Bicycle Mechanics - Carbon rims and spoke hole count

I've been considering a pair of chinese carbon rims for no reason in particular apart from the price. I strongly suspect that these chinese outfits offering generic rims are in fact the OEM's for expensive known brands where a set of stickers takes you up to $700+ per rim with no difference in quality. I could be wrong and I'm open to reactions at that point but my real question goes to spoke holes: How is the strength of a carbon rim affected by the number of drillings? I am thinking of building a track set with 50MM depth and 28 holes but I'm wondering if the strength of a carbon wheel would be reduced by having that many holes. Intuitively, I would think the opposite is true as with alloy but I'm not an expert on carbon. All the 20hole carbon wheels I see invites the question 'why so few holes?' Have at it guys...

Deep rims can get away with less spokes. There is more rim, so you don't need as many spokes. I bet if you tried lacing up an old box-section ~300g aluminum tubular rim with 16 spokes you would have serious issues, but with a 50mm deep rim it works. Less spokes = less weight, and more aero.

28 holes in any rim (Al, carbon, or whatever) should have no impact on its strength. I think some of the older carbon rims used to have that many spokes.

For your track wheelbuild, go with 28h in the rear if you want, but IMHO 28 in the front would be serious overkill if you're using a 50mm rim.

FWIW, those are load bearing decals, and the biggest thing that the extra $700 does for you is that it gives you an address to mail your broken rims to when it comes time to use the warranty.

FWIW, those are load bearing decals, and the biggest thing that the extra $700 does for you is that it gives you an address to mail your broken rims to when it comes time to use the warranty.

But do you even need the warranty if you can get three sets of rims for the price of one?

I've been considering a pair of chinese carbon rims for no reason in particular apart from the price. I strongly suspect that these chinese outfits offering generic rims are in fact the OEM's for expensive known brands where a set of stickers takes you up to $700+ per rim with no difference in quality. I could be wrong and I'm open to reactions at that point but my real question goes to spoke holes: How is the strength of a carbon rim affected by the number of drillings? I am thinking of building a track set with 50MM depth and 28 holes but I'm wondering if the strength of a carbon wheel would be reduced by having that many holes. Intuitively, I would think the opposite is true as with alloy but I'm not an expert on carbon. All the 20hole carbon wheels I see invites the question 'why so few holes?' Have at it guys...

First off, you really should be more careful about tension assumptions with regard to carbon rims.

While with most alloy rims today, you can assume a ballpark of 95-100 front and 110 drive side rear for 32/36 hole, it's a little more questionable for carbon rims.

For example you could pick up and old Zipp 404 and assume that it looks okay for 110 kgf - only to discover that it was actually rated for only 80 kgf.

It really is best to try to get a "word" from the source or manufacturer as to the kgf rating - better safe than sorry considering carbon rims can fail catastrophically...

Download my spoke length calculation spreadsheet at:

http://www.mrrabbit.net/wheelsbyflemingapplications.php

View the rimchart and see the notes for Enve, Zipp - and more importantly Jerry Store rims often bought off of eBay.

That'll give you some idea of what you are faced with.

=8-)

.. I strongly suspect that these chinese outfits offering generic rims are in fact the OEM's for expensive known brands where a set of stickers takes you up to $700+ per rim with no difference in quality. I could be wrong and I'm open...

How is the strength of a carbon rim affected by the number of drillings? I am thinking of building a track set with 50MM depth and 28 holes but I'm wondering if the strength of a carbon wheel would be reduced by having that many holes. Intuitively, I would think the opposite is true as with alloy but I'm not an expert on carbon. .

Yes, many (not all) Chinese rims come from the same place as the branded stuff, but there's a catch. Some may be identical, but marketed through the back door, so to speak. Which is fine if you're willing to benefit from stolen intellectual property. But often what comes from the back door sources are copies or rejects. It's a case of knowing your source, and understanding that sometimes you get a gem, and others just a lump of coal.

As for drilling. Actually more holes translates to more, not less, strength. The key isn't the local loss of strength from the drilled hole, nut the length of the span between each hole. It's the spokes that give a wheel it's strength. The rim is simply a compression ring to keep the spokes working and make a convenient interface between the spokes and tire. The stress on a rim comes from the spokes trying to change it's round shape to that of a polygon, and twisting it side to side as the spokes alternate right and left. As with any span, shorter is stronger.

32 hole with clinchers (depending on mfg) will be iffy at the valve span - I had 1 crack at the filler piece that is blended in there ( I assume this is a patch job for the where the air line inserts during production) -- my supplier replaced it with no issue. Watch your tensions and check with a tensiometer (unless you are a seasoned builder and can't be bothered, not sure why you wouldn't want one?) I use one and recently upgraded to Wheel Fanatyk's digital meter --- very nice and worth it IMO. I have found FROM SOME TRIAL ERROR 100-110 kgf is good at least drilled for normal nipples --- maybe higher with internal but again I don't think you gain much benefit with a deep, stiff rim anyway by going into the 130's & 140's. I have about 5 sets in my arsenal now and my last set is my new bench mark; 32H 3X disc hubs for CX no brake track in a clincher. My supplier just released a 24mm wide clincher in 50mm which I have on order now, these are for a build in the queue for a local CX racer's road bike in 28/28 2X on dt240's. Looking forward to seeing those soon.

QC note: most of the rims in question here are not comparable to ZIPP - Reynolds - ENVE in terms of fit & finish --- at around $150 a hoop who cares IMO! I have one set that I use on the road and I think they are OK- ish --- little noisy in the braking department so far. The ZIPP cork pads are the quietest so far with the ZIPP grey pads in 2nd place but wear fast - Swiss yellows run hot and turn the tracks a funny color.

One other thought --- disc brakes on the road is going create some promising developments in the next year or two in rim design for clinchers anyway with the whole brake track issue aside.

Thanks. "Jerry," presumably the manufacturer, indicated max tension of 150kg. He reports building wheelsets with these rims at 130 kg without any kind orim hole washer. (Also pointed out that using a washer will improve strength.) Any suggestions on as to washers for a deep carbon rim?

Thanks. "Jerry," presumably the manufacturer, indicated max tension of 150kg. He reports building wheelsets with these rims at 130 kg without any kind orim hole washer. (Also pointed out that using a washer will improve strength.) Any suggestions on as to washers for a deep carbon rim?

You bring up a good point, I like the idea of using nipple washers. Sapim makes some nice oval-concave nipple washers they're cheap. Bikehubstore sells them, just need to account for them when doing spoc calc.

Me suspects that he's recommending washers due to the poor centerline of the rims. The centerline tends to weave side to side - resulting in about a half dozen drilled holes being closer to a sidewall than what you typically see with an alloy rim. The result under tension is that a ripple or bulge results along the sidewall edge of the holes in question. Somewhere on the net - likely another forum - or even JerrrStore's own eBay reviews is someone who has reported eventually cracking at those specific locations...

I find it odd that here someone is reporting Jerry as stating 150 kgf as the max tension - when the customer who brought 'em to me about three months ago quoted him as saying 130 kgf max tension..

Jerry could certainly provided more up front documentation and specs in his eBay listings.

=8-)

For Mr Rabbit: I e-mailed "Jerry." He states 150 is the rated max but that 130 is the tension used by his techs - no washers. 150 is therefore a mostly useless number apart from suggesting a strong rim. You wouldn't have to be King Solomon to question the veracity of a chinese bike part salesman but I'm still building the wheels WITH washers at about 120. After all, my $2800 Reynolds 46's have the OEM sticker on there; Jing Jang or something like that...AKA "Jerry"?

@crewdoglm: do you already have 28h hubs? I have a set of 50mm carbon clinchers I bought from "Jerry" on eBay several months ago but never built them up... 20h front and 24h rear... Yours for $250 if you want 'em. Send me a PM if interested. I'm in San Jose.

-Mike

Your are right. Some carbon rims come from back door source.
There also some technicists who build small factory here, all the quality is the same with the big factory but the price is much cheap.
We also need to do many test to make sure the good quality for buyer.

We seem to have a response from the horse's mouth, so to speak.


Yes, many (not all) Chinese rims ........

And if they can copy rims as well as they can copy text, the rims might be OK. (see post 6)

Still a cookie recipe at the end of the day ... Ride em' THEY ARE CHEAP and your rims are a consumable component

Even the factory Reynolds DV46C tubulars I own that retailed for $2400 in 2009 have a less than 110 kgf tension fwiw -

SO what if the rims discussed here are copies on some level -- . As far as theft of intellectual property goes you should see some of the other internets finest bike forums regarding Chinese frames. Chinerello anyone?

One other thing I found in regards to profile bulge that Mrrabbit mentions ... As i have also observed some of those issues with my rims ... ZIPP turns out to actually use washers in the firecrest clinchers now ...

http://weightweenies.starbike.com/forum/viewtopic.php?f=3&t=96742