Yet Another Cycling Forum
General Category => The Knowledge => Topic started by: Somnolent on 28 June, 2014, 06:46:35 pm
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In the early stages of thinking what rim I might get for my next wheelbuild.
Thinking I want to try one the new generation of wider rims.
Amongst the options are H+Son Archetypes and the TB14
I've got a few things I don't like about the Archetype, one is the lack of eyelets - but apparently it doesn't need them. Yet to see how easy it is fishing dropped nipples out of the box-section as I am prone to do on non-eyeletted rims :facepalm:
The other, tart that I am, is that the grey anodised finish that I'd prefer is not available in 36h. and the hubs I'd use are 32F/36R
Anyway one of the alternatives is the TB14.
Eyelets ? Check
Anodises 36 h ? Check
BUT
What I've read is that TB14 is less stiff / has greater vertical compliance than the Archetype and I can see from the rim profile how this might be so if the rim is considered on it's own. It's just physics (innit) that the flatter profile will go more egg-shaped when it hits a bump than the taller profile.
Except that I'm not convinced that the rim stiffness had all that much to do with overall wheel stiffness when we're talking about 32 & 36 spoke wheels.
It's relatively easy to deform an aluminium rim in your hands ... until you brace it with all those spokes (made from high tensile steel) arranged in lots of nice triangular patterns, at which point the whole construct becomes stiffer than a very stiff thing (oooo-er Mrs)
Anyone any input on this?
Or experience of how unstiff a TB14 rim is?
If it's going to soak up energy by being too "compliant" I'll not be wanting them - I've little enough power to spare.
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I'd go whatever looks the best aesthetically.
One person will say a certain component is bendy/energy sapping and another will say the same part is comfortable. You get the situation where a part gets so stiff and rigid that you have compensate somewhere else. Eg, threadless oversize stems are or too stiff and you have to compensate with thick padded bar tape.
I don't like the look of deeper rims so I don't use them, by deeper I mean Open Pro, ie Open Pros look too deep for me. If shallow rimed wheels are less stiff, I would see that as an advantage of being more comfortable. That would mean you can have higher tyre pressure (less rolling resistance) compared to a vertically stiffer wheel.
Dark anodised rims look OK when new or if rim brakes have not used on them, but look crap after the sidewalls wear from brake blocks.
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A typical rim flattens enough to noticeably affect the spoke tension at the bottom of the wheel when taking your weight. Stiffer rim = less change in spoke tension per revolution = less spoke metal fatigue.
At least that's the conclusion I've formed after reading many discussions over the years. I can't quantify it.
In any case, there are extra advantages of stiffer rims, including easier building, greater crash resistance, and better aerodynamics in some cases. It comes down to how much weight/expense you don't mind.
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Biggest advantage of a stiffer rim* is that it can take higher spoke tension without Euler buckling, and it's easier to build because changes in spoke tension have a more gradual effect.
*I'm probably confabulating this with the second moment of inertia...any civil engineers here?
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Yet to see how easy it is fishing dropped nipples out of the box-section as I am prone to do on non-eyeletted rims
Small piece of Blu-Tak on the end of your screwdriver will hold the nipple in place until such time as it's connected to its spoke.
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I've not built with the
TB14 PL23 rims, but have seen first hand spokes pulling through this rim due to over-tensioning (apparently less that 120kgf caused this). If you're building a dished road wheel for a 8/10/11 speed geared bike, this rim may be pushing it a bit, especially if you are after something 'stiff'.
EDIT: Sorry, the rim I thought were TB14's were actually Pactenti PL23. Not seen any issues with TB14 rims.
General rule of thumb is the more profiled the rims, the higher the tension you can get away with, though you'll probably not want to go higher than 130kgf anyway. Higher profile wheels are also stronger wheels.
I'm a BIG fan of Pacenti SL23's - built quite a lot of them now, and they are ridiculously good quality rims - seems to build round/true on their own. You DO however pay a small fortune for this quality...
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I went for the Velocity A23 rim for my front dynamo hub. Not eyeletted and I got somebody to build it up for me. However I love the look of it.