Should I worry about ~1'' in axle to crown length?- Mtbr.com
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  1. #1
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    Should I worry about ~1'' in axle to crown length?

    Hello and thank you for checking out my thread. I thought you guys would be more knowledgeable than the speculation and nonsense that goes on in the fatbike forum.

    Here's my situation, I have a first gen. pugsley and recently upgraded to a salsa enabler fork. all is well, been running it for awhile now but I just noticed it has a 468mm axle to crown where the og surly has a 447mm axle to crown.

    I understand how this elevates the top tube, slackens the headtube and slows the steering but am I placing undue stress on my headtube and or headset?

    Surly posted this on the matter: Blog | Surly Bikes

    Am I worrying about it too much or is it a real concern?

    I ride this thing quite a bit, year around and xc too. Have a CK headset on it.

    Thanks in advance!

  2. #2
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    the numbers

    It's a bit of a difference. I put the numbers into BikeCAD and here's what it came up with.
    These #'s are with Endomorph 3.7" tires.

    Pug with stock fork -
    headtube angle = 70.5 deg
    Seat tube angle = 72 deg
    BB height = 12.4"
    Trail = 85mm.

    Pug with Enabler fork -
    New HT angle = 69.4 deg
    new ST angle = 71
    new BB height = 12.75"
    new trail = 91mm.

    For the fatbike in winter, you may not notice too much of a difference since the fat tires kinda "dull" the details IMO. But if this is your summer XC ride, I'd be surprised if you didn't notice a big difference. In my opinion, it went from being a already slack-ish bike to something in the "trail" bike category. The BB isn't terribly high especially when you account for fat tire sag, but I'd be surprised if you didn't notice the increased front end trail figure (theoretically worse at slow speeds, better at high speeds).
    All those numbers change though if you put on a Big Fat Larry on the front or something bigger than the tires in the 3.7" range. It'd get even more slacker so I wouldn't recommend doing that. You can always get a Mukluk to keep it consistent between brands and what they want you to ride.

    About the Surly warranty: the stock Pug isn't a suspension-adjusted frame/fork. So this is probably why they void the frame warranty with a longer/suspension adj fork like the Salsa or White Bros. This is because they are probably worried about the longer 'lever' up front and that could compromise the downtube (buckle it). But Surly tubes are plenty strong (thick) so i really wouldn't worry about that part of the equation...

  3. #3
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    Hey;

    Whit has a good technical critique, and common sense outlook. I doubt you are going to break it. The trail at around 3.5" is right in the "normal" zone. The HT angle is a tad slack for a snow bike, but not nuts for a trail bike. It comes down to the ride in the end. Even if it does feel a little weird at first, you'll likely adapt, and it might even make it a better trail bike.
    Most people ply the Well Trodden Path. A few seek a different way, and leave a Trail behind.
    - John Hajny, a.k.a. TrailMaker

  4. #4
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    Quote Originally Posted by western high plains View Post
    Hello and thank you for checking out my thread. I thought you guys would be more knowledgeable than the speculation and nonsense that goes on in the fatbike forum.

    Here's my situation, I have a first gen. pugsley and recently upgraded to a salsa enabler fork. all is well, been running it for awhile now but I just noticed it has a 468mm axle to crown where the og surly has a 447mm axle to crown.

    I understand how this elevates the top tube, slackens the headtube and slows the steering but am I placing undue stress on my headtube and or headset?

    Surly posted this on the matter: Blog | Surly Bikes

    Am I worrying about it too much or is it a real concern?

    I ride this thing quite a bit, year around and xc too. Have a CK headset on it.

    Thanks in advance!
    I would not worry about any extra stress on the frame.
    mtbtires.com
    The trouble with common sense is it is no longer common

  5. #5
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    It's not going to cause any damage to the frame. The question is do you like the way it handles with the new fork?

  6. #6
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    I really appreciate the input, guys.

    I've been riding it like this since September and I like it alright. The thought of it handling better though is enticing considering how much I ride it. I suppose I'll keep it in the back of my mind.

    As far as voiding the warranty, I'm sure I'm already outside that window (second hand '09 frame.)

    Thanks again frame friends, come over to the fat side sometime!

  7. #7
    bee
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    Rough guide would be for every 10-12mm change in axle-to-crown length, there is roughly a 0.5 degree change in HT and ST angle.

    The real problem is that a change in axle-to- crown royally screws up the BB drop.

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