Narrow Q by using double crank on MTB?

Okay, this might be the week's silliest question. But I've got this
mountain bike that I've pretty much had to give up on riding because the
pedal spacing -- Q factor -- is real wide, and it hurts my knees. My road
bike has a lot narrower Q and my recently-tweaked city bike's pedals have
been moved inwards with a different crankset and spindle and my knees are
very happy riding those.

But I'm tossing around the idea of building up a winter bike that can
handle a bit of road snow, just toying with the idea really. I could use
my mtb with maybe some appropriate tires on it. But I'd want to narrow
the pedal spacing.

The present triple ring pedals clear the chainstays by over 1 cm so I
reckon there's room to move in. That crank has some splined bottom bracket
spindle.

I don't need a triple crank, a double with a 44t-46t large ring and a 26t
or thereabouts small ring would work peachy for 95% of the riding I do.
I'm wondering if such a beast exists. With one less ring it might bring
the pedals closer to the seat tube.

The BB shell is 68 mm wide. I have a couple UN54 square taper bottom
brackets in different lengths.

--
Mike "Rocket J Squirrel"
Bend, Oregon

On Oct 30, 11:25*am, Mike Rocket J Squirrel
wrote:
Okay, this might be the week's silliest question. But I've got this
mountain bike that I've pretty much had to give up on riding because the
pedal spacing -- Q factor -- is real wide, and it hurts my knees. My road
bike has a lot narrower Q and my recently-tweaked city bike's pedals have
been moved inwards with a different crankset and spindle and my knees are
very happy riding those.

But I'm tossing around the idea of building up a winter bike that can
handle a bit of road snow, just toying with the idea really. I could use
my mtb *with maybe some appropriate tires on it. But I'd want to narrow
the pedal spacing.

The present triple ring pedals clear the chainstays by over 1 cm so I
reckon there's room to move in. That crank has some splined bottom bracket
spindle.

I don't need a triple crank, a double with a 44t-46t large ring and a 26t
or thereabouts small ring would work peachy for 95% of the riding I do.
I'm wondering if such a beast exists. With one less ring it might bring
the pedals closer to the seat tube.

The BB shell is 68 mm wide. I have a couple UN54 square taper bottom
brackets in different lengths.


Beware, some cranks won't skootch in even if you drop a ring,
depending on the design. If you can find a deal on a single speed
Sugino crank--that would be sweetest--just do a 1X setup with a
glorious MEGARANGE 11x34 clacking away in the rear. Of course, if you
have a happy bucket of bits, you can probably cobble together a SS
crank that will do--but most dastardly triples have knobbly bits that
keep you from reducing the Q. With an old road crank and some bmx
bolts you're golden.

On Oct 30, 11:25*am, Mike Rocket J Squirrel
wrote:
Okay, this might be the week's silliest question. But I've got this
mountain bike that I've pretty much had to give up on riding because the
pedal spacing -- Q factor -- is real wide, and it hurts my knees. My road
bike has a lot narrower Q and my recently-tweaked city bike's pedals have
been moved inwards with a different crankset and spindle and my knees are
very happy riding those.

But I'm tossing around the idea of building up a winter bike that can
handle a bit of road snow, just toying with the idea really. I could use
my mtb *with maybe some appropriate tires on it. But I'd want to narrow
the pedal spacing.

The present triple ring pedals clear the chainstays by over 1 cm so I
reckon there's room to move in. That crank has some splined bottom bracket
spindle.

I don't need a triple crank, a double with a 44t-46t large ring and a 26t
or thereabouts small ring would work peachy for 95% of the riding I do.
I'm wondering if such a beast exists. With one less ring it might bring
the pedals closer to the seat tube.

The BB shell is 68 mm wide. I have a couple UN54 square taper bottom
brackets in different lengths.

--
Mike "Rocket J Squirrel"
Bend, Oregon

With splined bottom brackets there aren't too many lengths. Usually a
triple crank length, and a double crank length if you are talking
about road cranks. For mountain cranks the manufacturer likely only
made the one triple length. The road version splined bottom bracket
may or may not be compatible.

An older square taper mountain bike crank would likely fit the bill.
Just grind off the built in triple spacers on the backside of the
crank. 44-32 rings should work. Then figure out the shortest length
square taper bottom bracket you can use. Start 1 cm or so shorter
than the recommended triple length. Maybe even 2 cm shorter. I was
able to use a Race Face Turbine LP crankset on a 103mm Dura Ace square
bottom bracket to get a 94mm bcd double crank capable of using
available 50 to 30 rings.

http://www.nashbar.com/results.cfm?s...20ATB%20Cranks
Cheap square taper mountain cranks at Nashbar.

On 10/30/2008 10:30 AM wrote:

On Oct 30, 11:25 am, Mike Rocket J Squirrel
wrote:
Okay, this might be the week's silliest question. But I've got this
mountain bike that I've pretty much had to give up on riding because the
pedal spacing -- Q factor -- is real wide, and it hurts my knees. My road
bike has a lot narrower Q and my recently-tweaked city bike's pedals have
been moved inwards with a different crankset and spindle and my knees are
very happy riding those.

But I'm tossing around the idea of building up a winter bike that can
handle a bit of road snow, just toying with the idea really. I could use
my mtb with maybe some appropriate tires on it. But I'd want to narrow
the pedal spacing.

The present triple ring pedals clear the chainstays by over 1 cm so I
reckon there's room to move in. That crank has some splined bottom bracket
spindle.

I don't need a triple crank, a double with a 44t-46t large ring and a 26t
or thereabouts small ring would work peachy for 95% of the riding I do.
I'm wondering if such a beast exists. With one less ring it might bring
the pedals closer to the seat tube.

The BB shell is 68 mm wide. I have a couple UN54 square taper bottom
brackets in different lengths.

--
Mike "Rocket J Squirrel"
Bend, Oregon

With splined bottom brackets there aren't too many lengths. Usually a
triple crank length, and a double crank length if you are talking
about road cranks. For mountain cranks the manufacturer likely only
made the one triple length. The road version splined bottom bracket
may or may not be compatible.

An older square taper mountain bike crank would likely fit the bill.
Just grind off the built in triple spacers on the backside of the
crank. 44-32 rings should work. Then figure out the shortest length
square taper bottom bracket you can use. Start 1 cm or so shorter
than the recommended triple length. Maybe even 2 cm shorter.

[snip]

A simple and elegant solution to an otherwise messy and embarrassing
problem! I have some UN54 BBs in a couple of lengths and I'll see if they
fit this old square-taper mtb triple I'm holding up to the computer
monitor so everyone can see it. See?

--
Mike "Rocket J Squirrel"
Bend, Oregon

On 10/30/2008 1:37 PM A Muzi wrote:

Mike Rocket J Squirrel wrote:
Okay, this might be the week's silliest question. But I've got this
mountain bike that I've pretty much had to give up on riding because the
pedal spacing -- Q factor -- is real wide, and it hurts my knees. My
road bike has a lot narrower Q and my recently-tweaked city bike's
pedals have been moved inwards with a different crankset and spindle and
my knees are very happy riding those.

But I'm tossing around the idea of building up a winter bike that can
handle a bit of road snow, just toying with the idea really. I could use
my mtb with maybe some appropriate tires on it. But I'd want to narrow
the pedal spacing.

The present triple ring pedals clear the chainstays by over 1 cm so I
reckon there's room to move in. That crank has some splined bottom
bracket spindle.

I don't need a triple crank, a double with a 44t-46t large ring and a
26t or thereabouts small ring would work peachy for 95% of the riding I
do. I'm wondering if such a beast exists. With one less ring it might
bring the pedals closer to the seat tube.

The BB shell is 68 mm wide. I have a couple UN54 square taper bottom
brackets in different lengths.

Numbers? My TA is 130mm tread. What width do you seek?

160 mm or less. My road bike is about 144 mm and that feels real good. The
mtb was a lot wider, the BB and crankset are off it right now so I can't
measure what its tread was.

My city bike was also too wide but I've been tinkering with BB and crank
and FD and have it at 160 mm and that's working pretty well.

I think I can narrow it more, though, with another crank I have on hand
but the FD, even this old-school bottom swing one that I put on, starts to
complain about too narrow a tread, can't swing close enough to the seat
tube to drop the chain onto the inner ring, and with my shortest square
taper UN54 the crank's inner ring needed to have it's bolt tabs trimmed to
avoid hitting the BB shell. I'll tinker with this more, using some longer
BB's that I have and see how narrow I can make the tread before the FD
craps out. That's for next week or so.

But in the meantime, I'm gonna mess with this mtb and see if I can make a
triple into a double and see how far I can move the cranks inward. Will
probably run into the same FD issue and have to get another bottom-swing
one, though.

--
Mike "Rocket J Squirrel"
Bend, Oregon

Mike Rocket J Squirrel wrote:
Okay, this might be the week's silliest question. But I've got this
mountain bike that I've pretty much had to give up on riding because the
pedal spacing -- Q factor -- is real wide, and it hurts my knees. My
road bike has a lot narrower Q and my recently-tweaked city bike's
pedals have been moved inwards with a different crankset and spindle and
my knees are very happy riding those.

But I'm tossing around the idea of building up a winter bike that can
handle a bit of road snow, just toying with the idea really. I could use
my mtb with maybe some appropriate tires on it. But I'd want to narrow
the pedal spacing.

The present triple ring pedals clear the chainstays by over 1 cm so I
reckon there's room to move in. That crank has some splined bottom
bracket spindle.

I don't need a triple crank, a double with a 44t-46t large ring and a
26t or thereabouts small ring would work peachy for 95% of the riding I
do. I'm wondering if such a beast exists. With one less ring it might
bring the pedals closer to the seat tube.

The BB shell is 68 mm wide. I have a couple UN54 square taper bottom
brackets in different lengths.

Numbers? My TA is 130mm tread. What width do you seek?
--
Andrew Muzi
www.yellowjersey.org/
Open every day since 1 April, 1971
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