Measuring ERD without spokes..

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robwizard

robwizard

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So I gots my rims.. I gots my hubs.. I needs my spokes! So I read some spoke sizing guides and the only measurement I'm short of is the ERD. Now most of the guides suggest using some old spokes.. measuring the distance between nipples once threaded then adding the combined nipple length (lololol) this seems sound but I have no spokes. I do however, in work at least, have a gigantic vernier caliper! So I'm thinking if I just use that to measure the internal diameter of the rim in a few places the average it.. then that will give me the ERD? Or am I way of the mark?

Cheers
 
Carrying on from this I measured the id of the rim in a few places and came up with 521mm. Using the dimensions given on this site http://www.elegantwheels.net/VELOSTEEL.html I come up with 248mm spokes.. The hub on the site is 32 hole and mine is 36 but the spoke calculator I used didn't ask for the number of spokes only the pattern, I will use cross 3 as that's how I have built BMX wheels before.. unless cross 4 would be better?

Any help with this would, as always, be appreciated! :) Primed the frame and forks today and some parts arrived from Germany so might be able to start putting it together over the weekend!! :)

Cheers
 
Gy's wheelbuilding specs on elegantwheels.net are accurate; I've used them to build a wheel around a Velosteel, plus they match what the EDD calculator has on its database. Further, if you do in fact have a rim with a 521mm ERD, then a 36h Velosteel with a 3x pattern would require 248mm spokes. My only concern is that 521 is a very small ERD for a 26" rim. Can you contact the manufacturer or seller of the rims to verify the ERD? I have built some 26" wheels with Sun MTX33s, which are fairly deep-profile rims, and those have an ERD of 534. More "typical" rims, like Rhyno Lites, have a 546mm ERD. So, unless you're running a 24" rim or something, I'm a bit skeptical about your ERD measurement.

Ps- 9 times out of ten, 3x will get you the best spoke angles in a 26" wheel, unless we're dealing with something that's got massive flanges, like a NuVinci. 4x can work for bigger wheels, or wheels with tiny flanges, like the Wald hubs from way BITD. A lot of 50s/60s era 26" weels ran a 4x. The beauty of 4x is, it minimizes differences in the flange diameter relative to the ERD. So, if you ever switch to a different 36h hub, you'll have improved chances of being able to reuse the spokes with a 4x than you would with a 3x. But that's a pretty minor advantage; the goal is to have the nip protruding from the frame at or around 90degrees....
 
Just measured the outside diameter of the rim with a measuring tape and it's like 23 inches? Sooooo.. something isn't right here! Using the measuring tape I get the ERD at 550mm..

EDIT: Apparently this could be "ISO 584 mm - 650B, 26 x 1 1/2""
 
The outside diameter of a 26" rim, or more accurately, just within that, where the tire's bead sits, should be 559mm in diameter. In inches, that's almost exactly 22". Add 2" of tire at both ends of the diameter, and you're right in the 26" neighborhood. So relax. I bet your rim is, in fact, a 26"...

But, if you're using those champagne-ano rims you'd linked up earlier, they look way too boxy and low-pro to have a 521mm ERD. I'd email the guys you bought them from, or even see about emailing the company that makes them. Maybe see if someone local can hook you up with some spare spokes for a more standard DIY measurement? Or, go to a bike shop for help, and then do the "right" thing and order your spokes thru the shop.

I'm a huge fan of Sun-Ringle and Velocity rims. Not only do they make a nice product, but they list the ERD on their websites. Always a plus, and TBH, that's the only way I've ever gotten an ERD for a wheel build.
 
The Monty rims ended up not being in stock when I ordered them so I got some no name Chrome ones.. I will have another bash with the big vernier. It is one of them manual ones where you have to subtract X from the outside measurement to give the reading.. I probably just took too much off and ended up with my dodgy measurement haha. I will go and have another go and post the results! I appreciate the help man cheers!!
 
Ended up with 521mm again. I emailed the company I bought them off and they don't have the information. I will try and find some spokes somewhere and measure it in that fashion and see if the results differ.

Cheers
 
Yeah.... none of those rims will take a "balloon" tire, or a normal 26" cruiser tire. Which one did you get? The 26x1 3/4 would take Schwinn s7 tires, which ere on a lot of Schwinn middleweights in the 50s/60s/70s. the 584s take 650b tires, which can be cool and come in some nice mtb treads these days, but may be too big to fit your frame unless you get skinnies. 590s are the old Raleigh Sports size; 1 3/8" wide. 635 are the old roadster size.... won't fit your frame.

What the Monty rims were is 559, which is like the "regular" 26".... aka Schwinn s2....
 
I got the 26 x 1 3/4 rims.. thinking they would fit a 26" tyre? You can see how I would be easily confused by that haha. I had already bought the tyres which are Schwalbe Returner. So they won't fit I'm guessing? Sucks. Finding the rims was maybe harder than the tires though so I guess that's what I should look out for? This is so annoying..
 
Found some tires on ebay which might be the correct size but it doesn't give the metric (?) bead seat diameter. I read the Sheldon Brown page and as you have stated above there are a whole bunch of "26 inch" tires. Finding whitewalls is going to be a nightmare.. might have to whip the old house paint out! And I still haven't found out the spoke size haha!!

Cheers
 
Whitewalls will be easy to find for 3 out of the 4 sizes but they'll all be skinnier than what you' originally planned
 
Right OK cool. Might this revelation in the size of the rim also indicate as to why my ERD measurement was so out? And just to clarify (sorry for being an idiot..) but what is the size of tire/s I am looking for?

Thanks so much!
 
All of the sizes available in that auction would have a larger diameter than a regular 26"and, therefore, should have a larger ERD. B/c they're Westwood-style rims, they do have a dropped center, but that'd be a heckuva drop.

Which exact size did you actually order? The auction offers 4 varieties: 26x1 3/8 (590mm),26x1 1/2 (584mm) 26x1 3/4 (571mm),and 28x1 1/2 635mm). Once you figure out which you've got, you can hunt for the tires.
 
just pick up a dowel rod and run it through, mark it and measure it. There's your erd unless you have double wall rims. Add for nipple height if you like ... or not. 2mm per nipple (4mm total) is what i would add if it were me. If it comes out to an odd number spoke length I usually round it down the lesser even # when ordering spokes.
 
and once you have your erd, you can measure from the spoke hole to the wheel lip, add it twice to your erd and it will be close enough to figure out your tire iso #
 

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