What's your Q Factor?

[sethschmautz]

I recently took an older SRAM XO carbon crank, swapped the spindle for a wider one, and installed it on my trail bike. The crank arms have a much more significant flare/jog from the BB spindle to the pedal interface and I'm realizing that the Q factor on these cranks are quite wide. I haven't measured it yet but I would guess that it's more in line with my (old) fat bike than with my gravel bike and I noticed my knee hurting on the initial ride on the crank. It has gotten me thinking a little bit about Q factor from bike to bike.

The little research that I've done suggested that road bike Q factor and mountain bike Q factor varies (150mm for road bike and 170 for mountain). I would guess that different Q factors were created as tires have gotten wider, hubs have gotten wider and even BBs have gotten wider. It seems, though, that Q factor ought to be as much a factor of body mechanics than it is of bike design - i.e. there is likely an ideal Q factor for each person rather than varying Q factors across several bikes in a person's quiver.

This started me thinking about Q factor across my three bikes - v1 Hightower (currently with the XO crank), Trek Stache (SLX crank with PF92 BB), and a Specialized Diverge (Force 1 crank w/ 386EVO BB). It *seems* that the crank arm interfaces are the same between the XO crank and the Force 1 crank. The Q factor of my gravel bike is much narrower than the Hightower. It would seem that I could achieve a "happy medium" by swapping the XO arms onto the Diverge and the Force 1 arms onto the Hightower.

I'm wondering where the holes are in my logic and whether any of you are making crank choices to get a more consistent Q factor? How did you determine your ideal Q factor? It seems as though this might be a good idea for my knee(s), even if it means getting new crank arms for my hightower. I'm interested in your input.

Seth

[Dee Hubbs]

For reference
Shimano MTB
Shimano XTR 9100-1x Q Factor = 162mm (race)
Shimano XTR 9120-1x Q Factor = 168mm (Trail or same as 2x)
Shimano XTR 9130-1x Q Factor = 171mm
Shimano XTR 9125-1X Q Factor = 174mm

SRAM MTB come in:
158mm (Race non-boost)
168mm (non-boost and boost)
174mm (Eagle DUB)

ROAD
Shimano Road
Shimano Dura Ace 9100 Q Factor = 146mm
SRAM Road
Most are Q Factor =145mm

[huckbucket]

I've never understood the fascination with Q factor. I watch guys who's pedal stroke puts their knees above the top tube and conversely see guys who look bow legged. Each of which suggests to me that there's a ton of variability in hip angle. If aero is the purpose (road and TT bikes) I can see the marginal gains of being closest to the BB, but that's bleeding edge stuff IMHO.

[grskier]

I have 0 tolerance for Q.




oh, wait, this is sprockets and not padded room...

whoops.

[nickel]

I've never thought about it for cranks but an picky with pedals. I hate when my pedals force crank pinching ergo I favor pedals with a wide q factor that put my feet in something closer to a natural width.

[XXX-er]

my FAT bike has a noticably wider BB cuz of the FAT tires but I can't say the differences i the rest of the bikes are all that noticable

I've ridden shitty exercise bikes in gyms with really wide BB's

[sethschmautz]

Here are two pictures of the crank arms installed on my Hightower and my Diverge. I suppose I'm not looking for an absolute Q factor number but wondering whether my knees would be better if I could make the Q factor consistent across all bikes. The curve of the arms on the Hightower fit the chainstay(s) pretty well but are just further outboard than they need to be. The diverge is super close to the chainstay(s).

Maybe a winter project will be to measure the Q factors, swap the arms and measure again.

[nickel]

Your pedals look to be exaggerating the q difference further. The pedals on the Hightower put you even further out by the looks of it although it could be an illusion from the naked spindle.

[skizix]

My queef factor is relatively low - just a quiet pfffffft.

[sethschmautz]

Bumping this back up. I ended up picking up a set of SRAM Red cranks for my gravel bike and have a perfectly good SRAM Force 1 crank in a box. I could sell it, but they have a much straighter crank arm than the XOs that I have currently on my Hightower. They look really similar. Is that crank (Force 1) weaker than the XOs? Am I gonna die?

I will have to swap the Force 1 arms onto the spindle that I currently have on that bike but I've just gone through that procedure and am familiar with it.

On the other side of the decision I did a long ride on my HT a few weeks ago with the wide Q factor and my knees felt fine so . . . I might just leave it as is.

[Benneke10]

The strength of the Force crank is probably fine, the issue is clearance. If the Force crank manages to clear your chainstays, you will still probably be bumping your heels against the chainstays. I miss when SRAM made a 156mm Q-factor XX crank and a 166mm model so you could tailor it to your frame and preferences.

[Andeh]

Forget Q factor, your bike is going to spontaneously combust because you're using Shimano pedals on SRAM cranks.

[sethschmautz]

Forget Q factor, your bike is going to spontaneously combust because you're using Shimano pedals on SRAM cranks.

I thought XT was just a little better than XO and not as good as XX?

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[Andeh]

I thought XT was just a little better than XO and not as good as XX?

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It was a joke, at the expense of people like me who get twitchy mixing and matching competing brands.

[sethschmautz]

It was a joke, at the expense of people like me who get twitchy mixing and matching competing brands.

I figured. Mine was as well. :-) It is kind of funny that it *almost* matches SRAM's model assignments though.