Carbon rims on a rigid singlespeed?
 

Carbon vs. aluminum has obviously been beaten to death but I'm wondering if anyone has upgraded to carbon rims on a rigid bike and liked the results. The fear is an overly harsh ride.

My singlespeed has aging Stans Arch rims that work fine. That said, I've been toying with the idea of going with a modern/wider rim to accept beefier tires. I figured I'd consider carbon while making the switch.

Any thoughts or experience with carbon rims on a rigid bike?

If the tires get wider and pressures get lower as a result of the wider carbon rims, I would expect a plusher ride.

How wide are you talking?

The question is moot. All wire tension spoke wheels (regardless of whether the rim is carbon or aluminum) are so stiff vertically, that they make no meaningful difference in ride "harshness". Tires (width and pressure) make the biggest differences. Like above, the biggest difference in rims is their affect on the tire's inflated width.

i ride a rigid single speed. and i have 30 mm id carbon rims on it. the ride is nice. of course, if i take this bike to technical rocky places, the ride is jarring. but i doubt this has to do with the carbon rims. it is a rigid. it has got to be harsh on specific terrain.

as others have said, put a wide 2.4+ tire on it and you'll be grinning all the way. :)

Right on--I appreciate the input.

My thinking was to put a 29 x 2.6 tire up (like a Maxxis Rekon) front and 2.4 in the back. I just moved back to Massachusetts and am expecting more rocks and roots than I previously had in NorCal.

I have a 2.6 Rekon on an i35 rim on the front of my Hightower. It’s awesome. Very underrated tire IMO. The Bonty XR4 is another solid choice at that size.

Similar. racing multiple cross seasons on 25mm deep carbon tubeless hoops. Love em.

I rode rigid with a 3.0 tire and carbon rims and don’t believe the ride was harsh due to the rims. Harsh because it’s rigid! The 3” tire at 10psi was money. I wouldn’t want alum rims on a riding rigid. Too much grunting over the front wheel and would be flexy.

I don’t have carbon vs aluminum input but have been running a 2.6 Rekon on a an ARC 35 rim up front and it’s been pretty great. Lots of grip and the increased volume helps.

Wire tension wheels are stiff vertically......from the hub up, where they are in tension. From the hub down, the spokes are under compression. Rim integrity matters there.

I'm going to assume we are talking about mountain bikes, so I'll base my statements on that thought. I had a rigid single speed that would not accept bigger than a 2.25 tire. With carbon rims (and tubes) that bike was downright spooky, particularly in rocky/rooty sections where cornering stability was needed. Okay, tubeless did improve things, but my other (steel) single speed was so much more palatable. I finally broke down and swapped the tubeless rims (only rims not tires) from one bike to the other and couldn't believe the difference in both bikes. I simply put those brand name carbon wheels aside for another situation.

That said, others here have offered tire suggestions. I agree, tubeless tires with enough volume will make a huge improvement in ride quality and rider confidence. My current go-to mountain bike is steel with a rigid carbon fork 1x10 drivetrain and 2.4/2.2 tubeless tires on carbon rims. My full suspension mountain bike has the same exact wheel/tire combination and hangs in the shop until the rides get long enough to require the extra comfort.

In a word, no. As long as the spokes stay in net tension (do not completely detension), they are just as stiff to compressive forces as they are to extensive forces. The main influence of rim stiffness is in determining how the load is distributed amongst the spokes at bottom - the stiffer the rim, the more spokes there will be taking the load, and the lower the stress in individual spokes. Theoretically, the more spokes taking the load, the stiffer the wheel will be, but even a single spoke has a stiffness of 5,000 - 10,000 lb/in, so the net stiffness of a wheel is typically 15,000 - 30,000 lb/in. Or in other words, for purposes of vertical compliance, the wheel is essentially perfectly rigid.

So why are some wheels more vertically compliant than others? This is an honest question, as I have no idea how a spoked wheel actually works. I do know that some wheels feel much stiffener than others, which according to your description isn't possible. Some manufacturers even claim their wheels are more forgiving vertically.

Since you asked ...

There are different modes of wheel stiffness: Vertical (radial), lateral, and torsional (rotational). It is immediately obvious that wheels can flex laterally - you can see this by flexing a wheel back and forth by hand. This flex can affect bicycle stability and handling, and different wheels can have very different lateral stiffnesses. But when it comes to wheel "comfort" and "ride compliance" we are usually referring to vertical stiffness. In this mode, there isn't enough flex in any wire spoke wheel to make a difference.

Then why do people talk about the difference in comfort between different wheels? I suspect it is mostly expectation bias: When people see wheels with deep rims, they expect them to be stiff and harsh, so that's what they "experience"; and when people see wheels with shallow rims, they expect them to be soft and compliant, so they "experience" that instead.

To see if the expectations meet with reality, people have actually measured the vertical stiffness of wheels. Here's one such test:

https://www.sheldonbrown.com/rinard/wheel/grignon.htm

Notice that in this test, the measured stiffneses are often the opposite of what is expected - the wheels with deep rims usually have lower vertical stiffness, while the wheels with shallow rims are usually the stiffest. In fact, the stiffest wheel in the test has the shallowest rim. What's going on here? If you take a closer look, two things jump out:

1) Wheel stiffness is more correlated to the spokes than to the rim. The wheels with more and thicker spokes have the higher vertical stiffnesses.

2) The stiffnesses of all the wheels is very, very high, measured in the tens of thousands of pounds per inch. If you hit a bump that caused a 200 lb. force to be exerted on a typical wheel, it would only deflect 0.010" There's far more flex in the tires, saddle, handlebars, etc. After all the flex that occurs in the other components, if the flex in the wheel alone changed from 0.008" to 0.012", you'd never notice.

Josh Poertner, an engineer at Zipp, has written about their tests on wheel comfort and compliance. In this story on developing wheels for the Paris Roubaix race, and convincing teams to replace their shallow aluminum rim wheels with deep carbon rim wheels, he measured different wheels and found the same thing as the above test - wheels with shallow rims and many spokes are stiffer than wheels with deep rims and fewer spokes. And, they found that tires make the biggest difference, so the wheels didn't matter for comfort at all.

https://silca.cc/blogs/journal/11517...complete-story

In this interview, Josh Poertner talks about conductint blind tests on wheels, to see how much difference riders could feel without knowing what wheels they were riding:

https://www.slowtwitch.com/Tech/Thou...tion_4571.html

So, the answer to your question is that for the most part, in the absence of real differences in the feel of wheels, people often feel what they "think" wheels should feel like.

All very interesting, thanks! And yes, I'm talking about vertical compliance, not lateral.

....Off topic anyway....