28" wheel build advice Andra 30 or 40 rims & Shimano DH 3N72

[steve216c]

I decided to retire my Shimano HB-NX30 dynamo hub/Vuelta rim wheel and build a new wheel around Shimano DH-3N72 hub.
 
Following the late great SheldonBrown guides, I have successfully rebuilt several wheels in the past on 26"/28" bikes, but where I purchased same replacement rims (usually Zac19) so could be sure I could reuse old spokes and had stock with a fair number of spare new spokes on hand of the same lengths. So I have never needed to calculate or measure spoke length till now. I am not daunted by threading the wheel- but I am a bit nervous on choosing the correct spoke length as I don't have any like wheel to use to compare correct spoke length against. Additionally I'm not 100% certain I understand various online spoke length calculators correctly and I'll almost certainly need to purchase a full compliment of spokes for this task.

Over the years I've had to several replace rims which had worn too thin on (V) brake surface. I even ignored a thin rim to the point that I blew wall out on a Marathon tyre when the rim wall exploded during a ride!  I've killed fewer with buckles as I've always been quick to replace broken spokes or true out minor wobbles. I'm hoping the Andra's braking surface will be a little longer lived- although with Maguras braking more evenly than V-brakes, wear may be less of an issue.

Planned wheel will have Shimano DH-3N72 (already purchased) as 32 spoke hub and Andra 28" for rim brakes for which I need to order spokes and rim still. So this is really for advice and guidance on which Andra rim and what spoke lengths I will need for building wheel myself.

I ride 150-200km/week mostly commuting on a Rohloff powered 28" wheel Winora Labrador. Of that around 50km are off-road on forest paths (mostly firm) and the rest on asphalt. My total weight including me/bike/loaded bike bag is likely to hit around the 110-115kg most days. Currently riding Marathon Plus 42-622 tyres, but have a set of 47-622 already on hand to replace in near future both of which fit either Andra 30 or 40 rims. Current rims are Vuelta and look like they are 19mm internal width.

The Andra 30 is going to be similar overall width. I'm assuming the Andra 30 is going to be more stable than the current 32 spoked Vuelta rims or the  Zac 19 rims I've run and replaced on and off for years on my non-Rohloff 28" bike. This may be enough for the way I use my bike.

But if I plump for Andra 40 rims we are looking around 6mm total wider. I believe my Maguras can be adjusted to take a wider rim of that magnitude. The Andra 40 should take more punishment but at a couple of hundred grams of weight over a pair of 30s.

1) Your recommendations- should I go for 28" Andra 30 or 40 rims?

2) What about spoke lengths on Andra 30?

What length spoke would I need for 28" Andra 30 and Shimano DH 3N72?
And for a matching 28" Andra 30 and Rohloff non-disk hub?

3) Same question on spokes lengths for Andra 40 rim.
What length spokes would I need for 28" Andra 40 and Shimano DH 3N72?
And for a matching 28" Andra 40 and Rohloff non-disk hub?

I want to have everything on hand for planned leave over Christmas- so want to have everything on hand for wheel build in advance of that.

[martinf]

Planned wheel will have Shimano DH-3N72 (already purchased) as 32 spoke hub and Andra 28" for rim brakes for which I need to order spokes and rim still. So this is really for advice and guidance on which Andra rim and what spoke lengths I will need for building wheel myself.

Not sure there is any difference in wall thickness between Andra 30 and 40. The wider rim should be better for wide tyres, and I would have preferred the Andra 40 for this reason if it had been available when I got my Raven Tour. But the Andra 30 rims work OK with nominal 50 mm width tyres.

You need the ERD (effective rim diameter) to calculate the spoke length. This is given on the Ryde website at:

https://www.ryde.nl/andra-40
https://www.ryde.nl/andra-30

For the hub, I found this:

DH-3N72:

Over Locknuts              99.7 mm   (nominally 100 mm)
Flange To Flange          56.0 mm   
Spoke Hole Circle Dia    70 mm   
Flange to fork LEFT       21.9 mm   
Flange to fork RIGHT    21.6 mm   

The spoke hole circle diameter is probably right, as I think I used 70 mm when I last built up a wheel with a DH-3N72 a few years ago.

You then have to enter the hub and rim details into a spoke calculator and choose the number of spoke crossings and number of spokes. There are several online, some of them might have the exact hub and rim you want already in their database. But it is wise to check any programmed measurements with your own.

I still use a spoke calculator that works in Excel that I downloaded ages ago, it's called "Spocalc", the current version can be had at:
https://www.sheldonbrown.com/rinard/spocalc.htm

[PH]

I have Roger Musson's excellent wheelpro book, I'd recommend it to anyone interested in learning or improving their wheel building.
https://www.wheelpro.co.uk/wheelbuilding/book.php

One of the first lessons is not to trust anyone else's ERD specifications and instead buy the rim and hub first and measure for yourself. 
Ryde are probably the worst to trust, I recently built a pair of wheels with their Andrea 321 rims.  The ERD is 599 on their website, 593 in the SJS spec and mine measured 595.

[martinf]

One of the first lessons is not to trust anyone else's ERD specifications and instead buy the rim and hub first and measure for yourself.

Yes. The downside to that is that you then need to order the spokes separately.

[PH]

One of the first lessons is not to trust anyone else's ERD specifications and instead buy the rim and hub first and measure for yourself.

Yes. The downside to that is that you then need to order the spokes separately.

This is undeniably true, though my spoke supplier sends them second class for less than two quid, so after measuring I'll have them three days after the rims.  My wheel building has never been on a timescale where that would be a factor and the OP is looking to get the stuff together before the Christmas break...

[steve216c]

I found this useful database on the net. It is in German, but I'd wager that most folks can figure out how to enter their wheel and hub data using the pull downs to get the recommended spoke dimensions for thousands of potential combinations of named hubs and rims.

https://www.komponentix.com/Speichen-Nippel/Wheel-Designer-Speichenrechner/?force_sid=grep11e8dnrqoiupmugir7vga4

But now I have another dilemma. I was kind of planning to go for Andra 40 rims- but it looks like my Magura rim brakes are only designed for rims 18-28mm wide according to the specs online. The Andra 40 rim is 30.8mm wide.

Has anyone fitted Andra 40 rims with Magura HS11/33 brakes with success?
Is there enough tolerance in those dimension specs to squeeze another 2.8mm more over those specs to take the 40 rim- or is this a path not worth bothering with?

The alternative is the Andra 30 rim which is within the Magura dimension specs.

[steve216c]

Just to update. Santa bought me Andra 30 rims for the 3n72 dynohub. Bought what was advertised on eBay as an unused box of Sapim leader spokes/nipples and received Sapim  Strong spokes set in post. No complaints there.

Built wheel on Christmas Day and fine tuned it this morning for first ride today. Hub rolls smoother than  Nexus Dynamo hub coasting or powering. I may try servicing the Nexus bearings at some time to keep it as a working spare.

I haven’t fitted 2nd rim yet on Rohloff hub. But I have a set of spokes in right length ready to fit when I get the urge. Probably when it is a tad warmer so the missus doesn’t complain about bike maintenance taking over the kitchen table.