a wheel that doesn't suck at high yaw.

I could be wrong with all this. I'm an electrical engineer, not an aerospace engineers. That was just my attempt to reconcile the Hambini analysis with prior analysis.

i don't get the sense that this is how the data was collected in the other studies. rather, that those studies were based on anemometers/pressure sensors attached to the handlebars. all bikes (it seems to me) experience 2 yaws: the lesser yaw of everything attached to the frame, and the greater yaw, everything attached to the steering column.

what we don't know, yet, is hambini's methodology, in any sort of granular detail. as in, what equipment was used? if i use my UPS scale to measure the weight of running shoes, that's a problem. further, hambini - correct me if i'm wrong - actually is a manufacturer. just, not of wheels (as of this writing), unless there are multiple hambinis and i'm referring to the wrong one! so, when hambini youtubes and writes about BB creak, are we to glean (using his own reasoning) that what he says and writes is untrustworthy?

i've reached out to him. i'm glad for his voice. but he needs to be subjected to the same scrutiny he applies to others.

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Dan Empfield
aka Slowman

I find that riding box-section wheels (both clincher and tubular) on gravel is noticeably more comfortable - even with higher spoke count. Not a night and day difference but more pleasurable and less likely to have a stiff neck or back after a longer ride. I run tire pressure lower than anyone I know, so not much room to play with that.

What? Why?

Please stop referring to a black box internet model as axiomatic when it comes to yaws experienced by a rider on a given course and day. Forecast.io may well be a good weather API but it’s quant inputs as the basis a model of yaws experienced by a cyclist are probably suggestive at best and utterly unproven.

Did you have an anenome or whatever the hell that is on you fork? No. So let’s have a bit of skepticism.

I reported what I used, and what it reported. I made no claim of accuracy. Either for Hambini or BBS. When a proven reliable "aero stick" becomes available, I'll use that.

But we can only use the tools we have available to us.

Because visual clues also contribute to rider perception ;-)

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http://bikeblather.blogspot.com/