I’ve been trying to get a crank-based power meter going on my wife’s Felt B16W bike for several weeks now. Stages doesn’t work because of the rear brake (placed at the chainstay).
I then ordered a Power2Max power meter with Rotor 3D crankset. Installed it and it just barely clears the rear brake and chainstay.
So I bust out the ruler and measure the Q-factor. The Rotor 3D crankset, when measured from the outside of the arms, comes in right at spec: 147mm.
Now the Felt B16w bike came with the FSA Compact Omega as stock. The FSA website claims the Q-factor is also 147mm. It is 147mm only if you measure from the MIDDLE of the crank arms. If you measure from the outside of the crank arms (like I did for the rotor), it is a whopping 160mm!!
I decided to measure my wife’s Trek WSD road bike. It measures at 158mm and is some Bontrager triple. So my wife has been riding cranks for Q-factors of 158mm and 160mm for the past several years and I ordered her a Rotor 3D powermeter crankset that has a Q-factor of a 147mm (a whopping difference). And this leaves about 1mm of clearance with the rear brake.
At this point, I’m utterly perplexed and don’t know what to do. We’re obviously concerned about a big fit change. But I’m wondering why on earth both of her bikes have such wide stances (and Felt’s stupid chainstay brake placement makes narrow Q-factor basically impossible). My own 2011 Cannondale Carbon Synapse (BB30 w/ FSA Gossamer) road bike has a measured Q-factor of ~148mm. And I’m huge compared to her.
Linked below are pictures where I was measuring from the middle of the crank arms. The Rotor 3D crankset is black. The FSA Omega is grey.
Apparently the state of Q-factors / stance is completely random across bikes, crankset manufacturers, and measuring practices.
And what would you guys do? Have my wife stick with the (entry-level) FSA Omega with the 160mm Q-factor?? She’s familiar with it and comfortable. I can just give up on affordable crank power meters and go PowerTap.
She’s familiar with it and comfortable. I can just give up on affordable crank power meters and go PowerTap.
Do you know she’s uncomfortable with the change? If not, and she doesn’t have some key races or training come up, just try it with the change and see what happens. It might not be a big deal. It might, but it might not.
Q-factor isn’t your problem, it’s inner clearance of the crankarm which is related to Q-factor but not the pure limit of possibility. There are some cranks that have better inner clearance than others. Also try a different brake, sometimes that helps. Also try playing with the spacers on your caliper shoes so you can pull a little bit more cable and get the arms closer to the rims. If non of those work just take it to the shop and bitch relentlessly till they give you a new one.
The Rotor crank clears the brake by about 1.5mm. I’m more concerned about taking an $1100 plunge that reduces the Q-factor by 13mm to what seems like a more “typical” Q-factor seen on road bikes. As opposed to this oddball crankset that Felt shipped on their B16W bike.
she might not even notice the small Q factor and if she does she can move her cleats in all the way to push her shoes out a few mm and she can add a pedal spacer or 2 to each crank arm to gain a few more mm. if she uses speedplay pedals, she can also get longer spindles to gain more Q factor. in regards to the clearance issue, I had the same thing on my Felt with my Quarq and used a few thin plastic washers on each side (0.5mm thick) to get the correct pre-load and clearance needed for the brake and chainstay.
I’ve never heard of lower Q-factors causing problems though I suppose they could. Also, the research on Q-factor says low Q-factor is better on average, though the difference isn’t huge:
(Note that these are extreme changes.) I think if it were me, as long as I was confident in that 1mm clearance being enough not to cause problems down the road, I would just go for it because I’ll bet she doesn’t notice it and if she does there’s a good chance she’ll prefer it.
I’ve been trying to get a crank-based power meter going on my wife’s Felt B16W bike for several weeks now. Stages doesn’t work because of the rear brake (placed at the chainstay).
I then ordered a Power2Max power meter with Rotor 3D crankset. Installed it and it just barely clears the rear brake and chainstay.
So I bust out the ruler and measure the Q-factor. The Rotor 3D crankset, when measured from the outside of the arms, comes in right at spec: 147mm.
Now the Felt B16w bike came with the FSA Compact Omega as stock. The FSA website claims the Q-factor is also 147mm. It is 147mm only if you measure from the MIDDLE of the crank arms. If you measure from the outside of the crank arms (like I did for the rotor), it is a whopping 160mm!!
At this point, I’m utterly perplexed and don’t know what to do. We’re obviously concerned about a big fit change. But I’m wondering why on earth both of her bikes have such wide stances (and Felt’s stupid chainstay brake placement makes narrow Q-factor basically impossible). My own 2011 Cannondale Carbon Synapse (BB30 w/ FSA Gossamer) road bike has a measured Q-factor of ~148mm. And I’m huge compared to her.
Linked below are pictures where I was measuring from the middle of the crank arms. The Rotor 3D crankset is black. The FSA Omega is grey.
And what would you guys do? Have my wife stick with the (entry-level) FSA Omega with the 160mm Q-factor?? She’s familiar with it and comfortable. I can just give up on affordable crank power meters and go PowerTap.
Have you considered a TRP T925-1B rear brake that offers additional clearance beyond the R740 rear brake that the bike comes with? I understand the new TRP brake allows the use of the Stages PM. http://www.trpbrakes.com/category.php?productid=1160&catid=182
The B16 frame (designed in 2006) had no trouble fitting Shimano, SRAM, FSA, Campagnolo etc cranksets with Q-factors as low as 144mm. If you want lower Q factor, you can get it. Did you measure the Omega from the pedal seat to the pedal seat? Did you contact FSA about this? I’ve never heard of this miscalculation before.
I’ve never heard of lower Q-factors causing problems though I suppose they could. Also, the research on Q-factor says low Q-factor is better on average, though the difference isn’t huge:
(Note that these are extreme changes.) I think if it were me, as long as I was confident in that 1mm clearance being enough not to cause problems down the road, I would just go for it because I’ll bet she doesn’t notice it and if she does there’s a good chance she’ll prefer it.
We saw a non significant trend towards 90mm being most efficient for women in that study, compared with 120mm for men, which is what you’d expect given the greater angle of the thigh to vertical in women (confusingly known as Q Angle). Women tend to have their knees closer together, which would predispose them to a higher efficiency at the lowest Q Factors.
Of course, you’ll be unable to get 90mm on a production bike - in our other experiments we’ve found that self selected and optimal Q Factor is around 140mm for most people. We have validated a test which predicts someone’s personal Q Factor where you don’t even need to go near a bike, the paper will be published soon. I recommend against a Q Factor of >150mm as we see decreased efficiency combined with more lateral movement of the knee which could be an indicator of potential injury.
I indeed contacted FSA and they responded. They acknowledged that the MegaEXO Omega Compact crank indeed has a Q-Factor of 159mm, whereas every other Compact crank they offer has a Q-factor of 147-148mm (even for MegaEXO). They also acknowledged that their website indicates the Omega Compact crankset has a Q-factor of 148mm but does not state that this is only for the BB30 version of the Omega.
Given that the majority of all Compact cranks sold have a Q-factor around 147/148mm, I’m surprised that Felt outfitted the B16W with such an outlier?? Was this intentional? Perhaps as others have said, that the majority of people don’t notice a difference.
I actually asked Stages about the use of a TRP caliper and they didn’t seem to have an opinion. I was pretty put off by Stages customer support for a couple other reasons. In contrast Power2Max customer support has been very helpful and responsive. Power2Max is similarly priced and doesn’t just multiple left-foot power by two. It seems like a nicer product actually.
