26" wheels on a 650B frame?

diy
diy Posts: 6,473
edited September 2015 in MTB general
My oldest kid, needs a new bike, I'd like to get him a decent used bike for the same money as an entry-mid level hard tail. The problem is, he's currently sizing up as a small frame on most bikes. Given that he's currently growing like a weed, I was wondering how stupid it would be to put 26" wheels on a 650b Medium framed bike and perhaps go with a shorter stem and/or inline post.

There are loads of 650bs around in medium, but very few small and xsmall framed bikes.

thoughts?
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Comments

  • .blitz
    .blitz Posts: 6,197
    Depending on the tyres you use the bike and the BB will be 10-12 mm lower and the fork offset will be different depending on travel/sag. You might also find the tyre clearance is tight around the fork arch.

    Small but not insignificant differences
  • The Rookie
    The Rookie Posts: 27,812
    I'm baffled by this, why put 26" wheels on a 650B framed bike, it doesn't make it any smaller, either buy a 650B in Medium - get one with (designed for) a setback seatpost and replace with an inline, that shortens the cockpit by 20mm (about one size) without affecting anything else. Or get a small 26".
    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.
  • diy
    diy Posts: 6,473
    To be honest, I'm not sure, which is why I posed the question. On other forums some XC racers are using 26" wheels on 650bs when the course is really muddy, to allow chunkier tyres and better mud clearance. I was focusing on reducing the standover and possibly top tube length due to the more compact frame on a 27.5.

    As per my OP, Small framed bikes are fairly rare.
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  • The Rookie
    The Rookie Posts: 27,812
    Improving standover by 12.7mm (ish) is pretty meaningless, yes if you want big tyres you can put the smaller wheels on (only restrained by width available then) but frankly I wouldn't bother.
    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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