Sunday, June 17, 2007

Quick weekend race report and new DH bike stuff

Out at the NMBS race at Park City, Fuentes was 18th and Yuki was (I think) 54th in the pro men's field.

Sarah and I stayed closer to home and raced the second Winter Park Series race - I got sprinted at the line (if you're going to have to finish on 1/4 mile of flat fire road, a 34x20 gear doesn't cut it, folks) and ended up 2nd, and Sarah won her category in expert for a second straight week. Best of all, we won some pint glasses, which is good because I've broken quite a few of ours in the last year or so. The course was fantastic, the turnout was killer (530 racers, and that doesn't even count the folks who dropped out and DNF'd!) and we went to our friend Aurora's place for homemade sushi and beer afterwards - you can't ask for a better day than that!

I didn't get any pictures, unfortunately. No racing this coming weekend, so I'm guessing we'll hit up Keystone for some DH riding.

Speaking of downhill bikes - I just got done building version 3.5. I was (and remain) very happy with the True Temper Supertherm (thanks Ben!) front triangle, but there was more lateral flex than I would like in the original rear end. After some surgery on the Shimano 105 bottom bracket that I was using, I realized that the crank shaft on the external bearing Shimano cranks runs on a PLASTIC sleeve - which requires a massive amount of contact area from the crank arm to be stiff enough to work. The sleeves with pinch bolts that I was using weren't providing enough area, and were actually digging into the plastic, causing a bit of noodlieness (though in all fairness, it was hardly noticeable to me when actually riding). Still, since my goal with this bike is to build something that I would (if I weren't a framebuilder) actually pay retail price for, and the original rear end wasn't cutting it. The super ghetto dropouts that I made from angle iron weren't so great either, and the whole thing was too wide - I hit my calves on the stays when pedaling (annoying), so I sat down and did some thinking about what to change. The original rear end went into the scrap bin last week, just so I'd have to get my butt in gear and build a replacement.

Here's the end result. The new bearing setup uses an 22mm axle FSA BMX bottom bracket (bearings are inside the shell, but it still uses a through-axle). The non-external bearing setup allows the rear end to be almost 20mm narrower, which solves the heel/calf clearance issue, and it also *doesn't use any plastic load-bearing parts*. That's key! The bearing races are steel and the cranks (or in this case, the sleeve clamps) press directly against them. Killer.

As you can see, I haven't really cleaned up the fillet brazing yet, nor had time to powdercoat the rear end. Apparently, my camera also decided to focus on everything *except* the bearing/axle/pivot setup, which was what I was trying to illustrate here. Hopefully you get the idea.

Ultra-ghetto angle iron drops were replaced with Surly Instigator dropouts (which happen to match up quite nicely with the stays) that I machined out to 12mm to accept the 12x150 hub.

I also shortened the effective chainstay length to 435mm (or about 17") from 450mm. I have a hard time telling the difference, but all the hotshot downhillers tell me that short stays are good on a DH bike, so what the heck. The only problem is that I want to run a front derailleur, and the el-cheapo LX e-type one on there now (the weird seat tube won't allow a conventional clamp-on setup) only gives the tire about 5mm of room. Doh. Whenever something more DH-appropriate than the Nevegal comes out, I will probably have to scrap (or heavily modify) the front derailleur. I imagine going to 1x9 wouldn't be so bad, but I'd like to have the granny option for when I want to ride uphill. The frame itself will take up to about a 29x3.0 without any problems, of course.

Oh, and for the record, the new rear end is SUPER stiff laterally. As good or better than any full suspension bike I've had. Weight might be a tiny bit more, but I've swapped some parts around as well, so it's hard to compare - the complete bike is still around 37 pounds, frame is about 10. Plenty light enough for what I want to do, which is mostly ride the chairlift up and haul ass back down. I'll try to post when Sarah and I plan to ride at Keystone this summer so that folks interested in a test ride can meet up with us.

1 comment:

ssportsman said...

you wouldn't have been out sprinted at the line if you had climbed faster earlier in the race :D

Good job.. I ran into another Walt SS this past weekend. I didn't get the owner's name, but she won the women's solo ss category at the 12 hours of SoCal on an orange WW..