My Motobecane Fantom Ti Boost Setup-
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  1. #1
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    Sep 2012

    My Motobecane Fantom Ti Boost Setup

    The limited information on this Motobecane Fantom Ti Boost bike here and elsewhere on the internet have been immensely helpful. I am going to go through what I was thinking in buying the bike and my reactions to it.

    First off, thank you to those who have posted here about their experience with the bike. The discussion about the low bottom bracket and some unrelated discussions in other forums led me to buying the frame/fork version and immediately buying a 120mm fork. Incidentally, I didn't buy a Pike, I bought a 2019 SID.

    I felt like the complete bike in 27.5+ (which is what I was looking at) had a lot of question marks. The hubs - is the Novatec rear hub going to hold up? Hmm, dropper seatpost (I want to try it), but there are some questionable reviews on it on Amazon. The complete bike has a fork I may need to trade out for a longer one and it will already be cut to my size (incidentally I thought the frame/fork version would be cut too, but it comes completely uninstalled). The seat, grips and handlebars are items I might need to tweak. Also, are i29 rims really appropriate for 2.8 tires? Not when I can buy some wider take-offs for cheap. And the crank, does it really just come in a 175? I ride a 170.

    So I decided that the frame/fork for $1600 were better for me than the built bike at $2500. I bought the SID fork in 120, and I bought some Sun Duroc 45 wheels (i41ish) that have 36 points of engagement. I love the Surly Dirt Wizard tire as a front, so I bought that and I went with the Rekon 2.8 on the rear because it's a fairly well reviewed tire. Chainreactioncycles had an awesome deal on an XT 2x build kit, XT brakes and their Brand X Ascend dropper post has a good reputation. Then I threw on a seat, stem, handlebar and grips that I like.

    Some background on my style is that I have an original Surly Instigator always with a 2.4 or 2.5 rear tire and currently a 2.75 Dirt Wizard front tire. I like high volume mainly for float over sand, but also for dampening. Going to a ti hardtail for arguably more dampening and then doing the plus thing in 27.5 seemed like a way for me to go modern (even though 27.5+ is more 2016). I've also ridden a 26" Jamis Dragon and a 29" Jamis Dragon (Reynolds steel 853 hardtails) and while I liked them, they lacked a lot of what I really enjoyed on the Instigator, which was the power and grip to plow through rough stuff. I also have a Niner Jet 9 and I've felt just a little better on it than the 29er Dragon. I discovered with 29ers the same thing everyone else discovers, that they have better rollover than 26ers, even when the Instigator effectively has a plus tire. So I was hoping to keep the 29er rollover ability on a shorter bike for me.

    I went with a non-boost crank because everything I've read suggests it isn't really that important. What is important with the chainrings is that they are located as close to the frame as possible to preserve chainline, while having them comfortably far enough out to not rub the frame. I achieved this with two spacers on the bottom bracket drive side (within Shimano spec) and none on the non-drive side. The chainrings are 26/36 and they have about 5mm of clearance from the stay, which is what I was shooting for. Notably, the chain does not rub the tire or even come close in L-L. The front derailleur also has plenty of clearance, and what I have is the XT side pull direct mount on an adapter. My cable routing is weird to accommodate the side pull, but no issues. Of note, the frame/fork purchased includes the FSA headset, which is cool, but looking at the bearings, they seem cheap. They're solid enough, but I can see inside them through a gap. I opted to upgrade to a Cane Creek 40 because I trust them.

    Regarding geometry, the head tube angle is right about there with current year other brands, and the seat tube is a little more slack that other brands, so there is just a little bit of marginally outdated geo with that seat tube angle, but I'm good with it. In putting on a 120 fork, I know I slightly slackened both the head tube and the seat tube a bit more. I scooted the seat a little farther forward than I have in my other bikes and have an 80mm stem, and am able to get the same distance from nose of saddle to the handlebar grips as I have on my Instigator, what I consider my honed in cockpit fit. It also allows me easier clearance behind the saddle when descending. So for the fit, I'm very happy. My build came in at 28 lbs, and admittedly those Sun wheels and Ascend post are not light.

    I've put 80 miles on the bike and I enjoy the fit. The steering has been comfortable and the shifting is fine, as installed. The seat position is also comfortable. I also achieve rollover on one pesky climb spot on my nearby trail that I wasn't getting on the Instigator, but would always clear on the Dragon or Jet 9 29ers. The Rekon tire measures around 2.7" and it is fast rolling, but does lack some grip, exactly as stated in their reviews. That was a problem though because I have grown accustomed to my climbing grip, and they are a little less than I wanted in the rugged climbs.

    One other problem, and it seems to be consistent with the 27.5+/29 swappable bikes - pedal strikes. For everything I gained in control with the tires, I lost it all on climbing momentum in my more rugged routes. I figured I would live with it a while and see if I can skillup my climbing to overcome it. But even with the increased fork length and slightly shorter than Motobecane spec crankarms, my pedals are a full inch+ lower than the Instigator.

    So I going to spend three weeks in Mexico at my mother-in-law's house and decided the Instigator was moving to Mexico. I was contrasting my most recent MTB rides on the Moto in CO, NM, TX with the Instigator in Mexico, where the trails are surprisingly great. I wasn't pedal striking. So I thought, the Moto is going to need more clearance if I'm going to enjoy it like the Instigator.

    As a result, I've ordered new hubs/rims/tires to make it a 29er and give me the pedal clearance I need for my skills. I went with XTR/XT rear/front hubs and i25/i35 rims. Motobecane/Bikesdirect says it will fit a 2.35 29 tire. Well on here, people are suggesting 2.6. So I figured something in the 2.5/2.6 range would be a starting point. The fork has clearance for 81 mm tires, which is well over 3.0. So I ordered what I thought was my favorite Surly Dirt Wizard for the front and then realized the listing was actually for a pair of tires. Since I already had my rear wheel assembled, I thought I'd try the Dirt Wizard on the back on a narrower-than-spec rim. The limited reviews on the Dirt Wizard for people trying it an an i25/26 rim have said it worked fine, and of course those who hadn't tried it flamed them. So I put it on and as expected, it rounds the tire a bit. The clearance to the chain stay before the tire stretched was a quarter inch and now it's still about 3/16 of an inch, which is close, but I've long pushed the limits of max tire size. The tire itself now measures about 2.8" wide and 2.3" tall on the i25 rim. The imprint it leaves when compressed at 20psi is 2.9". So when it contorts, it could potentially rub the stay. The 2x drivetrain still doesn't rub in L-L. I would definitely not go anything bigger than the i25 with the Dirt Wizard on this bike, and at that it's not something I'd recommend to anyone because it's already a bit close.

    What I find amazing is that I can actually get the 29 x 3.0 combo on this bike. The downside is that I wanted 27.5+ and ended up overthinking my way into 29+. I don't have the front wheel yet and won't for a couple of weeks, then off to Mexico again. So weather permitting, this stretched out 29+ Fantom Ti Boost isn't going to see dirt until probably March.

    If I subtract out the fork swap cost (assuming I sell the '18 SID for $500), then my cost on this bike came in around $2500 for the 27.5 version or $2600 for the 29 version.
    14 Surly Instigator 2.0
    18/19 Motobecane Fantom ti Boost 29
    99 Marin Pine Mountain
    07 Jamis Eclipse
    13 Surly Pugsley

  2. #2
    mtbr member
    Join Date
    Nov 2012
    Interested to see the finished build. Sounds like you looked into everything, and well have a bike truly fit for you.

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