Calling wheel-building experts. Spoke count or rim depth for stiffness???

[tonyzackery]

Me: 190-195lbs, tends to rely on high pedal torque (as opposed to rpm) to put out high power. Races predominantly crits.

Question is thus: I'm looking to build some carbon tubulars using the cheap carbon rims and relatively lightweight hubs you can source from eBay. I'm curious to know whether given the choice between the two options, should I look to go with a higher spoke on a shallower rim (say 28/32 spokes on a 38mm or 50mm rim) or a greater rim depth (60mm or 88mm) and less spoke count (20/24 spokes)? Needless to say, I want a stiff/rigid feeling aero wheel when I'm done with this endeavor. Sure, high count and greater depth would be stiffest of the options, but can I get away with choosing one versus the other?

Appreciate hearing from those in the know...

 

[swampy1970]

There's lots of good stuff from the author of The Bicycle Wheel, Jobst Brandt on this link:

http://yarchive.net/bike/index.html

Sheldon Brown has a few good links from Brandt too:

http://www.sheldonbrown.com/brandt/

Besides being an excellent read, The Bicycle Wheel is pretty much The Bible of wheel building. One of the ex GB team mechanics spoke very highly of it and I've had some of that guys wheels (Mavic GEL280s, 28 spoke) withstand really bad roads that had seemingly stronger wheels fail.

The spoke tension ,spoke gauge and the number of spokes have the biggest effect on wheel stiffness. Shimano used to tighten the spokes on the 7801 wheels to an ungodly high tension - tightened to a tension in excess of 350lb/ft and were very stiff despite their fairly low spoke count - 24 in the back I believe. With spoke tension comes a requirement for a stronger spoke. This normally means more material unless a better material is used.

All of Shimanos wheels were built very tight and despite their varying rim depth they were all very stiff - which lends credence to the 'spoke tension/count' argument. The 7801 carbon 50 wheels make Mavic Krysiums seem like floppy pretzels in comparison.

Such high tensions require a really good spoke and a good rim. It would seem that the good ol' DT blade spoke isn't quite what it used to be and the Sapim CX-Ray requires a very high tension to produce a stiff wheel - as I found out on my rear 32 spoke training wheel (that has my power tap). The CX-Ray spokes aren't cheap though - about $3 each. Avoid spokes with any mention of 17 gauge or thinner (1.5mm diameter). You'll save a gram or two and even more when you lose a few spokes when they snap and fall out.

Brandt had a novel but very effective way of tensioning a wheel - get the spokes tight and the wheel very true. Once that had been achieved keep tightening all the spokes until the wheel starts to deform (like a potato chip) and back off the tension slightly. That said, that was done on aluminum wheels with double eyelet spoke holes that helped spread the load. I have no experience with carbon rims and wouldn't want to be the one to pass on this info only to have you try in an hear the wheel go bang because the spoke pulled the rim through... If you have hubs of marginal quality, especially in the flange then avoid having to slot the spoke hole.

 

[tafi]

I would agree with most of that. The number of spokes is the biggest contributor to stiffness. The aero advantage comes mainly from the rim profile. Spoke count and profile have been shown over the years not to matter for aerodynamics any where near as much. For crits, I shouldn't think that super deep profiles will be necessary (are you likely to be off the front for most of the race?). In a crit the wind direction will rotate around the bike as you lap the course and you will definitely need nimble handling in the pack in such conditions so perhaps the mid depth rims are the best bet (from my way of thinking). For spokes probably tyhe most relaible woulfd be DT competition (2.0/1.8/2.0mm) ore equivalent.

Jobst Brandt's book is indeed a good read and busts a couple of myths (eg: that lower spoke tension increases comfort and that the bike hangs from the uppermost spokes). His ideas come from sound engineering principles (many of which are not understood by the average mechanic) and are based in the concept that reliability is paramount. You can't go wrong following his basic recommendations on components.

I would disagree with putting a blanket ban on thin section spokes. It is true to say that nobody needs revolution 2.0/1.5/2.0mm spokes. The weight savings over a competition (2.0/1.8/2.0mm) are minimal, they take much more care and time to build with, and one needs to counter the twist that occurs when tensioning; but they can still be built into a nice reliable wheel if you're up for the challenge (the challenge is all I really care about sometimes).

Nor do I buy the common argument (not necessarily an argument of Brandt's) that narrow double butted spokes are more prone to breakage. If a spoke was going to snap under tension, then it would do so when you are building the wheel. In any case spokes (even revolutions) can take a lot more tension than any rim can.
In use, spokes only break at stress raisers under fatigue loading. That means, head, elbow or thread after a certain number of stress cycles. The forged double butted spokes are actually better at preventing stress raisers because the shape and grain structure of the steel is better aligned to the direction of stress. Machinery strain bolts are designed around the same concept (and when you think about it a spoke is just a long, thin bolt). I've certainly never broken a revolution spoke, and I've never seen a quality, forged DB spoke break at its midesction unless it had been previously damaged (eg: gouged by an overshifted chain on an improperly adjusted derailleur) to add a stress raiser. In fact the only spoke I've ever broken (and it was only one spoke in 10 years) was a plain gauge spoke (at the thread).

 

[tonyzackery]

Looking at deeper section more for the stength/stiffness factor versus the greater aero qualities.

I appreciate the input thus far - I really do - but can someone give me a relatively short answer to the question originally posed? I want to know of the two carbon rimmed choices: higher spoke count/shallower rim or deeper rim/lower spoke count, which one would give me the best stiffness for the type of rider I am and the races I race. I'm aware higher spoke counts mean greater stiffness (all other things being equal), but does that also ring true when using a rim with a shallower carbon rim versus a carbon deeper rim but with less spokes? In your educated, prior wheel-building experience, does the larger carbon structure of the deeper wheels trump the increased spoke count of the shallower wheels?

 

[alfeng]

FWIW. I generally want my rear wheels to be as laterally stiff as is reasonably possible ...

You can use the following as a reference point, or not:

​

I believe that the 32h wheels were [COLOR= #ff0000]very rigid[/COLOR], laterally, BECAUSE of the medium profile rims AND they were laced with straight 14g spokes ... and, they would have been laterally less rigid if they had been laced with double-butted (14-15-14) gauge spokes.

Because the particular wheels were laced on disc hubs ([COLOR= #808080]which are high flange hubs, BTW[/COLOR]), I laced the driveside x4 & x3 on the non-driveside/disc... x4 on the disc side of the front & x1 on the non-disc side. I generally prefer to lace a standard hub x3 on the driveside & x2 on the non-driveside, BTW.

• While Brandt, et al, may be correct that a double-butted spoke has advantages, Brandt made one comment (not regarding spoke gauge) about a decade ago which suggests that his logic is flawed & it is possible that the so-called engineering he presents is consequently biased to validate his argument ...
• IF Brandt had not made the particular statement, then I might have been more inclined to investigate-or-to-give-weight-to the notion that a rear wheel laced with double-butted spokes might be better than one laced with straight gauge spokes ...
• Alas, my opinion of the message ([COLOR= #808080]i.e., that double-butted spokes result in a stronger wheel[/COLOR]) remains tainted by my impression of the one comment by the messenger ...

IMO, if you want a laterally stiffer wheel then I recommend that you choose the 32h rims and that you have them laced with [COLOR= #ff0000]straight 14 gauge spokes[/COLOR], particularly if you are using a narrow flange offset rear hub.

 

[swampy1970]

Originally Posted by tonyzackery .

Looking at deeper section more for the stength/stiffness factor versus the greater aero qualities.

I appreciate the input thus far - I really do - but can someone give me a relatively short answer to the question originally posed? I want to know of the two carbon rimmed choices: higher spoke count/shallower rim or deeper rim/lower spoke count, which one would give me the best stiffness for the type of rider I am and the races I race. I'm aware higher spoke counts mean greater stiffness (all other things being equal), but does that also ring true when using a rim with a shallower carbon rim versus a carbon deeper rim but with less spokes? In your educated, prior wheel-building experience, does the larger carbon structure of the deeper wheels trump the increased spoke count of the shallower wheels?

Spoke tension and spoke count make more of a difference to rigidity than a deep section rim. Depending on the rim there may be some kind of composite reinforcement that 'may' aid in stiffness. Using Shimano and Zipp wheels as an example, their deeper section rims with the same spoke count as the shallower rims don't seem to offer significantly more stiffness.


You could always go with more than 24 spokes in the rear. The rear of the bike is pretty much all dirty air anyway and adding 4 more spokes won't make a massive difference to aero drag.


Here's some blurb from Zipp on spoke count, "wheel feel", stiffness and reliability. They probably know as much as anyone about such matters.


http://www.zipp.com/_media/pdfs/technology/spokecount.pdf

If you want a set of uber stiff wheels on the cheap, see if you can pick up a set of Shimano 7801 Carbon 50s from 2006.

 

[Eichers]

Excellent info peoples ... how much more stress is placed on the rear wheel compared to the front wheel?

Hi tonyzackery, for crits where you need quick acceleration, so you really need light strong semi aero rims. Also the hubs and bearings (very low fiction) are important. That is really the answer, but you probably know that already

Hi tafi, how much does a chain nick on a flat 3mm aero spoke affect the strength of the spoke?

Hi swampy1970, reading the zipp pdf confirms that aero spokes provides a noticeable wattage difference but changing spoke count from 20 to 28 only a little wattage difference.

 

[tafi]

Originally Posted by KLabs .

Hi tafi, how much does a chain nick on a flat 3mm aero spoke affect the strength of the spoke?

The nick usually won't immediately appreciably affect the ultimate tensile strength of the spoke. What it does is significantly impair the spoke's fatigue resistance.

Every rotation, the spoke goes through a fatigue cycle of higher and lower tension. Under such loading any "stress raiser" (such as a scratch or nick), if significant enough, will cause the material to yield in a microscopic region around the tip of the stress raiser. This forms a crack which steadily propagates as the yield continues to occur in the area around the crack tip. As the crack propagates, the effective thickness of the spoke is steadily being reduced. Eventually it gets to the point where there isn't enough material remaining to take the tension load, at which point the spoke goes BANG!

Some stress raisers are built into the component (sharp corners, welds, holes, threads) and there's nothing which can be done about it. Usually an engineer does his/her calculations to ensure that the built-in stress raisers aren't enough to cause fatigue failure. In most cases a big safety factor is applied as extra insurance against unforeseen failures. This works well for heavy stuff like bridges, railways, trains, trucks, ships etc, but the extra weight implied by a high safety factor is an anathema to the modern cyclist who needs to be able to get up hills (same as with aircraft - they simply wouldn't get off the ground otherwise). So the onus then falls on the user/maintainer to ensure that fatigue is managed and doesn't become a problem. Air maintenance engineers spend most of their time checking components for cracks and replacing them when they reach a safe size limit.

This is a stochastic phenomenon which has only been determined through rigorous statistical sampling of materials (many types of steel, aluminium and Ti alloys), part shapes and defect types. How long the spoke would take to fail depends on the tension, your weight, spoke profile, spoke material, size and shape of the nick, and even the internal grain structure of the spoke material (whether it has been forged or not). Impossible to determine accurately (it could range anywhere between hundreds to millions of wheel rotations). It is safest to assume that it will happen eventually.

To clarify what I said in the above post: The only spokes I have ever seen fail in their mid section have invariably been previously damaged (thus providing a convenient stress raiser), and/or been made of poor quality plated wire (which probably already contain internal stress raisers from their manufacture).

In short, if I found a nicked spoke, I'd replace it before it becomes a problem. Better yet, I'd tune my derailleur so that it would never overshift into the spokes.

 

[Eichers]

Thanks Tafi, I had the bike mechanic look at it and he said everything was ok, and just a bit of light emery, and maybe a touchup with a file, should be sufficient One thing he did say to me about wheels was that a balanced rim is more important than aero or weight, and that if the rim was out of balance, the rider will use much more energy controlling the change in rim momentum ... guys, what are your thoughts on this :duck:

 

[531Aussie]

Originally Posted by alfeng .

FWIW. I generally want my rear wheels to be as laterally stiff as is reasonably possible ...

I believe that the 32h wheels were [COLOR= #ff0000]very rigid[/COLOR], laterally, BECAUSE of the medium profile rims AND they were laced with straight 14g spokes ... and, they would have been laterally less rigid if they had been laced with double-butted (14-15-14) gauge spokes.​

I agree. I use these 32h DT RR 1.2s with 'straight' DTs, which are pretty stiff, but I'd prefer even stiffer wheels. I still loosen my brakes a bit for a race.
I'd probably be just as happy with 28-spoke wheels, but 32h hubs are much more ubiquitous around here, especially at the local 2nd hand shop for cheap.



I'm no expert, but I've built or rebuilt most of my 20+ wheels. Some guys reckon they can build a stiff wheel with radially lacing and fewer spokes, but then you've got the issue of getting hub flanges that are designed to tollerate radial loads.


I dunno how a lot of guys use flexy carbon wheels for crits that require a lot of very hard mashing out of corners -- not saying that all carbon wheels are super flexi. I see guys racing on wheels that I've tested, and I think to meself: "gord, I hope you've loosened your brakes". I have some cheap-ish carbons (Flashpoint FP60s and Token C50s), and they're horrible for crits; they're flexi, dead-feeling, and don't have the 'snap' of stiff alu wheels. I figure more people would use stiffer alu wheels with 'lots of' spokes for crits if they weren't sucked into wanting to rock up to the start line with the bling, plus, they can't get their head around using an 1800g to 2kg wheelset. As far as weight goes, these DTs feel faster than my Open Pros with DB spokes, coz the DTs are stiffer], even though the Open Pros are nearly 400g lighter.


For Tonzackwery: at 190 to 195lb (~90kg), I'd seriously consider some 32h, deep-ish alu, or at least try some. And they'd be cheaper. But I gather you may have had some in the past, and know what they're like.

Also, on the 'cheap hubs' thing: watch out for generic Joytech/Novatech, because I found that the flimsy 13mm alu rear axles were easy to bend.
They don't bend a lot, but enough to make the hub run rough. I've replaced the Flashpoint rear axle 3 times. My stock Shimano rear hubs, with steel axles and hub bodies are only 55g heavier than my generic Joytech hubs with alu axles and hub bodies.

Maybe flexi carbon wheels is why lots of pros race with their brakes undone

 

[swampy1970]

Originally Posted by KLabs .


Hi swampy1970, reading the zipp pdf confirms that aero spokes provides a noticeable wattage difference but changing spoke count from 20 to 28 only a little wattage difference.

That's why I mentioned in one of my earlier replies my personal favorite spoke the Sapim CX-Ray. It's what Zipp uses too... Light, aero, very strong and you can get it almost as tight as TZ's temperament.

As for the nick on the flat spokes - I'd keep an eye on it. The only way you'll break something like a DT blade or a CX-Ray is via a ding. I've had a front spoke let go and it'll sound a bit like a gunshot when it lets go if it's built nice and tight.

The DT Bladed spoke was a good choice back when hub manufacturers didn't machine hub flanges really small and wafer thin. Now, if you slot the spoke hole it's almost like you're removing a significant percentage of the flange material. The DT bladed spokes were very stiff and made an excellent weapon of choice when you were dicking around and you wanted to slap someone across the back of the hand

Ozman - you know full well the pros who ride wide carbon rims have their quick releases open so they can use the standard 19mm rims from the service cars... You need to check out your bike shops for some factory built Dura Ace wheels - damn stiff, especially the carbon 50s. Any more TAN stuff you wanna drag in here? Did you get that new Miley doll yet?

I wasn't too sad when my the rim on my rear American Classic CR420 munched it in a pothole - a hateful wheel. I could hear that thing flex against the brake pads while I was in the saddle going up steep hills.

 

[swampy1970]

Originally Posted by KLabs .

One thing he did say to me about wheels was that a balanced rim is more important than aero or weight, and that if the rim was out of balance, the rider will use much more energy controlling the change in rim momentum ... guys, what are your thoughts on this /img/vbsmilies/smilies//duck.gif

My thoughts are that you really should buy your wheels elsewhere...


Wheel balancing is important on cars due to the rotational speed and the mass involved. A lightweight car wheel/tire combo is around 30lb (my Miata racing wheels with shaved tires - SSR 15x7.5 and Falken Azenis @ 3/32" tread depth weighed 32lbs and most of that was in the tire). Most car wheel/tires are in the 40 to 55lbs range.
Those forces can overcome the spring and shock/strut combo on a car leading to the familiar wheel hop sensation of an out of balanced wheel. The forces of the unbalanced car wheel don't act directly against the weight of the car. Car tires, due to their construction are unbalanced to such a degree that markers are placed on the sidewalls. The yellow dot should be placed near the valve stem.


In low speed car racing events some competitors don't even balance their wheels with wheel weights as getting the tire orientated on the rim correctly does a good enough job.


On a bike those forces are small and the weight of the rider/bike makes it a none issue. If it was, then 50+mph would be a very scary thing on a bicycle
when descending a mountain pass.

Now, if you did a craptacular job of gluing on a tubular tire and left a hump in it, that'll make things interesting at speed...

 

[531Aussie]

Originally Posted by swampy1970 .

Ozman - you know full well the pros who ride wide carbon rims have their quick releases open so they can use the standard 19mm rims from the service cars...

No I di'n't. Or at least I forgot if you told me last time.
There used to be a video on the Easton site spruiking their 'stiff' wheels, where some BMC pro said that during most sprints, he could hear lots of brakes squeaking as they rubbed on the flexing carbon rims, so I'm going with my theory.

I've kinda had my eye on the Dura-Ace 50mm clinchers for a while, but, to be honest, I can't get my head around a 16 spoke front wheel. I'm a bit of a masher when I do crits (and 80kg), so I really farkin hate flexi wheels. One race where I used my Flashpoints, I thought my bike was gunna collapse under me. After that, I never raced with them again.

I felt a bit burnt by the carbon Flashpoints and Tokens (a fair bit of money for no noticeable performance), so I'm never buying carbon wheels again unless I give them a long test. Also, at the moment, I'd rather spend the cash on a x-Flash Tuner for my 6cyl Ford Turbo.

I love that Miley pic.

 

[swampy1970]

Dude... you like retro. You should buy my pristine condition Campag Shamals Very stiff... despite the low spoke count and only ever used in time trials.



I've been halfway toying with the idea of digging out the old 8spd Campag stuff, nabbing some ergopower levers and a Cannondale CAAD 6/7/8/whatever off ebay and building a damned stiff roadbike that I don't mind stacking. That 11-18 cassette would require a bit less weight and more push on my part for the hills though

 

[tonyzackery]

http://www.rouesartisanales.com/article-23159755.html

Excellent article on wheel stiffness and results of testing some recent model factory built wheels...

Think I'm gonna go with some 38mm deep carbon rimmed tubs with 28/28 lacing and straight gauge spokes...

edit: wheel stiffness considerations:

Thus, in order to increase the lateral stiffness of a wheel one needs to:
- use a stiff and deep rim which will also comes with shorter spokes
- use larger spokes
- increase the bracing angle: hubs with flanges as far as possible
- high tensioned spokes to delay the moment when the wheel loses all its stiffness

The parameters playing a role here are not well known but when digging deep inside the stiffness/deflections at 180° sheet, there are at least two important parameters:
- the rim depth: the shallower it is, the smaller are the deflections between the brake pads, but the lower is the lateral stiffness of the wheel
- the spoking: the higher is the spoke count, the lower are the deflections between the brake pads, and the higher is the wheel stiffness.

Still no definitive answer to the question of which is most important - rim depth or spoke count, all other things being equal. The test gives many different examples, but there are just as many different construction methods for wheels, so a direct comparison of the results between deep rims/low spoke count wheels and shallow rims/high spoke count wheels is speculative, at best.

 

[531Aussie]

Originally Posted by swampy1970 .

Dude... you like retro. You should buy my pristine condition Campag Shamals Very stiff... despite the low spoke count and only ever used in time trials.



I've been halfway toying with the idea of digging out the old 8spd Campag stuff, nabbing some ergopower levers and a Cannondale CAAD 6/7/8/whatever off ebay and building a damned stiff roadbike that I don't mind stacking. That 11-18 cassette would require a bit less weight and more push on my part for the hills though

Funny, you should say, because I nearly bought some of those old Shamals last year. I figured if they were good enough for a lot of our Aussie track stars in the '90s, then they'd be good enough for me, but I didn't get them. I love riding to races, and I can't be stuffed dealing with a flat tubular on the way to a crit. A couple of older blokes at Veterans race on them, and swear by them. When one of them wasn't looking, I snuck over to his bike and did my "wobble the wheel from side to side" test to see how stiff they were, and they were pretty good. I've done that to a few guy's bikes.

Yeah, I reckon you should do the "8sp, uber stiff crit bike with no granny gears" thing. Cool. My main old 531 bike is 8sp with 11 to 19, and a 42 front small chainring. It's great for flat-land grinding.

 

[531Aussie]

Originally Posted by tonyzackery .

Think I'm gonna go with some 38mm deep carbon rimmed tubs with 28/28 lacing and straight gauge spokes...

Which rims? Gigantex?

 

[tonyzackery]

Originally Posted by 531Aussie .



Which rims? Gigantex?

I'll get some generics off eBay or another Chinese source. Seen 'em for <$200.

 

[tafi]

Originally Posted by KLabs .

Thanks Tafi, I had the bike mechanic look at it and he said everything was ok, and just a bit of light emery, and maybe a touchup with a file, should be sufficient /img/vbsmilies/smilies//smile.gif

One thing he did say to me about wheels was that a balanced rim is more important than aero or weight, and that if the rim was out of balance, the rider will use much more energy controlling the change in rim momentum ... guys, what are your thoughts on this /img/vbsmilies/smilies//duck.gif

Your legs would not be able to tell the difference between a balanced or an unbalanced wheel. A bike has two wheels so any imblanace is in the plane of motion (ie you won't notice). In a car, however there are four wheels and two wheels side by side control the direction of motion. An imbalance on one of those wheels is enough to make the steering funny (you've probably felt the steering wheel tugging back and forth on the expressway). But, as mentioned above, it's only usually noticeable at speed.

There was a thread on this a while back. A few back of the envelope calculations are enough to tell me that you would need a huge imbalance and/or be travelling at an ungodly (impossible on a bike - and probably impossible in most cars) speed for an imbalanced wheel to be a problem.


PS: The old Shamals are not legal for mass start road races (sadly). They're built with 12 spokes and 16 is now the UCI minimum allowable spoke count. Depends on how anally retentive your local comissaire is (in Australia ours are, VERY!)

 

[Peter@vecchios]

Originally Posted by tonyzackery .

Me: 190-195lbs, tends to rely on high pedal torque (as opposed to rpm) to put out high power. Races predominantly crits.

Question is thus: I'm looking to build some carbon tubulars using the cheap carbon rims and relatively lightweight hubs you can source from eBay. I'm curious to know whether given the choice between the two options, should I look to go with a higher spoke on a shallower rim (say 28/32 spokes on a 38mm or 50mm rim) or a greater rim depth (60mm or 88mm) and less spoke count (20/24 spokes)? Needless to say, I want a stiff/rigid feeling aero wheel when I'm done with this endeavor. Sure, high count and greater depth would be stiffest of the options, but can I get away with choosing one versus the other?

Appreciate hearing from those in the know...

28/32, 50mm, double butted spokes and it will be fine for you. 2 cross front, 3 cross rear. Mixed lacings including radial LH rear does nuthin and remember, 4 spokes weigh about an ounce.