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Thread: fork mod.

  1. #1
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    fork mod.

    I'm new to the whole mountain bike scene......have an extensive background in bmx..........

    My biggest hurdle has been learning to trust all this aluminum and super light weight stuff......

    My biggest issue at the moment is forks.....

    I'm running a marzocchi bomber all mountain 3 fork...
    ?.....my biggest fear is breaking the aluminum steer tube.........

    here is my idea........machine a steel insert and do a light press fit in to the stear tube............

    maybe over kill ....but just lookin for alittle bit of reasurance...lol

  2. #2
    FKA Malibu412
    Reputation: Glide the Clyde's Avatar
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    Yes, that's 3 skepticals

    Don't worry. Unless the al steerer is compromised in some way from stress, it will stand up to normal riding and airing it out some. Planning to do huge air and drops? If so, a bigger bike with a double crown fork might be more suited.

    Whatya planning to do?
    Everything that kills me, makes me feel alive

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    Not planning to do anything spectacular.......lol

    I rode vert ramps and did a lot of jumping back in the day so airtime doesn't scare me ...........until I got on a mountain bike I've never seen an aluminum steer tube on forks......scares the hell out a me , lol

  4. #4
    FKA Malibu412
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    The steer tube should be fine if riding the bike the way the fork is designed for. But hey, if you're handy with a lathe or know someone who is, have at it. Just be exact in determining tolerances for the press fit so the sleeve doesn't expand the steerer if too oversized or fall out on a ride and jam itself into the front tire if too small. It will add some weight which most mtber types are kinda sensitive to.
    Everything that kills me, makes me feel alive

  5. #5
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    Quote Originally Posted by Glide the Clyde View Post
    The steer tube should be fine if riding the bike the way the fork is designed for. But hey, if you're handy with a lathe or know someone who is, have at it.
    Have to disagree. If the insert has any effect on the strength of the steerer tube at all, it will be to weaken it. The insert will change the loading on the steerer in ways it wasn't designed to handle. If the steerer fails, the fork is going to fail, with or without the insert.

    OP if you are that worried, you need to find a fork with a steel steerer. Or, what I'd recommend, do some searching and see if you can find a single case of a properly installed fork steerer failing. It seems to my engineer-brain that if aluminum steerers were a problem, you'd see a few failures around, considering 100% of middle to high end forks made in the last 15 years or so have had them.

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    What do you weigh and what kind of air/jump/stunts are you riding ? The bomber should do just fine. Running 26" wheels? Try the Fox vanilla 36er or any other dj type of fork. For regular trail use it should be fine.

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    I'm sure it's all in my head......comin from a bmx world I'm just not used to seeing so much aluminum in such high stress areas.......lol...

    Oh and I'm 43.....6'4" and a slim 270 lbs.....big yes....fat no.........I'm big boned.....hahaha...............but I'm surprisingly smooth on a bike.......I've been riding pretty hard core since I was 11 ............

  8. #8
    turtles make me hot
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    I'm about exactly the same size as you, Glassman. Don't worry about it. I have never broken an aluminum steerer.
    I like turtles

  9. #9
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    Quote Originally Posted by the glassman View Post
    I'm sure it's all in my head......comin from a bmx world I'm just not used to seeing so much aluminum in such high stress areas.......lol...
    That's just the thing; it's not a high-stress area. It's fully supported by bearings. I believe the only reason bmx bikes don't use al steerers is the fork legs need to be steel and are usually welded to the steerer. A handlebar is much more heavily stressed than a steerer and it's been 20 years since anything but a wal mart bike had a steer bar.

    Look around for pictures and video of people doing crazy $hit, and keep in mind every one of them is on an aluminum steerer. I can't say that enough: there are millions of al steerer forks out there because that's all suspension forks have had for nearly 2 decades, people doing stuff a sane person wouldn't dream of. I've seen more frames shear in half than failed steerers.

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    Ok.ok I'll relaxe...lol

  11. #11
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    A little late to the punch, but in case there are still any anxiety issues...

    BMX forks are designed to handle *very* missed landings on a hard packed surfaces, and extreme port/starboard stress. If a jump goes off wrong and a racer lands front wheel first, misjudging double-jumps and clipping the apex, etc. As smooth as they look, BMX tracks are extremely hard and the bikes and riders, and they can put as much stress on their gear in a paved turn lasting 3-4 seconds as we do in a four foot drop on the trail that lasts half a second. Try riding your trail bke on a BMX track. I suggest you take it easy to protect your gear.

    Trail, et. al. bikes do not transmit anything close to those forces to the steerer tube, unless you are rotated way forward, in which case you are in trouble. Unlike a bmx track, you don't have a nice, wide, smooth area to recover and/or kiss the ground. It is expected that (on the trail) you will never be as far nose down coming off a jump as you might be on a bmx track.

    That said, I was riding trails on my Cannondale R600 back in the early 90's. With a mere 2.8Lbs wirth of frame and fork, I never managed to bend anything even though I jumped quite a number of very small trees, beat the crap out of myself running through rooted sections, and did a front wheel stand on occasion to show off. No landings were good landings, and some jumps were really bad, but I never did more than blow a tire. I was a heavy boy for a USCF racer back then at 180Lbs.

    Most of aluminum trail steerers are 7000 series, which is stronger than mild steel. They tend to be thicker than one would use with steel to provide a higher fatigue life, making them even stronger than their steel equivalents. Having worked with 7050, I can attest that it is some seriuosly tough you-know-what, and I'd rather drill mild steel.

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    Since I posted this geared up and said f - it and just rode........so far so good........I've done some pretty big drop ins......nothing to flat because I just don't see the point in riding off a ledge onto a flat surface...I prefer to land on a slope.........my fear of the unknown and new has left the building...lol.........

  13. #13
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    Glassman, I hear ya. I have BMX background also (tracks not vert or street)
    I've seesawed from 220 - 260lbs over the past 10 years riding. I ride what I'd call the conservative side of aggressive (baby steps on drops till I'm comfortable, nothing huge in terms of jumps, etc, but I charge and rail what I have become comfortable with). My biggest fears in terms of mechanical failures are handlebars and steerer tubes.

    In terms of builds, anything I build is what most would call overbuilt, but that's my nature.

    Like I said, have been riding for over 10 years. The tech these days is pretty good. You mentioned riding a Marz AM fork. They stopped making these several years back, maybe 06? They are also pretty long legged too, 150-160mm? or do you have the 130?

    With you being heavier (regardless of fit or fat) and the fork being older, you may want to consider budgeting for a new fork in the near future - say this year or next. You can catch great deals online at the end of every season, say Oct-Feb. If your frame will accept it, I strongly suggest a tapered steerer. In the meantime, I'd watch for any signs of fatigue in the current steerer (headset creak, headset loosening, maybe every month or so pull the steerer out of the head tube and visual check). If something doesn't sound or feel right, check it out! If you ride big or hard, know how to maintain our gear and stay on top of it.

    Some may call this extreme or unwarranted, but aggressive riding and heavier weights do wear equipment in an accelerated manner. I'd also also rather be excessive in safety than have to wear dentures well before my time. Just another point of view.

    Also, if you dont already, pads and other safety gear can save alot of pain and keep you on the trails longer. From the great wisdom of Voltron - the bigger they are, the harder they fall.

    Good luck, ride safe, have fun!!!

    Also, not meaning to scare anyone (I totally agree that forks these days are strong and safe, and failures are corner cases) but there have been steerer failures as well as other fork failures. Bottom line, know your gear, and if something doesn't seem or sound right - check it out!! We put A Lot of faith in this equipment, and if neglected, it increases the odds it will fail you when you need it most.

    This poor guy must have had the bolts come loose or drop on his lowers.
    Insane downhill crash - fork broke midair! - YouTube

    Steerer failure
    Dead Fork Crash - YouTube

    Steerer failure
    forks break - YouTube

  14. #14
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    Also, I agree that the proposed mod of the fork would likely make things worse.

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