chaadster

Yes, I think you have that all correct. However, whether a 28mm tire on a 29mm EW rim is faster (to any degree) is irrelevant to me, as I’m not going to run one in any case. I’m at the point that I’d expect my planned 35mm Herse rubber on a 33mm EW rim with 25mm IW and +50mm depth should be pretty sweet provided the wheels don’t weigh 1.9kg. Even if I were to conclude that marginal aero bennies were worthless, I could save a little weight (~55g) going with Lun Grapids which are deeper, better shaped (aka more aero) and externally wider than the Spinergy GX that currently carry those 35mm Herse tires, so that’d be a win no matter how I cut it.

tFUnK

Try to find some 45-55mm deep wheels that weigh under 1600g and you'll be good. There's no good reason (other than budget) to get a 50mm wheelset that weighs 1900g in 2023.

chaadster

Yeah, I think you’ve nailed it. It really was the weight of the Flo G700s which caught me out; was there any way getting to 55mm depth really worth 1.9kg? It looks like virtually all of us have our doubts, although jonathanf2 raised the off-road durability question, which I’ll leave open as the possible explanation for the G700 weight, because given their cost, it wasn’t for price-cutting.

Also, tacking on minimum widths of 24mm/30mm internal/external will be part of my decisionmaking, too.

msu2001la

In terms of durability, I have zero concerns smashing carbon wheels on rocks, roots, singletrack, etc. I feel that my carbon wheels are likely a lot stronger and better suited for this type of abuse than my alloy wheels are.

On the other hand, I don't think 1900g aero gravel wheels make any sense. You aren't getting any extra aero advantages compared to something like the 45mm Zipp 303S (which is roughly the same price and a whopping 400g lighter).

The more I read through Flo's marketing materials, the more I'm inclined to believe there aren't actually any aero gains with gravel tires. They show 7 watts of savings at 22mph with a 37c tire on their G700 wheel vs a Mavic Open Pro, but what they aren't telling you is how much of that comes from aero gains and how much is coming from improved rolling resistance due to the wider rim. A Mavic Open Pro has an internal width of just 14.5mm, so a 37mm gravel tire is going to be bulbed way out on that rim compared to something with a 25mm internal.

chaadster

Good points regarding Crr contribution, but wouldn’t a deeper rim always offer better sailing effect than a shallower one, though? Yeah, one can question how frequently those conditions present, but regardless of that, if sailing conditions are present, wouldn’t deeper always be better in those conditions?

msu2001la

I don't know for sure, but I think the answer to your question is "no". It's kind of an all-or-nothing situation.

Josh Poertner has discussed this on the Marginal Gains podcast in the past, and his conclusion seems pretty black-and-white: According to him, the external rim width must be wider than the tire to have any chance of recapturing airflow. 105% is optimal, but any ratio of "rim-slightly-wider-than-tire" will provide aero benefits. If the tire is wider than the rim, it's not possible to recapture the airflow and there are no real benefits to running deeper wheels.

Obviously real-world is different than a wind tunnel, so even a larger tire on a deep rim might still provide some benefits at certain yaw angles, but this is going to be very small compared to the aero gains that we typically associate with "aero wheels".

I think the marketing around carbon wheels is a bit misleading on this topic. It's not just Flo either. Zipp now sells this as "total system efficiency". They combine rolling resistance, vibrations and aero drag into one combined number to present watt savings, but are more vague on how much of that is actually aerodynamics. Many of Zipp's hookless wheels are not sized in a way that would allow 105% to work for most riders - the popular Zipp 303S for example has a 23mm internal/27mm external and they say it is "optimized" around a 28mm tire. I'm sure the rolling resistance is improved compared to narrower rims, but is that 45mm depth providing any measurable aero gains if the tire is wider than the rim? Maybe.

This is also why Zipp and Enve have gravel wheels that have no pretense of being aero. The XPLR 101 from Zipp is entirely focused on wider width, smoother ride, lower rolling resistance. Zipp knows that there's no chance of getting aero benefits when you've got a 40mm+ knobby tire on there.

chaadster

Thanks for the reply. The notion that it could be all-or-nothing doesn’t really ring true to me, and it’s all definitely complicated because of the myriad variables. However, I don’t want to miss the forest for the trees, as the saying goes, because we’ve been living in an aero wheel world since at least the early ‘90s, a time when both rim widths and tires were comparatively super skinny— e.g. ISO 622-13c andsay 21mm down to super racy 18mm tires— but still nowhere near the 105% Rule dictates. 30 years of intense scrutiny has been time enough to separate the wheat from the chaff, I think, and the result is that aero suceeded and persisted in track racing, road racing, time trialling, etc, so there must be something in it.

So I guess at this point, I’ll just look for an as-close-to-optimized-for-aero as possible wheelset for my fast conditions 35mm tires, and not worry about the 42mm rubber, which I primarily run in the winter when I’m dressed in bulky/draggy gear and not out that long anyway because it’s freezing. I’ll go as deep and wide as I can without having to take a real hit on the weight penalty. Someone upthread suggested 1600g, and while that’s about 1/4lbs more than I’m pushing now, I think it’s worth the hope that at some point on a given ride I get some aero gains, like if not during a sprint, maybe when I’m trying stuff my hulking mass into another riders slipstream trying to get some recovery!

SoSmellyAir

Nah, this is one of those scenarios where less (weight) is really more; just buy the lightest wide wheels within your budget.

chaadster

Haha! I’ll let you know how it goes!

chaadster

Wowzers…I was just poking around on the LightBicycle site and they’ve got a new wheelset with a rim called the WG44 that’s 30mm IW, 40mm EW, and 44mm deep that builds up to an estimated 1475g on the Bitex hubs for $962! That’s pretty impressive!

https://www.lightbicycle.com/700c-tu...isc-brake.html

tFUnK

I only mentioned 1600g as a benchmark as I find that to be the point where a wheelset feels noticeably heavy. If you can afford to go lighter, absolutely do it! 👍

tempocyclist

^ They look good! The closest I was able to find when looking around were some FarSports gravel wheels, deeper but not quite as wide (24mm IW, 30mm EW, 50mm deep @ 1330g).

https://www.wheelsfar.com/gravel-whe...hub-p0132.html

I bought a set of FarSports gravel wheels, but in a lightweight 30mm deep build. Dropped a lot of weight over stock wheels, but are obviously not aero.

JohnnyMagic

You will get a lot of widely varying views/opinions on a topic like this. 'everybody' is an expert.
The aero crowd will say one thing while the 'steal is real' bike packers will say another.

Aero DOES have an affect at low ( 12 -16) mph speeds.
Adding any triangle shaped fairing behind a cylinder will improve the CDA. Basic principals.

When I do the 'tire pressure calc. on Silca's site, I get the same suggested pressures no matter what I put in???

Going through the 'should I run a second wheelset for road', just get a faster gravel tire? Or just swap tires on these wheels???

The Blunt SL has been a great wheel for me. Can seat the bead 'tubeless' with a micro pump on the trail.

Since I am fortunate enough to work with carbon, build bikes, and have a complete fab shop;
building some 'spats, or rim fairings' seems the best way to go.


That build was about 2009'. Started supplying rear wheel covers right from the start. You can take a strong/light
spoked wheel and add covers for a lot less cost, weight and stiffer than most disc rear wheels.

The 650 covers on that bike came to a 'hard "V" and actually created handling issues at speed. (lessons learned)
Now all the deep dish wheels are rounded to varying degrees. Bigger radius helps in cross winds.
Tight "NACA" profiles are faster in straight line winds with little 'yaw' angles.

So tempting to just hit 'buy' on some of these. Can do 2 depths and build as many as I want if I build molds?

Lastly; OP mentioned he is a 'big guy'. If you take the total bike/rider weight into account. A 'pound' is hardly anything.
Probably not at the outside of the wheel?

Would like to see more Gravel bikes with deeper wheels. They just look cool!

JM

mstateglfr 

'Bennies'

Is this something that is said in the real world or just online?



Yes yes, this is me...

SoSmellyAir

So did you order these super wide gravel wheels?

chaadster

No, I haven’t. My money is not right yet, and I’m kinda leaning towards Lun Grapids for that and other reasons anyway, but I’ll post when I pick something up.

msu2001la

Wow, that's a wide wheel. So wide that it doesn't even look like an aero depth in the cross-section.

Fentuz

As others mentioned, Aero benefits occur at roughy amator triathlon speed (18mph average) but it is also conditional of the tyre setup; the surface between tyre and rim needs to be almost "seamless". In the case of a gravel setup with 38 to 42mm wide tyres, you would need a deep section wheel with outer width of 38-40mm to get the aero benefit.

the alternative would be running wider road aero wheels that work with 32mm tyres and but cyclocross 33mm (like the pros did in Italy)

Fentuz

I agree, these section is not bladed enough. With 40mm width, I would expect at least 55/60 mm depth to get similar shape proportion as a Road 40mm deep wheel