wheel building - Whats your way to measure ERD of a rim

[Tychevelle]

Hey Guys

Im just curious what your way is to measure the nipple seat diameter (ERD) of a rim to figure out your spoke length? I usually try to get as close of a measurement with a tape measure but while the rim is still laced up to a hub it can be tough and not super accurate, whats your way?

Ty

 

[rydr1]

I would also like to know this.

 

[scrumblero]

i have heard to use two spokes and nipples and then add them together with the space in the middle, but if i cant find the ERD online I just measure across the inside and add what I think the rim depth is .

 

[Crassly]

I've never done it, but if I had to, here is what I would do. Take a piece of string and go around the rim where the rim strip would go. Measure that length to get the circumference. Then go to: http://math.about.com/library/blcirclecalculator.htm or any of a number of online calculators. Plug in the circumference and ta-da you have the diameter.

 

[Danimal]

Crassly's idea is good. Never thought of that one. Another easy way is to run a piece of string accross two spoke holes that are opposite each other. Mark the string where they go through the rim seat and then remove and measure.

Or, if you want a real quick and dirty answer to your spoke needs, look here:

http://www.bikewebsite.com/spokes.htm

 

[Tychevelle]

That is a good idea, I thought about using the string to run from one edge across to the other but at that point with the wheel still build with a hub in it a tape measure is basically the same. With that calculator you plug the measurement into the circumference your ERD answer is the diameter correct?

 

[Crassly]

With the calulator I provided the link to, you enter the circumference and click on "solve others" and it will provide the diameter and area of the wheel. Or if you happen to know the diameter and are wondering what the circumference is, you can enter the known value and it will calculate the other two.