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What's the best way to measure ERD for one measurement?

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What's the best way to measure ERD for one measurement?

Old 04-15-20, 03:41 PM
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bikerbobbbb
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What's the best way to measure ERD for one measurement?

Measure a few times, take the average.

But for one measurement, what's the best way to get that? I'm thinking, take two spokes, secure those together after put through the rim. Pull everything tight. Mark where the spokes meet so you can put it back together later. Then pull the spokes out of the rim, put them back the way they just were, and then measure from just below the nipple head.... over to what point on the j-hook side that goes into the hub?

Or is there an idiot-proof tool that will give you a quick ERD measurement? (No, not just a tape measure.) Or maybe yes a tape measure? Up to the inner part of the rim. Then measure how much rim thickeness there is to where the nipple head would be.

Must not be a quick tool for it... Otherwise Park Tool would have something out already.
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Old 04-15-20, 03:44 PM
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Nice.

https://www.parktool.com/blog/calvin...e-rim-diameter

Two spokes, spoke up to the screwdriver head point on the nipple, pinch together with calipers like the middle picture. That looks easy enough. You still have to measure each side though. Every measurement is one more point to be a little off instead of measuring the whole thing at once.
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Old 04-15-20, 03:46 PM
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The spoke method is explained in the middle of this page: https://www.parktool.com/blog/calvin...e-rim-diameter
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Old 04-15-20, 03:46 PM
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Originally Posted by bikerbobbbb View Post
Nice.

https://www.parktool.com/blog/calvin...e-rim-diameter

Two spokes, spoke up to the screwdriver head point on the nipple, pinch together with calipers like the middle picture. That looks easy enough. You still have to measure each side though. Every measurement is one more point to be a little off instead of measuring the whole thing at once.
You beat me to it!
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Old 04-15-20, 08:25 PM
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Phil supplies their spoke cutter with the other method of measuring ERD. A flexible tape is used to measure the rim's upper edge circumference. Using Circumference=Diameter x PI (3.1415) ((is that still 7th grade math?) you can calculate the rim's outer edge diameter. Then measure from that outer edge to the spoke nipple bed in the rim. A straight edge held across the rim's edges with a ruler or other device to capture the depth to the nipple bed. Subtract two nipple depths from the rim's outer edge diameter and you have the ERD. IIRC the kit Phil supplies is the Sutherland's one.

At one time DT offered a poster with a direct ERD scale that you could hold the rim against and by using a couple of specific spoke nipples a direct reading could be made.

The two spoke method is a version of the Wheelsmith kit with their measuring rods.

I have the DT poster on my basement wall (laminated in plastic years ago) and have the Phil/Sutherlands kit at work. Both work well once you get the hang of them.

If you've never measured ERD I strongly suggest doing it a couple of different ways as well as a few times each way and averaging the totals. It's easy to have a mm or two of variance as you struggle to hold all the "tools" in place. Andy
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Old 04-26-20, 10:28 AM
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Looks like a useful video.

Glimpse into How To Measure ERD

Bill Mould
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Old 04-26-20, 01:43 PM
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Also, make sure you're measuring spoke holes that are exactly opposite one another. Look for the valve hole and the welded or pinned joint opposite.
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Old 04-28-20, 09:33 AM
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This last pic on this 2009 thread is incorrect, isn't it?

You measure ERD from the bottom of the nipple head, not the top? In other words, this pic is probably add 2+2mm or 4mm extra on the ERD? That's assuming the nipple head is the slot for the screwdriver.


Mavic A719 ERD

Originally Posted by Soil_Sampler View Post
make your own, two spokes, two nipples and a ruler.

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Old 04-28-20, 11:56 AM
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Reddog3, a poster on BikeForums, long ago (2011) developed an easy homemade tool to make for determining the ERD. Unfortunately that was back before Photo Bucket changed their policy so his pictures don’t work. Here’s what I put together for my wheel building class.

A metal rule is drilled at both ends and a fender bolt or pinch bolt from a brake cable is used to clamp two spokes to the rule. Each spoke is cut to a known length from the seat of the spoke nipple. 250 mm is a good dimension for 700C and 26” wheels. The cut spokes are clamped in the fender bolts like the figure below.



The distance between the two ends is read directly off the rule and added to the overall length of the two spokes as shown in the picture below.



In this case the length added is 36mm for a total ERD of 536mm.
The hardest part of the process was finding the rule.
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