Mini Mission DH part 2.

The completed project!

With the rear end on the bike and working well, it is time to tackle the next part of the equation. I am on a mission (haha!) to lower the bottom bracket and slacken the head angle. My initial thoughts were simple, run a shorter shock and if needed, add an angleset. However, like all good plans, it was never that simple.

The Mission has an  8.5x2.5 Fox RP23 on it. The next  availible size down from that is a 7.875x2.25. this would shorten the eye-to-eye (and lower the BB/slacken the head angle) but it would also reduce the travel of the bike. I didn't really want to reduce the travel, but it seemed like the easiest thing to do. After fitting the new shock and cycling the suspension through the travel, it was apparent that the shorter shock wouldn't work. Installing the shorter eye-to-eye, even with the reduced stroke, was still going to bottom out on the seatstay brace. I was prepared to trim the seatstay brace to accomodate the new geometry, but I didn't want to remove the entire thing!

The basic plan

After doing some simple calculations, I realized that shortening the shock that much would lower the B/B way more than I wanted anyways, so I'm glad it didn't work out. However, I now had to figure out how to still lower and slacken the bike.  The next simplest way would be to use some offset shock bushings. These essentially shorten the shock eye-to-eye length. The only issue with making those is that I don't have a lathe. It's on my list of things to aquire, but I don't have one right now. So that left me with the option I chose; cut off my upper shock and move the shock hole slightly higher.

Sacrificing a perfectly good bike is hard to do, but fun!

I went down to Diamondback and picked up an old medium Scapegoat frame that Billy Lewis rode last year and brought it home to face an unfortunate demise at the hand of my dremel. My plan was to remove the shock mount from the medium Scapegoat and bolt it onto my large Mission. This would move the shock mounting hole higher than stock, therefore, lowering and slackening the bike. The best part with this plan is that I can now change the geometry of the bike just by changing the plates on the bike.

New upper shock mount plate. By swapping plates, I can now change the geometry.

I cut off the upper mount on the scapegoat and after crossing my fingers, trimmed off the upper mount on my Mission. I bolted the whole thing together using some hardware from the local Home Depot. I had to make a new upper shock bolt. I luckily have a few old frames laying around my apartment. I had an old Transition Gran Mal frame that had a longer 8mm shock bolt that would work. I cut it down to size and assembled my contraption. I had to shave down one of the bolts to clear the end of the shock, but after a few minutes with the Dremel, that went together with ease.

I was really hoping I didn't just ruin my frame.

The hardest part was lining up and determining where to drill my holes. I didn't draw any of this out on paper, I didn't have any measurements, this was a complete estimation project. Fortunately, I was successful in my guesses and after a lot of assembling, removing, and reassembling, I had a complete bike. I removed all of the air from the rear shock and compressed the bike. As I expected, the seat stay brace hit the seat tube. I made some marks with a sharpie and started cutting. I'd trim back about an 1/8 of an inch at a time, compress the bike, trim some more, compress the bike and so on. I got it to the point where it wasn't hitting the frame under full compression. I had to remove about half of the thickness of the seat stay brace. The rear end is still stiffer than the stock offering however, as the brace is now a large "C" channel cross section. The rear end will still barely touch the seat tube if the bike blows all the way through the bottom out bumper, but that doesn't normally happen, and is something I'm willing to live with on this project.

Cutting out the seatstay brace

I had to remove a lot of material, but it's still stiff.

It's hard to see, but I had to grind down around the seat stay/knucklebox pivot too.

 The bike is now complete! The final geometry is now a 13.3" BB height (with the longer travel Fox 36 fork), a 65.5* head angle and a stiffer rear end. I managed to hit all of my goals with the project, won a DH race on the bike, and had fun making sparks in my living room! The bike is a little harder to pedal uphil with the new geometry, but a blast on the way down. I'm not racing XC with it, so I don't mind a little more of a workout on the way up. I'm going to keep this bike around and put a chainguide on the front to make it even more DH worthy. Hopefully some of these changes will be able to trickle down over the next few years and end up as features or options on future Diamondback models.

The blue tape on the shock is the size. I had 3 different sized RP23's and wanted to make sure I was measuring the correct one.

 Since I wrote this story, I've been hammering on the bike without any issues. Simon is currently riding it in Whistler and sent a message saying that the bike is awesome! There has been enough interest in the bike that there is talk of making a few Mission prototypes with this geometry to test out (Obviously with some refinements). Hit up the DB facebook page and let them know if you want to see this thing go into production, otherwise, I'll be the only one who gets to enjoy this set up!

-KT