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Discussion Starter · #1 ·
I will be building a disc wheelset for agressive XC use with a 32 hole 3 cross lacing pattern. It will be used on a 5" travel FS bike and I weigh in at 185 lbs.

It would seem like a lot of people are using 14g-15g-14g DB spokes for a more durable wheel which is less likely to have spoke heads fatigue. I would like to use 15G spokes all around to reduce cost and save weight. I was using this set-up and my wheels never needed to be trued, spoke tension was exaclty the same as when they were built (120kgf), and no broken spokes.

Is there a big advantage to using DB spokes or will a PROPERLY built wheel with 15g spokes be good enough?
 

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It depends on you.

A properly built wheel will be ok, depending on how fluid you are.

Will you be checking them periodically, or are you a plug-and-forget type?
 

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Discussion Starter · #3 ·
I would consider myself a very fluid rider, I routinely do 3-4 foot jumps while XC riding and have yet to break anything or had to retrue a wheel.

I will be building the wheels myself, and my bikes seem to get a LOT of attention.

I guess the real question is, will 15g spokes fatigue at the spoke head in time, or will they be okay?
 

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15g not really lighter....

For Wheelsmith products, using 1.8mm straight-gauge spokes will save about one gram total on a 32 spoke MTB wheel versus using their "DB14" 2.0-1.7-2.0mm double-butted spoke. The connection between the spoke head and spoke shaft on a 2.0mm spoke end is more than 20% stronger than the strength of a 1.8mm spoke end. That is a lot of strength to sacrifice to save one gram worth of weight. The only time I use straight-gauge spokes is when butted spokes aren't available in the size needed. (Like my daughter's 16" wheels.)
 

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Discussion Starter · #6 ·
bianchi4me said:
For Wheelsmith products, using 1.8mm straight-gauge spokes will save about one gram total on a 32 spoke MTB wheel versus using their "DB14" 2.0-1.7-2.0mm double-butted spoke. The connection between the spoke head and spoke shaft on a 2.0mm spoke end is more than 20% stronger than the strength of a 1.8mm spoke end. That is a lot of strength to sacrifice to save one gram worth of weight. The only time I use straight-gauge spokes is when butted spokes aren't available in the size needed. (Like my daughter's 16" wheels.)
For the weight saving I was comparing 14g spokes to 15g which is 42.5 grams per wheel. There still is 11.5 grams per weight saving with 15g vs DB 15-14-15 spokes though.

I agree that a 2.0 spoke end is more than 20% stronger than a 1.8 spoke end, since spokes fail due to bending stresses on the heads and not tensile stresses. A 2.0 spoke end is probably about 200% stronger. The question is, is this extra strength required?

The choice of 15g spokes over DB 14g-15g-14g spokes would be purely cost driven and not weight driven.
 

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1.8 - 2.0 = .2
2.0 / .2 = 10%

I've been riding sg 1.8's up front on a mavic disc 3.1 for over a year.
I weigh 220 lbs.
I notice no flex at all between this wheel and a sg 2.0 wheel.
I say build it, thrash it, and let us know what you think.
 

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Sneaky exponents involved...

thebronze said:
1.8 - 2.0 = .2
2.0 / .2 = 10%
Not exactly. What you are measuring is the cross-sectional area of the spoke, which in this case is circular. The area of a circle changes exponentially when you change the diameter. So reducing the diameter by 10% does not equal a 10% change in the strength or stiffness of the spoke. This is also true for determining the elasticity (stiffness) of the spoke.

The area of a 1.8mm circle is ~2.54mm squared

The area of a 2.0mm circle is ~3.14mm squared

This leaves you a differential of ~0.6mm squared, which is about 23.6% of 2.54mm.

If you don't want to mess with geometry, you can do a quick weight check and prove the accuracy of this. DT states 64 of their straight gauge 2.0mm spokes weigh 444 grams. The same number of 1.8mm spokes weigh 359g according to them. That is a difference of 85g, which works out nicely to ~23.67% of the 1.8mm spoke's weight.

Note that this same issue applies to the thickness of other items, like rims. You don't get a 10% reduction in strength and stiffness when you reduce the dimensions of the material by 10%, you get an exponential reduction which varies depending on the shape of the item.
 

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Discussion Starter · #9 ·
I agree, that is why I said that a 2.0 spoke is actaully 200% stronger than a 1.8% spoke, which by the way was just a WAG. You would need to calculate the actual moments of inertia and then derate this value to account for the larger radius when comapring strength.
 
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