shallow profile rims stiffer / less stiff

[Allen254]

Are shallow profile wheels say 30mm less stiff than 40mm + rim profiles ?
ive only ridden 40mm + profiiled wheels but bever ridden shollower rims has anyone had the chance of riding both or multiple probiled rims in regard to depth of wheel?

[Wookski]

So many variables to consider- hubs, spokes, tension, lacing pattern and rims

[F45]

If you think of the walls of the rim to be the vertical members in an "H" shaped beam, usually called an I beam or W beam, then everything else being equal, yes, the taller profile rim will be more laterally stiff than the lower profile rim. it will be even more stiff if it is a wide rim.

[Allen254]

If you think of the walls of the rim to be the vertical members in an "H" shaped beam, usually called an I beam or W beam, then everything else being equal, yes, the taller profile rim will be more laterally stiff than the lower profile rim. it will be even more stiff if it is a wide rim.

Oh okay so I’m theory a shallow rim could be just as stiff as a 40mm depth

[bm0p700f]

In general deeper rims are stiffer radially and laterally. Wider rims are laterally and if the rim has a curved profile it is radially stiffer than narrower ones.

Combine the two and you have a good rim not to mention the aero benefits. To think otherwise to me is fuzzy logic.

Thats just the rim. The spoke count, guage and hub bracing angles are the other factors so it can all change again.

You can have stiff shallow wheels and stiff deep section wheels or you can have both that are not stiff buy poor component choice. The stiffest wheel I build is a 31mm deep alloy rim because of the spokes used.

[TheKaiser]

And also it is interesting to note that a more flexible rim with stiffer spokes does not have the same qualities as a stiffer rim with more flexible spokes. This article summs it up nicely: https://www.slowtwitch.com/Tech/Debunki ... _3449.html

[Allen254]

And also it is interesting to note that a more flexible rim with stiffer spokes does not have the same qualities as a stiffer rim with more flexible spokes. This article summs it up nicely: https://www.slowtwitch.com/Tech/Debunki ... _3449.html

yeah for sure i rather have a much stiffer wheels set than a lighter one according to the article youll get moe benefit from a stiffer wheelset thana lighter one. thanks for the article.

[Alumen]

So many variables to consider- hubs, spokes, tension, lacing pattern and rims

Exactly that... And especially spokes/lacing pattern !

[hambini]

Yes, a shallow profile will be less stiff.

The technical term for stiffness in relation to cross sectionis second moment of area. You can read a description about it here

https://en.wikipedia.org/wiki/Second_moment_of_area

If you can't do with the technical theory, the simple way to think about it is if you double the thickness of an object you make it 8 times stiffer. An 80mm section wheel has approximately double the depth of a 40mm wheel so it's 8 times stiffer in the radial direction. It's not really much wider laterally but there is more material so it's only double the stiffness in the lateral direction. Shorter spokes also aid stiffness.

I've made some crude approximations above but the theory holds.

A practical example of second moment of area is trying to bend a ruler. If you twang a ruler off the end of the desk it's quite flexible, turn it on it's side and it's extremely stiff. this is second moment of area in practice.

Hope that helps

Hambini

[Multebear]

All else being equal, deeper section rims will be stiffer than shallower rims.

Just remember why it is you need stiffness. If it's because your wheels flex too much for them to fit between brakes and stays, then you obviously need stiffer wheels. But if you think that stiffer means faster, then you need to consult the countless topics regarding that issue.

[grahus]

And how are people gauging stiffness, just through 'feel', a perceived harsher/softer ride, or rims that don't hit the brake pads when powering uphill?

[Allen254]

All else being equal, deeper section rims will be stiffer than shallower rims.

Just remember why it is you need stiffness. If it's because your wheels flex too much for them to fit between brakes and stays, then you obviously need stiffer wheels. But if you think that stiffer means faster, then you need to consult the countless topics regarding that issue.

i agree that its dosnt mean faster thats up to the rider, but it can pull you up a climb much more efficientlly i truly belive that a flexy rim will be less efficient. i dont need need stats on that. i ridden a cheap flexy and a stiff bike and you you just feel the bike pushing you up more efficiently less power loss.

[Allen254]

And how are people gauging stiffness, just through 'feel', a perceived harsher/softer ride, or rims that don't hit the brake pads when powering uphill?

i mean although not a scientific mesure, i can say that ive ridden flexy bikes and stiff bikes and feel less power loss on a stiffer bike it feels like your being pulled up a climb ( slightly exagerated) but it is something you should be able to feel.

[Marin]

It's just imagination though, there is no gain of energy from stiffer components, it's just a marketing scam.

Some tests even suggest that more flex is better for human biodynamics.

[themidge]

I remember an old GCN video where they were comparing aero bikes and light weight ones, and Dan said something along the lines of:
"These aero wheels, when you look at them you think 'wow they look mega stiff' but when you actually get out the saddle, they're quite flexy. I'm even getting a bit of brake rub"
Can anyone explain this? I think they were zipp wheels and Boardman frames. I'll try to find the video tomorrow.