Advice neede

jimlews
jimlews Posts: 3
edited March 2010 in MTB beginners
I have just upgraded my fork to a Rockshock Recon 351 solo air; its fitted to my Merida Matts 60D (19" 2009 model) will this mess up the bike geometry; it still seems to rides ok?

Comments

  • supersonic
    supersonic Posts: 82,708
    How much travel does it have at the minute?
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  • benpinnick
    benpinnick Posts: 4,148
    Your merida had a 70.5 head angle on 100mm forks. Thats pretty aggressive XC angles. I think that you'll like the loss of a few of degrees on your head angle the new forks will bring, so probably nothing to worry about. Unless of course you like super-aggressive XC riding style, but if you did, why would you buy a 140mm fork!?
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  • BigmechUK
    BigmechUK Posts: 16
    provided travel is the same it should be fine
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  • jimlews
    jimlews Posts: 3
    Thanks; but what is the difference? I see some bikes with head angles of 68 or so, how does the angle impact on the bike
  • benpinnick
    benpinnick Posts: 4,148
    The head angle effects the steering of the bike mainly. bikes range from about 66 degrees on slack DH bikes to 72 on XC bikes. The steeper (larger) the angle the more direct the steering will feel.

    In effect this serves to dull or sharpen the character of the bike. For DH and freeride, a slack angle means that the front wheel won't twitch and dive into every corner, giving you a more solid stable ride, at the other end, XC racers want something that turns with speed and precision, and are willing to sacrifice the stability for that. 68/69 is generally regarded as the happy medium for bashing around trails.
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  • benpinnick
    benpinnick Posts: 4,148
    one other thing to remember is that as travel ramps up, you need a slacker angle to compensate. Imagine that a 70 degree head angle at full fork extension (uncompressed) would change to around 75 when the fork is fully compressed, making steering alot trickier. When you change your forks the angle of the head tube compensates for this. If it didn't, 70 degrees would go to 80 on a long travel fork, at which point, you'd be in all sorts of trouble.

    Also, as the sag on a 140mm fork will be considerably higher than on a 100mm fork, your effective head angle won't be as far from the original as it looks on paper.
    A Flock of Birds
    + some other bikes.
  • hard-rider
    hard-rider Posts: 460
    benpinnick wrote:
    The head angle effects the steering of the bike mainly. bikes range from about 66 degrees on slack DH bikes to 72 on XC bikes. The steeper (larger) the angle the more direct the steering will feel.

    In effect this serves to dull or sharpen the character of the bike. For DH and freeride, a slack angle means that the front wheel won't twitch and dive into every corner, giving you a more solid stable ride, at the other end, XC racers want something that turns with speed and precision, and are willing to sacrifice the stability for that. 68/69 is generally regarded as the happy medium for bashing around trails.
    Interesting and informative. It's answered a question that was always on my mind. So when would the head angle be considered aggressive? I'm looking at Scott Scales with head angles of 71.5deg. Is that aggressive and is it really noticeable over a headangle of say 70deg?
  • benpinnick
    benpinnick Posts: 4,148
    Hmm, difficult to say really. The scale is firmly an XC bike, and Scotts are generally quite aggressive head angles. Thats why you'll see so many of them at an XC race if you go. With the aspect being the trail equivalent (IIRC) and dropping a degree on the head angle. Size of the frame will also play a part, with bigger frames generally having steeper head angles. The reality is that yes, you would notice the difference if you owned both and rode them regularly, but the likelihood is you will like either one.

    If you are thinking of a bigger frame size though (XL, maybe even L), I would definitely consider a slacker angled bike like the Aspect. The geometry is normally optimised for a medium, and so everything else is a little bit of a compromise... sorry!
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  • hard-rider
    hard-rider Posts: 460
    Yes, I would be looking at an XL frame. I just compared the Aspect's geo with the Scale and they are very similar - only 0.5 deg diff. I know there is more to it than just HA and SA.

    For size XL: HA 71deg on Aspect, 71.5deg on Scale. SA are the same for both.

    If I go to the L size then HA 70.5deg on Aspect and 70deg on Scale. SA 73.5deg on Aspect and 73deg on Scale.
  • benpinnick
    benpinnick Posts: 4,148
    0.5 probably wont change alot, its on the steep end of XC, but not way out there. The Scott Scale is a very popular XC bike so they must do something right I guess.
    A Flock of Birds
    + some other bikes.

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