Road Bike, Cycling Forums banner
1 - 13 of 13 Posts

·
Registered
Joined
·
143 Posts
Discussion Starter · #1 ·
I was thinking about this issue recently as I was inspecting my new 7850SL wheelset. It seems that many of the bladed spokes are not oriented so that the long axis of the cross section is parallel with the long axis of the bike-- some are off by as much as 30-45 degrees, if I had to guess.

I'm going to straighten them out, but I was wondering if anybody had any data re: the magnitude of the effect this has on aerodynamics. I would imagine that a 2.3mm CX-ray twisted a full 90degrees would be much worse than a standard 14ga round spoke, but is this at all significant?

Incidentally, I wonder if this factor is rigorously controlled for in all of the wind tunnel data we've seen, or if it's even deliberately manipulated by unscrupulous wheel manufacturers to produce the results they want to see...
 

·
Registered
Joined
·
1,932 Posts
supercrank said:
I was thinking about this issue recently as I was inspecting my new 7850SL wheelset. It seems that many of the bladed spokes are not oriented so that the long axis of the cross section is parallel with the long axis of the bike-- some are off by as much as 30-45 degrees, if I had to guess.

I'm going to straighten them out, but I was wondering if anybody had any data re: the magnitude of the effect this has on aerodynamics.
It added about 2.6ish mph to my avg speed on my last TT.

All the best,
 

·
Registered
Joined
·
4,105 Posts
supercrank said:
It seems that many of the bladed spokes are not oriented so that the long axis of the cross section is parallel with the long axis of the bike-- some are off by as much as 30-45 degrees, if I had to guess.
It hasn't been tested AFAIK... but as you might imagine it is better to have them lined up pretty well.
 

·
Adorable Furry Hombre
Joined
·
32,340 Posts
You're not going to have a smooth flow over the spokes or wheel anyway--I *highly* doubt that it matters in any quantifiable manner for anyone not a pro athlete.
 

·
waterproof*
Joined
·
41,745 Posts
I'd be more concerned about a "new" wheel that hasn't been properly built. Wheelbuilders are supposed to account for spoke windup so that doesn't happen. If they messed up that step, what else is wrong with the wheels?

As far as aero, if it's really 40 degrees off, yeah that's probably causing drag - more than a round spoke fer sher. How much, dunno.
 

·
A wheelist
Joined
·
11,689 Posts
Creakyknees said:
I'd be more concerned about a "new" wheel that hasn't been properly built. Wheelbuilders are supposed to account for spoke windup so that doesn't happen. If they messed up that step, what else is wrong with the wheels?
That is my reaction. If the bonehead builder didn't know about this, what else didn't they know about?
 

·
Registered
Joined
·
143 Posts
Discussion Starter · #7 ·
Mike T. said:
That is my reaction. If the bonehead builder didn't know about this, what else didn't they know about?
I guess I shouldn't be too surprised. These are the Shimano Dura-Ace pre-built wheels, though they supposedly have a good reputation. I'm guessing it's not too big of an issue, since the spoke tension is high and uniform-- I have a feeling that the twist came about when the builder got lazy during the final, cosmetic truing.
 

·
p != b
Joined
·
2,303 Posts
supercrank said:
the builder got lazy during the final, cosmetic truing.
What 'final, cosmetic truing' are you talking about? Have Sheldon, Brandt, Schraner, Mike T., and anyone else who has written more than two words about wheel-building been missing out on this vital step?

Inquiring minds need to know.
 

·
Registered
Joined
·
143 Posts
Discussion Starter · #9 ·
bopApocalypse said:
What 'final, cosmetic truing' are you talking about? Have Sheldon, Brandt, Schraner, Mike T., and anyone else who has written more than two words about wheel-building been missing out on this vital step?

Inquiring minds need to know.
Easy there, I meant no offense to the wheelbuilding gods. All I'm referring to is a final touch up truing after all the tensioning, dishing, turing, stress-relieving etc to make sure that the wheel looks good. I never said it was vital-- I'm no wheelbuilding expert, but I know that truing the wheel so that it's cosmetically perfect doesn't affect the performance of the wheel, and could even be detrimental in terms of achieving uniform spoke tension. However, I have no doubt that this is done, since I've unfortunately bought wheels from builders who prioritized looks over build quality.
 

·
A wheelist
Joined
·
11,689 Posts
supercrank said:
I guess I shouldn't be too surprised. These are the Shimano Dura-Ace pre-built wheels, though they supposedly have a good reputation. I'm guessing it's not too big of an issue, since the spoke tension is high and uniform-- I have a feeling that the twist came about when the builder got lazy during the final, cosmetic truing.
Crank, Sapim sell a special tool (or one is very easily made) that holds the bladed spoke and stops it from twisting at all. So in this case bladed CX-Ray spokes are easier to build with than spokes of equal weight (Sapim Lazer, DT Revs) because twist doesn't have to be allowed for or eliminated. I just can't imagine anyone in Shimanos wheel team being allowed to touch XC-Rays without knowing this. But what's even more scary is that if they can't SEE the twist in CX-Rays then they can't know about it in "normal" spokes.
 

·
Registered
Joined
·
143 Posts
Discussion Starter · #11 ·
I'm sure their builders are aware of this issue, since the wheels actually come with two spoke wrenches, one end of which has a slot to hold the bladed portion of the spoke. Incidentally, I think the spokes on this wheelset are proprietary Shimano spokes, and I'm guessing their cross-section is not quite as long as that of a CX-ray (just based on eyeballing). The twist is actually a little difficult to see, but is fairly obvious by tactile examination, and even more so when the slotted wrench is applied to the wheel. A little disappointing, though the wheels are otherwise well-built (high, uniform tension).
 

·
p != b
Joined
·
2,303 Posts
supercrank said:
Easy there, I meant no offense to the wheelbuilding gods. All I'm referring to is a final touch up truing after all the tensioning, dishing, turing, stress-relieving etc to make sure that the wheel looks good. I never said it was vital-- I'm no wheelbuilding expert, but I know that truing the wheel so that it's cosmetically perfect doesn't affect the performance of the wheel, and could even be detrimental in terms of achieving uniform spoke tension. However, I have no doubt that this is done, since I've unfortunately bought wheels from builders who prioritized looks over build quality.
Actually, I'm being serious (aside from the snarky comment). What do you mean by truing the wheel to make it "cosmetically perfect"? Lining all the nipples up so they're all square with the rim? That's about the only cosmetic thing I can think of that you could do with a spoke wrench.
 

·
Registered
Joined
·
143 Posts
Discussion Starter · #13 ·
bopApocalypse said:
Actually, I'm being serious (aside from the snarky comment). What do you mean by truing the wheel to make it "cosmetically perfect"? Lining all the nipples up so they're all square with the rim? That's about the only cosmetic thing I can think of that you could do with a spoke wrench.
Sorry, I was a little unclear with my terminology. I was referring to the final few iterations of truing/stress-relieving for the purpose of correcting the last, small imperfections in radial and lateral trueness. I called it "cosmetic" simply because it's my understanding that these superficial corrections, while improving the appearance of the wheel on the truing stand, won't improve the performance/durability of the wheel, and in extreme cases (crappy builder using a warped rim) could lead to suboptimal spoke tensioning. If I'm way off base here, let me know.
 
1 - 13 of 13 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top