Extralite Cyberrear SP vs SP-T

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alcatraz
Posts: 2212
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

Hi ww...

I'm staring at the cad drawings of these two hubs and it seems they are very similar.

Image
Image

I'm looking at how the holes line up left and right and it seems they are the same. The flange size and spacing is the same too.

I've always been on the hunt to build a 21 spoke weenie wheel (I don't like 20h) and it seems that a 28h cyberrear is actually possible to do that by skipping every second nds hole.

One thing I'm unsure about is the DS side hole angles, and the thickness of that NDS flange. I'd be putting maybe 110kgf on a flange designed to hold around 70kgf. (I'm only 65kg and these hubs are rated up to 90-95kg). I'd also be angling the spokes a tiny bit different on a 21h rim than a 28h. I wonder if I'd stress the heads.

I'd love to hear your comments.

/a
Last edited by alcatraz on Fri Feb 01, 2019 4:31 am, edited 1 time in total.

shimmeD
Posts: 487
Joined: Thu Jun 28, 2012 10:52 pm
Location: eNZed

by shimmeD

I recall reading (Skunkworks?) using special Extralite hubs for a 2:1 wheel-build, so might be worth reaching out to Zak. He doesn't seem to haunt ww anymore.
Less is more.

by Weenie


petromyzon
Posts: 400
Joined: Mon Apr 05, 2010 4:14 pm

by petromyzon

The NDS holes are in the same position on the triplet hub but the body is extended outwards and wrapped in carbon to support the additional tension on the NDS spokes. the non-triplet one does not have this, as you can see from the two diagrams you have posted.

Despite the fact that 42mm is quite a broad centre to flange spacing 7 spokes will not provide a very stiff wheel. Personally I would build the 16:8 triplet with a slightly heavier NDS spoke.

I love my Cyberhubs but they are definitely on the bleeding edge of what is sensible. You may be light but if you cracked a flange it would be a 500 Euro bill at minimum before you start getting in to the risk of injury.
IMHO wheels are a system and you should build something that is a balanced selection of components. This would be a crap wheel design even if you laced it on a hub that will definitely take the flange stresses 3x over.

alcatraz
Posts: 2212
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

Thank you both for your input.

Yes I just noticed the maximum tension allowed.

SP 70kgf on nds
SP-T 110kgf on nds

That won't work.

On front hubs they limit to 90kgf. I was surprised to see this.

No wonder they created spx and spt hubs for proper tensions.

/a

petromyzon
Posts: 400
Joined: Mon Apr 05, 2010 4:14 pm

by petromyzon

I'm not sure that this would help? Slightly higher tension allowed on the NDS but significantly worse spacing (?34mm). If you try and build a wheel with 7 spokes spaced at 34mm on that side I don't care how light you are it will be inadequate.

Why are you so keen on a 14:7 triplet wheel? Do you have a Campy rim or similar to lace up?
If you just want a weenie build, buy one of the prebuilt Extralite setups.

bm0p700f
in the industry
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Joined: Sat May 12, 2012 7:25 pm
Location: Glermsford, Suffolk U.K
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by bm0p700f

You have to accept lower lateral stiffness and therefore more brake rub with the triplet hub due to its design.

This means with a deeper rim use thicker spokes for the rear wheel. A shallow rim like the Mavic open pro UST may be o.k with this hub. I would use something like the Sapim CX sprint spoke. Shasliwer rims are less prone to brake rub because the spokes can bend it to keep it between the brake pads.

The one thing this triplet hub does is provide high non drive side spoke tension which should increase radial stiffness hense why a shallower rim could work well. The kinlin xr22t or similar rim should be fine.

Stick to lacing the hub is meant for. The extra spokes will improve lateral and radial stiffness.

A 21 spoke 2:1 hub would be different.

The STD hub extralite do for straight pull spokes builds into a nice wheel with thin spokes. The low tension balance is not s problem.

moyboy
Posts: 447
Joined: Thu Aug 18, 2016 12:19 am

by moyboy

Email them at info@extralite.com
They are good at responding throughout working hours.

shimmeD
Posts: 487
Joined: Thu Jun 28, 2012 10:52 pm
Location: eNZed

by shimmeD

viewtopic.php?f=113&t=148127
This is the thread I was referring to :beerchug:
And also check this out https://www.instagram.com/p/BtLM1MsAshn/
Less is more.

alcatraz
Posts: 2212
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

Thank you very much :thumbup:

I was surprised to see the reported tension balance at 72 nds and 110 ds in that thread. This is way off what extralite presents in their specs. They show 110nds 120ds.

Is it possible that extralite uses an asymetric rim? Even then it's hard to account for such a big difference.

The regular SP has a tension limit of 70kgf on nds. When using a regular non-assymetric rim maybe a normal Extralite SP would do the trick with 110/72 or thereabout. Sure it wouldn't be a solid build by any stretch @21 spokes, but it could be a fun experiment.

I'm not going to go through with it, but should a Cyberrear 28h fall in my lap at a low price I would wake up the idea.

UpFromOne
Posts: 757
Joined: Wed Apr 08, 2009 5:23 am
Location: Olympic Nat'l Park, WA

by UpFromOne

alcatraz wrote:
Fri Feb 01, 2019 3:27 am
I'm staring at the cad drawings of these two hubs and it seems they are very similar.

Image
Image

I'm looking at how the holes line up left and right and it seems they are the same. The flange size and spacing is the same too.
The NDS flange on the SP-T is machined with a little extra material to withstand the higher tension of 8 spokes.

alcatraz
Posts: 2212
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

Right...

Right now my dream build is to find an extralite J-bend SL-2 rear hub with 28h and lace it as a 21h triplet. I know the pros don't like this idea but it's light, supports my weight 65kg, requires no titanium/scarce spokes and the flanges can take the tensions 120-110kgf.

I might be crazy but I like to experiment. :D

by Weenie


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