Shallow or Deep Rims for Gravel?

[GParkes]

Originally Posted by 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.

I second this. I have two sets of Emporia GA Pros, they are excellent - bomb proof. At about 1600 grams for the set, not much of a weight penalty. Depth is 24 MM, but for this application, not really concerned over the aero aspect. Even so, I'd likely stay mid-30's in depth for gravel.

[Mark Davison]

Red D at Snoq Pass.jpg

Here's the bike I rode with NHAero.

This photo is at the brew pub on Snoqualmie pass, shot earlier in 2017 near the end of another suffer fest organized by Bob Freeman. IIRC the route was Green River to Naches Pass, to Umptanum Ridge, Ellensburg and return via a mix of roads and gravel trail.

The bike is my 1990s Davidson light touring bike converted to 650B in a fashion very similar to the Terry. Also obsolete, Frankenbike, and particularly twee with the hammered aluminum fenders and Gilles Berthoud handlebar bag.

I'm on my second fork and second paint job with this bike. There are literally none of the original 1990s parts left on it.

[Mark Davison]

I completely forgot the takeaway on this--when I was doing these conversions the supply of rim brake compatible 650B rims was pretty limited, and none of them were wide, so we wound up with 650B x 38 tires on 19mm internal width rims. J Heine says not to worry, so I don't. Disc brakes certainly open up rim options, as you know. Also the rim tracks have to be reinforced, so these are not even the lightest aluminum rims.

[rothwem]

Originally Posted by 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.

Innteresting about the rim depth, did not know that.

The 50mm carbon wheels I've got right now are 24mm internal, 30mm external. I went wide for my road set because I was running 30mm tires to try to make the trail number not so different between my knobbies and slicks. So because of the wide internal width, they do pretty well with my 38mm gravel tires.

[rothwem]

Originally Posted by November Dave

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

Man, I've got a set of shims, but I could never get it exactly right. The Sram HRD calipers that I use have such a tight clearance that the shims weren't precise enough, one shim thickness would take me from almost rubbing one side of the caliper to almost rubbing on the other pad. I eventually got it so that they wouldn't rub in the stand, but one of the wheelsets always had a slight rub while standing to pedal, so I found myself adjusting the brakes every time I swapped wheels to ensure that the disc was centered in the caliper.

My better solution was just to adjust the calipers to be right with one set of wheels, then build up a road bike for road biking. Wala!

[November Dave]

Originally Posted by rothwem

Man, I've got a set of shims, but I could never get it exactly right. The Sram HRD calipers that I use have such a tight clearance that the shims weren't precise enough, one shim thickness would take me from almost rubbing one side of the caliper to almost rubbing on the other pad. I eventually got it so that they wouldn't rub in the stand, but one of the wheelsets always had a slight rub while standing to pedal, so I found myself adjusting the brakes every time I swapped wheels to ensure that the disc was centered in the caliper.

My better solution was just to adjust the calipers to be right with one set of wheels, then build up a road bike for road biking. Wala!

Well, that's a good solution! But if your pads are giving that small a clearance, then the pistons aren't retracting fully. To fix this, remove the wheels and brake pads, put the thin bleed block in the caliper, and squeeze the brakes so the pistons extend. Scrub the pistons and that whole area with isopropyl and a Q-Tip, then carefully put a small dab of DOT fluid on each piston, and push the pistons back in using the thick bleed block. Then replace pads and wheels. Sounds complicated, but it takes less than 10' to do both and it works.

You could/should have roughly double the clearance it sounds like you have. I have SRAM Red calipers and there's more than a shim's width of clearance on either side of the rotor, and zero rotor rub/squeal.

[ColonelJLloyd]

^ this

I use SRAM HRD calipers and the November shims. 700c and 650b are interchangeable; plug and play.

[rothwem]

Originally Posted by November Dave

Well, that's a good solution! But if your pads are giving that small a clearance, then the pistons aren't retracting fully. To fix this, remove the wheels and brake pads, put the thin bleed block in the caliper, and squeeze the brakes so the pistons extend. Scrub the pistons and that whole area with isopropyl and a Q-Tip, then carefully put a small dab of DOT fluid on each piston, and push the pistons back in using the thick bleed block. Then replace pads and wheels. Sounds complicated, but it takes less than 10' to do both and it works.

You could/should have roughly double the clearance it sounds like you have. I have SRAM Red calipers and there's more than a shim's width of clearance on either side of the rotor, and zero rotor rub/squeal.

I don't want to be a downer, but man, I've done all that. I've cleaned the pistons probably a hundred times trying to make them not be sticky. I've even rebuilt the front caliper with new seals, and within 5 rides the brakes are back to being their ornery, low clearance selves. They work okay as long as I don't mess with them, I've just resigned myself to not being an N-1 kind of rider.

I didn't really like the limited gear range anyways, and I didn't like riding a bike on the road that was dirty from a gravel ride. I guess I'm just an N=(ride type) kind of guy.

Now when my superbike comes in, I'm not totally sure what I'm going to do with the Cannondale, I've really grown to like it. But that would make me an N=((ride type)+1) guy and I'm not sure that's me.

[djg21]

Originally Posted by 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.

I use Flo Cycling G700 wheels.

https://flocycling.com/collections/g...700-disc-brake.

https://mountain-road.com/blog/flo-g700-review

https://www.ridinggravel.com/compone...at-the-finish/

https://www.bikeworldnews.com/2023/0...%20and%20width.

I’m 6’3” and over 190lbs. The wheels are stiff, comfortable, have a wide internal width and work great with tubeless, and are very competitively priced, especially with a discount code. They are fast in the flats and on downhills. At our size, a few extra grams on the uphill doesn’t matter and we want something durable: weight doesn’t matter if you can’t make it to the finish. These wheels are durable. And the Flo team has been really good to work with and stands behind their products.

If you are interested — I have a spare rear wheel I can sell you and can save you some money. I probably can get you a discount code for a new front wheel. You can send me a PM.

[rice rocket]

Originally Posted by jdp211

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

https://www.nextie.com/new-gravel-clincher-NXT27GR45

This one?

I have them ready to go to the LBS for a build, they seem well finished.

[Mark McM]

[QUOTE=November Dave;3349497]

Originally Posted by Mark Davison

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.

I agree that deeper rims are stiffer laterally, but I think that the bracing angle change is only a secondary contributor in many cases. Spokes have very high longitudinal stiffness (typically between 5,000 - 10,000 lb/in depending on thickness). Rims have a much lower radial stiffness. When a rim is loaded laterally, this will try to "stretch" the spokes bracing the rim. But as the spokes are very stiff, they stretch little. Instead, a shallow rim may bend inward (radially) slightly at the spoke, allowing the spoke to deflect laterally with little stretch of the spoke. Because of the shallow bracing angle, it takes very little inward bending of the rim to allow a meaningful lateral displacement.

Of course, the relative contributions of rim flex and spoke stretch under lateral loads will depend on the relative stiffnesses of the rim and spokes. For a very shallow rim with many thick spokes, most of the lateral flex will be due rim bending; for a very deep rim with few thin spokes, most of the lateral flex will be due to spoke stretching.

[Mark McM]

Originally Posted by Alistair

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).

I'm not sure that's the way I'd put it. Instead, I'd say that the wider the tire, the deeper the rim needs to be to have a meaningful aero affect. The goal of the rim shape is to keep the air connected to the surface and rejoin smoothly behind the rim. With a wide tire and shallow rim, the air can't take the tight bend to follow around the back of the tire & rim, and the air will separate and become turbulent. So the rim needs to be deeper to allow the air to follow around the tire and stay connected. (Not only does the rim need to be deeper, but it should also be wider, to minimize the abrupt transition from tire to rim, particularly at higher yaw angles.)

[November Dave]

Mark - I often measured more stiffness in wheels with deeper rims and never settled on a why. A 220mm CX Ray sure acts a lot differently than a 290mm CX Ray. Your explanation may be it, I don’t know. But wheels with deeper rims, absent some strange variable, are stiffer.

Totally agree on aero. The 3 to 1 concept is still valid. Put a 40mm tire on a 30mm deep rim and a 40mm deep rim and both will have messy airflow. A 40mm wide 30mm deep rim would have cleaner flow than a 30mm wide and 40mm deep rim with that 40mm tire. But you’d really need a 40mm wide x 80ish mm deep rim to get things working well aerodynamically (40mm tire height + 80mm rim height = 3x 40mm rim width). Generally speaking.

[Mark Davison]

Does it get to the point where the tire is so wide that a matching aero rim is impractical?

I just looked at Jan Heine's piece on the bike he used for his FKT of the Oregon Outback:

https://www.renehersecycles.com/oreg...od-or-madness/

Those are definitely not deep rims. Maybe for that course flotation (from 2.3" wide tires) is more important than wheel aerodynamics.

[prototoast]

Originally Posted by Mark Davison

Does it get to the point where the tire is so wide that a matching aero rim is impractical?

I just looked at Jan Heine's piece on the bike he used for his FKT of the Oregon Outback:

https://www.renehersecycles.com/oreg...od-or-madness/

Those are definitely not deep rims. Maybe for that course flotation (from 2.3" wide tires) is more important than wheel aerodynamics.

Basically everything about that setup is the worst possible from an aerodynamic perspective. In general, I believe with wide tires the main benefit of the deeper rim is from reduced spoke length, and that can be offset by penalties in weight or handling, but still shouldn't draw conclusions about aerodynamic effects from somebody with a giant front bag on his bike.