A stiffer wheel wanted. Spoke type, number, or rim depth?

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Mr.Gib
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by Mr.Gib

I do enjoy my 1260 gram Farsport Kaze 35mm on Carbon Ti 20/24 CXray on my rim brake Factor O2 VAM. As nice as they are, I feel that something laterally stiffer would be more appropriate for hard riding. I had plans for a second wheelset and figured I'd go with something deeper, 50-55mm.

The question is will a 20mm deeper wheel with the same build provide the stiffness I am looking for, or will I require stiffer spokes in the rear (drive side) such as Sprints? Or is it better to go up to 28 spokes in the rear but stick with CXrays?

Of course all of the above is an option, but there are weight considerations. We are afterall talking about a VAM 8)

TKS.
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C36
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by C36

Replacing the cx-ray (that shouldn’t be used in any rear wheel to me...) by the sprints would bring a small 10% stiffness if I recall some older measures. The real difference would be going to 28 spokes that would add (ballpark) 15-18% stiffness.

You could go bigger than the cx sprint. Pilar has a large range of thicker blades spokes.
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Rubik
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by Rubik

Going to a deeper rim won't make the wheel "stiffer". The rim is already too stiff as it is, and will likely just increase brake rub if that's the problem you're having.

Going 28 and/or going with thicker spokes as mentioned above is the only way to alleviate that.

I'm dealing with the same issue on my new 45mm 1360 gram wheels. I'm about to replace all of the drive side CX Rays with Sapim Race because I get brake rub even at just 500 watts standing. Drives me nuts.

alcatraz
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by alcatraz

Maybe get lightweight wheels?

Or try a hub with big flanges and use thicker spokes than cx-ray. 35mm is a pretty good depth for a stiff build. If the rim is superlight it might not be ideal.

Zipp/Lightweight/Campy rims are relatively stiff and they have high temp resins. I suspect that the high temp resin can help to stiffen the rim. Chinese rim manufacturers are very excited about reducing weight. If you can find a rim that isn't aimed at the lowest price or lowest weight, you have a chance of getting a strong rim. It's risky to buy heavy rims as they could be low tech. There is a lot of old stock that needs to be moved and the sellers could try to take advantage. Choosing a modern feature as textured brake track could help to ensure you get a modern rim.

NovemberDave
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by NovemberDave

What aspect of stiffness do you need to increase? What are the symptoms of lack of stiffness that you're hoping to eliminate?

Carbon Ti rear hubs don't have the best bracing angles, so there are a lot of rear hub options that can improve that.

28 CX Rays will provide a stiffer wheel structure than 24 CX Sprints, at slightly lower weight (120g of spokes vs 130g of spokes). We've used CX Rays as our primary spoke for about 10 years and there are no performance or durability problems when using them in a well designed and constructed wheel.

Deeper rims provide slightly improved bracing angles, which stiffens the build. They also shorten the spokes, which effectively stiffens the spokes. The also shorten the span between spokes on the rim. They also decrease the amount of spoke tension drop a wheel suffers when you mount a tire, because of their higher hoop strength. Changing rim depth has a big effect on wheel properties.

High temperature resins in and of themselves don't increase rim stiffness. Resin systems are complicated, and while they have an impact on the rim stiffness and for sure its strength, just switching from lower temp to higher temp resins has no effect on rim stiffness. Generally, higher temp resins create a bunch of challenges for making successful composite parts. Zipp/Lightweight/Campy may indeed make stiff rims, but chalking it up to their use of high temp resins would be a mistake.

alcatraz
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by alcatraz

I was referring to the property combination of 1. non-ultralight and 2. high temp resin (directly or indirectly) creating a higher chance of delivering a competitive rim for the OP's purpose.

Like testing for diseases, you might look for a condition the disease creates, instead of looking for the disease itself which could be difficult or impossible.

A question for you Novemberdave. About the benefits of shorter spoke and improved bracing angle of a deep rim build. Considering that the spoke/rim interface moves closer to the hub as the depth increases, won't the lateral forces on the interface also increase with the now longer lever created by the deper rim?

Is then a 40mm deep wheel really laterally less stiff than a 90mm? (if hubs/spokes/count are equal) Does the added carbon in the 90mm rim flex less than steel in the spokes it replaced?
Last edited by alcatraz on Tue Feb 09, 2021 4:13 pm, edited 1 time in total.

NovemberDave
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by NovemberDave

I'm sorry, I read "I suspect that the high temp resin can help to stiffen the rim" and immediately wept for the future of my inbox when people would ask for rims with high temp resins (which by and large make worse rims) because they heard they are stiffer. They are not.

Rim weight and stiffness are directly correlated. Rim depth and stiffness are directly correlated. High Tg resins, which started to really surface en masse ~2013, might possibly indicate a more modern rim, but Campagnolo has been making stiff carbon rims with and without high Tg resins since well before that.

NovemberDave
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by NovemberDave

alcatraz wrote:
Tue Feb 09, 2021 3:52 pm
I was referring to the property combination of 1. non-ultralight and 2. high temp resin (directly or indirectly) creating a higher chance of delivering a competitive rim for the OP's purpose.

Like testing for diseases, you might look for a condition the disease creates, instead of looking for the disease itself which could be difficult or impossible.

A question for you Novemberdave. About the benefits of shorter spoke and improved bracing angle of a deep rim build. Considering that the spoke/rim interface moves closer to the hub as the depth increases, won't the lateral forces on the interface also increase with the now longer lever created by the deper rim?

Is then a 40mm deep wheel really laterally less stiff than a 90mm? (if hubs/spokes/count are equal) Does the added carbon in the 90mm rim flex less than steel in the spokes it replaced?
To address additional questions..

Damon Rinard's famous old test https://www.sheldonbrown.com/rinard/wheel_index.html addresses this in priciple (emphasis points are mine):
"Smaller wheels are stiffer than larger wheels. If they are built on the same hubs, then the bracing angle is larger for smaller rims. If everything else is the same, 650C wheels are about 25% stiffer than 700C wheels.

Note: smaller wheels often have fewer spokes than larger wheels, and this is as it should be. For similar strength, spoke spacing at the rim is what should be held constant, not spoke count. Consequently, a 650C wheel with 28 spokes is about the same strength as a 700C wheel with 32. This is the case with the wheels I measured to identify this 25% difference in stiffness: wheels 69 and 71."

A 25mm deep 650b rim and a 45mm deep 700c rim are going to have very similar ERD of around 550. The 700c wheel's tires will be farther out circumferentially, exerting more leverage over the wheel, but the rim doesn't "hinge" on the spokes.

Note that in the test I link above, rim depth is listed as the #5 factor in wheel stiffness. The rim depth range that was used to arrive at that conclusion was much much smaller than the ranges we talk about these days. We have replicated Rinard's test with 52mm deep versus 34mm deep rims, holding hub, spoke count, and spke type constant, and rim depth makes a big difference with that big a rim depth change.

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Mr.Gib
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by Mr.Gib

Wow, thanks everyone (particularely NovemberDave) for all the great info.

Very happy with my wheels. The Farsports rims are excellent. The lack of stiffness is relative. I have no real problems with the wheels. They are no less stiff than any other similar build carbon wheels I have ridden. But they are just a touch "soggy" feeling relative to my Shamal Ultras for example. They do help soak up the road but I am prepared to let my tires do more of that.

Sounds like the easy solution is just to up the spoke count and maybe go a bit deeper on the rim.

@NovemberDave, what rim brake rear hub do you like for stiffness?
wheelsONfire wrote: When we ride disc brakes the whole deal of braking is just like a leaving a fart. It happens and then it's over. Nothing planned and nothing to get nervous for.

NovemberDave
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by NovemberDave

Mr.Gib wrote:
Tue Feb 09, 2021 6:07 pm
@NovemberDave, what rim brake rear hub do you like for stiffness?
It ight sound like a boring answer but White Industries T11s work every time. They have good geometry, approriate flange sizing, and the steel axle actually helps keep things in check.

alcatraz
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by alcatraz

Trying to improve bracing angles by going deeper is probably not what a customer would like to do. It's good to know however that you don't lose anything by doing so. You might want to use the best hubs and rims before going that direction. (or even better, go full carbon a la lightweight)

What's the deepest rim used by the tdf sprinters? What do big brand wheel manufacturers offer for sprinters? I'm just posing this question before someone attempts to build an 88mm sprint wheelset with standard hubs and ultralight rims. It might not be ideal.

NovemberDave
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by NovemberDave

From the OP: "I had plans for a second wheelset and figured I'd go with something deeper, 50-55mm." This move, from the current 35mm rim, will improve wheel stiffness given same hubs, spokes, and changing only rim depth.

Wheel stiffness, and its effects, are generally poorly understood. Mavic made a bunch of wheels with varying stiffnesses in a long-ago experiment and learned that no group of cyclists (from club to pro) could succesfully pick out the stiff wheels by riding them. After 10+ years of building wheels professionally, thousands and thousands of wheels with tons and tons of feedback, I have very few concrete answers. The ones I have are that front wheels with inadequate stiffness handle poorly in hard steering, and that rear wheels with inadequate bracing angle and/or spoke stiffness (NOT rim stiffness) rub the brake pads.

The OP references a soggy feeling in these wheels. My guess is that this isn't a lateral stiffness issue at all. It could be an audio difference, it could be a rim inner width issue leading to a "the 'same' tires aren't really the 'same' tires on both rims" issue, it could be other things. But I don't think it's a lateral stiffness issue.

Most of the pro tour sprinters I see are on 60mm deep rims, plus or minus. But when you want to evaluate stiffness, look at high torque dynamic climbers. They're the ones who really stress wheels out. An attack on a steep hill, in the small ring and a large cog, is a greater transmission of torque into the wheel than launching a final sprint from a high speed leadout. Contador was reportedly the single most reliable wheel killer ever.

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by NickJHP


jlok
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by jlok

Pogačar was winning climbjng stages with 50mm Bora rear if I remember correctly.

Would a 28h i9 1/1 road rear hub (142) serves as a good foundation for a average rider at 72kg? NDS/DS flange distance are 35/20 and the they are 47/60 tall.

If it is paired with a 420g 50mm rim, is it better to go 28h 3x/3x for the almost tangential spoke angle?
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biwa
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by biwa

NovemberDave wrote:
Wed Feb 10, 2021 1:33 am
The OP references a soggy feeling in these wheels. My guess is that this isn't a lateral stiffness issue at all. It could be an audio difference, it could be a rim inner width issue leading to a "the 'same' tires aren't really the 'same' tires on both rims" issue, it could be other things. But I don't think it's a lateral stiffness issue.
I'm curious to learn more about how the inner width affects things here.

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