Building new rear for mountian bike

[WheezyRider]

I'm building a new back wheel for my mountain bike and I wanted to check with the experts here about the required spoke length.

I want to lace in a Bafang BPM into a 36 hole Ryde Andra 40 rim (with rim brakes), with a crossing pattern of 1:

Andra 40 - Ryde

The Andra 40 rim is optimal for use with tyres ranging from 44 mm up to 65 mm.

www.ryde.nl

According to the Sapim calculator I get 195 mm.

Spoke calculator | Sapim

www.sapim.eu

But I am guessing a rim material thickness as 5 mm, as I can't see that on the Ryde webpage. Does 195 mm sound right?

 

[Jodel]

I would check the ERD on the actual rim you intend to use before you order any spokes. I have used Ryde Sputnik rims in the past and the ERD can vary by several mm (600mm to 606mm) from rim to rim. That is enough to make quite a difference to the required spoke length.

I have used the Grin spoke calculator with good results - accurate to less than 1mm. https://ebikes.ca/tools/spoke-calc.html

It is intended for hub motor wheels and will probably have the correct parameters for your Bafang motor already in the database.

 

[guerney]

Do bike shops usually have spoke threading machines? I must ask my local, in case I accidentally order slightly longer than I need... but the owner is a complete crook, so I'm certain to be paying through the nose for such work.

 

[Sturmey]

You did not say what sized wheel your mountain bike is. But assuming that your wheel is 26 inch (iso559) and the erd is 534mm as specified in your Andra 40 link, the grin calculator works out (I think, a quick look) at approx 189mm.
https://ebikes.ca/tools/spoke-calc.html?hub=B_BPM&pair=false&rim=cust_dia559_e534_lo1_ro1_w23.6&cross=1&lelb=in&relb=out

However, I am fully in agreement with Jodel above in that you need to actually measure the rim. I have fitted a number of Ryde rims lately (Zac 2000, Explorer & Sputnik) and in all cases the actual erd was larger than specified and the spokes needed to be about 2mm longer and rounded up. (my guess would be about 192mm in your case) This has also been reported by other users. There has been some suggestion elsewhere that Ryde do not allow for the extra 2mm for spoke to fully engage into nipple head but I dont know.

Ryde rim; ERD fairy tales - Cycling UK Forum

 

[WheezyRider]

Interesting about the ERD being so variable. I will have a look when the rim arrives. Shame, I wanted to order the spokes at the same time. Yes, it is a standard 559 wheel size.

 

[Nealh]

Tbh one can't order spokes until the rim is in front of you to double check, one only has to guess wrong and find the rim ERD to be 2 or 3mm different and then need to buy more spokes.