Monstercross Bicycle Build / ..

After riding my Schwinn touring bike on more and more dirt trails, I started to encounter the limits of that bike. The skinny touring tires ran out of traction at around 18-20% dirt grades and I found my legs running out of oomph about the same time. I have a MTB, but I find I don't ride it very often, especially on the 15-25 mile road trips to get to and from the dirt trails that I like to ride and I don't like to throw the MTB in the truck to drive to the hills.

So, the goal was to build a bicycle nearly as capable as the MTB off-road and as easy to ride on pavement as my touring and road bikes. So wanted lots of gears (3x10 setup) with really low hill climbing gears as well as decent road gearing. Tires with a bit more grip in the dirt without being dogs on the pavement and disc brakes to handle the descents.

Here is the bicycle I have put together:

  56cm Origin8 CX700 frame, Vuelta 700C Pro SL wheels, 130mm rear disc hub, Avid BB7 disc brakes.  Frame (all steel) came in right at 6 lbs., fork is about 3 lbs. 2 oz.  I liked this frame because of the flexibility it offered, multiple brake options, lots of cable routing options, threaded bosses for water bottle cages, fenders, racks, 130/135mm rear hub spacing, set up to run either geared or single speed, clearance for 2 Shimano SLX M660 crank (20-32-44) and XTR-M971 FD, HG-62 cassette (11-36) and XT-M770 Rapid Rise/RD.  The RR/RD makes shifting to lower gears going uphill easier and also sets up the front/rear shifters to shift in the same sense. A 44cm Ritchey Biomax bar, RetroShift (Tektro) brake levers w/ Shimano SL-BS79 10sp indexed bar end shifters, Schwalbe Marathon Mondial 700x40 tires.  The shifters are set up that thumb pressure shifts to a lower gear ratio and finger pressure shifts to a higher gear, same for front and rear.  I am really liking the feel of the shifters set up like this.  The rear is fully indexed (10 speeds) and the front is basically in friction mode, although it does have a detent for the middle ring.  I have since adjusted the FD shifter so that it sits out at about 45* in the small ring, straight down in middle ring and about 45* inward in the big ring.  The RD shifter is shown in the big cog position and by 4th gear is pointing downward and swings all the way inward in 10th.  One other thing I like with the shifters, is the lever position functions as a gear indicator.  To keep the shifters and brakes working well with time, I ran full length Gore RideOn sealed cables. To improve the 50mm chainline of the MTB crankset, I pulled the 2 - 2.5mm spacers on the drive side to give a 45mm chain line.  Instead of one spacer on the non-drive side, I needed to run 2 since the crank bottomed out on the splindle splines.  Plenty of chain ring clearance at the chain stays, even with the crank in close like this.  I later narrowed the spindle and removed these 2 - 2.5mm spacers to center the crank. As a result, with the 43mm center on the 10-sp. cassette, the small ring lines up about even with the 4th cog, so the small-large combo is not far off.  That low gear is really nice for spinning up the steep hills, gives me a 15.2  

  To fit a 20 tooth small chain ring on the crankset, I shaved 2mm off the head of the crank bolts, from 12mm to 10mm OD in a lathe.  Then using the smaller bolt head as a guide, I used a flat file to take down the top of the crank boss to match the bolt head.  So in all took off 1mm of material. This was enough to let the chain links seat fully onto the teeth of the small chain ring.  Swapping from 22 to 20 teeth dropped my low gears 10%. In order to make a 9 speed MTB rear derailleur to work with an 11-36 tooth 10 speed cassette, I had to put in a longer B-tension screw (pretty much dead center in the image).  I used an M4-16mm screw and it seems to be long enough to do the trick, moving the RD jockey wheel enough to just clear the 36 tooth cog. And yes, this a Shimano XT Rapid Rise 9 speed rear derailleur on a 10 speed cassette and it is being shifted with a 10 speed road bar end type shifter and it works perfectly.  I also added a Hanger Banger to the skewer to help add support to the RD mount.  You can also see the Gore RideOn sealed cable attached to the shifter.  So far the fully sealed cable and grub seal seems to do an excellent job of keeping dirt out of the cable.  I really like the 10 speed cassette.  It has 2 tooth jumps from 11-21 so rides a lot like my road bike at higher speeds, then the 24-28-32-38 tooth cogs are great for the hills.  I can physically shift into all 30 gear combinations, although the chain is really slack in the small-small combo so I only use the big 7-8 cogs with the small ring.  Likewise, the chain angle is pretty bad in the big-big combo, so I usually avoid that as well, so that leaves 27 useable combinations.  I generally shift the front for conditions; small ring on steep hills, big ring for the flats and middle ring for everything else.  Then with 10 cogs in back, you can shift up and down and almost never run out of gears! First test ride in the hills, this is a shot descending the Stevens Canyon trail near Cupertino, CA. after climbing Montebello Road.  Really impressed with the grip of the Marathon Mondail tires.  Started running them at their minimum pressure (50psi) and they felt a bit hard, so dropped to 45 then 40psi.  They felt better at 40, but am still lowering the presure slowly, and now at 32psi and they work as well on the trail as on pavement.  Also installed an XFusion HiLo dropper seat post so it is quick to drop the seat up to 4  

  Single track riding on the White Oak Trail in Montebello Open Spacer Preserve.  Rode up Alpine Road from Portola Valley after a tour of the Military Vehicle Technology Foundation.  Then down White Oak and Stevens Canyon trails back to Cupertino, about 10 miles of dirt riding.  45 miles and almost 4000 ft. of climbing: Shot from the saddle between Mission Peak and Mt. Allison east of Milpitas, CA. on a ride along the Bay Ridge Trail from Ohlone College to Ed Levin county park. 43 miles and 3100 ft. of climbing: Finally getting out on some longer and tougher rides.  This one south on Hicks Rd. then north on the dirt Woods Trail and up the flanks of Mt. El Sombroso.  Caught this view of the quarter moon rising over the old radar tower base ( View from top of Mt. El Sombroso (2999') looking south to the top of Mt. Umunhum and the A few minor changes, first added a set of cross brake levers, those are great for those long fireroad descents.  Also chnaged to a 60mm stem from my original 100mm.  After about 1200 miles of riding and going lower and lower on the tire pressure, I decided to give tubeless a try.  I had wanted to get a set of wider rims for the 40mm wide tires, and the Stans ArchEX at 24mm seemed like a good fit and the 135mm wide rear hub fits right in place and improves the chain line about 2.5mm over the 130mm hub.  

  So I mounted up the Marathon Mondials on the ArchEX rims and the fit like a glove.  Didn't put in enough sealant the first time so had to pump in another ounce with a home made injector.  They are now sealed up nice and am running 27/30psi F/R and the ride is nice but still fast and easy on pavement.  I tried as low as about 25psi (rear) and found I bottomed out on a fist sized rock at speed, so it seems 28-30psi in the rear is the lowest I can safely go.  I've seen 1-2MPH faster than the same tires w/ tubes on some flat and downhill pavement sections.  

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