Interlaced spokes, or not?

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squeaker
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Interlaced spokes, or not?

Postby squeaker » 9 May 2019, 11:05am

Just lost a front spoke on a 2-cross 406 rimmed (32h DA16) wheel with SP dynohub. Built myself about 7 years ago (basically copied a disc braked wheel I'd had built professionally): failure at the point where the interlaced plain 14g spokes cross - suspect fretting + crevice corrosion, so probably should re-spoke the wheel.
However the rear wheel is the original 12 year old 3-cross 406 DA16 non-interlaced with a SRAM dual-drive hub, which has given no problems. Both wheels use disc brakes. Both wheels are suspended (HPV Grassshopper).
I've read a lot on-line about the reasons for interlacing, but if it introduces fretting / corrosion (the former would seem inevitable) is it worth a punt rebuilding the front wheel non-interlaced and see what happens? (One big snag being that a catastrophic failure at speed is not an attractive outcome!) Thoughts?
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Brucey
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Re: Interlaced spokes, or not?

Postby Brucey » 9 May 2019, 11:48am

IIRC the weight distribution is a bit front-heavy on that machine and the SP hub flanges are closer together than in many other hubs. These two things can mean that the front wheel sees more load (and together with low tension perhaps) makes rubbing at the spoke crossings more likely.

In 20" wheels it is a bit of a toss-up whether you should brace the spoke crossings or not; I've seen good wheels built both ways. However this is very much the least important thing about the wheel vs basic issues such as loading, overall wheel stiffness, spoke tension, and how the wheel was stress-relieved.

FWIW if rubbing at a spoke crossing helped initiate a failure then I'd usually expect to see signs of the rubbing such as brown stains at the crossings; this is a good sign that the conditions might have favoured crevice corrosion too. Because the braced crossings in a small wheel put a bigger kink in the spoke, it is important that the spokes are correctly stress-relieved, else they can just fatigue at the kink, even if there is no rubbing.

cheers
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squeaker
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Re: Interlaced spokes, or not?

Postby squeaker » 9 May 2019, 2:01pm

Thanks, Brucey. IIRC I did stress relieve using the 'squeezing spokes together' method, but this was the first wheel I built ;) Static weight distribution with me on it is about 50:50 F:R, though of course under heavy braking this gets close to 100:0 :lol:
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Brucey
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Re: Interlaced spokes, or not?

Postby Brucey » 9 May 2019, 4:18pm

I still think it is a bit front heavy for most riders; when in the riding position, one's CoG is somewhere very near the sit bones. You can verify this by sitting on the floor and seeing how you can tilt yourself by moving your arms and legs around.

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the seat places the sit bones nearer the front wheel than the rear; this seems inevitable with a bike of this design unless the wheelbase is very short or the handlebars have a strong tiller action; underseat bars (an option on this?) allow more flexibility in weight distribution.

cheers
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squeaker
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Re: Interlaced spokes, or not?

Postby squeaker » 9 May 2019, 4:45pm

That's an FX, I think, which seems to have the seat a bit further forward than my older model (with it's non interlaced wheels front and rear). But I agree that there is some forward bias. (I might have been getting confused with a Mistral I had, which had the most interesting heel strike from time to time :roll: )
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RickH
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Re: Interlaced spokes, or not?

Postby RickH » 9 May 2019, 5:39pm

I have a Circe Helios tandem with 20" (406mm ETRTO) wheels. This came with, & still has, 1 cross non-interlaced spokes (36 per wheel). Particularly the rear with a large flanged Alfine hub, the spokes would have to be considerably bent to interlace. It has discs too. I did consider if it was worth switching to 2 cross but thought that the extra angle the spoke nipples (or kink in the spoke leaving the nipple) would not be worth it.

I did have some spoke breakages once it started getting used for substantial mileages with 2 adults aboard but I think that was more slightly to low spoke tension. The spokes "ping" at a much higher pitch for the same tension because they are shorter than larger wheel bikes. If you are used to the sound of 700C spokes then spkoes on 20" wheels can sound as though they are horribly tight even though they aren't.

nigelnightmare
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Re: Interlaced spokes, or not?

Postby nigelnightmare » 9 May 2019, 7:52pm

With tadpole trike front wheels you want the spoke tension high due to the lateral forces when turning.
Also with 20" wheels it is harder to get them to pringle.

nigelnightmare
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Re: Interlaced spokes, or not?

Postby nigelnightmare » 9 May 2019, 8:07pm

From what I've been told (Chris at ICE) one of the reasons that ICE don't offset the rear wheel is for greater lateral strength/stability when cornering.
Chris used to build all their wheels.

I have recently built two front wheels for my ICE using SA hubs & 3 cross spoking instead of the 2 cross that they supply theirs with.
It may be all in my mind BUT I think the ride is smoother than 2 cross.
Using the same tyres at the same pressure I feel that the road noise/vibration is less.

I've only had them on since February so time will tell, but at the moment they are still true and the sppoke tension is even.