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-   -   Wheelbuilders: I have questions about 650b HED Belgium Plus rims (https://www.bikeforums.net/bicycle-mechanics/1137293-wheelbuilders-i-have-questions-about-650b-hed-belgium-plus-rims.html)

Metaluna 03-03-18 09:10 AM

Wheelbuilders: I have questions about 650b HED Belgium Plus rims
 
I'm about to start my first 650b build using HED Belgium Plus Disc rims, once I get the spokes ordered, and I just wanted to confirm a few things with the experts before I mess anything up too badly.

I just got them and the ERD measures out closer to 553.5 than the 555mm stated on the website. Does this sound like a reasonable level of variability for HED? If these were Velocitys (my usual brand), I wouldn't think twice about a 1.5mm discrepancy, but I just wanted to make sure I'm in the ballpark for this particular manufacturer, and my calipers aren't giving a bad reading.

553.5 actually makes more sense than 555 anyway. They spec their 700c rims as 592mm ERD. A 650b rim should be exactly 38mm smaller (622-584 = 38). Assuming they use the same die extrusion for both, the ERD therefore should be 592-38 = 554, so that seems like a good sanity check. Maybe they add an extra millimeter to account for the nipple heads?

Second, the rims have this sticker on them:

https://i.imgur.com/OyfXRHs.jpg


Does this mean the nipple seats are angled asymmetrically to account for the shallower bracing angle on the drive side of the hub? If so, it makes sense to flip the rim around on the front since the rotor (left) side would now have the shallower angle.

Finally, any suggestions on max spoke tension? I didn't see anything on their website so I'm going to assume 120 kgf for the drive side is pretty safe. I weigh 220 and these are only 32h rims so I don't want to go too low, but don't want to crack the rims either.

P.S. In case anyone's wondering, the silver metal peg sticking out of the nipple hole in the picture is one of the Wheelsmith rim rods.

CliffordK 03-03-18 11:21 AM

Double check your ERD in a couple of places, then go with what you measured. Specs can be wrong.

Are you including the nipple and any washers in your calculations?

Nipple holes probably are angled as you think.

FBinNY 03-03-18 11:41 AM

Your question about the ERD discrepancy is evidence of the problem with ERD as a spec. Keep in mind, that the ERD isn't an actual measurement, but the desired diameter of the theoretical circle at the ends of the spokes. As a practical matter, it's measured to the tops of nipples in the rim, less a small margin to account for the spokes ending shy of the top.

IMO that makes ERD a fail as a spec since it relies on various assumptions, namely the thickness of the nipple heads, and the amount of allowance for ending shy. Because of that it's not only possible, but highly likely that two people measuring ERD will come up with different measurements.

For my part, I wish that rim companies would go back to providing the actual rim diameter, measured at the nipple seat. Then we'd all know where we stood, and could add our own allowances for spoke engagement into the nipple head, without playing the Newlywed Game and trying to guess what the rim maker had in mind.

As for the right/left lacing direction, I don't believe it's because of different angles drilled, since the difference is too small to make a difference. As a basis of comparison, consider that the difference is right/left angle is less than the difference in the forward/back angle you see in crossed patterns. I suspect that the rim may have a right/left offset or asymmetry in spoke vs. tire placement, like the one shown here.https://cdn.shopify.com/s/files/1/02...g?v=1478090630

Metaluna 03-03-18 01:25 PM


Originally Posted by CliffordK (Post 20202601)
Double check your ERD in a couple of places, then go with what you measured. Specs can be wrong.

Are you including the nipple and any washers in your calculations?

Nipple holes probably are angled as you think.

I'm using Damon Rinard's Spocalc spreadsheet, so I'm not sure if he includes allowance for the nipple heads or nipple length. I've used it many times in the past though and it's usually dead on for 12mm nipples without nipple washers, especially if I measure the rim with the Wheelsmith rods, which I think measure the true diameter that FBinNY was talking about. Also I checked the numbers against Freespoke and they agreed to .1mm when I used the same rim and hub measurements.

I also ran the numbers for 553.5, 554, and 555mm erd and compared the spoke lengths, so I think I found a set of lengths that should work well for the two smaller measurements, and might still be usable for 555, or at least I'd still be able to use at least half the spokes by moving them around to other places.

Metaluna 03-03-18 01:48 PM


Originally Posted by FBinNY (Post 20202635)
As for the right/left lacing direction, I don't believe it's because of different angles drilled, since the difference is too small to make a difference. As a basis of comparison, consider that the difference is right/left angle is less than the difference in the forward/back angle you see in crossed patterns. I suspect that the rim may have a right/left offset or asymmetry in spoke vs. tire placement, like the one shown here.

Hmm, I don't think this is an offset rim, but I'll take another look at it. It would be awesome if it is!

I agree with your comments on ERD vs (NSD? nipple seat diameter?). Transparency is always good at this level of technical knowledge. There's no need to dumb the numbers down since anyone attempting a wheel build in the first place should be assumed to be sophisticated enough to understand all the factors involved (or at least, once all the books and online tutorials get updated to reflect the new methods). The exception might be rims with proprietary nipples and washers, like the DT Swiss ones I considered for this build.

FBinNY 03-03-18 02:08 PM


Originally Posted by Metaluna (Post 20202832)
Hmm, I don't think this is an offset rim, but I'll take another look at it. It would be awesome if it is!.....

If the rim isn't offset, then you're seeing another example of guilding the lily. Folks have been building both front and rear wheels, including highly dished rear wheels without regard to specially angled drilling, even with pointy aero rims, which rigidly set the nipple angle.

However, with the internet, and all sorts of dialog about tiny meaningless details, manufacturers seek to be beyond perfect by making subtle changes and claiming they're an important improvement.

Years ago when folks were still using large flange road hubs, Mavic had an inspiration and tried drilling in sets of four, right/left, and forward/back. It ended up creating confusion, and often caused problems when used with hubs that had dedicated elbow in and elbow out holes. So, while technically more "correct" it created more problems than it solved, and the idea was quietly abandoned.

So, whether it makes a real difference or not, go ahead and follow the maker's decal based on preferred dish orientation. I say this, because there's no reason not to.

well biked 03-03-18 09:19 PM


Originally Posted by Metaluna (Post 20202427)
I just got them and the ERD measures out closer to 553.5 than the 555mm stated on the website.

FWIW: Wholesaler QBP is a distributor of those rims, and they publish both the manufacturer's stated ERD and their own hands-on ERD measurement. QBP measured the ERD at 554.5mm. Again, FWIW.

FBinNY 03-03-18 09:34 PM


Originally Posted by well biked (Post 20203484)
FWIW: Wholesaler QBP is a distributor of those rims, and they publish both the manufacturer's stated ERD and their own hands-on ERD measurement. QBP measured the ERD at 554.5mm. Again, FWIW.

Given that there's no precise standard for nipple head thickness, nor precise agreement about spoke engagement, ERD specs to a half 0.5mm are a farce.

Another example of BS implied precision where no such thing exists. It's no wonder that we see variance in this spec.


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