July 11, 2010

A new bike – finally

My personal bike (essentially resurrected from the dead/pulled out of the trash, which doesn’t fit me) is becoming an embarrassment. Hence, I’ve been spending the weekend building myself a new frame. I’ve incorporated some interesting features (well, interesting to me, anyway) so I thought I’d do a quick post.

A quick warning: if you don’t know what terms like “steering trail” and “front center” mean, this isn’t going to make tons of sense, necessarily. So go google up some bike geometry terminology and come back.

Here’s the basic rundown:

-70 degree head tube, 74 degree seat tube (offset from the BB shell for rear tire clearance). I’ll use a setback post with this bike, most likely a Thomson layback. Trail is at 90mm with a 44mm rake fork, so pretty far on the high side. But that’s what I like – stable and predictable. Twitchy bikes are not for me.

-68mm BB drop/11.9 or 12″ BB height, depending on tires. I like my BBs low, and I’m not a big pedal-strike complainer. This is quite a bit lower than I would normally build for a customer planning to run 175 cranks.

-20.5″ seat tube, 6″ head tube, 23.4″ effective toptube. Why such a weird combo of attributes? Well, I’m 5’11” tall with a ~36.5″ inseam (with my shoes on). That means my BB to saddle measurement is 81cm – and to get the bars anywhere near saddle height, I either need a huge stack of spacers (ugly), a giant riser stem (fugly) or a long head tube. I chose the long head tube here. Standover is pretty high at about 32″, but that’s not an issue for me. And I need the short-ish toptube to keep the front-center reasonably short with the slack head angle. Also, that way I can run a 90 or 100mm stem comfortably.

-Black cat swinger dropouts (more thoughts about them in another post, once I’ve had some time to ride them) with 415mm (about 16.5″) effective chainstays. Yes, I’ve apparently joined the short-stay mafia. And yes, the tire clearance is fine. With the wheel slammed forward all the way, there’s reasonable clearance for a 2.3, and with it pulled back a few mm to tension the chain, I think pretty much any tire on the market would work fine. I may very well pull the dropouts way back and run something closer to 440mm chainstays, but this gives me the option of going super short just for fun.

-I’ll probably add a direct mount front derailleur mount (it’s pretty low profile) and I’m using dropouts with a hanger, so if my knees give out, I can put some derailleurs on. Of course, that’s what I did on my last SS frame, and I never actually used the hanger, so we’ll see.

This frame was inspired by conversations with my CB friend Matt (who is far and away the best technical rider I know) about how he wants a 29er version of his favorite frame – the trusty Chameleon. It’s a VERY close replica of that geometry, tweaked to fit me better and for our local trails (ie, the steering geometry and wheelbase are very similar, but the BB is lower and I’ve made the frame really tall to accomodate my long legs).

I *should* have it assembled enough to ride later today, if all goes well. Perhaps more pictures then.