# Aero Rim Depth Help for Cross and Gravel



## TheHamster (Sep 1, 2006)

I am shopping for some aero wheels that will be used for cyclocross and gravel racing. I would like to get rims that are deep enough to plow through the mud and muck yet will not be affected by cross winds. I am not interested in time trialing but just looking for some extra speed on endurance events and new to these types of racing. Need to decide between rims 24-50mm deep as I am getting the impression that cross winds become an issue at 50mm and above. Any help is appreciated.


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## Mike T. (Feb 3, 2004)

TheHamster said:


> I am shopping for some aero wheels that will be used for cyclocross and gravel racing. I would like to get rims that are deep enough to plow through the mud and muck yet will not be affected by cross winds. I am not interested in time trialing but just looking for some extra speed on endurance events and new to these types of racing. Need to decide between rims 24-50mm deep as I am getting the impression that cross winds become an issue at 50mm and above. Any help is appreciated.


I can't imagine how deep rims could benefit you and your riding at all. I watch pro cyclocross every weekend and the top pros average about 16mph, if that. My thousands of miles of gravel road training rides were at about 15-16mph average speed - 18 for my fastest circuit. No rim will give you "some extra speed on endurance events". 

What does "rims that are deep enough to plow through the mud and muck" mean? Deeper rims don't go better through deeper mud. The bottom of the tire is still in the same place. The brake track is still in the same place.


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## mafu (Nov 4, 2013)

Mike T. said:


> I can't imagine how deep rims could benefit you and your riding at all. I watch pro cyclocross every weekend and the top pros average about 16mph, if that. My thousands of miles of gravel road training rides were at about 15-16mph average speed - 18 for my fastest circuit. No rim will give you "some extra speed on endurance events".
> 
> What does "rims that are deep enough to plow through the mud and muck" mean? Deeper rims don't go better through deeper mud. The bottom of the tire is still in the same place. The brake track is still in the same place.


That's odd because actually most "pro" (ie people who can afford it/are sponsored) racers in cx DO have deep rims and say that's exactly for this reason: go through mud.

You see, when your wheel is inside the mud, if the rim is not very deep, the mud will cover the rim entirely and cause much higher friction. having a deep V style rim will indeed "cut" through mud.

Physically speaking, this is exactly the same reason why those rims are faster/more aerodynamic (at higher speeds) on road bike. Except air viscosity is much, much lower than mud viscosity, thus, this works at extremely low speeds when your wheel is in the mud.

On gravel at "low" speeds, this will make "no" difference (at least nothing easily measurable)


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## TheHamster (Sep 1, 2006)

I started the thread because I am preparing to try these events for the first time. Up to now, the only off road riding I have done on my cross bike is some very tame hardpack rail trails using my super skinny non-aero road wheels. I have seen many references to the advantages (through mud) of aero rims and also read about the experiences of gravel racers that had to get off their bikes because they did not have deeper rim wheels to ride through muddy patches. But I have also noticed that the winners of these events (most likely sponsored) were in fact using 40mm deep aero rims. I agree that these events will be WAAAAAY slower than a road event, but if I am going to build up (or buy) some wheels for the purpose may just want to get something that will handle all the possible conditions. But I would also think that when you are on the hard flats with no mud and have a tail wind might be able to pick up some additional time with the deeper rims in a gravel race.


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## Mike T. (Feb 3, 2004)

Do you *really* think that the extra depth of a rim (about 1" in 24mm versus 50mm depth) is going to make *any* difference in your velocity through mud?


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## ergott (Feb 26, 2006)

He's talking about this kind of buildup.


















The taller profile rims work better a few ways. They keep the spoke/nipple bed higher and less likely in the mud to begin with. They are usually more v-shaped so there is less surface area around the spokes and nipple. The mud that does cake up there is further away from the brake track. Finally, there are usually fewer spokes so again, less mud to cake up.

If you do lots of that terrain an inexpensive set of 50mm wheels will help. There are plenty around that are cheap enough that you can kill them with little remorse. I would seek recommendations from local racers. Every race scene is a little different.


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## Mike T. (Feb 3, 2004)

Smartest 'crosser I saw under those conditions (or worse, there was one mud hole that was hub deep) was the Canadian national champ years ago in a race my club put on - he ran all the extra muddy stuff where the ordinary Joes took it as a personal challenge to ride as much as possible. When he was all done he was 5 minutes ahead of the next guy and a lap ahead of most of them and he was the only rider not to have spokes as thick as my thumb and brakes that you couldn't even see. His bike must have weighed 10lbs less than theirs. Smart fella.

The rest of them could have been using Sven's wheels and they wouldn't have beaten him.


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## al0 (Jan 24, 2003)

OK, I have no cyclocross experience - but such experienced cyclocrosser and bike mechanic as Lennard Zinn strongly believes that high-profile rims are advantageous for cyclocross http://velonews.competitor.com/2013/09/bikes-and-tech/technical-faq/technical-faq-sealing-gluing-and-inflating-cyclocross-tires_303950



> Why aero wheels for cyclocross? *Dear Lennard,*
> Why are aerodynamic carbon wheels prevalent in ’cross? Doesn’t seem like much advantage in a one-hour race at ’cross speeds, plus they tend to be heavier and therefore harder to accelerate out of turns.
> _—Jim_
> *Dear Jim,*
> ...


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## Roland44 (Mar 21, 2013)

ergott said:


> He's talking about this kind of buildup.


Wow, I feel sorry for this bike. Dirty but cool though


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## SBard1985 (May 13, 2012)

ergott said:


>


Nothing is more satisfying than getting muddy while riding your bike.


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## coachboyd (Jan 13, 2008)

SBard1985 said:


> Nothing is more satisfying than getting muddy while riding your bike.


Drinking a nice cold beer afterwards may be.


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## Warpdatframe (Dec 9, 2012)

So your telling me not a single person had a 2nd bike?


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## Mike T. (Feb 3, 2004)

Warpdatframe said:


> So your telling me not a single person had a 2nd bike?


Club event. Champ was local. Most people were lucky to have *one* bike. No-one had two.


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## QuattroCreep (Nov 30, 2009)

My vote is: Run what you have until you know what you need.

Go through your local race series this year with whatever you have. See how it works. Watch the guys you are racing against and the "A" race. Is there a lot of deep mud and sand? Would you be better served with a set or two of inexpensive tubular wheels?

Right now you don't know enough about what you need to make a choice. With this kind of information a forum might lead you to something that works for you or not. It is tough to say.

If you are itching to spend money now look at something the depth of a Zipp 303, it seems to be a popular.


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## TheHamster (Sep 1, 2006)

No. I really don't think I am going to go faster in the mud with a 50mm vs. 24 mm rim. But when I am not in the mud and might be using the wheels on a dry road with road tires, I might go faster with the 50. Ah but here is another question, does cross and gravel racing require a wheel with more spokes than if the same wheel were going to be used purely for road riding?


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## TheHamster (Sep 1, 2006)

Sounds like good advice to me. I might just try my velocity aeroheads and see what happens. But I probably can't go wrong with at least a mildly deep rim.


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## TheHamster (Sep 1, 2006)

Thanks guys. I thought all of the responses were very interesting and helpful. It appears that if I do decide to get deeper rims for off road purposes at slower speeds should stick with rims under 50mm. Or I can just start with what I have and see whether I really need it. I will get more depth with larger cross tires 32-38 that I plan to run but now worried that my narrow road rims might not be as effective as some of the newer wide rims. I might like more spokes on a shallow road rim for off road use.


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## pmt (Aug 4, 2009)

coachboyd said:


> Drinking a nice cold beer afterwards may be.


I do judge my CX races by how fast I can get a beer after I cross the finish line. This past week at Ed Sander Memorial that was measured in seconds.


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## QuattroCreep (Nov 30, 2009)

I just built up a set of Velocity A23 wheels for cross. I have been really happy with them so far. The wider rim seems to round out the Mud2 tire nicely and give it better feel and grip in the corners. Still not as nice as tubulars but much better then the wheels I had before.

I went 32f/32r with brass nipples and Sapim race all round. I like that I never have to question my gear before a race. Might not be the lightest setup but it works.


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## krisdrum (Oct 29, 2007)

A few years back CXM did one of their "field tests" on deep vs. shallow rims in various conditions. If memory serves they said deeper rims did shed sand and mud a bit better, but not significantly. I think they said only in the harshest of muddy conditions did the build-up make a difference. Unless you are vying for a podium spot, I don't think it really matters. Even after a few seasons on and off racing cross, I'm still not at a point where it is my bike and equipment that is holding me back from a "competitive" performance.


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## TheHamster (Sep 1, 2006)

Thanks for the advice. Everyone has been really helpful. I am sure my equipment is not holding me back. And from what everyone here is saying, the deep rims may be occasionally helpful but not critical and certainly not a deal breaker. I currently own no aero rims and don't plan to start time trialing any time soon. But I do have to buy a set of wheels for the new cross/gravel build I am working on and may as well get something just a wee bit deeper than a standard box section rim. Most of the time it won't matter, but will probably be stiffer and there when I need it. So I am going to pick something that is only slightly deeper than an ordinary road rim, stick a fork in it and call it done. I probably won't even go carbon as good ole aluminum will be fine for me and the additional weight is miniscule. I just wish I could find a semi-aero rim that does not weigh a ton and build my own wheels with hubs I like rather than go with an off the shelf wheelset. They might offer a nicer rim that uses less spokes but I don't believe any of the hubs are as good as Kings, DT Swiss, White, etc..


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## Mike T. (Feb 3, 2004)

TheHamster said:


> .......off the shelf wheelset. They might offer a nicer rim that uses less spokes but I don't believe any of the hubs are as good as Kings, DT Swiss, White, etc..


You got that one right.


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