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Crankset length/bb compatibility questions

clantonclanton Posts: 1,288
edited June 2013 in MTB workshop & tech
Not sure if this belongs here or over in road but.....

I get some toe overlap with my cross bike - tiny amount but it irritates me intensely. I have tried shifting my cleat position but didn't get on with it and now thinking about shortening my crank arms (well actually fitting shorter cranks!) Currently they are Tiagra 175mm. Happy enough to buy decent cranks but don't want to shell out loads and then find I hate the shorter ones or that they haven't solved the problem!
So will 172.5mm cranks be noticeably different to ride? Will they make enough of a difference (only just snag it - but is 2.5mm enough?)
Also - will mtb cranksets fit with a road type Hollowtech II bb? If so it widens my options for finding something cheap and nasty to try out before committing to something expensive.
Finally - anyone got 172.5mm cranks surplus to requirements? Does not matter what state the rings are in but the BCD needs to fit compact
50/34 rings.....


  • nicklousenicklouse Posts: 50,675 Lives Here
    Don't bother and most MTB cranksets are 175 as it is the norm.

    Yes they would fit but you might have fun finding rings o the size you need and then ther is the chain line to think about as MTB cranks need two 2.5mm spacers on the drive side and one on the non drive side for a standard 68mm BB.

    It is more of a riding style change or a frame change.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • bikaholicbikaholic Posts: 350
    Toe overlap is a side effect of compact and semi compact frame geometries. I've had numerous road bikes and hybrids that exhibited this issue but I never had a problem with them - it's just timing that you need to practice.

    The possible solutions to your problem include:

    1. Replace the current forks with one that has a greater rake;
    2. Fit thinner tyres;
    3. Fit shorter cranks (square taper cranks come in various lengths eg 155mm, 160mm, 165mm etc);
    4. Fit smaller wheels, eg 650b (though you may need to use rim brake adapters if your brakes aren't disc).
  • clantonclanton Posts: 1,288
    Thanks for replies to date - so MTB cranks essentially not an option.
    Re other options: Would a new fork not also affect the steering/hnadling? Loathe to go down that route...
    Thinner tyres might be worth thinking about - though it did happen with the original tyres the bike came with too..
    Shorter cranks seem the way forward to me - but how short?
    Smaller wheels - they are disc wheels (and 29er ones to boot which may be contirbuting to the issue) so could look at that - but again would the character of the bike change? Also may cost more than just cranks.

    I like the way the bike rides, just hate buzzing my feet on the front wheel - inevitably happens in traffic or when attempting something low speed and technical and I find it unnerving.
  • The RookieThe Rookie Posts: 27,810
    Measure it up carefully (clip the show in) will 172.5 or 170's clear?

    You almsot certainly won't notice the difference!
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
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