February 9, 2012

Pictures and words for Cody

I figured if Garro can throw frames in the snow to take pictures of them, so can I, darn it!

Seriously, Cody, don’t freak out, it won’t hurt anything.

This is a singlespeed, rigid, no-suspension-ever-no-matter-how-much-you-whine XC bike. It’s an interesting case (and I’ll be very interested to hear how Cody likes it) because of how it compares to his previous frame (not built by me) which he likes pretty well, but I sort of think is not the best design.

So, for reference, here’s the old geometry. Keep in mind, Cody’s not super tall, rides twisty/tight trails, and likes his setup pretty stiff out of the saddle.

As you can see, the bike has a pretty low trail number (73mm) and shortish front center (63cm). So far, basically so good. I did some tweaks to lengthen the front center and add some trail (71 HTA instead of 72), and we decided to lengthen the head tube as well for a tiny bit more upright position/less need for spacers. Both of those changes were intended to address Cody’s feeling that on steep downhill stuff, the bike was a bit scary and he felt like he was potentially headed OTB. So front wheel moves forward, maybe bars go up a little, but not that much. We didn’t want TOO long of a front center or high of a trail number, since the majority of the time, the riding won’t be on super steep DH.

It’s at the rear end that I felt the bike was really odd. 45cm chainstays (that number isn’t shown on the drawing, but that’s what they are) for a rider whose saddle height is 70cm, riding singlespeed on tight terrain? A wheelbase of 107.3cm? IMO, that’s criminally long in this case, so I whacked a full 25mm off of the chainstay length.

The end result is a frame with a bit higher trail number and less tucked-under front wheel that should reduce anxiety a bit in steep terrain. A much shorter overall wheelbase should allow quite a bit better maneuverability on the tight stuff, as well as much easier front wheel lifting and general front-to-back weight shifts (or, if you’re either very talented or very stupid or both and showing off in the parking lot/tossing the rear end around a switchback, back-to-front).

Here’s the whole set of numbers:
-71 degree HTA, 73 STA
-12.4″ BB height, 635mm front center, 82mm trail
-59cm toptube, 45cm seat tube
-Rigid only (didn’t get a picture of the fork, doh) and SS only
-105.2cm wheelbase, 42.5cm chainstays (actual, that’s 42cm effective)
-S-bends (this was the fallback, I had a hard time with doing segmented stays and bailed to what I know, I’ll have to spend some time working on the segmented thing before I sell any to customers) and clearance for a 2.4″ tire in the rear/2.5″+ in the front.

Hopefully the end result will handle pretty much all terrain better than the old geometry – we’ll find out in a few weeks. Could we have gone even shorter on the rear? Yes, definitely. But Cody does like his existing bike pretty well, so I didn’t want to go completely nuts – 25mm shorter is already a huge amount, and at the length we ended up at, life is easy (relatively) for component compatibility and chainring/tire/etc clearance.