Out of sheer coincidence, two people asked me within a week to add slotted disc tabs to their track bikes. What are the chances of that? .. and also what are the chances that they've both worked at the same bike shop, though now they live in different cities.
The first bike is a yet to be seen in person, IRO mark V, belonging to a chap named Konrad. He's a true shop guy, dedicated to doing his best, and his bikes are really well executed and awesome, so I'm excited about where this bike is going. I'm not even entirely sure, but I think it may just become a disc equipped SS cyclocross bike.
The next bike is polo-new Milwaukee Bruiser, straight from the polo court to my shop. Srsly. Our friend, (lets just call him Cam) bought a frame at the East Van Crown, and took it straight to my doorstep. how cool is that?
The reason I have photos of their dropouts is for purely scientifical purposes. You see, a long time ago, I took some tracings of some interesting dropouts that were laying about at a certain framebuilder's shop..
At the time I didn't know who made the slotted disc tab, but I was planning on using it on a dedicated SS 29er. That never happened..
Fast forward to today, and I need that tab... or do I?
Well it doesn't matter, as its made by Kirk Pacenti, and he won't have any more in stock for months... so. I guess I'm making my own. I've seen quite a few designs out there, some of them looking cool and some looking hokey. The design constraints I laid out for myself are as follows:
- must meet the ISO and Shimano spec for caliper placement for 25mm of axle movement (I chose 25mm as thats a whole chain link)
- must have two weld points to the bike, one on the dropout itself and one on the seat stay. This is to clear any possible brazed areas.
- must fit bikes with drastically different dropouts and rear triangle geometries.
- must not look ugly (to me)
- must be intuitive for the framebuilder to mount correctly using a standard ISO jig
Okay I knew it was going to be a challenge when I started it, but it was way bigger than I thought possible.
I basically ended up importing blocks of sketches all into the same model and layering semi transparent scaled about dropout jpegs on each other before sketching on top of them. Eventually, it got pretty messy in my head and on the computer.
Finally it dawned on me. The pictures of brake calipers I had grabbed off the internet were all fronts. I ran out to my shop and ripped the BB5 off my mountain bike's rear end, noting that it had the 160R mount I needed. .. and of course I photographed it.
This of course solved all the problems I was having with having enough room on the slotted tabs for the caliper. Its all pretty much sorted, now.
Oh, and just for fun I re-registered over on frameforum and did a quick search for slotted disc tabs. Interestingly I found a post by Rody of Groovy Cycleworks where he's advising a novice framebuilder to use paper and draw out everything I just did in CAD. Glad to know my design principals are sound.
I'm not going to post the final design just yet, as it may change slightly in the next day or so, and I'm trying to figure out a creative and structurally sound way to add a Vallie Components logo to it. Laser cut dropouts anyone?
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