I’m looking to replace the rim on an old set of 26” wheels. The current rim is a Mavic ex823 so, because it uses threaded spoke inserts, the spokes are comparatively short. I can’t get hold of a new ex823 rim so I’ll need new longer spokes to go with whatever new rim I get.

I’ve found spoke length calculators which give a very precise required length, but from that, how do you choose which length to buy??

Is it the closest available length which is longer than the theoretical value or the closest shorter one? How close do they need to be to the theoretical length??

How close do they need to be to the theoretical length??

Within a mm, ime, for a good wheelbuild.

Although by switching between 12mm and 14mm nipples you can make some adjustment (well 2mm).

Totally inexperienced at this but have been looking into my first wheel build. From what I can tell if you HAVE to be a mm out, a mm shorter is better than a mm longer.

If spokes are too long they’ll stop tightening or start cutting into the spoke shaft, it’s better to be a bit too short, longer DT nipples can be used to correct issues up to 2mm too short if absolutely necessary. Always round down with the spoke calculator for example 270.6 buy 270, ideally you wanna be less than a mm short, although you can get away with being a bit too long with sapim D-light spokes.

Often we are faced with a 2mm range between available lengths. The vast majority of the time I would just choose the smaller difference, especially if I am confident about the rim and hub measurements.

In contrast to the previous posters though, I prefer to err on the long side. That’s because when the spoke threads don’t reach into the head of the nipple there is a risk of the head cracking off. Also, you can always add a nipple washer to adjust if they are so long that you cannot achieve full tension. Typically you can screw a nipple on 3mm past the bottom of the slot so you have a good margin for error before you start crunching the threads.

I work on the idea they can be 0.5mm too long or 1.5mm too short (which covers the usual 2mm steps most shops stock in).

It also varies by spoke calculator. Some are just using trigonometry, others assume the spokes stretch a bit when tensioned.

And by nipple length. And by nipple length in spoke calculator! The DT one for example only deducts 1mm when you add 2mm to the nipple. I guess because the threaded bit maybe doesn’t begin in the same place relative to the end?

Also, it depends on the spokes and rim. Drive side rear spokes I would always round down as they’re stretch more. Non drive side rear always round down if they’re revolutions with low spoke tension rims otherwise they won’t be stretched enough, comps it’s less of a problem (unless you can’t get enough tension, in which case revolutions).

And perhaps most importantly, short spokes + 12mm nipples, then if you’ve messed up you can use 14 or 16mm nipples (£1.50 for 40) rather than having to buy new spokes (£20 for 40)!

That’s because when the spoke threads don’t reach into the head of the nipple there is a risk of the head cracking off

It would be interesting to model that in FEA. In general when you have a stiffer material inside the softer one all the load is taken in the first few threads. So a hypothetical brass spoke in a stainless nipple would concentrate the load at the head, but a stainless spoke in a brass nipple then anything longer than necessary isn’t doing anything.

FEA wouldn’t be that interesting in this case I think. You don’t need a hypothetical when the real thing exists. We have plenty of real world failures that demonstrate the issue. The stress riser at the base of the nipple head is well known.

Spokes finish short of the head, head flexes where it enters the rim and cracks off. Simple. Takes longer with brass than alu nipples.

Longer nipples do not in themselves good this problem because the spoke still doesn’t reach any further into the rim

You only find out the hard way that your spokes are 0.5mm-1mm too long, and have to start all over again if you can’t add another half turn or so, whereas finding them 0.5mm-1mm short of ideal length its absolutely no problem.

If the spoke end does not reach three or more threads into the nipple head, as per the picture from DT Swiss, then you have a problem because the nipple is at risk of cracking. I’ve already said that a millimetre short (middle picture) is ok so I’d s say that’s a straw man. It is however the minimum acceptable engagement, so it would be foolish to aim for

If you cannot reach full tension because you have run out of thread you obviously have a different problem.

My point is that when they’re too short the problem is potentially hidden. You may appear to have a solid wheel and only find out the issue when some nipple heads crack off. Whereas if they’re too long you find out in the comfort of your workshop 🙂 you could even add some threads if you have the tool.

I’ve explained why I err on the long side, do whatever you like with your own wheels.

Is that what the pic shows? Got a link to where it comes from?

I know its a way in which they can fail, but its not one I think Ive seen on my own wheels in 20 years of mtbing. Wheels either die catastrophically, just reach a point where thr rim wont stay true, or the spokes snap (generally where they enter the nipple).

Its one of those things I think get overegged as a problem with wheelbuilding. A bit like I always pay a lot of attention to the direction the spokes go with regard to how a derailed chain would jam, or whether the spokes push in or out under braking. The latter in particular wont ever be an issue on modern wheels but ive had spokes hit the calliper on some early 29er wheels i built so its now something I always double check rather than just build whichever way the rim drilling is aligned.

Thanks for all the responses.It definitely feels like I’m out of my depth here… However hope DH rims are in the CRC Black Friday sale and have an ERD of just 2mm different to my 823. Since this should equate to 1mm per spoke, I’m going to give it a go with the existing spokes and pay attention to exposed threads/how close to protruding through the nipples the spokes get.

you could even add some threads if you have the tool.

Although doing this will significantly weaken the spoke.

Mark Beaumont got some custom short spokes made for a rohloff hubbed wheel for his first round the world trip and they all started snapping before he was out of Europe.

The picture is from Sheldon Brown’s site, taken I think from DT Swiss originally (assuming from the file name). Also shown in Roger Musson’s book I believe.

You shouldn’t be seeing it in your own wheels unless you have a habit of leaving the spokes significantly short, 1.5-2mm error from ideal. Three threads engaged is an old engineering rule of thumb for fasteners, maybe you can get away with less if there is some suport of the nipple neck.

Anyway, check the rim ERD yourself, aim to be within 1mm out, and if you do find the spokes are well short of the slot then weigh up the risk yourself versus buying a few new spokes.

1mm will probably be fine.

Ive got some FUNN XLrater 26″ rims and spokes that are sized for a hope pro2 hub. Built up but only used for a couple of rides (long story). If they’re of any use then let me know, they’ll probably be cheaper than CRC!

Im having a clear out and stripping the hubs out of old 26″ wheels. Decided I have way more spares than are worth keeping on the off chance I ever buy an old DH bike!

Double post

Ahh, I thought you meant three threads into the ‘slot’.

I usually make the first pass winding the nipples on so the thread dissapears (on 12mm nipples this is the point where the driver tool dissengages). In the unlikely event that was too much tension already (i.e. the rim is massively oversize) Id go up a nipple size. That pic does explain why the calc only adds 1mm for a 2mm nipple though, theyre longer by 2mm in eachbexample right to left but the spoke is threaded 1mm shorter each time.

@NewRetroTom

Although doing this [adding threads] will significantly weaken the spoke.

Mark Beaumont got some custom short spokes made for a rohloff hubbed wheel for his first round the world trip and they all started snapping before he was out of Europe.

You say that like it’s fact. There are several theories and many discussions about his spoke failures and the root cause

I think its safe to say the OP, and probably most home mechanics, and the majority of LBS’s wont use or have a spoke cutting / threading tool!

Thats well into niche custom build territory!

But on that subject. The OH has an e-bike and the drilling of the rim is blatantly at the wrong angle, they’re angled across the rim to the flange, but not arround the rim to allow for 3x (3d rather than 4d drilling as some manufacturers refer to it) so the nipple/spoke is strained quite heavily due to the large hub motor.

Seems like it needs something like the SRAM caliper alignment washers, but for spokes. Does anyone make such dished spoke washers?

When/if they break Im planning to rebuild it as a 1x lacing which should bring the angles back to something closer to normal, but obviously there is a lot of torque in the wheel.

Sapim HM washers are like that and their polyax nipples also help with angles.

You can also alter the hole drilling angle with a drill bit by hand if there are no eyelets.

You can also alter the hole drilling angle with a drill bit by hand if there are no eyelets.

I thought that, but presumably the holes are drilled into the rounded bit of the rim to get the angle right, there’s no extra profile inside (non eyeletted rim). I think the OEM rim is eyeletted anyway so it’s a moot point, just thkining for the future.

I’ll order some of those hm washers and see, I need some posh washers anyway for some magnesium rims (nothing rational, I’m just a bit nervous about how thin the extrusion seems!)

@alexnharvey

Interested to know which bit of the Mark Beaumont story is under discussion?

As far as I was aware I stated two facts:
He got some custom short spokes made by a bike shop (The Bike Chain Edinburgh I think).
His spokes started snapping before he got out of Europe and he had to get his wheel rebuilt with new spokes.

Yes, where is the evidence that the cutting and spoke threading had anything to do with it? Did they fail at the threads?

Spoke threads are rolled rather than cut and shouldn’t significantly weaken the spoke, especially if well engaged in the nipple 😉

I think the original anecdote was that the Polish repairer told him they’d been overtightened and rebuilt it ‘looser’. That seems spurious or lost in translation and so on various forums people have advanced other theories, including a bad spoke angle at the rim which also leads to failures at the threaded end. Maybe a combination of the two issues, angles and some defect in the threading.

https://forum.cyclinguk.org/viewtopic.php?t=39900

Just tried to build a E-thirteen TRS+ on a DT Swiss 350 hub using squorx nipples. I used the DT Swiss spoke calculator adding an extra mm for the spoke washers. The spokes were miles too short, couldn’t even see the end of the spoke through the nipple. Not sure what went wrong unless the stated rim ERD was wrong. Will have to use standard nipples now.

@mudmonster Do they reach with a standard nipple but not the squorx? You could use the spokes and nipples you have to measure the erd, then you can eliminate one potential issue and have some more confidence ordering what you need.

https://www.parktool.com/blog/calvins-corner/measuring-effective-rim-diameter

Tried a normal nipple and it looked like it should be ok. The last wheels I built I could’t use the squorx nipples which is why I used DT Swiss’s calculator this time. I’m quite disappointed it didn’t work out again. I will type the readings from the dt Swiss calc and use them in another one to see if I get the same results.

@NewRetroTom:

I haven’t seen the stories about Mark Beaumont, but surely rolling threads onto a spoke is how they’re made in the first place; so, a spoke with a few new threads rolled on to it will be exactly as strong as one without? What am I missing?

I’ve seriously considered getting the tools to do it myself (that is, cut threads into blanks) but I don’t build wheels often enough to make it worthwhile…

He got some custom short spokes made by a bike shop (The Bike Chain Edinburgh I think).

I can categorically state that is not the case. 😉