Stiff Wheel Question

[mso]

I was getting ready to order the Campy Shamals when I read that because they're a "stiffer" wheel they are not very comfortable descending rough roads? I'm a superlight spinner/climber and what goes up must come down, so comfort and stability are really important. Also how are they in a crosswind? Little confused on what a "stiff" wheel really means.

Thanks

[Mark McM]

I was getting ready to order the Campy Shamals when I read that because they're a "stiffer" wheel they are not very comfortable descending rough roads? I'm a superlight spinner/climber and what goes up must come down, so comfort and stability are really important. Also how are they in a crosswind? Little confused on what a "stiff" wheel really means.

Thanks

Frequently the meaning of "stiff wheel" refers to some vague perception by the rider. But it rarely refers to the actual vertical deflection of the wheel under load, because all wire spoke tensioned wheels are so stiff radially that any vertical deflection is virtually undetectable by the rider.

The radial stiffness of wheels is typically in the 10,000 - 20,000 lb/in range, which means that if suddenly hit by a bump force of 200 lb, the wheel would deflect by 0.01" - 0.02". With everything else that is deflecting under load, do you really think you could feel that small amount of deflection, let alone the difference between 0.01" and 0.02" of deflection?

Some direct measurements of wheel deflection of a variety of wheels can be found this article: Aero Wheels Under Scrutiny (http://www.sheldonbrown.com/rinard/wheel/grignon.htm) .

Interestingly, the wheel with the highest radial stiffness is also with one with the shallowest lightest rim (Mavic GL330 with 36 straight 2.0mm spokes). While it may be counter intuitive that a wheel with a lightweight shallow rim can be vertically stiff, a closer look reveals why: The hub and rim are connected through the spokes, so the spokes (number and thickness) play the greatest role in vertical stiffness. As it happens, the GL330 wheel also has the most and thickest spokes.

Personally, I've ridden a variety of wheels with rims between 15mm and 42mm deep, and with between 12 and 36 spokes, and I haven't really felt any difference in vertical stiffness. Sure, wheels can differ in lateral stiffness, weight, and rotational inertia, but given the much greater difference in vertical compliance in other components (tires, forks, handlebars, saddles, even seat posts), wheels can be considered as nearly completely rigid radially.

[vqdriver]

I know almost nothing about the details of wheels and how they are designed.
But according to my butt dyno , ksyriums were much too harsh for me. Is that stiff? I don't know but it wasn't comfy. My shimano wheels were sluggish to spin up and my campy eurus wheels are my goldilocks wheels. Same frame and tires.

[Craig Ryan]

Thank you for the thoughts Mark. Many ideas concerning bicycles seem to originate in a cloud from the past, and become tradition. Makes me wonder about wheels. Once upon a time wheels weren't built with a means of measuring spoke tension beyond the builders finger pressure. It's possible those old wheels did have more vertical compliance than their modern counterpart. I've spent a lot of time on Ksyriums the last few years, and don't perceive them to much different than any other wheels I have. Differences I do feel in my various bike/wheel combinations seem to be attributed mostly to tires. People like laterally stiff wheels, but that means they will also be stiff vertically. I've used vertically compiant too many times here, so I'll let others chime in with opinions.
Craig Ryan

[rice rocket]

The radial stiffness of wheels is typically in the 10,000 - 20,000 lb/in range, which means that if suddenly hit by a bump force of 200 lb, the wheel would deflect by 0.01" - 0.02". With everything else that is deflecting under load, do you really think you could feel that small amount of deflection, let alone the difference between 0.01" and 0.02" of deflection?

I disagree, .01 vs .02" is essentially doubling the amount of distance and time you accelerate, normal to the pavement when you hit a bump. So if the impact was 10g acceleration on a soft wheel and 20g on a stiff wheel, you're gonna feel that resonate right up your ass and through your spine.


And Sheldon even said that in the article you posted:

There is no doubt that the difference in ride quality between a 20000 lb/in wheel and a 13000 lb/in one is immediately apparent to a 70 kg rider. Lighter guys should avoid stiff wheels.

[false_Aest]

Can someone who knows explain to me why I immediately start thinking about tyre pressure when the phrase "stiff wheels" gets used?

[djg]

Can someone who knows explain to me why I immediately start thinking about tyre pressure when the phrase "stiff wheels" gets used?

Hard to say. Something in your childhood.

I'm curious to read an explanation of the claim that the wheels are uncomfortable when descending. Are they extra comfy going uphill or just so-so?

Different wheels really do feel different, but it's hard to imagine that vertical compliance in the wheel itself has much to do with it. The sorts of numbers being bandied about are tiny relative to tire deflection . . . even with narrow tires, over-inflated, under a small rider.

For the OP, Campag makes great wheels IMO. Never had the shamals though, so no experience there.

[oldpotatoe]

I was getting ready to order the Campy Shamals when I read that because they're a "stiffer" wheel they are not very comfortable descending rough roads? I'm a superlight spinner/climber and what goes up must come down, so comfort and stability are really important. Also how are they in a crosswind? Little confused on what a "stiff" wheel really means.

Thanks

Anecdotal but I find wheels with fat aluminum spokes 'feel' really uncomfortable, even on short test rides after service. Plus we have had more than a few riders who get speed wobbles, mostly in gusty winds where replacing the front wheel with a wheel with stainless(smaller) spokes solves the problem.

AND if ya break a spoke somehow..bring your wallet. Spokes are tough to et and expensive.

For the $, I think there are better choices out there for you.

Like a set designed specifically for you and your needs? From a good local builder? Just a thought.

[John M]

Can someone who knows explain to me why I immediately start thinking about tyre pressure when the phrase "stiff wheels" gets used?

+1. I was thinking the same thing. Going from a 23 to 25mm tire and dropping 10 PSI smoothes out a ride that is too harsh in most cases.

[1centaur]

This thread is pretty funny in the way it covers the gamut of human reactions to the same thing. We have engineering reasons why "some vague perception" really requires therapy rather instrumented confirmation; assertion that tires matter way more than wheels even at identical pressure; a recommendation to use vast changes in tire pressure to offset wheel differences that may or may not really exist; the engineering counterargument that small numbers don't mean you can't feel it; and the vague perception claim that even if we don't know why it's there it still is there.

I'll take the last one with a little bit of the second one. Same tires, same pressure, I've found wheels to differ in their perceived stiffness, which I would associate most with the manner in which they transmit vibration rather than vertical compliance, per se. Also, I am finding that tires renowned for their comfort can make some difference to perceived wheel stiffness. And I'll note for the record that I've heard some people claim that they can't tell the difference between metal and CF frames but they can tell the difference between different forms of very thin rubber. Vague perception is what a lot of cycling reviews are about. Hard to prove people don't perceive what they perceive.

BTW, ascending vs. descending, I don't think that's a valid comparison. Descending gives relatively little ability to adjust your line to avoid bumps and puts a premium on relaxed confidence in your bike to handle what it faces without throwing you off your concentration. Wheels that are too stiff could make you think about control and comfort even if you try not to. Ascending is much more about your physical limitations and efficient transmission of power.

[0nelove]

First, Shamals are fine/good in x winds, no worries there.

Second, comfort and stability are really completely dependent on the individual's preference. I like stiff wheels and bikes, because the increase feedback and response makes me feel more in control. Putting the bike on edge and having it feel rock solid is nice to me. For other people, it's the exact opposite. This is the same with anything: bikes, cars, airplanes, etc. What's twitchy and hard to control to one person, is responsive and allows more control to another.

The stiffest wheel in the world is not going to lose contact with the road anymore than a noodley wheel because the tire is going to deflect far more and far quicker than the rim- IF the tires are inflated properly. But, can you feel a difference? Absolutely.

FWIW, the Shamals are stiff wheels.

[Ralph]

Would it be fair to say many people over inflate their tires? For their design, their intended use, road surface, their body weight, etc. I'm riding my tires, both 23 and 25's, a little softer than I used to years ago, and I can't tell they roll any worse.

[Mr. Squirrel]

Some direct measurements of wheel deflection of a variety of wheels can be found this article: Aero Wheels Under Scrutiny (http://www.sheldonbrown.com/rinard/wheel/grignon.htm) .



"Deep section rim aero wheels achieved large scale public awareness when Campagnolo introduced its Shamal series in 1993. At first, they were used only as time trial instruments. But in 1994, the Italian Gewiss team raced on Shamals in every road event. And they were incredibly successful, scoring victories in Milan-San Remo (Furlan), Fl�che Wallone (Argentin), Li�ge-Bastogne-Li�ge (Berzin) and the Giro d'Italia (Berzin). A high performance every day road wheel was born."


i do believe it was found that there were "other" reasons for the teams success....and it was not almond butter.

hazelnut/hozlenut.

mr. squirrel

[djg]

This thread is pretty funny in the way it covers the gamut of human reactions to the same thing. We have engineering reasons why "some vague perception" really requires therapy rather instrumented confirmation; assertion that tires matter way more than wheels even at identical pressure; a recommendation to use vast changes in tire pressure to offset wheel differences that may or may not really exist; the engineering counterargument that small numbers don't mean you can't feel it; and the vague perception claim that even if we don't know why it's there it still is there.

I'll take the last one with a little bit of the second one. Same tires, same pressure, I've found wheels to differ in their perceived stiffness, which I would associate most with the manner in which they transmit vibration rather than vertical compliance, per se. Also, I am finding that tires renowned for their comfort can make some difference to perceived wheel stiffness. And I'll note for the record that I've heard some people claim that they can't tell the difference between metal and CF frames but they can tell the difference between different forms of very thin rubber. Vague perception is what a lot of cycling reviews are about. Hard to prove people don't perceive what they perceive.

BTW, ascending vs. descending, I don't think that's a valid comparison. Descending gives relatively little ability to adjust your line to avoid bumps and puts a premium on relaxed confidence in your bike to handle what it faces without throwing you off your concentration. Wheels that are too stiff could make you think about control and comfort even if you try not to. Ascending is much more about your physical limitations and efficient transmission of power.

Your guess about transmission of (HF presumably) vibration rather than compression of the wheel, along the diameter, seems entirely plausible to me, even if it's just conjecture. Partly because the story about compliance of the wheel seems like such a stretch. On the tire differences . . . well, do we really need precision tools and a large n to see that tire deflection swamps the change in shape to the wheel itself? Somebody sitting on a bike with 23c tires will produce easily visible compression of the tire at the contact patch whether the tire is at 95 psi or 120, no? The wheel? Not so much, right? I'm not saying that it's immeasurable, much less that it's null, just that, pre-empirically, it seems like a different order of magnitude.

None of this is to say that small differences cannot matter, or that people should ignore their subjective preferences. And playing with tire choice and 5 psi increments is relatively cheap and easy.

[11.4]

+1 on 1Centaur's comments. Ride comfort, which may not be totally definable but is definitely a somewhat reproducible phenomenon, is not so much about impact hits as about vibration. That's why chipseal can wear you out in ten miles, even if it's fresh and otherwise smooth. And why riding faster makes a wheel seem smoother ... it's the rider doing 16 mph on those carbon deep section rims that tends to find them uncomfortable, not the rider who goes 25 mph.

But further, the math cited earlier is a bit odd. It isn't about a 200 lb impact, because 200 lb is a static measurement. If a rider weighing 150 lbs hits a bump or pothole edge at 25 mph, you have the combination of the rider's weight, the speed, and the localization of the hit to a potentially very small target area. When you calculate out the lbs per square inch per second, you get a pretty damned big number and yes, you get a measurable spoke deflection. If you've ever watched UCI certification of a wheel, you absolutely see it ... the test is basically designed to look like a wheel approaching a curb at a fixed speed and the UCI wants the wheel to pass unscathed, though high speed photography shows very significant flexion. And the flexion isn't just in the plane of the wheel, but very much sideways as well. In such films, a 65 mm section rim may only deflect in plane about 3 mm, but it deflects momentarily as much as a centimeter from side to side ... basically it wants to taco but recovers. That happens to be a very neat characteristic of carbon rims relative to alloy, which don't recover anywhere near as well.

I've watched a number of UCI and similar impact tests, including fully destructive tests, and learned a lot about how wheels react both in recovery and failure modes. Very educational, and not at all like some of the quant-poseurs like to pretend it is in their pseudo-mathematical analyses. It's a lot more complicated than that. But a lot more interesting.

[dd74]

Tire pressure. That's where I would begin to examine stiffness/compliance.

[Mark McM]

I disagree, .01 vs .02" is essentially doubling the amount of distance and time you accelerate, normal to the pavement when you hit a bump. So if the impact was 10g acceleration on a soft wheel and 20g on a stiff wheel, you're gonna feel that resonate right up your ass and through your spine.

That might be so if the only thing between your ass/spine was the wheel, but it isn't. A tire can compress about an inch under less than 10 g acceleration (pinch flats occur when the tire compresses fully at the impact point), plus various other components also deflect (fork, stem and handlebars at the front, seatpost and saddle in the rear), so the difference between 0.01" and 0.02" may be only 1% of the total deflection. So rather than decreasing the acceleration by 1/2 it might only decrease it by 1/100.


And Sheldon even said that in the article you posted:

Actually, the quote you cite is by the author of the article, Francois Grignon. Sheldon Brown merely hosted the article on his web page.

[Mark McM]

Anecdotal but I find wheels with fat aluminum spokes 'feel' really uncomfortable, even on short test rides after service. Plus we have had more than a few riders who get speed wobbles, mostly in gusty winds where replacing the front wheel with a wheel with stainless(smaller) spokes solves the problem.

There are very few wheels made with aluminum spokes, maybe you are referring to Mavic Ksyriums? In Damon Rinard's wheel stiffness test (http://www.sheldonbrown.com/rinard/wheel/index.htm) they were found to be a bit on the flexier than most wheels; a front Ksyrium was about see 35% less stiff than a 32 spoke Mavic Open Pro on a Dura-Ace front hub (see wheels number 50 and 96 in the table of wheel deflection data (http://www.sheldonbrown.com/rinard/wheel/data.htm).

[Mark McM]

I'll take the last one with a little bit of the second one. Same tires, same pressure, I've found wheels to differ in their perceived stiffness, which I would associate most with the manner in which they transmit vibration rather than vertical compliance, per se. Also, I am finding that tires renowned for their comfort can make some difference to perceived wheel stiffness. And I'll note for the record that I've heard some people claim that they can't tell the difference between metal and CF frames but they can tell the difference between different forms of very thin rubber. Vague perception is what a lot of cycling reviews are about. Hard to prove people don't perceive what they perceive.

I often wonder if it is indeed the difference in vibration frequencies, rather than the shock magnitudes, that people are responding to. Specialized published some frequency response graphs white paper on Zertz inserts (http://www.specialized.com/OA_MEDIA/pdf/Witchcraft.pdf). If you look carefully, the graph shows most of the attenuation is in the frequency range starting at 100 hertz or more, with little attenuation at lower frequencies. The lower frequencies are where shock is transmitted to the rider – the higher frequencies where attenuation occurs is mostly is in the audio region, so it can be heard more than felt. So the question is, do the Zertz inserts really reduce shock forces to the rider, or do they instead “muffle” the audible sounds of shock loading, so that the rider merely perceives the frames to be shock absorbing?

[Mark McM]

But further, the math cited earlier is a bit odd. It isn't about a 200 lb impact, because 200 lb is a static measurement. If a rider weighing 150 lbs hits a bump or pothole edge at 25 mph, you have the combination of the rider's weight, the speed, and the localization of the hit to a potentially very small target area. When you calculate out the lbs per square inch per second, you get a pretty damned big number and yes, you get a measurable spoke deflection. If you've ever watched UCI certification of a wheel, you absolutely see it ... the test is basically designed to look like a wheel approaching a curb at a fixed speed and the UCI wants the wheel to pass unscathed, though high speed photography shows very significant flexion.

I’m not familiar with the units of lbs per square inch per second, but yes, impulse loading can be very high – it can be many hundreds of pounds when hitting sharp edge bumps. But the UCI wheel test is not a good example either, because it purposely impacts wheels to destruction, and we’re discussing comfort to normal road forces, far below destructive forces.

We also know that hitting a sharp edged bump can pinch flat a tire at well below the destructive force of the wheel, which requires the tire to deflect about an inch (depending on tire diameter). This is between one and two orders of magnitudes greater than the wheel itself deflects under the same load. So the difference in deflection between one wheel and the next might be only a percent or two of the total stiffness, or roughly the same difference as if the tires were inflated to a few psi higher or lower. Depending on the inner tubes and changes in barometric pressure, the air pressure in the tires can vary by a few psi during a single ride – can you detect the differences in stiffness during a ride?

[RPS]

This thread is pretty funny in the way it covers the gamut of human reactions to the same thing. We have engineering reasons why "some vague perception" really requires therapy rather instrumented confirmation; assertion that tires matter way more than wheels even at identical pressure; a recommendation to use vast changes in tire pressure to offset wheel differences that may or may not really exist; the engineering counterargument that small numbers don't mean you can't feel it; and the vague perception claim that even if we don't know why it's there it still is there.

I'll take the last one with a little bit of the second one. Same tires, same pressure, I've found wheels to differ in their perceived stiffness, which I would associate most with the manner in which they transmit vibration rather than vertical compliance, per se. Also, I am finding that tires renowned for their comfort can make some difference to perceived wheel stiffness. And I'll note for the record that I've heard some people claim that they can't tell the difference between metal and CF frames but they can tell the difference between different forms of very thin rubber. Vague perception is what a lot of cycling reviews are about. Hard to prove people don't perceive what they perceive.

BTW, ascending vs. descending, I don't think that's a valid comparison. Descending gives relatively little ability to adjust your line to avoid bumps and puts a premium on relaxed confidence in your bike to handle what it faces without throwing you off your concentration. Wheels that are too stiff could make you think about control and comfort even if you try not to. Ascending is much more about your physical limitations and efficient transmission of power.
Unfortunately the more technical analysis is simplified (either for ease of communication or for lack of understanding) the more exceptions are created. And it is in finding those exceptions that I fear creates skepticism towards those who try to objectively quantify what is occurring. In my experience working in a marketing-driven company if we make technical matters too precise few will care about or understand much of anything. On the other hand make it too simple and someone will inevitably find the rare exception to punch wholes in the analysis. It’s a fine line when discussing technical matters with non-technical people.

I try not to argue against perceptions but rather try to explain what probably leads us to have those “feelings”. I trust there is always a scientific explanation whether we know it or not. In this case I wouldn’t argue against the perception that wheels are important but rather offer an explanation that makes sense to me from a scientific standpoint. To simply state wheel stiffness doesn’t ever matter is not right. Sometimes it matters a lot and other times it doesn’t matter much. Knowing the difference is critical.

For starters, impact loads and vibration reduction must be separated and treated as two different problems (which may or may not have a common solution). I’d go into more details about why theory and practice don’t always agree but it’d be well outside the scope of this thread.