Spoke length confusion

amaferanga

Popped a spoke today and I'm trying to work out what length I need (the lazy way without removing another spoke since I'm at work). The spoke has broken at the end of the thread and without thread measures about 280mm.

Rim is IRD Cadence Aero - ERD stated by manufacturer is 576mm. Hub is a PowerTap Pro+ with the 15mm axle and according to the Saris user guide the dimensions are as follows:

Flange distance -- 33.9mm non-drive / 15.9mm drive
Flange diameter -- 70mm / 70mm

Wheel is built 2x non-drive and 1x drive and its a non-drive spoke that's broken. 28 spokes.

So I plug the numbers into the DT Swiss spoke calculator and it comes out with 269mm for the non-drive side. Tried another couple of spoke calculators and the result is the same so I must be doing something daft because the broken spoke I have in front of me minus the thread is longer the the spoke calculators are giving me.

Can anyone tell me what I'm doing wrong here or even better what length spoke I need? Spokes are CX Rays - does anyone know the thread length on them? Could do with knowing asap so I can nip out at lunchtime and hopefully get a replacement spoke.

schweiz

Wheel Pro http://www.wheelpro.co.uk/spokecalc/ reckons

268.3 2x NDS
256.0 1x DS

Which seems to tally with DT Swiss.

Not being funny but are you forgetting to count the cross which is right by the hub flange? In which case your spoke lengths would be:

282.9 3x NDS
266.6 2x DS

which seems to fit the length of your broken spoke quite nicely

schweiz

I think you're mis-counting the number of crosses.

I remembered that when I built my PT wheel there was something about the minimum number of crosses due to the torque on the strain guages. A PT has to be built at least 2x on both sides.

Page 6 of http://www.saris.com/pdfManuals/308.pdf

amaferanga

Definitely 2x and current spoke length is 280mm + thread length so would be more than 283mm anyway. I've built quite a few wheels and never had any issues so I can't quite work out what's going on here. Drive side is definitely 1x and spoke length is 280mm (measured and confirmed by an email from Wheelsmith back when they were being built - didn't mention the ND spoke length though unfortunately).

schweiz

And just to add to the mix my PT PRO+ is built into a CXP33 rim with an ERD of 599 mm and I have

NDS 3x 294mm (Spoke Calc 294.2)
DS 2x 280mm (Spoke Calc 278.0)

amaferanga

Rubbish photo, but you can see it's 1x drive side and 2x non-drive side.

schweiz

hmmmm, and rim looks deep enough for your ERD to be correct too :?

[edit]

Your Hub dimensions are correct too.

amaferanga

See why I'm so confused! Just sent an email to Derek at Wheelsmith who will hopefully clear it up. If the rim and hub dimensions are right then it can only be something to do with the spoke pattern, but if it's not 2x / 1x then I don't know WTF it is.

schweiz

and you're measuring the length of a spoke correctly?



not that I think that's the problem, just want to rule out everything!

amaferanga

Yep. Elbow to start of thread is all I've got though. Thread will be around 10mm I suspect so my spoke is approximately 290mm. Just doesn't tie in with the spoke calcs though.

amaferanga

Just whipped a spoke out and measured it and it's 290mm. Not sure what's going on still, but that's what I need anyway.

2Phat4Rapha

Sure you have a Cadence Aero and not a Cadence Road. ERD of the Road is 604 which on my calculator (http://www.dalynchi.com/wbpe.html) gives 282 / 270 for 2x/1x @ 28. :?:

amaferanga

2Phat4Rapha wrote:

Sure you have a Cadence Aero and not a Cadence Road. ERD of the Road is 604 which on my calculator (http://www.dalynchi.com/wbpe.html) gives 282 / 270 for 2x/1x @ 28. :?:

Its a Cadence Aero.

huuregeil

The quoted ERD of that rim might be wrong. E.g. a dt rr1.2 (same "depth") is 582mm. Hub dimensions have relatively low impact on the spoke length, ERD is where the action is.

It's possible also that the wheelbuilder has used spokes that are slightly too long (for reasons of e.g. what he might have in stock), and knows he can get away with it with a rim of that depth without it e.g. eating into the spoke tape. That might also explain the spoke breakage at the thread end (nipple cuts into the spoke leading to a stress riser)!

huuregeil

PS Can you see the end of the spoke coming out of the nipple head?

ugo.santalucia

huuregeil wrote:

The quoted ERD of that rim might be wrong. E.g. a dt rr1.2 (same "depth") is 582mm. Hub dimensions have relatively low impact on the spoke length, ERD is where the action is.

It's possible also that the wheelbuilder has used spokes that are slightly too long (for reasons of e.g. what he might have in stock), and knows he can get away with it with a rim of that depth without it e.g. eating into the spoke tape. That might also explain the spoke breakage at the thread end (nipple cuts into the spoke leading to a stress riser)!

+1 quoted ERD are often wrong.

It seems your nipples are fairly long, maybe 16 mm ones? that could account for some of the difference... 290 seems a bit long for a profiled rim with quite large flange built 1 and 2 X

amaferanga

:oops: :oops: :oops:

I've been using a printed ruler I got off the internet that was lying on my desk to measure the spokes. Turns out the f*cking thing is the wrong length! Just measured it with a proper ruler and the 30cm paper ruler actually measures 28cm.

Spoke length from the elbow to the start of the thread is actually 260mm so adding 10mm for the thread, it's entirely consistent with the spoke calcs.

Stupid stupid stupid.... What a muppet :oops:

(not sure what Derek was on about now when he said he was waiting for 280mm spokes though)

amaferanga

Now does anyone know where I can buy a single 270mm CX ray? Only JE James seems to come up on Goggle searches and they don't have any 270mm.

2Phat4Rapha

I was going to post a funny suggesting your ruler was out!

http://www.chickencycles.co.uk/index.php?cat=22&sub=39&ord=2
Don't know about their stock but they have 268/270 listed.

or could try...
http://www.cyclebasket.com
http://www.sjscycles.co.uk

cycleclinic

I never trust published ERD's either. Best measure yourself.

schweiz

amaferanga wrote:

:oops: :oops: :oops:

I've been using a printed ruler I got off the internet that was lying on my desk to measure the spokes. Turns out the f*cking thing is the wrong length! Just measured it with a proper ruler and the 30cm paper ruler actually measures 28cm.

Spoke length from the elbow to the start of the thread is actually 260mm so adding 10mm for the thread, it's entirely consistent with the spoke calcs.

Stupid stupid stupid.... What a muppet :oops:

(not sure what Derek was on about now when he said he was waiting for 280mm spokes though)

Good job it was a slow day in the office yesterday, I spent ages keep going back and looking at that picture trying to see what I'd missed! Glad you got it sorted though.

moonshine

amaferanga wrote:

Now does anyone know where I can buy a single 270mm CX ray? Only JE James seems to come up on Goggle searches and they don't have any 270mm.

If you got the wheel from Derek @ wheelsmith, Have you asked for if he will send you a replacement? I think (hope) he would....

amaferanga

moonshine wrote:

amaferanga wrote:

Now does anyone know where I can buy a single 270mm CX ray? Only JE James seems to come up on Goggle searches and they don't have any 270mm.

If you got the wheel from Derek @ wheelsmith, Have you asked for if he will send you a replacement? I think (hope) he would....

He is (even though the wheels are over 2 years old and the broken spoke is in no way a reflection of the quality of his build since I actually rebuilt the wheel myself last October after a rim swap for the summer).

moonshine

cool! another example of good customer service.