Spoke length and inverted nipples

[ebsilon]

Hello all

I am about to build a new set of wheels. The wheels in mind will be build with internal nipples.

Now I need your help how to calculate the spoke length. I know that the rim has a ERD of 603 mm. The diameter of where the nipple head is resting/carbon surface is 599 mm and finally the diameter of the rim between the outer surface is 593 mm (the carbon thickness where the spoke hole is drilled is 3 mm).

I am going to use hubs with 32 Spoke Hole Drilling and the wheel will be build with 3x all over.

The dimensions of the hubs is:


FRONT:
Axle Width (mm): 100

Flange Diameter Drive Side & non-Drive Side (mm): 57.4

Center to Flange Drive Side (mm) 31.3

Center to Flange non-Drive side (mm) : 22.2

REAR:
Axle Width (mm): 135

Flange Diameter Drive Side & non-Drive Side (mm): 57.4

Center to Flange Drive Side (mm) 20.1

Center to Flange non-Drive side (mm) : 33.9

NIPPLE:
Sapim Inverted Nipple 8.5 mm


I would like to have the spokes to enter the rim so that it is not possible to see the spoke thread and when the spoke is under maxium tension the spoke thread has to be somewhere in between the the thickness of the spoke hole.
The thread of the spokes (Sapim CX-Ray) is 10 mm. Maybe the spoke will pass through the nipple, but then I will cut of maybe 1 mm of the spoke thread before assembling the wheel.

So my questin is: How do I calculate the spoke length so that I can fulfill my wishes?

Thank you so much in advance for your help.

Ciao
Esben

[Berg]

I will assume you only have very little room to work with inside that shallow section 29'er rim (from Light-Bicycle?), thus you don't want the spokes any longer that neccesary

So if the internal diameter of the rim is exactly 593mm, I think you can just add 20mm (2x10mm thread) to that, and get a correct ERD for internal nipples - in this case 613mm. If you then calculate your spoke length based on 613, that should put the base of the thread right at the inside edge of the rim when untensioned. Then with full tension, they will stretch app. 1mm, and the thread should be completely hidden inside the rim, and leave around 8mm thread sticking up inside the rim cavity.

I would measure it though, using the method with two spokes cut off at precisely 200mm, and the upside down nipples threaded on flush with end of spoke. Then it is easy to check, by inserting spokes from opposite sides of the rim, and measuring the distance between the spoke ends. This method could give a ERD of around 615, which I would round down a couple mm to allow for spoke stretch, and to make sure the spokes don't poke out the top of the rim (or calculate with 615, and then round down to next spoke size).

I think a 296mm spoke should work all way around - both front and rear both sides. But to be certain the thread is hidden completely, you could go 298, and the perhaps have to trim the ends a bit.

But do measure and calculate - don't take my word for it

[ebsilon]

Hello Berg

Thank you so much for your answer

I have had the same thoughts my self - so it is nice to have another to confirm it.

Yepp, we are talking about the LB wider 29'er rim.

ERD 613:
As you have come up with, the 296 could work. I am just afraid that the thread will be visible FRONT DS and REAR BS. Maybe it would be wise to use 298 mm spokes cut down to 297 mm on FRONT DS and REAR BS.

ERD 615
When using the ERD 615 and 298 mm I would be 100% sure that the treads are hidden by the rim wall (3 mm thick). But I would have to cut down all the spokes. FRONT DS + REAR BS to 297 mm and FRONT BS + REAR DS to 296 mm. All this cutting to make sure that the thread ends before the end of the inverted nipple and to take the spoke stretch of 1 mm into account.

Man it is tough to be a "do it yourself" kind of guy

What would your choice be??

Ciao

Esben


I have attaced the calculations for ERD 613 and 615.

ERD 613


ERD 615

[Berg]

I think I would go with 298mm all round. Unless you use really high tension (eg. like 140kg driveside, and the same on left front), the CX-Rays wont stretch so much, so 298 might turn out to fit perfectly to top of nipples - with a bit of luck

Will you be using washers under the nipples? - they are generally recommended for carbon rims.
Like these: http://www.speedwareshop.de/Sapim-Speichenscheibe-Washer-23-x-45-x-05-mm

I actually have the exact same rims on order, so I recognized the 603 ERD. Mine will be regular type nipples though.
How do they look?? Fit and finish? Quality ok? Could you post some pics?..

[ebsilon]

Will you be using washers under the nipples? - they are generally recommended for carbon rims.
Like these: http://www.speedwareshop.de/Sapim-Speichenscheibe-Washer-23-x-45-x-05-mm

Hello Berg

No, I will not use the washers. Not many carbon wheels are using them these days. Btw. the washers you have a link to are for use between the spoke head and hub flange.

If you are going to use washers then you should look at these:

http://www.speedwareshop.de/Sapim-Nippelscheibe-Washer-oval-klein

or

http://www.speedwareshop.de/Sapim-Nippelscheibe-Washer-konisch-rund

Yes, I think the 298 will be the best choice.

I don´t have the rims yet, but I think they will arrive in a couple of days - I hope

/E

[Berg]

I know the washers I linked are made for spoke head/hub flange, but they also work very well inside the rim for internal nipples. The Sapim washers you link to are meant for regular nipples - they have 4.5mm size hole. I have used a similar type, but from Cnspoke/MAC on previous carbon rim builds. Perhaps the reason some carbon wheels are build without, is simply that it is easier to produce that way, and the factory will save a bit of time/money? I always use the washers on carbon rims, as it makes a lot of sense to me from a "mechanical" point of view. And it definitely can't hurt any