Project Mini-Mission DH

This is not a DH bike...yet.

The bike I spend most of my time on is my Diamondback Mission. Most mornings I'll go ride XC at Duthie, Grand Ridge, or Tokul. I love that it can be set up to ride almost anything. I usually have mine set up with a Fox 36 up front, RP23 in back, Crossmax wheels, Hammerschmidt, Saint Brakes, 30.5" Gravity Light bars, and a 50mm Gravity light stem. As a downhill racer, I refer to this as my XC bike. I like to have my bike set up like a mini DH bike. I can pedal it to the top, but still rip corners and hit jumps and hard lines on the way to the bottom.


A few weeks ago, I went and shuttled a local NW riding spot. I was with a friend of mine who had never ridden DH, so I gave him my downhill bike to use and decided to use my Mission. I was blown away at how well my mission handled the steep, root covered, DH trails. This turned on a light bulb in my brain and made me think that the Mission might be an ideal DH race bike for some of the more mellow DH courses.

In order to convert my bike to the ultimate mini DH machine, I wanted to change a few things. These would reduce the all mountain ability of the bike, but would make something that would work great for my needs. My wish list went as follows:

1. Slacker head-angle
2. Lower bottom bracket
3. Stiffen the rear end

My initial plans were to run either a shorter eye-to-eye shock and/or offset shock bushings to lower the BB and slacken the head-angle. There wasn't much I could do to stiffen the rear end, but I figured I could build a rear wheel with a bolt on axle that would help a little. A quick side note, when I say I want the rear end stiffer, I'm coming at this after being used to my really stiff DH bike with a 150mm bolt on rear end and am smashing this bike into turns as a pro DH racer whose just shy of 200lbs. I am putting a lot of force into a bike that wasn't intended to be raced downhill. 95% of riders would never notice these flex issues, but this is my dream list. I figured I would try and make it feel more like my DH bike.

Prototype swing arm on the left, production swing arm on the right

Diamondback does a lot of testing of frames and parts that will never make it to market. They produce prototype parts for the proof of concept and to just see how various ideas will work in the real world. One of these pieces was a new swing arm for the Mission. DB had made a new assembly to test how much stiffer it could be than the current set up. The swingarm also had the new 142mm through axle standard to test as well. As soon as I saw it, I immediately asked if I could test it out. This would stiffen up the rear end just as I was hoping! Unfortunately, I found out it was designed only as proof of concept and would actually hit the seat tube under full compression. After talking with Mike Brown, the brand manager for Diamondback, he said I could try and make it work and gave me some different sized shocks to play around with and hopefully find a solution.

150 mm thru axle from an old Giant DH Team, cut down to fit the new 142mm rear end.

I went home and immediately bolted it on my Mission to see how much it was hitting the seat tube. Under full compression, it luckily almost cleared the seat tube. I talked to Mike again and he told me I could do whatever I wanted to modify it! I took a file and started filing the weld to make it clear the seat tube. A few minutes later, I could see light all the way around under full bottom out. After lacing a new wheel to a 142mm hub and cutting down a 150mm through axle to fit, I had a ridable bike. It still had stock geometry, but it had a much stiffer rear end now.

I didn't have to remove much material for it to clear the seat tube

I took it out for its maiden voyage at Duthie the next morning. Duthie is a great place to test an "All Mountain" bike. It has lots of berms, jumps, drops, and quite a bit of XC trails too. I took the bike out of the van and dropped into the first corners of Step-It-Up. The bike was noticeably stiffer and popped out of the corners with much more exit speed and held its line over the rough with much more precision. I was really excited and decided to see how hard I could push it. I went and hit some of the drops and jumps at the park. While doubling the rock garden at the entrance to the Braveheart trail, I heard a loud CLANG! I figured I had broken something, so I stopped and looked. I had put a slight dent in my seat tube. It was a little muddy that morning and with the dirt packing up, combined with the full bottom out, the swingarm had hit the seat tube. Luckily, it hit the seat tube lower than my seatpost will ever go even when slammed. The frame is solid there and the dent is barely noticeable. No big deal, but I'll have to do some more filing to get some more room here.

Apparently I needed to remove more material than I thought. The minor dent in the seat tube.

Overall though, I was really impressed with the upgrade. The bike feels much stiffer and I'm happy with that. However, the brace hits the seat tube, so that will have to change. I still haven't lowered my bottom bracket or slackened my head angle, so now the next step is to put on a shorter shock. The Mission runs an 8.5 x 2.5 shock stock, so my next possibility is to go to a 7.875 x 2.25. This will reduce my travel slightly, but will really slacken and lower my bike. I'll have to do some major cutting to the new brace, but that's what this project is all about!

As it sits for now.

More updates after the next round of modifications. The goal is to be able to race this bike at the 2nd round of the All Gravity Series at Silver Mtn on June 19th.

-KT