RE: [CR]Help: reasonable drive side tension for classic tubular rims?


Example: Events:BVVW

Content-class: urn:content-classes:message
Subject: RE: [CR]Help: reasonable drive side tension for classic tubular rims?
Date: Fri, 5 May 2006 01:57:59 -0700
Thread-Topic: [CR]Help: reasonable drive side tension for classic tubular rims?
Thread-index: AcZvxWH5TnEE55VnTai+2rlRpd4OXAAVacAA
From: "Mark Bulgier" <Mark@bulgier.net>
To: "Doug Van Cleve" <dvancleve@cox.net>, <classicrendezvous@bikelist.org>


Hmm, no one's tackling this? Ok here goes nothin'

Doug Van Cleve writes:
> I am retensioning/truing a set of Campy high
> flange/Nisi-Evian tubular wheels [snip] I typically shoot
> for 110-120 KgF on the rear drive side
> (measured with my Park tensiometer). I am not sure an older
> rim like this is up to that, but I also want a reliable
> wheel. What tension should I strive for? Rims/hubs are 36
> hole, spokes are 1.8/1.6 double butted.

I usually go for somewhere between "nice and tight" and "really tight".

I built a few at "wow that's tight" (especially at low spoke numbers - say 24 or 28 in the classic era) but had some problems of cracking the rim around the spoke holes, usually many miles down the road.

Seriously though, 36 spokes is plenty for a racing bike, so load carrying capacity should be adequate as long as the spokes are "sorta tight". Tight enough that the left side spokes (sorry, "non-drive side") don't loosen up in use - that's the lower boundary. Not so tight as to cause cracking or taco-ing*. That's a pretty wide range, between those extremes -- and it's easy enough to be sure you're in that happy land without a spoke tensiometer, in my opinion. With some practice anyway, and you already have that much practice and more. Yes there is probably some optimal tension for a given wheel, but I don't think reliability falls off very rapidly with tension to either side of that.

The longevity of wheels built between those extremes will be determined more by whether the spokes were properly stress-relieved, than by the tension number. If you're not sure what stress-relieving means (many people have incorrect or incomplete notions about this), read Jobst Brandt's book, or at least the paragraphs that describe stress-relieving, I think he gets it right. It does NOT mean releasing the residual twist in the spokes so the wheel doesn't make springing noises the first you ride it. That's nice to do too, but if you aren't putting gloves on to stress-relieve a new wheel, you may not be doing it right. Squeezing spokes that hard with bare hands kinda hurts.

The guy who taught me how to stress-relieve in the early 70s did it the Jobst way. His explanation of why we do it was wrong, but his results were good - just about no broken spokes. He was an old Italian dude who learned in Italy and just always did it that way because that's how HE was taught. Wasn't until I read Jobst's book that I learned WHY it works. Hint: it's not because the spoke "beds in" - makes that little groove where it exits the hole in the hub flange. That might be a small part of it, but the real answer is all within the metal of the spoke.

Wow all those words and I didn't even answer your question. I am very sorry about that.

Mark Bulgier Seattle WA USA

*On the West coast, wheels taco. In the East they pretzel, and I'm told they potato chip in the Midwest, though I have not experienced this first hand. ;)