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Front Mechs - Road v MTB

OldSkoolKonaOldSkoolKona Posts: 655
edited November 2010 in The workshop
Just a simple question about intercompatibility between road and mtb front mechs. I've to replace the front mech on my mtb commuter after a silly incident which resulted in me bending the existing mech.. (basically, if you've got alloy bolts on your chainset and you lose a couple, don't expect the remaining, say oh, 3 bolts to take the strain, particularly coming away from the traffic lights :oops: )

I've a spare road mech which has the correct clasp size, but I wanted to check if they are actually interchangeable (ie running a road front mech with mtb shifters). Is the cable pull distance per click on the shifter the same for both?

Posts

  • deswellerdesweller Posts: 5,271
    Sadly for you, nope.
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  • Cheers, you saved me a lot of heartache over the weekend trying to get it to work, phew :lol:

    And on a slightly related query - can you run a 8 speed system with a 9 speed mech or does the design of the 9 speed for a narrower chain mean it won't work? My OldSkool set up is getting to be a bit of a pain in trying to get components! :)
  • neiltbneiltb Posts: 332
    8 speed on a 9 will work fine, did it for years on my own old skool kona.

    [edit] misread that as you're goin 'tother way, but other tahn a smidge more chain rub at extended chain angles, i can't see a problem.
    FCN 12
  • SalsaSalsa Posts: 753
    I run a Dura Ace 7803 triple front mech with an XO trigger shifter, works fine.
  • nicklousenicklouse Posts: 81,520 Lives Here
    I run a rival with an X9 trigger, only 2 MTB rings but works fine.

    9spd front mech can be made to run fine but you may get a tad more rub than you would really want.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • The RookieThe Rookie Posts: 27,747
    I see no problem with running a road mech, I've run a Sora with Deore shifter OK., not sure if Campga have a different cable pull, but any SRAM or shimano would be OK AIUI.

    As Nick says you may be more prone to some rub due to the narrower cage, if running a 9speed on an 8 speed setup, but many bikes are still sold as 8 so components are still available.

    Simon
  • Despite some anecdotal evidence above, in theory they are not compatible. In practice, a bodge can sometimes be reached, especially for a 2 ring system. The two problems are:

    - Curve of the road derailer outer plate will probably be too great (designed for 50T, usually) so the derailer won't be optimally positioned for your 42/44T (I'm assuming). The inner plate won't reach down far enough for upshifts, you might get rub on the smaller rear gears, and it'll be easy to drop the chain.

    - Pull ratio is different so unless you are running a double, there's a low likelihood of having good shifting on all 3 rings.

    SRAM and Shimano front derailers have the same cable pull ratio, so it doesn't matter which mtb shifters you have. If by chance you have a 48T big ring, it might be worth a go to get functional if not fantastic shifting.
  • Ok, so in the interests of science, I fitted both the Road (105 Triple) and the MTB (LX)

    I can categorically say that a 105 Triple will not work with standard rapidfire shifters (my are old Deore's but they've all the same cable pull ratio) for a three ring chain set.

    With the road front mech, it shifted straight from granny to outer and required a lot of force on the lever.

    The LX mech on the other hand is very smooth and requires very little force to move between rings. I just went with the 9-speed mech, (I have a 8 speed, '95 set up, though in a 'my grandfather's axe style' :lol: )) which since slightly narrower has a bit more chain rub, but tbh since the Kona is only used for commuting on roads, I only really need the higher gears.

    Sadly, I've managed to snap my rear wheel axle, :oops: so the smooth running was short lived - job for tonight is to fix that one!
  • sc999cssc999cs Posts: 596
    Ok, so in the interests of science, I fitted both the Road (105 Triple) and the MTB (LX)
    ...

    Sadly, I've managed to snap my rear wheel axle, :oops: so the smooth running was short lived - job for tonight is to fix that one!

    Related to the mechs or just coincidental? Enquiring minds want to know...
    Steve C
  • The RookieThe Rookie Posts: 27,747
    That should certainly not be the case, sounds like the classic wire the wrong side of the bolt scenario, which often is seen in the workshop forums even with the 'right' mechs!

    Simon
  • Axle snap was purely coincidental, was an old wheel. Will have a look at it when I take it out to see the failure mechanism.

    Interesting point on the cable on the right side of the bolt. It followed the routing shown on the destructions and the but I'll look again
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