Brompton rear wheel build - spoke lengths

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hoogerbooger
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Joined: 14 Jun 2009, 11:27am
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Brompton rear wheel build - spoke lengths

Post by hoogerbooger »

I'm confused! Anyone able to spot the obvious ?

I've built two rear wheels for my Brompton....... using the spoke pattern and advice that Brompton provide in their trade leaflet. 2 cross. Spokes are not interlaced and spoke lengths used are the same on each side of the wheel and flange. Trailing spokes on the outside of the flange, leading on the inside.

( 1st was a SRF5w; 2nd was on a pre NIG steel shelled AW)

On both wheels, I end up with the trailing/outside spokes having about 2.5 mm thread still showing ....whilst the inside of flange have the thread extending beyond the nipple top.

(I've used the 146mm spoke length they recommend for the BSR hub .....that appears the closest match)

Now when I look at my factory built BWR wheel, there's no spoke thread showing below and looking from the top each spoke sits uniformly just below the top of the nipple.......despite the trade sheet saying all spokes are the same length.

I've been staring at...comparing factory vs mine and concluded there is nothing wrong with my lacing and the path length should be slightly different for the inside/ outside of flange.......and thinking they must use different lengths for inside/ outside of flange in the factory ?

Or am I missing something obvious.

Ultimately I would want all the thread to be in the nipple for strength......and am wondering if I should rebuild with differing lengths......( although the 1st wheel has survived for 4 years)
old fangled
fastpedaller
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Location: Norfolk

Re: Brompton rear wheel build - spoke lengths

Post by fastpedaller »

Is it the trailing spokes from both sides of the wheel showing threads, and the leading spokes from both sides beyond ends of nipples?
Is the rim central between the locknuts (verified with a dishing stick)?
If the above are both the case, it could be there is enough difference between outside and inside of flange to create the issue (given the small size of the wheel). I've just drawn on paper a line 7 1/2 inches long (my guestimate of spoke length) at an angle representing half the distance between hub flanges. With a line similarly drawn 4mm towards the 'centreline' to represent the flange inside/outside spokes (I hope that makes sense) the difference in length is only 1.5mm., So would appear (on paper) to not be the problem.
Are the holes spaced correctly across the hub? ie If a spoke is put through a hole on one flange, perpendicular to the flange and across the hub to the other flange does its end touch the opposite flange exactly midway between two holes?
alexnharvey
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Joined: 10 Jan 2014, 8:39am

Re: Brompton rear wheel build - spoke lengths

Post by alexnharvey »

Have you considered removing a factory spoke, or one per side to measure and compare?

Are the hub and rim data published anywhere, so you could calculate the lengths?
rogerzilla
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Re: Brompton rear wheel build - spoke lengths

Post by rogerzilla »

The inside/outside length difference is apparent with non-interlaced spokes, so all x1 and radial wheels are affected; e.g. heads-out radial wheels need slightly shorter spokes than the calculator says.

You can interlace the spokes if you like, which equalises the lengths and doesn't actually cause any problems, other than being a bit harder to do with short stiff spokes. It does sound as if there is a lacing error, though, since the difference you have is so large.
hoogerbooger
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Joined: 14 Jun 2009, 11:27am
Location: In Wales

Re: Brompton rear wheel build - spoke lengths

Post by hoogerbooger »

Thanks for the comments - all.

Yes: Exposed threads are on all the trailing spokes from the outside of the flange ..both sides. All leading spokes, both sides... beyond head of nipple.

My head thinks it agrees that the difference seems too much to simply be the thickness of the flange effect....but I can't spot the difference in lacing between all my Brompton wheels ?

Probavly best tat I sleep on it. ... and compare them again after a strong coffee tomorrow morning ( and a perhaps a barefoot run around the garden th e frost)

Both wheels I've built are on the current angle drilled rims. Pretty sure I've got the key dpoke andvlacing to fit the drilling....but I'll check that. ( BWR wheel is an older non angle drilled rim.....but I don't think that's it)

( Brompton advice is not to interlace .... saying it's more likely to cause problems......so as I'm a relative novice at building wheels I won't attempt this on 16" wheels)
old fangled
fastpedaller
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Re: Brompton rear wheel build - spoke lengths

Post by fastpedaller »

Interlacing would be extreme bending due to the short spoke lengths.
Are you absolutely sure the lacing is correct. I got this wrong once in my early wheelbuilding 40+ years ago, with a similar result.......
Looking across the wheel, identify a spoke on the flange furthest away from you both at the hub and its other end at the rim. with a straight edge across the hub locate the spoke on the nearest flange, and to the right of your straight edge. Where the other end of this spoke meets the rim should be 1 spoke to the right of your 'first spoke'
I recall it had me baffled all those years ago, but i'd laced one side, then put a spoke in the other flange. This spoke I'd put through the flange hole immediately to the right of the one on the opposite flange, but put it through the rim to the left of the one on the opposite side. Some spokes appeared 'short' some appeared long, but I knew they were all the same length. I learnt a lot that day!
hoogerbooger
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Re: Brompton rear wheel build - spoke lengths

Post by hoogerbooger »

fastpedaller: I was sure your suggestion would be it. On both the BWR and my made wheels: I located the key spoke on the RH drive side....which is a trailing spoke on the outside of the flange. Taking a straight line across the hub( and viewed from the RH side) the opposite trailing spoke is in the hole to the left of the straight line. All wheels are the same. Key spokes all 2 holes to right of valve hole ( as viewed from right)

I've had a strong coffee and the garage is nobbling.....and I still can't spot the reason ! Will re check the drill angle alignment when time allows

If I do work out that I have done something wrong....I will report back. Thanks all for the advice.
old fangled
fastpedaller
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Re: Brompton rear wheel build - spoke lengths

Post by fastpedaller »

hoogerbooger wrote: 9 Dec 2022, 10:51am f Taking a straight line across the hub( and viewed from the RH side) the opposite trailing spoke is in the hole to the left of the straight line.
Disregarding the key spoke aspect - is the opposite trailing spoke in the next rim hole or 2 from it (which could be the issue). It's difficult to describe (and even more difficult for someone reading my description :lol: ), but a movement of 1/28 around the hub should be matched by a movement of 1/28 on the rim. If I can draw it on my computer I'll try. It might be easier for me to carefully photo my Brompton. We'll get to the bottom of it!
hoogerbooger
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Re: Brompton rear wheel build - spoke lengths

Post by hoogerbooger »

The opposite trailing spokes are always one hole to the left...when viewed from the right. Same for the opposite leading spokes. All wheels the same.

I'm disconbobulated....even after 2 strong coffees
old fangled
fastpedaller
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Re: Brompton rear wheel build - spoke lengths

Post by fastpedaller »

hoogerbooger wrote: 9 Dec 2022, 11:31am The opposite trailing spokes are always one hole to the left...when viewed from the right. Same for the opposite leading spokes. All wheels the same.

I'm disconbobulated....even after 2 strong coffees
Is the trailing spoke in the opposite side also in the hub flange immediately to the left of the one in the nearest flange?
If so, the only conclusion is that the holes aren't aligned correctly, as the holes in the opposite flange must be central between the holes in the other flange (straight-edge across hub to confirm).
I was asked by a customer to build a front wheel - he gave me the hub, which was very expensive and from a then recent newcomer to cycle manufacturing, who could be confused with a luxury car brand. I'm sure they have improved over the years. Anyway, this hub was nigh-on impossible to build into a rim, and when I examined it closely it became apparent...... on one flange some holes were directly in line with the opposite flange holes, and some were (correctly directly between them. One flange appeared visually correct, the other was visibly incorrect, and even by eye it could be seen that some holes were closer to their neighbours than others. I returned the hub to the customer, but he wasn't a technical person, and probably didn't appreciate the problem. In fact it's a miracle his bike kept going, it was so poorly maintained, but that's another story.
fastpedaller
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Re: Brompton rear wheel build - spoke lengths

Post by fastpedaller »

I hope this works. A picture speaks a thousand words....... disregard the 'floating o' outside of main picture. O's on flange represent holes- I.m not very good with paint app. Assume nearest flange is blue
wheel spokes.png
hoogerbooger
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Re: Brompton rear wheel build - spoke lengths

Post by hoogerbooger »

Have double checked and flange drilling is correctly offset ....so hole on one side matches up with midway between hole on the other.

My head thinks the discrepancy is too much and something is wrong ....but the eyes can't spot it.
old fangled
fastpedaller
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Re: Brompton rear wheel build - spoke lengths

Post by fastpedaller »

I thought the same when I laced the wheel I wrote about earlier. It took me several looks to notice (referring to the diagram) the blue spoke was to the left of the black spoke at the hub, but it was to the right of the black spoke at the rim.
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531colin
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Re: Brompton rear wheel build - spoke lengths

Post by 531colin »

hoogerbooger wrote: 8 Dec 2022, 7:09pm................

On both wheels, I end up with the trailing/outside spokes having about 2.5 mm thread still showing ....whilst the inside of flange have the thread extending beyond the nipple top............
If its laced correctly, you could correct it by setting all the nipples so that the spoke thread is just about to disappear into every nipple....
but you know that.

So I suspect whats going on is something like fastpedallers suggestion...a spoke starts off in front of a particular spoke from the opposite flange, but finishes behind that spoke....so the leading and trailing spokes approach the rim at different angles.

a rim where the spoke holes are angled both "front to back" and "flange to flange" should make this very obvious....half the nipples will be wrongly angled (front to back) at the rim.
hoogerbooger
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Joined: 14 Jun 2009, 11:27am
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Re: Brompton rear wheel build - spoke lengths

Post by hoogerbooger »

Just stared at the wheel again. Nothing looks wrong. Looking from the RH side each matching trailing and leading spoke dutifully starts at the LH flange hole that is at a half space to the left and ends up at the rim one hole to the left of it.

This will probably drive me mad and I" ll gave cut off an ear or something.
old fangled
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