Wheel size and Head Angle- Mtbr.com
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  1. #1
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    Wheel size and Head Angle

    Currently I'm riding a 6" travel bike (Banshee Rune) with a 66 degree HA. I will be buying a 27.5 frame soon, probably Ventana's Zeus, and running it with 160mm of travel. I 'm a fairly aggressive rider (lots of time on trails like National in Phx) though not extreme. I absolutely love the HA on the Rune and want that matched on the 27.5 bike I build. Most frames offered in 27.5 seem rather steep to me (67 - 8). I was planning on getting Ventana to slacken the HA on the Zeus for me. Before I do however, I was wondering if the bigger wheel size compensate for some of the steepness I perceive and actually make the bike slacker.
    Thanks

  2. #2
    orthonormal
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    You want to match trail more so than head angle. Trail is the distance between where your steering axis intersects the ground and the center of where your front wheel touches the ground. More trail = more stable.

    trail = [(wheel radius) * cos(head angle) - fork offset]/sin(head angle)

    Fork manufacturers are using different offsets for different wheel sizes these days (not true when I bought my first 29er in 2005) but if the offset isn't different enough, you'll end up with more trail at the same head angle when you go to a larger wheel.
    The glass is twice as large as it needs to be

  3. #3
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    Interesting, thank you.
    This prepares me for the discussion I'll have with the frame maker.

  4. #4
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    If you do a quick google search, there is an online calculator that will calculate trail based on wheel size, head angle and fork offset. That way you can find the exact (or close to) trail figure to what you are currently riding.

    Andy is also right that fork manufacturers are adding more offset to newer forks intended for larger wheel sizes to bring the handling closer to parity at a given head angle. I believe Gary Fisher was one of the first companies to ask Fox to do this for their 29ers with a 51 degree offset. This 51 offset is now standard on the 34 series 29er forks.

    Edit:

    Here is the link to the calculator for you.

    Bicycle Trail Calculator | yojimg.net

  5. #5
    Committed
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    Quote Originally Posted by GhostWind View Post
    Interesting, thank you.
    This prepares me for the discussion I'll have with the frame maker.
    My Turner Burner has a 66.5 HA and is compatible with an angle set for further tweaking.

  6. #6
    Killer of Chains
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    Norco Range, Rocky Mountain Altitude, Turner Burner, all are pretty slack bikes.

    Rocky Mountain's Flip-Chip allows some pretty nice fine tuning of BB drop, HTA, etc.

  7. #7
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    Got me thinking. Thanks for the ideas and the link/

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