Problems with DT Aerolites/Sapim CXrays

[Pants]

I'm looking at rebuilding my 28H 10sp Dura ace/Mavic Open Pro/DT Comp spokes and Alloy nipple, 2X front and rear combo wheels with either Dt Aerolites or Sapim CXrays (same configuration) to save weight and have them a bit more aero. These will be pretty much my race wheels. I'm around 85kg and like a sprint. I race mostly crits.

I'm looking for some feedback on this. Has anybody had any problems/experience with similar combos. I quite like a stiffish wheel and dont really have a problem with my current setup. Would I also be better of building the rear wheel with DT comps or similar on the drive side for extra strength/durability?

Thanks all !

[frd]

Great wheelset, maybe 3x drive side would be better?
I would use aerolite or cx ray front and rear, they make for nicely stiff and light wheels.

[rruff]

The stiffness of stainless steel spokes will be inversely proportional to their cross section... all else being equal (like spoking pattern and lateral bracing angle). So, if you go with lighter spokes then the wheel will be less stiff, *unless* you improve the bracing angle by lacing radial heads in where possible. Since you are reusing old hubs, this isn't an option (ie you should use the same lacing as before).

So you can save a little weight and gain a little aero... but lose a little stiffness. I think I'd leave those wheels alone unless there is a problem with them... and build up some new wheels with aero spokes and rims. Aero is more important than weight even in a sprint.

It's a good idea to use brass nipples and heavier spokes on the drive side.

[2 wheels]

The stiffness of stainless steel spokes will be inversely proportional to their cross section...

Ae you sure about this? So what you are saying the smaller cross section, the stiffer spoke. That doesn't sound very likey,n this would mean a cross section of zero would result in the stiffest spoke.
Are you sure ididn't mean just proportional and not inverselyproportional?

[rruff]

Are you sure ididn't mean just proportional and not inverselyproportional?

Sorry... yes you are correct.

[ScienceIsCool]

Are you sure ididn't mean just proportional and not inverselyproportional?

Sorry... yes you are correct.

And just to be Mr. Pedantic... The change is most likely not linear. To figure out the stiffness, you would need to calculate the "second moment". For a rectangular cross-section this would increase with the cube of the thickness. For a circular cross-section, yada, yada, yada. You get the idea. Thicker spokes are stiffer. Less aero, but stiffer. And don't forget that the rim stiffness plays a really big part in how much the wheel will flex.

John Swanson

[Pants]

Thanks for your input guys, although I dont really understand all the physics involved. Could you try speaking in laymans terms?

I thought I'd point out that I have been building my own wheels and for friends for over ten years and and have pretty much exclusively used Dt comp' spokes, alloy nipples, mavic rims and various 2 and 3X combos without ever having a failure.(I am fastidious about maintenance though!).

I have never used CX rays or Aerolites due to the cost here in oz $6 approx. But since getting rid of my race only wheels I thought I'd rebuild the prviously mentioned combo. So they will still be 2X front and rear but I'm not sure if I should go the heavier 14/15 gauge on the rear drive side or lightweight bladed all round.

Oh, I do still have a training set of wheels.

Any further feadback is greatly appreciated.

[rruff]

To figure out the stiffness, you would need to calculate the "second moment".

Spokes are only loaded in tension... so there are no moments... or am I missing something?

[ScienceIsCool]

To figure out the stiffness, you would need to calculate the "second moment".

Spokes are only loaded in tension... so there are no moments... or am I missing something?

Yeah, I screwed that one up too at first. I figured that the stiffness of the wheel had to come from spoke tension almost exclusively, but that isn't the case. The "bending moment" or second moment is independent of any tension on the spoke. I was finally able to visualize it by imagining a spoke that was held at one end and had a weight hanging from the other end. Pushing on the spoke, it'll bend sideways the same amount regardless of how much weight you use.

The result is that almost all of the lateral stiffness of a wheel comes from the rim stiffness and the spoke stiffness. This has been shown experimentally by measuring lateral stiffness versus spoke tension. It doesn't change until the spokes are completely slack.

I guess the general rule is the thicker the spoke, the stiffer the wheel...

John Swanson

[rruff]

The result is that almost all of the lateral stiffness of a wheel comes from the rim stiffness and the spoke stiffness. This has been shown experimentally by measuring lateral stiffness versus spoke tension. It doesn't change until the spokes are completely slack.

I know that the tension of the spokes has nothing to do with stiffness... but I still don't see what that has to do with moments. And where would the wheel stiffness come from if it was not the rim and the spokes? For the rim of course bending stiffness is important, but spokes only apply vector forces along their lengths... so their stiffness is only a function of their cross-sectional area, elastic modulus, and length. For a rim the stiffness is highly dependant on shape... but not for a spoke.

As I recall Rinard tested two sets of wheels that were indentical except one used Revs and the other used 2.0mm straight gauge spokes. The rim was a heavy MTB model. The difference in stiffness for the rear wheel was ~22% even though the Revs by themselves had half the stiffness. So... yes, the rim is a big factor. That is why I recommended that the OP use a stiffer aero rim if he wants to use light spokes... considering that he is very concerned about stiffness.