Straight pull spoke calculation
 

Hi all,
Looking to swop out some straight pull areo blades for nice round spokes, and I have found that the existing spokes are 2mm longer due to the spoke nipples having a castelated crown for adjustment from the tyre side, within which the thread runs right to the top. Almost like a sapim 12mm nipple with an extra 2mm on the head.
In fact screwing a sapim 12mm onto the blade spokes results in nipple not even contacting the rim.
I figure I could just buy the new spokes 2mm shorter, but I'd like to calculate it for the sake of it. And here is where it gets fun.
The hubs are hunt race aeros, the front wheel radial, the rear radial on the NDS, and 2 cross on the DS.
I am having trouble finding a calculator that will do this, for example the specific design of the pitch circle.
Anyone know of a good calculator for straight pull?
Any hints tips etc also greatly appreciated.
Cheers!

I've used this DT calculator for many years with good results. While I don't usually build radially spoked wheels this calculator does have a "straight pull" hub option (as well as nipple options). Do know that radial spoking has less "fudge factor" in the inputs to get the best length. Exactly where on the hub I would call the flange diameter I am not sure... Spoke calculator - DT Swiss

Having known spokes in use makes the reversing math to get flange diameter easier. I pretty much will always trust a spoke in use before a calculation, WRT lengths for a specific wheel. Andy

Nice one Andy, that's exactly what I was looking for.
I really like your idea of working the maths backwards, I can't believe I didn't think of that as I do it in my job every day....

Bugger, that calc wont let me choose 18 spokes for the front wheel, or different lacing for each side of the back wheel.
Any other ideas anyone?

I build a lot with straight pull and rely almost exclusively on this calculator. https://www.wheelpro.co.uk/spokecalc...E3KT8fJx3NpcxM Note that you can select for normal (J bend) straight pull or triplet. If you don't understand any of the fields, just click on it an an explanation will pop right up. It was written by Roger Musson and is very comprehensive.
The exception is when using DT Swiss hubs, then I use the DT Swiss calculator.

Run the calcs twice, once with one scenario on both sides, then the other. Radial, number of spokes doesn't matter so run it with more.

Brilliant, thanks very much guys :thumb:

It's no different than with any spoke calculation.

Just verify 3 things and you're home free.

1. On hub, be sure to use a diameter at where the head pockets, so it matches the holes for J bend spokes.

2. Measure ERD including the nipples you plan to use. Deduct 1-2 mm ( per side) if you wish to spokes to end shy of the top.

3. Know your calculator. Some expect an ERD measured at the nipple seat and add 3-4mm for the nipple head. Others expect you to enter rhe ERD where you expect the spokes to end.

So, you might need to adjust the result according to the above 3 factors, but that's easy enough if you know what you're doing.

Why would one choose to end the spoke at the nipple stress riser?

Why would you ask that?

Normal spoke calculators put the end of the spoke at the base of the nipple. If you subtract 2mm from that, your spoke is now going to end right where the nipple shaft transitions to the 2mm head. That's a stress riser and where nipples break.

So what is the function of subtracting 2mm and not putting the spoke to the end of the nipple where it is strongest?

Did you bother to read steps 1 & 3?

FWIW Maybe you could put half the effort into posting positive advice that you put into challenging others.

I read every post of yours in this thread, and when you suggested doing something that sounds like making the spokes too short I asked you why.

Why don't you just answer the question instead of acting like your honor has been challenged? Maybe I misunderstood, maybe other people trying to understand your instructions will also misunderstand and you have the opportunity to clarify.

Sometimes it's more about who and how than what.

99% of the time, when someone asks me to clarify a post, I do so willingly.

However, you're reasonably knowledgeable, and I'd expect you to correctly interpret all three steps in toto.

So, given your history, I assumed you were simply being argumentative.

If I was wrong about that, I apologize. But, you'd have to concede that you responded before giving much thought to what I wrote.

No, I still have no idea what step two is for. I've built hundreds of wheels from my own measures and calculations, and that experience brings no clarity to your suggestion.

Still asking.

OK

I measure to get an ERD that INCLUDES the nipple, ie. to the top of the nipple.

(FWIW I never rely on published specs)


So most most calculators would generate a length that ends the spoke at the top of the nipple.

I offer the OPTION (IF you want.....) of biasing shy of the top, for single wall rims.

Step 3 is because some calculators I've used in the past assume the ERD is at the nipple seat, and a correction to bring the spokes out into the nipple. Since I already include the nipple, this would cause spokes to be over long by 3-4mm.

Note: while I didn't mention it there's already a small. <1mm. bias to the long side because of how spokes are measured.

Personally, I only think about it when rounding, and it's safely disregarded if working within 1mm of spot on.

There is one more factor for straight pull which is spoke head offset. Usually a positive number which means it is added, but on rare occasions it can be a negative. The adjustment is made in the same way that half the spoke diameter is subtracted for J bend.
https://cimg1.ibsrv.net/gimg/bikefor...8a21c0caf2.jpg

You are conflating two completely different kinds of "straightpull" and two different kinds of offset.

The straightpull in the OP refers to spokes that are laced with no flange offset.

But you are referring to spokes that have no elbow, the opposite of J bend.

Some straightpull laced hubs use straightpull spokes, some offset lacing hubs use straightpull spokes, and most J-bend hubs can be laced offset or straightpull. Straightpull spoke hubs generally are good for a single lacing angle/cross (e.g. straight or 2 cross). While J bend hubs will usually let you lace them the straight, 1x, 2x, 3x etc. I think there is also a lacing between straight and 1x.

The offset in your diagram is more like a flange diameter issue, but really you have to deal with it directly by correcting the product of the calculation as you would for added nipple washers.

I read the OP to mean calculating for straight pull spokes as in no elbow. I still don't see anything, even upon re reading about no flange offset, which I assume means spoke holes directly across from each other.
My response was to FB who omitted the spoke head offset necessary for the calculation.
Also, it appears what you are calling straight pull with regard to J bend spokes is what the rest of the world refers to as radial.

Yup, I'm the one who confused the two. Thanks for the correction.

Reading this,I think back to when I started buidling wheels. There were no spoke calculators. There were barely calculstors, definitely no internet.

So we calculated spoke length by hand.

I sometimes think that why 4x 36h builds were SOP. Since, the spoke went to the centerline, it was half the diameter, allowing for the nipple, plus about 1mm for each 10mm of flange offset, plus 1mm for good luck. When I was building different patterns, simple measurements and basic arithmetic worked fine.

From time to time, I still use the graphite calculator I've trusted for half a century.