21 hole rear wheel design - input appreciated.

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alcatraz
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by alcatraz

Hi wws

I know a guy in Xiamen that can get all kinds of cool custom stuff cheap so I'm experimenting with a new rim with a new braking surface and making it weightweenie.

It won't cost much so I'm going crazy with the design.

I decided to go 21 hole triplet. I'll be using J-bend spokes. (I'm a light guy.)

Now I realised that I can choose the rim hole spacing as I like and I was wondering what you think would be the stronger design. Is even spacing the best?

According to a pic I found at extralite a "triple" specific rim is not even spaced. Is that for a good reason or just to look cool?

Image

by Weenie


Marin
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by Marin

@bm000pf or however Malcolm's nickname is spelled needs to answer this!

bm0p700f
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by bm0p700f

Ok n the 24h triplet the ds spokes are tangential to the flange. For 21 spoke rear with 2:1 that is not the case for evenly spaced holes on the rim do that's why campag have G3 lacing. You need to replicate that to maximise torsional stiffness. That's probably what extralite has done. A drawing is needed. I might try and do one. I'm curious. What the rim erd and the flange pcd?

Maybe when I pay for my sample 2:1 hubs I should get a pair fine in 21h drilling.

bm0p700f
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by bm0p700f

Make your ds pcd bigger for a start.

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F45
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by F45

For a shallow rim being ww not sure you'd get it round going with bunched spokes.

alcatraz
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by alcatraz

This is the rim and the guy guaranteed it will be around 380gr. I wish I had a better pic. (I'm getting it "unbranded" :lol:) It's a clincher rim that's 38mm deep and 25mm wide (brake track), 27mm middle. I could have gotten a lighter rim but then it wouldn't have this new textured brake track.

I have 2-3 hub choices. One has a large ds pcd one smaller. Weight penalty is 30gr.

If I go with the smaller I can get the wheels under 1200gr.

This will be one of 3-4 wheelsets so I'm kind of trying different stuff.

As for the hole spacing I was thinking about doing a bora spacing but I see that the lacing pattern by extralite is different. What to do, hmm. Also like someone said, it might be impossible to true the wheel.

My friend is on extralite sp-t 24h hubs and he's like 105kg ride weight. They don't have a huge pcd ds flange.
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bm0p700f
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by bm0p700f

I could not follow your drawing. I tried doing on on my phone but drew a 24 spoke wheel instead.

Which hubs are you using. This drawing is based on an erd of 580mm with a D's flange pcd of 54mm.

Image

The nds spokes can be placed so the rim is evenly drilled. You will have problems with roundness if you go with campags G3 pattern. Campagnolo start with 50p coin shaped rims.

alcatraz
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by alcatraz

Cool! (I wish I had the hub geometry, still looking.)

I see you went with 3x and extralite with 2x.

Obviously the geomety is not identical but in their tension balance they get 110kgf on nds and 120kgf on ds.

With 3x it will further shift tension to the nds side. Good maybe?

Edit: I see now what you mean by tangential spokes. By going 3x you come closer to them remaining tangential when going from 24 to 21.

You were right to assume 52mm pcd, it's in that ballpark. I can get the crazy large pcd like 65-70 ones on a future wheelset.

Edit2: Extralite's is indeed 3x:radial too. I can't put my finger on the difference. Seems your pattern has one more cross somehow, hmm.

/a

bm0p700f
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by bm0p700f

That drawing is as I said for a 24h wheel. I am struggling to do one for 21h on the phone but for 21h wheels and 14 spokes DS 3x is still possible and desirable. I do 3x on 28 spoke disc brake wheels to maximise torsional stiffness. That's 14 spokes each side with 59mm pcd flanges. The nds, in the proposed wheel, is not transmitting torque so the torsional stiffness in the DS should be maximised.

Do a proper 3d cad drawing for this wheel to determine spoke lengths. 3x DS radial NDS.

Forget using lacing pattern to shift tension balance your is using. 2:1 lacing. Better wheels are made by maximising lateral, radial and torsional stiffness not by trying to get a 1% on the tension balance.

Also use a hub with the wide flange seperation. The extralite triplet hub give you wheels slightly less stiff, than a wheel built with there STD hubs. The bitex 21h 2:1 hub is a waste of time. As you wheel will loose lateral stiffness compared to there standard hub. This is why the campag wheels work well because they get hub/ wheel design, and out the nds flange 45mm from centre.
Last edited by bm0p700f on Tue Dec 25, 2018 6:14 pm, edited 1 time in total.

alcatraz
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by alcatraz

Ok so I'll probably get a wobbly ride and brake rub unless I get the large pcd hub on there. I can choose two 21h hubs. A ~52mm J-bend and a ~64mm sp one.

In china the rim is like 90usd, hub 30usd, spokes 20usd. If I need to swap something out it's not the end of the world.

Seems however that going triplet and minus 3-4 spokes isn't always weightweenie if the hub needs a giant pcd flange. Bit of a disappointment.

I got the spoke lengths already from the seller. I'm wondering what kind of pattern they are for. I'll ask, then double check.

No calculators support 21h but I'm not nervous. It's just an interesting challenge.

Again, thanks for the generous help. :beerchug:

alcatraz
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by alcatraz

bm0p700f wrote:
Mon Dec 24, 2018 1:18 pm
I could not follow your drawing. I tried doing on on my phone but drew a 24 spoke wheel instead.

Which hubs are you using. This drawing is based on an erd of 580mm with a D's flange pcd of 54mm.

Image

The nds spokes can be placed so the rim is evenly drilled. You will have problems with roundness if you go with campags G3 pattern. Campagnolo start with 50p coin shaped rims.
The more I look at this picture the more I think it isn't possible. The Nds holes won't line up with the spaces left in the rim.

Here is a pic from the seller. This is the pattern they use. (Not the same hub). Looks the same as extralite and the ds spokes look pretty tangential to me.
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bm0p700f
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by bm0p700f

The photos of the wheels are poor resolution but they look 2x laced to me with large DS flange pcd.

I have done 24h triplet with 3x lacing before and it worked.

Image

alcatraz
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by alcatraz

.
Last edited by alcatraz on Wed Dec 26, 2018 1:36 am, edited 1 time in total.

alcatraz
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by alcatraz

Cool. Seems your picture is possible but the spokes need to be one step further apart to allow the nds one to come inbetween.

I'm surprised to learn that going 2x to 3x doesn't really change the spoke angles all that much. And 3x does look better at the flange with smaller pcd. I'll tell the guy so I can double check the new spoke lengths.

Thanks! Found this great calculator by the way. spokecalculator.net
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F45
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by F45

I'd do 24h. 3 spokes is only 15g.

by Weenie


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