Originally Posted by
aljohn
I intend to build a pair of wheels. Never done it before but I fancy having a go. I've read several articles and for simplicity Sheldon's page is the one I'll probably follow. I've looked at the spoke calculators and feel happy to use them. But, after using these to determine the correct length it occurred to me that I'm unsure where the spoke should end at the rim. Is it flush with the inside of the rim or should it enter the rim slightly? Is there a rule for this? I feel daft asking because I've replaced plenty of spokes in the past on different wheels and none are consistent - as far as I can remember. I really don't want to make a mistake. Or does everyone use a calculator and just go on trust?
Yes, there's a rule (sort of). It's just good engineering practice. The spoke must reach into the head of the nipple which acts as the nut that holds against the rim. Most consider a spoke reaching between the bottom of the screwdriver slot and the top of the nipple to be ideal.
Here we get into a bit of confusion. Most calculators use a formula which has the spoke reach up the the diameter you entered as the ERD (effective rim diameter). Most rim makers allow for the height of the nipple when publishing the ERD for their rims, adding 4-5mm to the actual diameter. Others don't and you have to either add 2-3mm to the resulting calculation, or 5mm to your measured rim diameter at the spoke hole where the nipple seats.
This 5mm difference between the so called effective rim diameter, and the actual diameter is the cause of many spoke length calculation errors, and for my part, I'd rather that folks published
actual specs which can be measured and verified, rather than guess at the nipples I plan on using and "correcting" for me accordingly.