Q-factor

[Nick Payne]

Out of curiosity I just spent a few minutes measuring the q-factor on
some of the bikes in our garage. To avoid comparing apples and oranges,
I only measured those bikes that had 135mm rear spacing and which were
setup with two chainrings and either nine or ten speed cassettes.

Deore XT M737 - a low profile 94BCD Shimano MTB crankset from the
mid-90s, mounted on a Phil Wood 98mm BB to get the correct chainline:
Q=153mm

Sugino PX - a TA Cyclotouriste copy, but with a low profile to give both
derailleur and heel clearance. Mounted on a 107mm BB: Q=149mm

Ritchey Logic 94BCD - nice forged crankset actually manufactured by
Sugino. Also mounted on a Phil Wood 98mm BB to get correct chainline:
Q=146mm

TA Cyclotouriste, mounted on a 118mm BB: Q=142mm
This crank could have gone on a shorter BB (maybe 115mm), but the 118
was needed for the inside of the crankarms to clear the chainstays on
this particular frame, which has bent chainstays to provide fat tyre
clearance.

Ritchey Logic 110BCD - another badge-engineered Sugino crankset mounted
on 107mm BB: Q=140mm


Nick

[Alex Wetmore]

From: Nick Payne <nick....@internode.on.net>

> Ritchey Logic 110BCD - another badge-engineered Sugino crankset mounted
> on 107mm BB: Q=140mm

Is this one setup as a double or triple? As a triple the stock BB for this crankset is 120mm long.

I mostly end up running them with a single chainring on bikes with Rohloff hubs, but still run them with a 118mm BB to get correct chainline. The Rohloff needs a 54mm chainline, which is the outer ring position on a triple MTB crank.

My knees are happiest with a tread or Q-factor of about 150-155mm. Due to tight hamstrings and prior patella injuries this is probably the area of bike fit that I'm most sensitive to. Too narrow causes my knee to patella to track poorly through the pedal stroke.

This also works out well for my preference towards wide tires. The 151mm Q-factory Ritchey cranks on my 650B Gifford clear the chainstays by less than 2mm. I used a single bend chainstay to get 65mm clearance between the chainstays at the tire, enough to fit a 50mm tire safely. A double bend chainstay would have provided me a little better crank clearance.

My commuter bike with 700x35 tires and straight ovalized chainstays but very wide dropouts (135mm rear spacing on pivoting dropouts, this is like building a bike with 150mm rear dropouts) also has tight crank and chainring clearance.

alex

[Ryan Watson]

Thanks for the data, Nick!
I have some of the same cranks, and measured for comparison. I measured in situ, measurements from each side added together, so a little uncertainty there, but still....

> Sugino PX - a TA Cyclotouriste copy, but with a low profile to give both derailleur and heel clearance. Mounted on a 107mm BB: Q=149mm

How'd you get a 107 to work with that PX? Mine is on a Phil 115 and the there's barely 1mm between the drive side crank and the BB shell!
Interestingly, I get about 139mm Q with that setup.

> Ritchey Logic 94BCD - nice forged crankset actually manufactured by Sugino. Also mounted on a Phil Wood 98mm BB to get correct chainline: Q=146mm

That's about what I get using a campy taper 102, much easier to find than a 98! (From memory, I don't have the bike here with me)
That's about my upper limit for comfort.

> Ritchey Logic 110BCD - another badge-engineered Sugino crankset mounted on 107mm BB: Q=140mm

About 134 Q on a 103 BB for me.
I got sub-130 with the same setup before on a different bike.

I think my ideal Q would be under 100mm, but I settle for "as low as reasonably achievable"

Cheers,
Ryan in Albuquerque

[Nick Payne]

On 08/03/14 01:47, Alex Wetmore wrote:
> From: Nick Payne <nick....@internode.on.net>
>> Ritchey Logic 110BCD - another badge-engineered Sugino crankset mounted
>> on 107mm BB: Q=140mm
> Is this one setup as a double or triple? As a triple the stock BB for this crankset is 120mm long.

I don't think we're talking about the same crankset. The one I have
can't be setup as a triple - there are no mounting points for a 74BCD
chainring on the back of the arms. It's only intended as a compact road
double. Photo of it as I have it setup here:
https://www.dropbox.com/s/4ecl1nwz9ubnmsk/Litespeed_650b.jpg.

Nick

[Nick Payne]

On 08/03/14 04:14, Ryan Watson wrote:
> Thanks for the data, Nick!
> I have some of the same cranks, and measured for comparison. I measured in situ, measurements from each side added together, so a little uncertainty there, but still....
>
>> Sugino PX - a TA Cyclotouriste copy, but with a low profile to give both derailleur and heel clearance. Mounted on a 107mm BB: Q=149mm
> How'd you get a 107 to work with that PX? Mine is on a Phil 115 and the there's barely 1mm between the drive side crank and the BB shell!
> Interestingly, I get about 139mm Q with that setup.

Not all PX cranks are the same - later ones were lower profile with more
heel clearance, which is the model I have. My wife has a set of the
earlier ones, which are presumably what you have, and they have minimal
heel clearance and are mounted on a longer bottom bracket.

Nick

[Nick Payne]

I took a photo from above of the cranks installed on the 107mm BB (a
Shimano UN-72): https://www.dropbox.com/s/svbv6xassni59cz/px.jpg.
There's a 1.5mm spacer under the fixed cup on the BB to provide a bit of
clearance between the chainring mounting bolts and the chainstay.

Nick

[satanas]

FWIW, I've used the Logic 110/74 cranks as a triple on a 107mm Shimano UN7x BB with two 1.6mm Sturmey-Archer spacers behind the RH cup. Chainline was fine with 130mm 8 speed rear and very short stays (Softride), and I like the LH crank being inboard rather than symmetrically spaced, in part due to an old break. YMMV.

BTW NIck, where did you get the 98mm Phil BBs??? (They seem to imply that even shorter is possible, but no info on availability.)

Later,
Stephen

[Nick Payne]

On 11/03/14 03:16, satanas wrote:
> FWIW, I've used the Logic 110/74 cranks as a triple on a 107mm Shimano UN7x BB with two 1.6mm Sturmey-Archer spacers behind the RH cup. Chainline was fine with 130mm 8 speed rear and very short stays (Softride), and I like the LH crank being inboard rather than symmetrically spaced, in part due to an old break. YMMV.
>
> BTW NIck, where did you get the 98mm Phil BBs??? (They seem to imply that even shorter is possible, but no info on availability.)

You have to e-mail Phil Wood and ask them about the shorter bottom
brackets. I have one of the 96 as well installed on another bike. These
BBs have a narrower cartridge width than their normal units - the cups
sit completely inside the bottom bracket, whereas with their normal BBs
the cups protrude slightly from the bottom bracket shell.

Nick