Re: [CR] Drillium


Example: Racing:Wayne Stetina

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Date: Mon, 31 Jan 2011 18:35:27 -0800
From: Mark Bulgier <bulgiest@gmail.com>
To: Eric Keller <eekeller@psu.edu>
Cc: CR <classicrendezvous@bikelist.org>
Subject: Re: [CR] Drillium


Eric Keller wrote:
> In retrospect, I'm actually a little surprised that there was no drilling
> of
> rims back in the heyday of drillium. Or maybe there was and I just didn't
> know about it.

Yeah there might have been more of that going on than than was visible from the outside. I doubt I'm the only person who's ever done this:

On the race bike I made for my wife around 1990, light weight was a priority because she's light. 2.4 lb (1.1 kg) lugged steel frame! I used Saavedra clincher rims because she rode clinchers and the Saavedra was the lightest I had heard of, yes even with the rim "washers". I added three more holes in the inner wall, where the rim tape goes, between each of the big holes at each spoke, maybe 10 or 12 mm each? The new holes were the same size as the existing holes. Made the rims significantly lighter, though I forget how much exactly, I just remember being pleased with the number at the time.

And I don't think I weakened them one bit! Unless I'm not thinking this through correctly -- but it seems a chain is as strong as its weakest link, and adding more weak links equal in strength to the existing weakest link doesn't make the chain any weaker -- right? I only added more holes the same size as the ones that were already there.

We replaced those rims after a pretty respectable number of miles when the rear was starting to get little cracks at each nipple -- but that's in the outer wall, nowhere near where I drilled 'em. Such a light rim with only 28 spokes (rear) can be expected to crack at the nipples eventually anyway, so I don't think my holes in the outer wall caused the cracks she got.

In theory this could be done with tubulars also, but probably not a good idea since you'd be reducing the surface area for glue.

Hmm let's see, 28 x 3 = 84 "extra" holes. If we assume 10 mm holes and the wall thickness = 1.0 mm, then the volume of aluminum drilled away is Pi x 25 x 84 = 6597 mm^3. Given a density of 2800 kg/m^3, that gives us a weight for the drilling chips I made of 18.5 g per rim. Hmm, I'd hoped it was a bigger number than that, for the amount of time it took! Actually I think the holes were probably bigger than 10 mm and the wall was probably over 1.0 mm thick, so maybe I got 25 or 30 grams shavings/savings per rim, big whoop.

"Normal", visible drillium isn't about the weight of course, it's about style and flash. Super Record perforated brake levers being heavier than N.Rec. and all that. But if it's hidden inside to where you have to take the tires and rim strips off to see it, it'd better be actually reducing the weight!

Mark Bulgier
Seattle, WA
USA