# Offset spoke hole rims: How to calculate spoke length?



## Ohm_S.Ohm (Aug 21, 2004)

I'm thinking of building a wheelset with IRD Cadence rims. They manufacture a rear rim that has offset drilling. What is the difference in spoke length, if any?
Any recommendations on how to determine this.
Thanks!

FYI:
Campy Record hubs
DT Revolution spokes Front/Rear Non Driveside, Competition Driveside 
IRD Cadence Niobium/Aluminum alloy rims


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## TurboTurtle (Feb 4, 2004)

Ohm_S.Ohm said:


> I'm thinking of building a wheelset with IRD Cadence rims. They manufacture a rear rim that has offset drilling. What is the difference in spoke length, if any?
> Any recommendations on how to determine this.
> Thanks!
> 
> ...


Use Renard's spocalc.xls (Google it). You enter the offset. - TF


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## Ohm_S.Ohm (Aug 21, 2004)

*Got it...*

I've been using Spokcalc but never noticed the field for offset. What a useful program! 
So sounds like I'll actually purchase the rims then physically measure the difference of offset to get the value to enter in the field.
Thanks TT!
I wonder if the difference in spoke length warrants buying two different lengths...?


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## Kerry Irons (Feb 25, 2002)

*Multi spoke lengths*



Ohm_S.Ohm said:


> I wonder if the difference in spoke length warrants buying two different lengths...?


I've built a lot of wheels over the years, and IMO the whole "different lengths left and right" thing is highly over rated. So you have a little bit more spoke engaged in the nipple on one side or the other - big deal. If I have the same hub type front and rear, I use all the same length spokes for everything (only have to have one size to service the wheel) and have never had problems. The only thing that matters is if there is enough spoke in the nipple to prevent stripping threads and that there's not so much that the nipple won't bottom out - that's a large range. If you use a longer spoke on the NDS, that just means more nipple threads engaged, and since there's little tension on those spokes, you don't need more threads engaged. I've build a few wheels with OC rims and have used the same spoke lengths on both sides. NOTE: an OC rim will REDUCE the difference between DS and NDS spoke lengths, making it even less of a worry to have two different lengths.


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## Ohm_S.Ohm (Aug 21, 2004)

*!!!!!*

Exactly what I wanted to hear! Thanks Kerry. Your advice confirms that I won't have to order any more different lengths than I have already. 

Even though I've used Spokecalc each time [4] I've built a set of wheels, this time, I had doubts because the IRD Cadence rims weren't to be found under the rim info listings.

One final question before I dive in:

Is it recommended to use hubs designed for OS rims when utilizing such a design? Or will my Record rear hub work too?

Thanks for your advice.


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## Anti-gravity (Jul 16, 2004)

Ohm_S.Ohm said:


> Is it recommended to use hubs designed for OS rims when utilizing such a design? Or will my Record rear hub work too?
> 
> Thanks for your advice.


The Record will work fine, excellent choice. Hubs that are "designed" for assymetrical rims usually have a taller NDS flange or move the NDS flange inward a few mm. Overall it does little to even out the spoke lengths. For the assymetrical rims I've built up I used the same length spokes on both sides. Worked for both mountain and road wheelsets. I think the difference came out to be 1-2mm on the spoke calculation, hardly worth worrying about.


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## weiwentg (Feb 3, 2004)

Ohm_S.Ohm said:


> Exactly what I wanted to hear! Thanks Kerry. Your advice confirms that I won't have to order any more different lengths than I have already.
> 
> Even though I've used Spokecalc each time [4] I've built a set of wheels, this time, I had doubts because the IRD Cadence rims weren't to be found under the rim info listings.
> 
> ...


I don't really know that there are any hubs specifically designed for offset rims. some hubs, like DT Swiss, Am Classic and Ritchey, have the NDS flange moved inwards, which equalizes the tension. you can use those with a standard rim; if you use them with offset rims, the tension will be further equalized. you can also use a standard hub with an offset rim.

there may be some debate on whether moving the NDS flange inwards results in a stronger wheel or not. it does increase the NDS spoke tension, but it does decrease the bracing angle (bad). Kerry Irons seems to think (iirc) that such hubs aren't a great idea. some hubs, like White Industries and Chris King, have an oversize drive-side flange, which increases the bracing angle on the DS spokes. I think that's probably a good idea - certainly it won't do any harm.

while an offset rim will definitely build a stronger wheel, you should note that people have been riding on Campy 10 hubs laced to non-offset rims like Open Pros for quite a while. a lot of people have no issues with those setups. ymmv, especially with the skill of the person building the wheel.


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## Mark McM (Jun 18, 2005)

*Reduced offset hubs and oversized flanges*



weiwentg said:


> there may be some debate on whether moving the NDS flange inwards results in a stronger wheel or not. it does increase the NDS spoke tension, but it does decrease the bracing angle (bad).


I don't think there is really much debate on this subject. Dished rear wheels have assymetrical strength - they are stronger to forces from the left than to forces from the right. Moving the NDS inward slighlty increases strength to forces from the right, but it drastically decreases strength to forces from the left. Although there may be a closer balance in right/left strength, overall the wheel is weaker.

A secondary affect is that moving the NDS flange inward will decrease the lateral stiffness of the wheel. This can often be seen in a greater tendency for the rear brake to rub the rim when out of the saddle.



weiwentg said:


> some hubs, like White Industries and Chris King, have an oversize drive-side flange, which increases the bracing angle on the DS spokes. I think that's probably a good idea - certainly it won't do any harm.


I think you'll find that flange size has virtually no affect on bracing angle - especially for crossed spokes. Lateral bracing angle is:

Bracing Angle = arc-cotangent( [(Rim Radius) - (Flange Radius) x cos( Crossing Angle )]/(Flange Offset) )
Crossing Angle = 720 deg. * (Number of Crosses) / (Number of Spokes)

Consider a typical 32 spoke rim with a 600 mm radius and 3X lacing pattern, and rear hub with a 20mm right flange offset: Increasing the flange radius from the standard 23mm to 30mm only increases the bracing angle from 3.93 deg. to 3.96 deg. - a difference of only 0.8%.

There is an entirely different reason that freehubs like those from White Industries and the Chris King have a large drive side flange - these hubs have their ratchet pawl mechanisms located directly under the right flange, and due to their oversized axles and pawl mechanism size, they have to enlarge the right flange simply to fit everything inside.


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