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Deep section rims for gravel?

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Deep section rims for gravel?

Old 01-18-20, 03:17 PM
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avrilboazmoss
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Deep section rims for gravel?

Is there any point in having a deep section rim wheel for gravel? Considering the tires go 37C+ and with way more aggressive threads than road ones and at slower speeds, there canít be much aero benefit to deeper rim, can it?

Sure deeper rims are more rigid and perhaps allow for fewer spokes, but the rims also get heavier especially when wider as gravel tires would require. So what am I missing that gravel marketed wheels are not basically the same as trekking ones?
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Old 01-18-20, 03:27 PM
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Even at the slower speeds there's still an aero advantage that might be significant over a 100+ mile race. Very marginal gain, but still a gain.
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Old 01-19-20, 12:56 AM
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Originally Posted by tyrion View Post
Even at the slower speeds there's still an aero advantage that might be significant over a 100+ mile race. Very marginal gain, but still a gain.
when the tire is much wider than the rim, you are just carrying extra rotational weight, so it is actually a marginal loss
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Old 01-19-20, 06:15 AM
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There's always an aero advantage with deeper rims, and it adds up the longer you are on the bike riding. When the tire profile doesn't transition smoothly to the wheel you start losing the aero help quickly though and since most gravel tires mounted on even the widest gravel rims look like a light-bulb profile, the help is more than offset by the added weight in most cases.
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Old 01-19-20, 08:01 AM
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Is anyone worried about exposing more carbon to potential hazards?

I'd go with shallow carbon, rock strikes are still plenty possible but they don't have a long thin section just begging to get slapped by rocks. Lighter too.
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Old 01-19-20, 08:34 AM
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Originally Posted by tyrion View Post
Even at the slower speeds there's still an aero advantage that might be significant over a 100+ mile race. Very marginal gain, but still a gain.
Also, if you encounter mud deeper rims shed mud better.
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Old 01-19-20, 11:50 AM
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Originally Posted by Chi_Z View Post
when the tire is much wider than the rim, you are just carrying extra rotational weight, so it is actually a marginal loss
Has anyone tested this? I think Hambinini said as a general rule any increase in aspect ratio will decrease drag.
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Old 01-19-20, 12:18 PM
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Having owned and put thousands of miles on a 40mm and a 44mm wheelset Iíd say the 2 main advantages are as follows; you will definitely look cooler at red lights and wherever other cyclists may congregate. You will have a gentle push sideways whenever a gust of wind hits you from the side. Perhaps that push sideways will translate into forward momentum.
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Old 01-19-20, 02:24 PM
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Originally Posted by tyrion View Post
Has anyone tested this? I think Hambinini said as a general rule any increase in aspect ratio will decrease drag.
Starting around 1h mark of his video linked within, he has the slides below. So if it is true that it requires 80mm deep rim for 28mm wide tire to have aerodynamic benefit, what is that modern 42C gravel wheel are trying to achieve? He also claims that wider rims are useless if not deep enough in terms of aero gains.

It was actually basis for my question, because if it is worthless to have deep section rim at those tire widths, then one may as well look at sturdy alloy rim with minimal weight with lowest possible profile. It will be arguably stronger than carbon one at similar weight. Which is where one gets to 19mm wide touring wheels.



Source:
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Old 01-19-20, 02:28 PM
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Originally Posted by Ghazmh View Post
Having owned and put thousands of miles on a 40mm and a 44mm wheelset Iíd say the 2 main advantages are as follows; you will definitely look cooler at red lights and wherever other cyclists may congregate. You will have a gentle push sideways whenever a gust of wind hits you from the side. Perhaps that push sideways will translate into forward momentum.
That's what I had suspected, but wanted to have inputs from people running such setup. I am going to be swapping road and "gravel" wheels in a CX frame and all I guess to focus on is to get low weight with reasonable strength for the gravel wheels, aerodynamics can be completely disregarded.
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Old 01-19-20, 02:30 PM
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Originally Posted by Marcus_Ti View Post
Also, if you encounter mud deeper rims shed mud better.
Isn't there actual more surface for the mud to attach onto?
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Old 01-19-20, 02:40 PM
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Originally Posted by tyrion View Post
Has anyone tested this? I think Hambinini said as a general rule any increase in aspect ratio will decrease drag.
according to enve, putting 28mm+ tire on their SES 3.4 gives similar aero properties of a box section rim, thus the new wider SES 3.4 AR designed to match the wider 28mm tire
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Old 01-19-20, 02:59 PM
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Originally Posted by avrilboazmoss View Post
...what is that modern 42C gravel wheel are trying to achieve?
While those fat tires make it far far away from optimal (105 rule or Hambini's exception/refinement), my guess is increased aspect ratio generally decreases drag. Of course those aero gains might be so marginal with fat tires it's not worth the weight penalty. I have no idea where the trade-off lines intersect, where the sweet spots reside.

I'm pretty sure the wheel companies and engineers like Hambini and Poertner haven't really dug into the aero/weight optimization of 40mm+ tires yet (the big money is still in road racing), so it's all rules of thumb and subjective experience.
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Old 01-19-20, 03:06 PM
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Originally Posted by Chi_Z View Post
according to enve, putting 28mm+ tire on their SES 3.4 gives similar aero properties of a box section rim, thus the new wider SES 3.4 AR designed to match the wider 28mm tire
Just checked their web, it goes on to say: ďDifferentiated rim depths are fundamental to the SES range, delivering optimized aerodynamics along with incredible stability thanks to the highly developed rim profile and the shallower front rim. For the second generation of the 3.4, the depths have been revised to 38mm at the front and 42mm at the rear, with the extra benefit of a more refined aesthetic.Ē

Why would they make the front rim shallower if anything?
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Old 01-19-20, 03:11 PM
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Originally Posted by tyrion View Post
While those fat tires make it far far away from optimal (105 rule or Hambini's exception/refinement), my guess is increased aspect ratio generally decreases drag. Of course those aero gains might be so marginal with fat tires it's not worth the weight penalty. I have no idea where the trade-off lines intersect, where the sweet spots reside.

I'm pretty sure the wheel companies and engineers like Hambini and Poertner haven't really dug into the aero/weight optimization of 40mm+ tires yet (the big money is still in road racing), so it's all rules of thumb and subjective experience.
That’s what I was getting at, the wheels that the current gravel bikes come with don’t seem to be particularly finding some sweet spot, they just look more like road wheels but then with wide tires what’s the point.

There must be some sweet spot for light and sturdy gravel wheel that may or may not take aerodynamics into consideration at all because it may be negligible. If it was so, then the weight aspect comes as first. I can certainly feel when I put heavier wheels on, even heavier tires, but I wonder if someone can feel 14C shallow vs 19C deep rim difference on a road bike even in terms of less drag.
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Old 01-19-20, 03:18 PM
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Originally Posted by avrilboazmoss View Post
Isn't there actual more surface for the mud to attach onto?
More surface area, yes. But the profile means that the rim cuts through goop better and the steeper sloped slides make goop want to slide off it more.

There's also the reality that carbon rims can be made the same weight as alloy rims and be deeper (potential aero gains). Or they can be the same depth and lighter. So there isn't necessarily even a weight penalty....sure there are light and stupid-light alloy rims, but even the ostensibly-well-designed light rims don't live very long lives (Looking at you Pacenti SL23 and Forza). Cost per rim, a HED Belgium rim is $150 each versus a Light Bicycle rim that is $155-180 depending on what rim you get.

From a wheel building POV, CF rims come out of the box straight consistently...versus even nice alloy rims that don't.
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Old 01-19-20, 03:51 PM
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Originally Posted by Marcus_Ti View Post
More surface area, yes. But the profile means that the rim cuts through goop better and the steeper sloped slides make goop want to slide off it more.
I may be missing some subjective experience but surely the centrifugal force of a turning wheel is way stronger than gravity that would cause it to slide off. I mean - if it wasnít than we wouldnít need mudguards much. May it just be that deep section rims happen to have no flat spoke bed which causes the mud to slide off one side or another? But then any rim with any depth with such cross section should be just fine.

Originally Posted by Marcus_Ti View Post
There's also the reality that carbon rims can be made the same weight as alloy rims and be deeper (potential aero gains). Or they can be the same depth and lighter. So there isn't necessarily even a weight penalty...
This was the reason why I posted the question. If it turns out the aerodynamics effects are negligible and I were to focus on weight savings, what would be the best example of low profile carbon rim and how much lighter would it be than comparable alloy one?

Originally Posted by Marcus_Ti View Post
From a wheel building POV, CF rims come out of the box straight consistently...versus even nice alloy rims that don't.
So they are easier to build for the people selling them to me at potentially higher margin?
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Old 01-19-20, 03:51 PM
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I grappled with this same question about a year ago. The conclusion I can to is the same one the the OP seems to be leaning toward: that it depends on the tires you run; the bigger the difference between tire and external rim width, the less aero benefit deep rims provide.

I was never able to find any sort of documentation that showed any theoretical model or experimental data to determine how much aero benefits drop off as tire/rim width ratios increase. But the fact that wheel makers have explicitly pursued wider rims to allow for aero gains using wider tires seems to back up this conclusion the Enve AR series are one example of this. The Hunt gravel aero wheels are another:

Hunt 48 Limitless

I generally prefer to ride tires >40mm and do a lot of climbing.
As a result, I went with a shallow and light XC wheelset. 24mm wise (internal), 24mm deep, 1230gr
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Old 01-19-20, 04:01 PM
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Originally Posted by avrilboazmoss View Post
That's what I had suspected, but wanted to have inputs from people running such setup. I am going to be swapping road and "gravel" wheels in a CX frame and all I guess to focus on is to get low weight with reasonable strength for the gravel wheels, aerodynamics can be completely disregarded.
I run Chris King built wheels on my CX bike with HED Belgium+ rims. They are strong and are built with R45 hubs and weigh about 1500g. Iíd recommend them any day.
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Old 01-19-20, 05:57 PM
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This is just a data point- I'm not looking to argue.

I've run a whole bunch of rims on road bikes- Deep dish cosmic carbones clincher 1800 gm and tubular aero mavics1500gm/ semi aero mavic sscs 1500gm / non aero- lightweight zipp 202 tubulars1200gm (more or less.... )
I think the "looking cool at stoplights" is right on lol. I would also add- the aero wheels ad a lot of real estate to add cool graphics. Also- they make you feel like a faster rider. Only problem being- you'd better have the goods to deliver if you show up to group rides with aero wheels.
My seat of the pants non scientific appraisal is such- below 20 mph ave speed, especially when low speed steep climbing is involved, light weight rules. Between 20-25, it's kind of a toss up between aero/non or "semi" aero. Above 25- I feel the benefits of aero. Above 30-35 total aero.
If you can get a 1500gram aero wheelset, go for it, it's the best of both worlds, and would look cool, but otherwise, unless you are tooling around at / above 20mph average on your gravel bike, you might not benefit from heavier aero wheels as much as a lighter weight wheelset may help you more in climbs/ acceleration vs. whatever advantage a heavier deeper wheelset provides.

Living in the mountains, the zipp 202's are the BEST climbing wheels, but aren't the fastest overall, or the most stable. I rarely use them. I find the 1500 gm mavic ssc's the best overall wheel. The 1800 gm cosmic aero wheels are heavier and more stable on descents, and that heavier weight also helps in high speed crosswinds more than you'd expect- which is kind of counter intuitive. I don't find them unstable, but I also think about the idea they are "sails" at certain angles, and as much as I'd like to believe I might be catching some wind advantage in some angles, I also seem to find I can also find perpetual headwinds, which might detract as much as the elusive tailwind provides.

I am currently looking for a set of lightweight gravel wheels, and I haven't really been concerned about dish depth. I'm thinking more about weight- but again, I live in the mountains. It's all about climbing out here.

Also- living in the mountains, and having taken all these rims on muddy gravel roads at times, they all seem to catch mud, the deeper dish wheels catching more splash/ mud due to more surface area. In heavy mud, they are all covered and weight a bunch, but then so is the rest of the bike/ rider. I'm envisioning this mental image of a low dish rim catching mud, and then the centrifugal force of a deep dish rim "shedding" that mud, but then in my mental image, the mud ends up getting splattered on me, where it sticks anyway lol....

Last edited by dualresponse; 01-19-20 at 06:08 PM.
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Old 01-19-20, 07:21 PM
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Originally Posted by dualresponse View Post
I'm envisioning this mental image of a low dish rim catching mud, and then the centrifugal force of a deep dish rim "shedding" that mud, but then in my mental image, the mud ends up getting splattered on me, where it sticks anyway lol....
Thatís rotating weight moving onto you, so still a gain overall, right? 😉

Thanks for the comprehensive answer!
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Old 01-19-20, 07:44 PM
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It just so happens that Iím running the second gen SES 3.4s for gravel. Reason being is that their 21mm hooked internal width was optimum at the time I bought them. Running with 38mm tires.

Do they ride like a box rim? Are they aero? Haha... I actually liked box rims back in the day, so I guess Iím a bad person to ask. But I doubt at my speeds theyíre aero...

I had assumed the front wheel was a shorter profile to help mitigate crosswinds influencing the steering... but I have no data to support this.

I like the lateral stiffness they provide and have been extremely robust. Went through a few pairs of other wheels before I got these.

The AR version is hookless so Iím not interested.
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Old 01-19-20, 08:44 PM
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Originally Posted by avrilboazmoss View Post
I may be missing some subjective experience but surely the centrifugal force of a turning wheel is way stronger than gravity that would cause it to slide off. I mean - if it wasnít than we wouldnít need mudguards much. May it just be that deep section rims happen to have no flat spoke bed which causes the mud to slide off one side or another? But then any rim with any depth with such cross section should be just fine.


This was the reason why I posted the question. If it turns out the aerodynamics effects are negligible and I were to focus on weight savings, what would be the best example of low profile carbon rim and how much lighter would it be than comparable alloy one?



So they are easier to build for the people selling them to me at potentially higher margin?
A) I think CXMag might have tried to test it a bit. It gets semi-apocryphal, but for years crossers have preferred deeper rims. They tend to be as light or lighter and cut through muck better.

B) You can get disc brake 380 gram 29er carbon clincher rims in 28mm tall by 22mm bead-width that will be reliable and take a 125KG rider for $200/rim without even so much as a sale coupon. And the LB folks are reliable IME, unlike many fly-by-night Chinese rim brands. You will not find an alloy clincher that IRL will be durable in 700C that weighs less than 440-450 grams/rim at a minimum weight. Pacenti tried 5X with their SL23v1 and v2 and v3 and Forza now twice to make 420gram rims--and failed resulting in pissed customers and broken rims/wheels and pissed wheelbuilders refusing to do business with their name ever again....what is more those two linked rims---it isn't even apples/apples as the LB rim is a wider and taller profile, still. Something more comparable like the AForce AL33 (a nice rim), that is 19mm wide at the beads and 32mm tall will still be narrower and weigh 500+gram per rim IRL, and cost $150USD per rim.

C) Easier and more reliable to build. It isn't like wheelbuilders are becoming millionaires--their margins are poor, too. Wheelbuilders that build even with quality rims like AForce and HED and Easton have piles of unusable rims they couldn't use because the extrusion process left a rim that wouldn't true well enough to meet a professional standard. Fewer than with cheapo rims--but still pile of waste metal...but they meet a nominal trueness metric enough to ship. CF rims lace up and go--generally. I think Psimet has ranted about this a bit come to think of it.
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Old 01-20-20, 01:28 PM
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Originally Posted by Marcus_Ti View Post

You can get disc brake 380 gram 29er carbon clincher rims in 28mm tall by 22mm bead-width that will be reliable and take a 125KG rider for $200/rim without even so much as a sale coupon. And the LB folks are reliable IME, unlike many fly-by-night Chinese rim brands. You will not find an alloy clincher that IRL will be durable in 700C that weighs less than 440-450 grams/rim at a minimum weight. Pacenti tried 5X with their SL23v1 and v2 and v3 and Forza now twice to make 420gram rims--and failed resulting in pissed customers and broken rims/wheels and pissed wheelbuilders refusing to do business with their name ever again....what is more those two linked rims---it isn't even apples/apples as the LB rim is a wider and taller profile, still. Something more comparable like the AForce AL33 (a nice rim), that is 19mm wide at the beads and 32mm tall will still be narrower and weigh 500+gram per rim IRL, and cost $150USD per rim.

Thanks for the links, based in Europe I was not familiar with any of those brands. I would wonder whether 22C rim with 35-42mm wide tires is any much difference to 19C (which seemed to be kind of standard CX for a while). That's because 22C rim for road 25mm wide tire with its outside witdh "hugs" the tire in a smooth transition, but that will never happen with 35+ ones. I believe by ETRTO 19C or 21C are also both just fine for way above 42mm tires.


On this basis - that aerodynamics does not seem to matter at CX tire widths and road rims - looking at the weight the 380g is nice, but I wonder - why don't the manufacturers make even wider / shallower / otherwise lighter cabon ones for CX? Even if I did not have any budget contraints it does not seem that there is anything lighter in the market than using wide road carbon wheel for gravel, but one cannot go as wide as would be necessary and may as well stay 19C (to save weight).


On the alloy ones, I would wonder what's wrong (in comparison with your quoted ones) with e.g. Open Pro UST that apparently represents 19C alloy rim that does not bother with deep profile (at 22mm) and goes for well under $100 listed as 430g? If I were to match the width then the 465g would be represented by HED Belgium Plus, but I do not want to go that route because it's clearly going to get heavier with wider ones for not much additional aero gain.


Originally Posted by Marcus_Ti View Post

It isn't like wheelbuilders are becoming millionaires--their margins are poor, too. /.../ CF rims lace up and go--generally. I think Psimet has ranted about this a bit come to think of it.

Noted, I was getting at the fact I am building myself, so having less or more work with truing is not an issue. Unless the carbon rim would provide significant benefit (for the CX use in terms of weight), I would rather avoid the material for structural reasons. If I receive badly egg-shaped alloy rim I would be just returning it, not sure I can spot quality issues with carbon ones with naked eye before on the road...
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Old 01-20-20, 01:45 PM
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Most (all?) of the fancy aerodynamic analysis being done on wheels assumes smooth tires. Knobby cross/gravel tires will chop up the air before it has any chance of flowing around the sidewalls and rims in a smooth manner...
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