milesj

I'm building some wheels for use on minor roads in winter in UK. Box section rims 32H spoked x3 seem like a good idea. Interestingly, this is what the pro Peleton use for Paris-Roubaix (admittedly with tubs rather than clinchers). This is quite reassuring ~ the roads around here are almost as bad as the roubaix pave !. Now, here is an interesting thing::

If you look at the wheels the pros use, e.g., https://www.cyclingnews.com/photos/20...gbBoonenBike01
you will see they *ALL* use plain gauge spokes.

Why ?

If you read Jobst Brandt or Gerd Schraner they insist that DB spokes are stronger (through cold forging and tending to fail in mid-section rather than at the spoke elbow). The DT swiss site says the same...

So, why do the pro's use plain gauge spokes for Roubaix ?

operator

Sapims are oval. Although they don't specify that they're cx-rays or other. Which is it?

LarDasse74

I am not too sure why pros use them... possibly for the same reason I use them when I build my own wheels - they make a stronger wheel.

Butted spokes make stronger spokes - the stress is spread out along the length of the spoke and is less concentrated at the elbow - where most spokes break. But straight guage spokes make a stiffer wheel, and hence a wheel less likely to allow plastic deformation of the rim from a crash, landing, or hitting a pothole. Butted spokes will last longer, but if you are only riding 200 miles and you want the best chance of not warping your rim when you slide off the wet pavé into the ditch then PG is the way to go.

AndrewP

Stiffer wheels will give more responsive handling at the expense of reduced comfort

DannoXYZ 

Butted makes for a "stronger" wheel that doesn't go out of true as easily. But as for actual spoke-strength and fatigue-resistance, it's about the same if the tension is the same and the gauge is the same at the bend. I doubt these wheels are used for more than this event before rebuilding anyway.

On that Roubaix wheel, it's the usual criss-cross function of conflicting priorities. Tubulars on box-section rims are great for bump-absorption to to the vertical compliance of the rims. They're also more resistant to pinched flats as well. And you're able to ride and corner on a flat tubular.

However, they're not as aero as deep-V rims. So the oval-spokes are to make up some of that aero difference.

LarDasse74

I don't get it. Butted spokes make for a more flexible wheel, as they are more flexible spokes, right? Then the rim is more likely to be allowed by the spokes to go into its plastic deformation range.

Is the theory that the spokes are the things that permanently deform when wheel goes out of true?

127.0.0.1

they absorb shock better. the ride is sweeter. you ride cobbles at 28mph you know

DannoXYZ 

No, the spokes actually LOSE tension when the wheel is loaded. A wheel goes out of true when the bottom part in contact with the ground deforms enough that the spokes lose ALL tension. This allows the nipples to rattle and spin lose, which causes the wheel to go out of true. Nothing is actually damaged or exceeds its yield strength when this occurs.

The trick with butted spokes is that they stretch MORE for the same tension and the rim must be deformed MORE before the spokes lose all tension and allow the niples to rattle. Basically you have to apply a higher load to the wheel before it goes out of true with butted spokes.

daveornee

It is hard to tell if the Sapim spokes in the picture of the wheel are Sapim Leader 14 G or Sapim Strong 13/14 G. Sapim Strong spokes have 2.3 mm diameter at the elbow and 14 G after the butt... all the way to the rolled threads.
It is difficult to know what choices the pros make and why, but they certainly want what will make them have the best chances of winning the particular event.
Sapim Strong model spokes are very reliable and slightly stiffer and considerably more reliable than 14 G Leader model straight gauge spokes.
Different combinations of spoke types with rim cross sections will provide different ride qualities, stiffness, etc. Any combination that allows spokes to go slack makes for lesser wheel durability.
I use Sapim spokes from CX-Ray to Strong models. They each have their place; depends on budget and application.

eddy m

Sew-ups give a much smoother ride because they have much more flexibility in the sidewall than a clincher of the same width and pressure. The spokes and rim have nothing to do with. Ride quality is determined almost exclusively by the tires.

Straight gauge spokes make a wheel that is stiffer than one with double butted spokes, but the important difference is in lateral strength, not in vertical strength or compliance. Some very light wheels are flexible enough that big riders should avoid them. There is more about that here: https://www.rouesartisanales.com/article-23159755.html

It's possible that Boonen wanted straight gauge spokes for a more laterally stable wheel, and to compensate for the relatively flexible rim section. Judging from the size of his bike he's a pretty big guy. Or maybe they were trying to save money, or maybe those are oval spokes.

em

eddy m

I'm not so sure of the second part of that explanation. Unless the rim is really rigid (that sew-up rim is certainly not), the same load that makes straight gauge spoke go slack will also make a DB spoke go slack if the pre-load is the same. The only way to allow a higher load on a wheel is to increase the pre-load, and that is limited by the strength of the attachment to the rim, not by the spoke.

I don't think there is any difference in strength between straight gauge and DB. Straight gauge spokes have a shorter fatigue life, but that is not the same as strength.

em

LarDasse74

I think it makes perfect sense. The spokes act like a spring. You never want the spokes to be completely detensioned (just like too-loow stress causes spoke breakage) , and the added flex of butted spokes allows more wheel flex without losing tension.

I think my expalnation also holds for a different method of failure - DAnno is talking about a wheel losing spoke tension, I am talking about a rim getting bent.

FWIW, I build my wheels with very high tension PG spokes and they stay true like gangbusters!

eddy m

No. If I preload a spring with 1000 lbs it goes slack if it is compressed by a load of 1000 lbs. If the spring has a spriing rate of 1000 lbs/inch, it compresses one inch under that load. If it has a spring rate of 500 lbs/inch, it compresses 2 inches, but it still goes slack. It's the same with spokes.

What's a PG spoke?

em

well biked 

Plain gauge-

miamijim

The pros use them becuase they have better success with them. Otherwise they wouldnt use them.

milesj

its an interesting one isn't it !.

From my reading of the situation:

DB spokes show greater elastic deformation for a given load, with a failure point typically in the butted midsection.

OTOH, plain spokes are more rigid for a given load, i.e., show less elastic deformation for a given load, with a failure point typically at the spoke elbow.

My suspicion is that for similar materials and manufacturer the difference is simply a function of cross-sectional area. However, I've got no evidence for this assertion. Does anyone actually *know* ?

In wheel building, the rim is deformed by spoke tension (hopefully into a 'true' shape ;-) to produce preload.
So, the following (complementary) statements can be made:
(a)- For a given preload plain spokes need to be stretched less than DB.
(b)- For a given spoke stretch plain spokes produce a higher preload.

As rim deformation is limited before rim failure will occur case (b) becomes the critical factor. So, a PG spoked wheel can be built with higher preload and such a wheel will be stronger:

The other, prosaic, factor in of PG spokes is that they tend to twist less when truing. This makes it easier to achieve high tensions.

I suspect what is happening when people quote DB spokes being 'stronger' is that they are referring to failure tensions. In testing spokes the final possible tension may be higher in DB spokes (because plain spokes will break at the elbow before high stretching becomes possible). However, while this is true, It seems to be irrelevant as spoke failure tensions are much, much, higher than those achievable in building a wheel. Schraner says that you will round brass nipples, i.e., not be able to achieve higher tensions, in the range of 1300 newtons for PG spokes. Whereas failure on spoke testing machines occurs in the the tension range of 2500-2800 newtons.

The conclusion that PG spokes build stronger wheels thus seems correct in terms of the theory (as above). And, after all, it must be the case : there has to be a reason the pro's build with PG spokes for Roubaix !

Equally, the downside of high tension PG spokes in a wheel is that their low elasticity will lead to earlier failure - which is *fatigue* process. It is NOT due to going over bumps (which, as noted correctly above de-load the spokes). So one would expect a PG wheel to be less long lasting. This, of course, is not an issue for pro teams.

dabac

Never seen that happen. Failures at elbows though - sure.

Spoke tensile strength is rarely an issue, even with butted spokes, so usually you'll be quite capable of collapsing the wheel into a taco shape even if you're using butted spokes.
So it's (a), less stretch for a given load that makes a SG wheel laterally stiffer(stronger) by doing a better job of keeping it from flopping over into its other stable configuration(the dreaded taco) when exposed to a drastic load.

Failure tension is a secondary issue. A typical bike application is so far from breaking strain while JRA that pretty much all failures are either fatigue related or caused by catastrophic overloads. (deep potholes, something snagging a spoke, impact in immovable object ASO.
DB wheels have a strong tendency to be more durable, but less laterally stiff. The higher degress of stretchiness protects them from fatigue by allowing them to remain under tension better, while the higher degree of stretchiness does increase the possibility for the wheel to deform to the point where it will flop over into taco configuration.



Same as why they're favoured by DH MTBers, increased lateral stiffnes protects them against going taco at hard hits.

Exactly! Given all the other costs of running a pro team, retiring a wheel set early isn't a significant cost, particularly if the "short-lived" wheel is what's gets them onto the podium.

urbanknight

I think you're overthinking this. The double butted spoke has to stretch FURTHER in order to reach the same tension, so that means the rim can compress more before the spoke loses ALL tension. It's losing all tension and then snapping the tension back on that leads to premature spoke failure.

As for the comment of straight guage spokes being stiffer, I don't see how that would prevent the rim from collapsing since the spokes never push outward on the rim. I could be missing another aspect of it, though.

capsicum

So there is a lack of proper materials science/engineering terms here.
stress is the load as the material sees it
strain is the amount the material is deforming due to stress
yield strength is the limit of springiness, the point where permanent deformation happens
ultimate strength is the point where the material breaks
preload is the static stress on the material before a working load is applied
In this case we are talking about the same material in different shapes so the modulus of elasticity is the same for either spoke type. Using thicker spokes is the same as adding more spokes, which would be spreading out the stress and thus reducing strain.

More stress for the strain is what "stiff" refers too.

Tensile stress and strain are the only significant forces applied to a bicycle spoke.

Second your not comparing apples to apples
13\14 db spoke is really just a 14 with re-enforced connections(hook and thread areas)
Are you comparing the 13\14 to a 13 or 14 straight guage spoke?

As far as the thickness of the hook and thread portion go it really has no significant affect on the operation of the wheel below it's the failure point. It does have a large affect on the fatigue life and ultimate failure strength of the wheel as they are often weak links.

urbanknight

^ I'm pretty sure the comparison is for 14g spokes vs. 14/15/15 double butted. Most hubs don't have holes large enough for 13g.

JustChuck

This whole thread starts with a photo of one wheel from one riders bike. In the accompanying article it says that support is all along the course with spare wheels(and guys ready to do the quick change) and that the rider has six (Yes six) bikes at his disposal for the 50K race.
I did not see any mention of spoke size. Those might be straight 1.8 or butted 2.0/1.8/1.8.

Building wheels for the dirt jump/trials/freeride/downhill dudes I find 2.0/1.8/2.0 to be reliable and forgiving of abuse.

DannoXYZ 

These two statements are contradictory. First you say that the rim's vertical stiffness has nothing to do with ride-quality. Then the next statement says that the rim isn't stiff. Which is it?

If you press vertically on a box-section tubular versus an aero-clincher before building them up, you'll find that the clincher is easily 2-3x stiffer than the tubular rim.

urbanknight

Ummm, the race is actually 260K long. 50K is the cobblestone portions.

daveornee

Most hubs have ~ 2.5 mm diameter spoke holes which as more than adequate for 13 g spoke.
I regularly use Sapim Strong spokes which have 13 g (2.3 mm diameter) neck & j-bend area. They fit fine in all the Shimano, Campy, Phil Wood, Formula, Chris King, and White Industry hubs I have used.
Sapim Strong spokes use 14 g nipples.

eddy m

My statements aren't contradictory at all, and you prove my point. The rim is the flexible part of the structure, but it's held rigidly by the spokes. Once you build up the rim, you can't compress the wheel vertically by any noticeable amount, no matter what gauge or spoke pattern you use, The difference in total length change in response to a typical vertical load between a PG and DB spoke is only a few thousands, so the rim alone is not rigid enough to prevent a vertical load from detensioning a spoke. OTOH the tire will easily compress 10% or more of it's width, which is more than 2mm even for the narrowest tires. Almost all the vertical compliance is in the tire, not the wheel.

Laterally is a different story. Some wheels are flexible enough under lateral loads that they occasionally approach the point of instability in normal riding, at least for heavy, strong aggressive riders. That's why taco failures are the most common catastrophic failures that you see, and that's where the benefit of thicker spokes comes in. A wheel with 2 mm spokes should be about 20% stiffer laterally than a wheel with 1.8 mm spokes. That's enough to make a difference.

em