Shallow or Deep Rims for Gravel?

[Mr.Appa]

Sounds like you've already got it figured out...run the deep 50mm on the road wunderbike and keep the shallow on the gravel bike. You maybe lose out on some gains of some sort, but you do keep some extra $$$ in the wallet. As an aside, if you are anything like me, the more spare parts you have in your bin, the more tempting it is to build a whole bike around them and then, bam, N+1.

That being said, the deep (mine were 38s) carbon rims on a skinny tube gravel bike with fat tires definitely looks the business.

[Mark Davison]

Originally Posted by prototoast

Basicallyhttps://www.renehersecycles.com/aero...-gravel-bikes/ 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.

For a contrary opinion, see

https://www.renehersecycles.com/aero...-gravel-bikes/

Of course descriptions of the supporting wind tunnel tests are locked behind the paywall of back issues of Bicycle Quarterly.

[jdp211]

Originally Posted by rice rocket

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.

Ah yeah, guess I was mistaken on the death of these rims. Glad they're still making them.

[Alistair]

Originally Posted by Mark McM

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.)

Yeah, I phrased it poorly, no question.

I can't remember where I read a detailed description of rims widths/depths vs tire size, maybe over at TrainerRoad's forum? Anyways, from what I recall...

Once you loose the laminar airflow at the tire-rim transition, the rim depth doesn't make much difference. And if I'm remembering correctly, the rim should be as wide as, or slightly wider than, the tire to maintain good airflow (which isn't going to happen with a 40-50mm wide gravel tire - most rims are <40mm external width).

If you're chasing podiums, by all means experiment, but for most of us a standard 20-30-ish mm deep rim, with a 25-30mm internal width, is going to be more than adequate.

[sparky33]

Gosh, I'd say shallow is better for gravel because they are lighter and theoretically more compliant, and aero doesn't matter at gravel speeds.

But I suppose the equation is different for someone at #200+, likely producing more watts, where an extra 200grams of rotating weight is less of a hurdle. I agree that mid-depth wheels look so so good.

[Mark McM]

Originally Posted by sparky33

Gosh, I'd say shallow is better for gravel because they are lighter and theoretically more compliant, and aero doesn't matter at gravel speeds.

Gosh, I hope those shallow rim wheels aren't compliant! If the rim deflected inward by a millimeter (or even less), the spokes at the bottom of the wheel would completely slacken, taking all tension off the nipple and potentially allowing them to unscrew, which can set the wheel out of true. Not to mention that if this happened often enough, the spokes would fatigue and break from the cycling back and forth between 0 and full tension.

Don't look for vertical compliance in the wheels. Even the "softest" wheels have a vertical stiffness of about 10,000 lb./in. (meaning a 100 lb. bump force will only cause a deflection of about 0.01 in.).

[Likes2ridefar]

Originally Posted by Mark McM

Gosh, I hope those shallow rim wheels aren't compliant! If the rim deflected inward by a millimeter (or even less), the spokes at the bottom of the wheel would completely slacken, taking all tension off the nipple and potentially allowing them to unscrew, which can set the wheel out of true. Not to mention that if this happened often enough, the spokes would fatigue and break from the cycling back and forth between 0 and full tension.

Don't look for vertical compliance in the wheels. Even the "softest" wheels have a vertical stiffness of about 10,000 lb./in. (meaning a 100 lb. bump force will only cause a deflection of about 0.01 in.).

That’s why my rim (101 xplr) pivots which has a similar effect on overall feel.

[Alistair]

Originally Posted by sparky33

... aero doesn't matter at gravel speeds.

It absolutely still matters. At least if you're racing or trying to go fast.

[Mark McM]

Originally Posted by Likes2ridefar

That’s why my rim (101 xplr) pivots which has a similar effect on overall feel.

So, if you hit a rock on the side edge, the rim will twist to absorb some of the shock, but if you hit the same rock dead straight, the wheel won't absorb the shock at all?

Why not rely on the pneumatic shock absorption of the tire, which can obstacles of a variety of shapes, and can deflect far more than any rim?

[sparky33]

Originally Posted by Alistair

It absolutely still matters. At least if you're racing or trying to go fast.

and there's my problem, the going fast part.

[Likes2ridefar]

Originally Posted by Mark McM

So, if you hit a rock on the side edge, the rim will twist to absorb some of the shock, but if you hit the same rock dead straight, the wheel won't absorb the shock at all?

Why not rely on the pneumatic shock absorption of the tire, which can obstacles of a variety of shapes, and can deflect far more than any rim?

Yes and I take advantage of both. The simplest way I can describe the effect is it’s like adding ~5mm tire size of volume to the tire.

[BRad704]

Originally Posted by 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.

Originally Posted by Mr.Appa

Sounds like you've already got it figured out...run the deep 50mm on the road wunderbike and keep the shallow on the gravel bike. You maybe lose out on some gains of some sort, but you do keep some extra $$$ in the wallet. As an aside, if you are anything like me, the more spare parts you have in your bin, the more tempting it is to build a whole bike around them and then, bam, N+1.

That being said, the deep (mine were 38s) carbon rims on a skinny tube gravel bike with fat tires definitely looks the business.

All performance conversations aside, these 50's with knobbies look dope AF/bangin/radical/the cat's pajamas (to cover all generations of lingo).. so I'd do THAT.

[Likes2ridefar]

Have had both deep sets and shallow on this bike and I prefer the look of shallow (plus the elimination of terrifying mountain descents in suboptimal conditions) (love that rock lobster though )

[saab2000]

Originally Posted by Likes2ridefar

Have had both deep sets and shallow on this bike and I prefer the look of shallow (plus the elimination of terrifying mountain descents in suboptimal conditions) (love that rock lobster though )

I definitely prefer the aesthetics of the shallow wheels. My new Boyds just look right on the bike they’re on. I now have at least a couple dozen miles of showing off on them.

Hopefully more come springtime. Rides are short and cold right now.

[oldpotatoe]

Originally Posted by sparky33

Gosh, I'd say shallow is better for gravel because they are lighter and theoretically more compliant, and aero doesn't matter at gravel speeds.

But I suppose the equation is different for someone at #200+, likely producing more watts, where an extra 200grams of rotating weight is less of a hurdle. I agree that mid-depth wheels look so so good.

Theoretically is right...Mark McM for the 'answer' about rim compliance right above.

Adding or subtracting 200g of 'rotating weight' as it 'may' apply to performance is lost in the noise. For any rider of any strength...