How many spokes....?

by bikedoofus   June 25, 2014  

I'm thinking about building myself a new wheel set. I use a disk brake front and calliper brake on the rear and I'm very happy with this set-up. Looking at the few high-end disk wheel sets coming onto the market like the specialized ROVAL RAPIDE CLX 40 they seem to still use fewer spokes at the front (24) than at the back (28). This seems odd to me as the disk brake is obviously far more powerful than anyone's legs. Unless the higher spoke count at the back is purely for stiffness (and thus efficiency when pedalling) or for fatigue life, given that the rear wheel is always driven whereas the front wheel is only occasionally braked?

Thoughts on spoke count for front disk wheel? I've half a mind to say sod it and go 32 front and rear - only a difference of 53g, but more drag. Anyone have experience with this?

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If you're not racing then why worry about drag?

Yes the rear wheel is subject to pedalling forces but IIRC the force is applied unequally, so rear wheels may be laced with more spokes or higher tension on the drive side compared to non-drive side. I'm sure Specialized have a reasonable idea of what they're doing speccing wheels like that.

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posted by Simon E [1940 posts]
25th June 2014 - 13:55

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Simon E wrote:
If you're not racing then why worry about drag?

Part of me absolutely agrees with you - who cares? The other part says I may as well take every advantage I can get. 24 spokes cost less than 32 spokes too... Wink
I am undecided...

posted by bikedoofus [8 posts]
25th June 2014 - 14:21

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Interesting - new Trek Domane disk bike is 24 spokes front and rear.

posted by bikedoofus [8 posts]
25th June 2014 - 17:42

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Magic 8 ball says...... 28 !

...or whatever you want really. Go have a good chat with some other wheel-builders too.

i'd have thought 24 was a bit un-necessarily few unless you're built like Quintana, 32 might be on the higher side unless your a strapping lad/lass but none the worse for that. Plus, 28 still gives you a lot of good rim choice and spoke-wise, if you're worried about cost then Alpina double-butted spokes seem cheap and rather well regarded.

Just a thought - IANA wheel builder mind, but was taking a lot of advice from people who do know recently when thinking about something similar-ish.

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posted by fukawitribe [354 posts]
25th June 2014 - 18:34

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Wheels with fewer spokes are generally designed to support more tension on each spoke. They use stiffer and heavier rims. Those wheels are generally faster due to less air turbulence. With 32 spokes you can use a lighter rim, and less tension. You also get more rim choices.

You didn't mention what kind of riding you do, so it's hard to guess which wheel would be better for you. My choice would be the wheel with more spokes. For one thing, if you ride in remote country and consider breaking a spoke, the 24 spoke wheel is probably going to fail and your epic ride will become an epic walk.

posted by Derny [51 posts]
25th June 2014 - 20:36

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fukawitribe wrote:
Plus, 28 still gives you a lot of good rim choice and spoke-wise

I do like the idea of 28 as a compromise. Slight problem - I'm only finding 32 hole front hubs. I know you can lace 24 hole rims to 32 hole hubs, but it's a pain in the rear to calculate the spoke lengths and get the tensions right. 28 into 32 - just won't go surely? Missing two spokes per flange, though I guess you could offset them so the missing spokes were 90 degrees on one flange to the other? Tricky. Might have to CAD it but gut feeling says P.I.T.A.

Anyone seen any 28 hole disk compatible hubs about...?

posted by bikedoofus [8 posts]
25th June 2014 - 20:58

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As St Sheldon suggests:

"If you have the same number of spokes front and rear, either the front wheel is heavier than it needs to be, or the rear wheel is weaker than it should be."

posted by pdf500 [13 posts]
25th June 2014 - 23:04

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Would he have said the same with disk brakes? Surely very hard braking with a hub brake is the most strain you can put on a bicycle wheel? But then as I mentioned earlier, that's only peak load. The rear may be under greater continuous strain so might fatigue quicker... So maybe Sheldon would still be right.

Edging closer to "sod it 2x32" decision now. And round and round we go...

posted by bikedoofus [8 posts]
25th June 2014 - 23:18

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Derny wrote:
Wheels with fewer spokes are generally designed to support more tension on each spoke. They use stiffer and heavier rims. Those wheels are generally faster due to less air turbulence. With 32 spokes you can use a lighter rim, and less tension. You also get more rim choices.

You didn't mention what kind of riding you do, so it's hard to guess which wheel would be better for you. My choice would be the wheel with more spokes. For one thing, if you ride in remote country and consider breaking a spoke, the 24 spoke wheel is probably going to fail and your epic ride will become an epic walk.

All true. I don't race, though I sometimes ride with others so I'm not going to lie and say I wouldn't be glad of any extra advantage! But yes 32 is looking the best choice. I lost a spoke on my rear 32 two weeks ago on caerphilly mountain. Barely noticed. And I can get below 1500g for a pair with 64 DT Swiss Revolution spokes for not much money. Going to bladed might cut drag but it would add £75 and I'm not convinced the difference would be significant.

posted by bikedoofus [8 posts]
25th June 2014 - 23:40

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this is of minimal use to the OP right now but I have a pair of handbuilt disc wheels - 28F 32R - ready to ridden. I can report back in a few months but I guess you're in a hurry Smile I would quite surprised if the 4 fewer spokes caused a problem - or if they made a significant difference over 32.

you're right about the choice of hubs being slim. You can get shimano cx75 hubs which are 28h f&r, DT swiss have various models, as do Hope, Chris King. I have Hope Pro2 Evo which are available in 28 and 32. You can probably get Novatec hubs in pretty much any combination, any MTB disc hub with QR will work though.

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posted by joemmo [787 posts]
26th June 2014 - 13:46

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Interesting. I've been playing with spoke patterns in cad and note that it seems possible to lace 24 holes using crowsfoot or 2-cross lacing on a 32 hole hub without too much issue.

I'm quite liking the idea of crowsfoot lacing for the front 24, giving a mix of lateral stiffness (8 radial spokes) and torque transfer (16 tangential spokes).

Interesting to note that Hope come in 28 and Novatec come in 24 and 28 - thanks!

posted by bikedoofus [8 posts]
26th June 2014 - 17:23

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My DA C24 is rubbish with 15 spokes (and only a little better with 16) ..... don't go for that! Crying

posted by veseunr [281 posts]
27th June 2014 - 12:47

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I find myself tempted toward a 24 spoke build with crowsfoot lacing on the disc/drive sides and 2-cross on the non-disc/drive side. This means of the 24 spokes 4 are radial on the dished side (maybe offset some of the loss of lateral stiffness due to dishing) and all the rest are tangential, giving 10 spokes to take the torsional load in either direction. Seems an elegant compromise, not sure if it's going to be a bugger to true though...?

posted by bikedoofus [8 posts]
27th June 2014 - 13:50

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