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forteh

Mismatched holes!

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I need to lace some 32 hole hubs up to 48 hole rims. Obviously every third spoke is missed out but should spoke lengths be the same as a conventional 32 hole rim build?

I'm guessing that there will be enough thread spare on the nipple to pull it up but has anyone got experience of lacing wheels like this? :)

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I very much doubt it. You're dealing with different spacing between each spoke hole on the rim. Sounds like a nightmare to me. What size wheel is it as well? If its a 20"rim you're probably more likely to get away with it than a 26" rim.

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20" rim onto a mountainbike hub, building 4 wheels for a pedal race car but unfortunately finding 4 rims with 32 holes was virtually impossible!

It might be a case of sit down in a local bike shop, lace one set of spokes up and see what lengths the others come out at. Might make them dishless wheels which will simplify things with not having to have offset spoke lengths side to side.

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If it was 36h and divided into 48 nicely that'd be one thing, but with it being 32h that's going to be a bit of a shambles however you go about doing it in all honesty.  Can't really think how you'd get around it without having to do a bit of trial and error action for the spoke lengths.  You'll get a reasonable amount of lee-way with the nipples and spokes if you're happy to grind down any excess, but I don't know if that'll really be enough.

Good luck!

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36 to 48 is harder isn't it due to  the lack of a common demoninator?
32 to 48 will be missing 16 spokes from the rim with 32 spokes fitted, that will give equidistant spacing of the gaps around the rim (fit two miss one).
36 to 48 will be missing 12 spokes which doesn't play nicely with 32 no matter how you shoehorn it :D
I've tried some combination of 32/36 before and that was all over the shop, I think trial and error is the key phrase here!

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I've done a 32h hub onto a 36h rim, and the reverse, both times with just a single spoke length (in both cases, the length calculated for the smaller hole-count).
I know the change in angle will be smaller than the setup you're talking about, but just for some input.
I'd guess they'll be pretty awkward to build, but would just about work with a single spoke length.

Err on the slightly long side rather than short and use 14mm nipples, just to be safe? :lol: 

Edited by aener

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On 04/12/2018 at 1:38 PM, forteh said:

36 to 48 will be missing 12 spokes which doesn't play nicely with 32 no matter how you shoehorn it :D

I don't really get the bit about playing nicely with 32? 

I see what you're saying about the 32/48 combo though, I hadn't really thought of it that way before.  

In my head 36 to 48 should still work better though just as the hole drillings in the hub are going to be closer to where they'd need to be for a 48, and 36 still goes into 48 fine (i.e. you're essentially just removing 3 spokes from each 'group' of spokes - i.e. drive inboard/drive outboard/non-drive inboard/non-drive outboard - rather than the 4 for 32h).  I would assume that would mean less inconsistency with spoke lengths required, but that's by the by.  If you're going 32h then that's that, and it'll just be a case of it being a bit of a mindblag trying to work out what lengths to use anyway.  Flipp's right about the longer nipples though (Y) 

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Long nipples is a good idea!

I've modelled the wheel in solidworks, I can play around with spoke lacing and lengths to see what I can get away with and then try to make it work from there.

Looking at building it as a dishless wheel (it's for a pedal car so offset isn't an issue) which should help.

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So I've got the wheel modelled in 3D now, based on completely arbitrary rim and hub dimensions I can build it with equal length spokes on the disk side, valve hole is at 12 oclock.

The non disk side then needs alternating spoke lengths 7mm longer and 5mm shorter respectively, this puts all of the spoke thread ends within 0.5mm of the rim bed, empty nipple holes inbetween each group of two spokes.

It's not ideal because I currently don't have directly opposing spokes so relying more on the rim strength than the build as it won't be possible to tension it quite as high.  Only a case of rejigging the assembly model and tweaking the lengths :)

2.jpg

1.jpg

Edited by forteh
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Would it screw with the lengths too much if you staggered them the opposite way? Latecross style. I know it leaves the seam exposed so getting the bob out might be a challenge, but probably nothing smashing it against the floor won't sort ;) 
That would put your opposite side spokes together, which might make the build easier, And you'd be able to offset the sides a bit more normally.

Think this is how roadies group their spokes, right? And they've got shit tonnes of money to pour into R&D :P 

 

Super pro image below to illustrate. Ignore the magenta dots - they were just a rough as hell spacing thing I forgot to remove.
forteh.thumb.jpg.003f8417ea5d98f5a6e18166ce83f906.jpg

 

 

Edit: Just realised that if you have zero offset rims you could get super cheeky and push the trailing spokes back by one hole. Both sides of trailing spokes would then be on the "wrong side hole", but it would even out the tension over the circumference a little. So the pattern going clockwise from the valve hole would be: 

Green
Light Blue
Light Red
Green
Dark Blue
Dark Red
[repeat]

Edited by aener

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Good info, I've now accurately measured and modelled both rim and hub so I can play more with the lacing. The spoke holes are offset from the rim CL by 1.7mm ±0.1mm, will play with putting them in the wrong hole (fnaarrr!) and see what happens. I'll see how laying it up on your sketch works out and fiddle with lengths accordingly, the beauty of having it fully modelled is I can play around with the position of the first 4 spokes and instantly pattern them around the rim to see how it looks :)

Would have been sooo much easier if tarty had 4 of the 32h monty rims in stock instead of 3 :D

edit:

Something like this, red spokes are 178mm, green spokes are 176mm; both lengths are within 1.2mm of the spoke bed which is plenty of scope to take up with nipples. Not sure how I've ended up with 2x but setting it as 3x really seemed to screw things up, as it is the spokes are evenly spaced and pulling from the correct sides of the flanges so should be much easier to tension!

Now where can I get 178 and 176 (64 of each) from?

 

3.jpg

Edited by forteh

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How light is the pedal car? Enough that radial lacing would be sufficient? Shorter spokes, but super easy to lace up and get tension right :lol:

Would imagine Tarty should be able to help with spokes - must be in the ballpark of 19/20" trials wheel specs?

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9 hours ago, forteh said:

Not sure how I've ended up with 2x

I was going to call you out on that - I thought you were better than that - but when drawing it out I realised that 3x created some pretty insane angles and assumed you'd tried that and switched down to 2x :lol:

3x3x is The One unless there's specific reasons not to. (I have a 2x2x front wheel because most companies don't make spokes long enough for 3x on such a tiny hub flange and relatively large ERD ((single wall 20")) ).

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Believe TB do 175mm, 177mm and 180mm so not quite what you're looking for unfortunately.  Just had a look at some BMX shops but it seems they typically go longer than that...

@aener - if you're looking to go 3x3x in future, Source BMX do spokes in the right length for you (192mm?) in black or silver.  They're £14.99 for a set of 40 spokes and nipples.

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1 hour ago, Luke Rainbird said:

How light is the pedal car? Enough that radial lacing would be sufficient? Shorter spokes, but super easy to lace up and get tension right :lol:

Would imagine Tarty should be able to help with spokes - must be in the ballpark of 19/20" trials wheel specs?

Pedal car weight will be in the region of 20kg + driver, problem with radial lacing is that we need to be able to drive and brake with the wheels as well :)

 

28 minutes ago, aener said:

I was going to call you out on that - I thought you were better than that - but when drawing it out I realised that 3x created some pretty insane angles and assumed you'd tried that and switched down to 2x :lol:

3x3x is The One unless there's specific reasons not to. (I have a 2x2x front wheel because most companies don't make spokes long enough for 3x on such a tiny hub flange and relatively large ERD ((single wall 20")) ).

I did fiddle around with the angles to try to get 3x but it does go a but squiffy and the spoke lengths seemed to go off on one!  I'll have another hack around with it on the model when I have a fresher head (not 1am) and see if I can't balance them up a little.

The car should be used on fairly smooth tracks (possibly some road use as well) so wheel strength isn't of utmost importance (with regards to bashing), as long as they can stay straight and not noodle all the time then jobs a good un.

@Mark W, thanks for the heads up, I could probably get by with 175 and 177; I've used the same set of spokes on the triton for the last 8 years, despite changing rims and hubs - fiddle with the lacing .  We do have a couple of local bike shops on board who would be preferential (as they'll do them for trade price) but push comes to shove we've still got money in the kitty :)

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Had another play and got it to 3x, spokes are now 190 and 188 but will obviously give a stiffer wheel :)

Reckon I'll get away with this level of spoke/flange interface at the hub?  Obviously I will be prebending the outside spokes inwards as I lace it.

4.jpg

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