Originally Posted by
onespeedbiker
Well according to the
http://lenni.info/edd/ site that I use and have added to, there are two possible senarios becasue the Mavic Reflex rims come in two different ERD sizes, 316 and 313. For the rear with 613 ERD and 3 cross lashing 292.3 left and 290.8 right. For the front I get 292mm. With the 616 Erd I get rear I get 293.7 and 292, for the front I get 293.5. I give you these not to use, but to verify you are using the charts correctly. First, the ERD is simply the interior diameter of the rim plus about 3mm; the point being measuring through the spoke hole to where the head of the nibble will be.
If you go the the spoke chart, first click on Campagnolo under the
Rim box. That will activate a drop down list and you need to find your hub; hint: they are named
Campagnolo all 126mm hi-flange, rear and
Campagnolo all hi-flange models, front. Depending only which one you are going to use just click on it and it will open a blue box; you need not do anything with the dimensions unless you want to double check the measurements; simply leave the box open. Next, go to the box under the
Hub box and click on Mavic. Again that will activate a drop down list. scroll down and look for Mavic Reflex. Your will see numerous matches each saying
Mavic Reflex---MEASURE TO BE SURE!!. Once you measure your rim and determine the ERD, simply chose Mavic Reflex that has the same ERD and again leave the box open. Next go to the top and choose number of spokes and crosses and the spokes length necessary will be in bold numbers on the right.
ERD = Effective Rim Diameter
Effective rim diameter is the distance from the end of one spoke to the end of the opposite spoke at 180 degrees in an already built and functional bicycle wheel - not the rim itself.
Problem is that the wheel builder like a weather forecaster doesn't have the luxury of stepping into a time machine, grabbing the wheel already built in the future, measuring the ERD and then stepping back into the present to plug the number into a spoke length calculator.
Like the weather forecaster, the wheel builder in the present has to come up with a guesstimate using a handful of variables. (The weather forecaster has 10 times more variable to consider...)
The variables are:
- the nipple type
- the nipple and thread min/max insertion behavior
- the rim itself
- the rim joint sleeves if present AND if raw or non-countersunk
- the wheel builder's personal aiming preference
...ultimately, the wheel builder decides - no one can decide it for them. Hence why it is really best whenever possible to measure your own.
ERD, is not static, a white paper spec, or and industry standard. It it dynamic and largely driven by the wheel builder. The same wheel can have easily 3-4 ERDs as a function of changes in the nipple type, size and behavior.
For measuring ERDs, I use two Phil Wood 14g spokes (they have 90 degrees elbows), two 12mm nipples, and a quality steel caliper.
Each spoke is exactly 249.50mm
I set the nipples such that the spoke ends just touch the screwdriver flat. Position in rim. I then use the calipers in a snug fashion to measure the distance left between the insides of the elbows.
249.50 + 249.50 + Caliper Reading = ERD
I try to measure 4 different spots in rough half circle and average out the results.
If the rim has an unfinished joint sleeve, I'll use a nipple on a stick to determine the additional thickness and then decide if it's safe to add for all spokes - or only the two holes that reside in the joint sleeve. Carbon rims tend to have a spot that will 2mm more as opposed to .5mm or 1.0mm - so I often will have 2 ERDs for a carbon rim.
=8-)