Shallow or Deep Rims for Gravel?

[rothwem]

I've got a previous gen Specialized Crux that I really like, I bought it new in 2020. I cracked the frame of my previous road bike, and having read a review talking about how good the Crux would be such a good bike for an N-1 type of build, I went for it. I kept the alloy stockers for gravel, and got a set of Farsports 50mm deep wheels for the road setup. Time went on though, and I realized that I hated swapping wheels because I could never get the brakes just right and I just left my fancy carbon wheels to sit in the corner of the garage.

One day while I was grinding up my knobbies on my heavy alloy rims during a 100% road ride, I decided to take the parts from my broken road bike and put them on another road frame. I eventually got a cheap road frame (CAAD8!), hung my old parts, and with my road setup sorted, I went and mounted my gravel tires on the carbon wheelset. I've been using the Crux on gravel with deep carbon wheels for about two years now. Its pretty good, feels fast, and with the wide internal width, I can run pretty low pressures in my 38's and have a TON of grip. I don't really have any complaints. However...

I'm getting a new road frame, and its fancy. Aero cable routing and hydraulic discs. I want some fancy carbon wheels to go on it. The question is, do I buy another set of 50mm deep carbon wheels for it, or should I get a set of shallow crabons (intentionally misspelled) for the gravel bike and put the 50's from it on the new wunderbike? Is there a downside to using deep rims on a graveller? Is there a downside to using shallow rims on the graveller?

FWIW, I'm about 200 pounds and my local gravel is pretty bumpy and hilly. I like stiff wheels, and I'm not overly concerned about subjective ride quality since its a pretty rare occasion when I can get in a ride over 3 hours. So what would you guys do? Part of me likes the redundancy of having two identical wheelsets, but the other part of me thinks that its a waste. Marketing tells me that gravel=shallow, and that seems to make sense because my average speed on most gravel rides is around 14 mph.

Anyways, please knock me out of this analysis paralysis.

[Likes2ridefar]

I went as shallow and wide as I could go and prefer it over deep aero wheels for the all road bike. Mine are single wall and 27mm wide internal which is great for 40mm and up tires.

[November Dave]

I have a current gen Crux as my N=1 road/gravel setup (I now have N>1 mountain bikes, though) and use 35mm deep x 25mm internal wide rims with 38-40mm tires for gravel, and 46mm deep x 21.5mm internal wide rims with 30mm tires for road. Truthfully if there were no tires on either set of wheels I would need to look hard to notice the depth difference. Both work wonderfully for their main purpose, but both would be pretty great at both purposes if pressed.

Mid-30s depth is pretty great in carbon for a mix of building a strong stiff wheel and still being light for a strong rec rider of your size. I'd go 25ish for the internal on the new wheels.

Do yourself a favor and get some rotor shims and standardize your calipers and rotors on all wheel/bike combos and never worry about switching again. https://novemberbicycles.com/product...shim-pack-of-4

[bigbill]

Another vote for shimming your existing wheels. I have two sets of wheels for my all road bike, one with Boyd hubs and the other with Bitex. About 30 minutes and a bag of November spacers allowed me to find the ideal setup. My Boyd wheels are OG Altamont from 2017 with 32mm tubeless heavier tires for the roads here in NW Arizona. If I go somewhere else with nice roads, I can swap to the BTLOS wheels and go.

[ZaddyWatts]

I would probably just get a less deep wide set of wheels for the gravel bike. Like others have said, 25mm internal width with 30-32mm external would be perfect. They don’t even need to be carbon. HED Emporia line of wheels are a solid buy and have the width and depth you’d need and they’re not overly heavy either.

[Alistair]

My primary concern would be internal width for any new wheels. These days, 25mm internal seems like a reasonable minimum for gravel and possibly pavement (assuming you're going to run a ~32mm tire).

My recollection is, from an aero perspective, as the tire gets wider, the depth of the rim matters less. IE, for a 50mm deep rim isn't getting you an aero advantage over a 30mm rim when the tire is 40+mm (rough numbers).

So, I'd move your existing deep rims to the new road bike and shop for a gravel set for the gravel bike. You don't need to worry so much about depth - I'd probably get a moderately deep set and save a few grams over a 50mm deep set.

[ridethecliche]

I don't really see the point of going over 30-40mm depth for gravel unless you're doing 'mild' gravel or racing.

For my use case that's what I prefer. I bought some BTLOS wheels from the forum and have been very happy with them.

[fignon's barber]

I use Campagnolo Shamal Carbons on my gravel/road bike. Perfect.

[Mark Davison]

Are you racing, or just riding around? If you are racing, or riding with fast riders on your road bike, I would put the wheels with deep sections on the road bike and get wheels with rims of suitable width for your gravel bike. At 14mph it won't really matter for your purposes how deep the rims are on the gravel bike.

If you are racing on both bikes then the story is different--I would have a look at what the professional racers in your discipline are using.

Deep rims with widths matching the tires will provide you a small aerodynamic advantage, which becomes more noticeable as you go faster. Probably not a big deal at 14mph.

Wide rims with wide tires provide some handling advantages, especially improved steering on the road, because the tire cross section looks more like a U than an old incandescent light bulb, and the tire doesn't squirm as much.

This is more of an issue with a bike used for mixed rides with both paved and unpaved surfaces. On loose gravel the steering is terrible no matter what the width of your rims is--but the steering is best if the tire is wide enough to not dig into the gravel.

This last issue is most relevant in dry areas of the West, or anywhere trail maintenance is performed by pouring gravel into the trail without tamping. (Here in the Seattle area you sometimes are riding along on a perfect unpaved trail of gravel embedded in a matrix of soil, and you run into a pothole that has been repaired with a fresh pour of new loose gravel. It's like running into a runaway truck ramp unless you remember to bunny hop over it.)

I don't think there is any noteiceable improvement in comfort by using shallow rims on a gravel bike. Using wide tires with proper inflation pressure is much more important, which you are already doing.

Correctly tensioned spoked bicycle wheels are very stiff vertically, and somewhat compliant laterally, no matter how deep or shallow the rims are, as explained in Josh Poertner's blog on the Silca web site. He relates how when he was working for Zipp, he was trying to figure out why their carbon rims were cracking during professional road races on cobblestone, while the traditional aluminum rims were not. It turns out that the wheels with carbon rims and the wheels with aluminum rims were about equally stiff vertically--the aluminum rims just bent instead of cracking. Both rim types were failing, they just had different failure modes. This is what led Poertner to convincing the professional team he was working with to use wider tires and lower tire pressures, so that they could gain the advantage of the improved aerodynamics of a deeper rim with an aerodynamic cross section.

See https://silca.cc/blogs/silca/road-to-roubaix

I can't figure out whether riding at road race speeds over cobblestones is an act of athletic heroism or lunacy, but there you have it. The film "A Sunday in Hell" is certainly entertaining.
https://en.wikipedia.org/wiki/A_Sunday_in_Hell

[Mark Davison]

When NHAero and I rode from North Bend to Cle Elum on the rail trail (now called Palouse to Cascades) we encountered a stretch of fresh new gravel just before Cle Elum that was miles long. We were both on 650B x 38, which was too narrow for that gravel. Thinking back on that experience makes me understand why J Heine used 26 X 2.3" to log his FKT on the Oregon Outback.

[November Dave]

[QUOTE=Mark Davison;3349492]Correctly tensioned spoked bicycle wheels are very stiff vertically, and somewhat compliant laterally, no matter how deep or shallow the rims are(snip)[/URL]

Deeper rims are stiffer laterally, all else being equal, because of bracing angle improvements with deeper rims. Properly designed/built deeper rims also suffer less tension loss with mounted tires than shallower carbon and alloy rims do.

My complete tire-to-rim width TedTalk here - https://novemberbicycles.com/blogs/b...078ec95d&_ss=r Written over 6 years ago and still to the letter in-line with my beliefs and observations.

[jdp211]

I run deeper (45mm) rims on my gravel bike because they look cool. They also came in a width suitable to the tires I run.



But mostly they look cool and kind of silly

That all said, I think Nextie stopped making these rims. Probably because the market for deep section carbon 650b rims is incredibly small.

[saab2000]

If I were building my gravel bike today I’d go for shallower and wider. I’ve got the really nice DT-Swiss wheels with a 24mm internal and a deepish profile. They’re great wheels but I’ve been on a couple of windy rides where they did get blown around a bit.

The riding I do isn’t true ‘racing’ anymore though it might include a race or two. I’m not at the pointy end so I’d opine that aero is virtually meaningless for me. If you’re at the competitive end of a real race like Unbound or something along those lines I might think differently.

I’m generally a fan of Boyd wheels and if I were building my bike today I might well get some of his Jocassee wheels. They’re comparatively affordable and have a 26mm internal.

[tomato coupe]

Originally Posted by jdp211

I run deeper (45mm) rims on my gravel bike because they look cool.

They look good with those tires.

[Mark Davison]

Marc R on Iron Horse.jpg

Here's NHAero on the aforementioned short gravel tour to Cle Elum. I'm not sure why he is pathfinding--we were headed up to Snoqualmie Pass and the route has no turns for the next 20 miles.

Discerning viewers will note that he is riding a 1990s Terry Symmetry sport touring bike intended for women (and purchase for my wife.) The finish is mint green metallic, with lavender decals, and lavender bar tape to match. But in this case fit is more important than loss of dignity, since Terry designed the frame for people with long inseams and relatively short arms--57cm seat tube CTC and 55cm TT CTC.

I did the 650B conversion with the canonical Tektro 559s and a Shutter Precision dynamo driving a Bush & Muller IQ-X light. (In the conversion I lost the color matched green anodized Shimano medium reach side pull brakes. Alas, wide tires beat color matched components.) Chain stay clearance limits the tires to 650B x 38.

Somehow, even though it was 2017, the frame had not rusted through in 25 years and we made it all the way to Cle Elum and back.

I'm not sure whether the resulting rig is vintage, retro, obsolete, Franken-bike or twee, but it sure is fun. Marc and I passed on using vintage attire and wore whatever we pleased. I'm glad we had extra clothes and bright dynamo lights because the mile long railroad tunnel under Snoqualmie Pass is really cold.