Stumpjumper Expert Carbon 29 on a Diet.

My bike has seen a lot of modifications since it first left its boxy womb. I think it has about 3 stock parts left, if you count the frame and fork. I thought it would be fun to chronicle a bit of it since I’m a weight weenie and spend far too much time lurking web sights looking for light ideas. I should point out this is my race bike. A lot of this stuff is pretty durable, but most of the choices I make regarding what I use are based on weight reduction more than the need for long-term durability.  Having said that, racing is hard on parts and I want them to work flawlessly during a race, but I don’t buy lightweight race tires and expect to get a year’s worth of riding out of them.

It’s really cool that a guy can go to his local shop and buy a mountain bike off the floor that weighs under 20lbs stock. Frankly, that’s a pretty big deal. However, I like personalizing my bikes and one of the best ways to do that is to buy a new bike and switch out a bunch of the parts before my wife realizes what I’ve gone and done…

I suppose this post will… be just fine. ahem.

Gordon at B&L Bikes had some great ideas and was instrumental with my project and really helped dial it all in. Dude’s a master at tickling out those hidden grams. I like light, but my shits gotta work, too,  and he had it nailed. Thanks! If you’ve been riding a while, a lot of this stuff you can probably already do, either by cannibalizing a current bike or digging through your bike box with a bit of imagination.

Starting with a Stumpjumper Expert Carbon 29 in size XL ringing in at about 24.6 lbs, we cut some big weight just by pulling the tubes and swapping the heavy stock cassette for an XT 9spd I had lying around. Switching to a carbon bar and lighter stem also helped.

One of the biggest places I saved weight was by switching to the S-Works double crank.

This alone saved about .5lbs from the XT triple.

Though I suppose that crank might not be lying around in your bike box… I really think this crank played a big roll in how my bike eventually got to the state it’s in now. Once I felt the awesome potential of the double up front, I became more motivated to adapt my entire drivetrain to match. But at this point I think my bike was hovering around the 23-23.5lb mark with pedals.

That was a pretty good weight and it stayed like that for a while. I made some more mods, but they were more about improving shifting performance in the front than losing weight. I put XX rings up front and ended up putting a XX frnt der on as well which gave me super reliable front shifting. The only problem was I had to use an old twist shifter to work the front der properly. It worked fine, but I’m a trigger guy.

I also cut the excess steerer tube:

Lighter saddle and post:

Especially with Thomson Ti hardware:

And my bike was sitting happily at just under 23. At that weight, my bike was really feeling fast. A little weight reduction makes a huge difference. So much of mountain biking is breaking and turning and climbing and accelerating and lifting and hopping.  Every time you do any of those, a few grams here and a few grams there are working against you, even if just a tiny bit. But you add all those small changes in movement together over your ride; it accumulates into hundreds if not thousands of additive repetitions wearing you out. Sure, if you take 30g off your bike, your not gonna feel a thing, but if you do that in ten different places, it makes a difference.

And wheel mass is the most critical mass to lose. For simplicity, just think of it like this:

Imr2

where the objects resistance to change (accelerating your wheel) is equal to the mass of its outermost weight (your rim and tire) multiplied by the radius of your wheel squared (yep, squared!). For a 29er, that can really add up. So of course, you need light rims and tires.

I chose Stans new Crest rims and had them built up with an old set of American Classic hubs to get me a 1507 g wheelset. Not ridiculously light, but strength and durability were also an important consideration since I plan to race Breck Epic with them. Even so, I saved almost an entire pound by switching to the new wheels. And that is something I can absolutely feel every time I turn my cranks.

Other fun weight weeny activities which weren’t remarkably expensive include:

Ashima rotors are a bit lighter than stock. Not as light as alloy, but a fraction of the price. Add some Ti hardware and your good to go. I should mention I prefer the performance of the Avid rotors but for two-hour Kenda Cup races, they are fine.

Gold alloy bolts for all the brake connections saves some weight on the race bike and looks sweet, taboot.

Oh, and I switched to a 140mm rotor in the back.

Plus, the gold bolts match my gold nipples! Everyone has red these days.

Alloy bolts for my levers, too. Ti bolts for the stem. The ESI grips are light, comfortable, and come in my favorite color. The Campy top cap is one of my favs.

So what with the wheels and all my sparkly bolts, my bike was down to 21.89 with pedals and bottle cage.

At this point, I was pretty much done.

Until I held this…

The XX cassette. Once I put that in my hand, I was a goner. That thing is light!

I had planned to upgrade to a 10spd drivetrain eventually, but my 9spd was working so well, I really hadn’t planned to do it so soon. But, well, you know… Breck epic is coming and I just need that 36 tooth in the back.

Which, with pedals and cage, has my bike down to this

Whoa Nelly! Pretty good for an XL 29er. Sweet, especially since the Conti Race King tires on there are 70g heavier ea compared to Specialized Fastrak LK S works tires.

Well at this point my bike is pretty sick. Without question the best mtb I’ve ever owned, and most of the parts are durable, real-world parts.

Word.

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10 Responses to “Stumpjumper Expert Carbon 29 on a Diet.”

  1. Wow, what a diet! 😀

  2. Great inspiring read.
    I don’t do too much MTB races anymore (switched to triathlons), so I will keep my 2007 Stumpjumper HT, but this artcle shows how much you can actually do even if the frame has to take into account aero and durability as well…

    Good luck in your racing

  3. Hey Ben,

    Just found the website. I was wondering what twist shifter you are using and how light it is. I have an XX crank/rings and was wondering if I could shed some weight there from the double triggers I have there now. http://www.sram.com/node/122/brand/sram-road/src/cat

    Thanks and great racing as of recent!

    • bencycles Says:

      Hey Robert,
      The twist shifter was borrowed from one of the guys at B&L Bikes until I could get my hands on XX triggers. I think it was XO from a couple years ago… Not sure of the weight of the twister but modern trigger systems are pretty light.

  4. when you first swapped your crank, did you get decent shifting with the stock triple shifter and f/d?

    • bencycles Says:

      Hey Myk,
      The shifting itself was decent, but because the cage of the stock front derailleur was designed for a triple, I had to run the derailleur high above the XX big ring because the triple cage was hitting my chainstay before I could get it any lower.The frnt der wasn’t doing a good job of keeping the chain on the big ring in rough descents and I was dropping chains. It worked fine just riding but in races I got burned a couple times.

      I have also been able to sort of run a triple shifter pod with the XX frnt der in a couple different methods. The first was using an old twist shifter for the front, which worked fine. The other happened when I was racing Breck Epic (awesome race!), I crashed really hard the first day and broke my XX shifter. All I could find in short notice was a Shimano triple shifter pod and the mechanic at the race (full mechanical support, again, awesome race!) was able to get it working well enough that I raced the entire rest of the week with the system.

      I know some guys that also used road frnt der’s (before 2X10 was available) successfully as the cage is more amenable to the double, I think.

      So, short answer: if you aren’t racing or the descents aren’t too rough, I think you could get away with it for a while, but having the dedicated shifter/der was an improvement.

      Hope this helps.

      Ben

  5. Where did you find the alloy bolts for the brakes..etc and what difference did you see when changing to the 140mm rotor in the rear brake

    • bencycles Says:

      Hey Sean,
      First, I should point out I’m 165 lbs with shoes on and I use these alloy bolts (especially for the calipers) on my race bike which I usually only use on race day. For all around durability, Ti or steel is a better way to go. I also replace the critical bolts such as brake caliper and brake lever pinch bolts each season. I haven’t used alloy bolts for my rotors, only Ti.

      OK, having said that, I’ve had good luck with this supplier:
      http://www.torontocycles.com/
      All the anodized goodness you could want.
      Your brake calipers probably mount with M6 bolts. You will want to measure how long the original bolts were and match them up. Other bolts, like water bottle, shifter and brake pinch bolts are usually M5.

      The 140 rotor saved a little weight but there is a bit less power in the back. I think it’s more noticeable since I’m using it on a 29er. Everything is a trade off and you have to consider where and how you’ll be riding. For longer, bigger events, I’ll go bigger. I have a selection of rotors between 140 to 185 and I’ll set up different combos for different courses.

      Keep in mind, I really like tinkering with my bikes/suspension/wheels and I swap stuff out a lot. Plus I am a bit of a weight weeny. I really like trying out different stuff. If you just want to forget it and ride, I’m not sure all this is worth the bother, but for me, I find it to be lots of fun.

      Hope this helps.

  6. NM_MTN_BIKER Says:

    Will you help a fellow Stumpjumper Expert Carbon 29’er out? What size bolts did you order from Toronto Cycles? I want to replace the ones around the disc brakes and the ones around the trigger shifters and the brake levers. Basically same ones you did. I would rather not have to try to figure out how to measure them.

    I see that you have the size of the bolt but not the length?

    Thank you!

    • bencycles Says:

      Sorry for the slow reply. I don’t remember the specific lengths for them but you can pull one bolt at a time from the calipers and measure from the base of the head to the end to get length without messing up the caliper position.

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