@Jackofallgrades That’s a great point on the Q-factor. I’ll need to give that some thought and try to determine how I “feel” from the stance perspective. Sourcing is another great point and it’s helpful to knwo that you don’t notice the difference on 165mm cranks.
@Northshorerider Good point. It sounds like L/R is nice, but not much more than that unless you’re really looking at changing your form or have a rather significant disparity.
Given that I’m looking at shortening the cranks from 172.5mm, don’t plan on selling the bike anytime soon, and when I eventually upgrade to a new bike power meters may even be standard three-to-five years from now, I’m probably going to target a spider-based power meter. At this point, the real decision is on going with Quarq and dealing with the BB90 conversion or Power2Max with 24mm 1104S Rotor cranks. Any DIY mechanics/engineers have strong opinions on this topic?
Counterpoint: if you break your pedal (ie, in a crash) you are out a looooot of cash. Granted, I bought my first PM about 3 months after breaking a pedal in a crash, so I was little traumatized about going with pedal-based power. But one of my friends broke her pedal in a crash this past fall, too.
It really isn’t…unless you are dealing with an injury, there is not much to glean from L/R balance.
IMO, of course. 
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I’ve never seen or heard of a garmin vector 3/rally pedal breaking from a crash…
And if a pedal body does break, they are available separately anyway.
I have been on 165’s for years. Just for reference I’m 179ish cm. Short-ish inseam though. Anywho, as far as cost benefit: First I don’t think many could tell a difference between 167.5 and 165. Second, IMO, there is virtually zero performance benefit of a DA crank v. Ultegra. So, again IMO, the crank comes down to how much disposable income you have to spend and which one you think looks better.
Regarding Q factor, IMO it’s way overblown. Between my CX, TT and road bike my Q factor varies almost 10mm and until this thread I never checked. Never knew. I think for the vast majority of peeps it’s the same. There might be a small % who are really sensitive to a change in stance width. If you’re really worried measure your bikes and see how the pedal based will affect this and adjust your current cranks to match how much the Assioma shi will increase Q by.
Looks like you’re leaning crank based PM and I don’t think you will be disappointed. For me it would be really attractive to use the same pedal based PM across a number of bikes. Not necessary just a luxury. Regarding Assioma v. Garmin I’m not the best to ask. DC rainmaker has some amazing posts about both loaded with more information I could ever hope to cough up.
Lastly, agree 100% with @Power13 about L/R balance. Nearly useless info IMO.
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Don’t over think the 2.5mm of crank arm. 165…170… it won’t change much. Go look at a 5mm allen key, that the total difference up/down you’re looking at.
The bigger issue is the BB90 bottom bracket. I haven’t had good luck with single bolt crank arms here. GXP (SRAM) arms seems to fail after a while and I’ve had a Rotor Aldhu fail because you’ve got to get the arms on the tapered splines and the preload perfect. A better solution here is the prior Rotor pinch bolt 3D24 with the BB or just use pedals.
I’d use Treks (NSK) bearing and cups with whatever here with the frame rather than aftermarket ones because they are top notch and they seem more durable here.
@jfranci3 Thank you for the insight on the tapered splines. It sounds like there BB90 is a bit more of a headache than anticipated (you have to love the standardization in the bike industry). I’ll take a closer look at the options around the 165mm range and assess the spider vs pedal options further.
Thank you for the feedback. I appreciate your thoughts on the L/R power topic. It sounds like estimating a split of total power is definitely better than any single-leg or pedal options.
Single leg- have you ever cared EXACTLY how accurate your HRM or Speedo is? Single side is a fine tool. The biggest difference you’ll notice if that it doesn’t measure your “lead-off” foot.
Also, your trainer is giving you a fudged number, and the real number will vary depending on where you measure it and how your computer/app averages it. Unless you’re doing something peaky -track sprints maybe, it doesn’t make practical sense given the $$. There’s little reason to spend more than a single sided pedal setup.
BB90 isn’t really the issue, Single bolt crankarms aren’t really the issue, but when you add the factor of bearing cup behind the bearing (y/n), different thickness bearing seals, lack of clarity what spring/o-rings are needed, exact measurements expected per crank, yada, yada - there’s a lot of relevant room for error.
Except in cases when you have developed a leg imbalance: I upgraded from a single-sided 4iiii power meter to a Quarq DZero when getting a new bike, and my leg imbalance was atrocious (55:45 was the default). Simply having the 20-second average of the left/right power split on my Wahoo during TR workouts pushed it back to 51:49 to 50:50. My body is smart-lazy and efficient: it knew that to increase the power reading by 2 W, it had to increase the power output of my left leg by 1 W. (I know that spider-based power meters can only infer the power split, but not actually measure it. Yet, I expect that if I have a power imbalance, it’ll pick it up.)
Now I may be the exception and I would definitely get a one-sided power meter again on e. g. my mountain bike (in fact, I did 
). But I do see benefit in having left/right power balance and total power. If you have the money, I’d at least get a power meter that actually measures total power.
I’m a big fan of Quarq power meters, my DZero has been completely boring since I got it almost a year ago. I just had to replace the battery once. That’s it. The power numbers always looked accurate (unlike with my 4iiii which took about a month to settle in) and track with my Elite Suito. It measures cadence beyond 200 rpm whereas my 4iiii crapped out at 160 rpm. It is just a nice piece of equipment. And Force or Red cranks (corresponding to Quarq D2 and D1 cranks) are very nice, too.
Go 165mm. In my opinion, shorter is better. Also go the Assiomos. If you go Quarq you will be forever tied to your Quarq and crankset and maybe even that bike!
I also highly suggest going the pedal-based route. I’ve had Stages left arm PM, three Quarq spiders and bought Assiomas last summer.
Quarq pms work well but swapping bikes and cranksets is always a bit of hassle, especially now when the stock is pretty limited. Also, if you buy a Quarq pm you are also buying into the Sram ecosystem which might be a negative, or not.
I love the simplicity with Assiomas: Just screw them in and they work. If you decide to upgrade your drivetrain, no need to worry about powermeter compatibility. If swap your bike, again, you have your powermeter no matter what. The resale value on the Assiomas is pretty solid as well. Used ones sell usually at around 450-500 euros so it won’t be a huge loss if you change your mind afterwards.
No you’re not….people move their crankset all the time between different bikes. Sure, you are tied to the Quarq power meter, but that is true no matter what PM you buy.
I could just as easily say if you went with Assiamo, you are “forever” tied to that pedal platform, which some people don’t like.
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@jfranci3 Great points on the setup options. The real issue with using spider-based cranks from Quarq (SRAM) and Rotor are related to human error when setting things up. The benefit to using something like a single-sided power meter with Shimano cranks (given my setup) or pedal-based is that it removes the BB conversion errors out of the equation.
@OreoCookie I appreciate the feedback and sharing that the Quarq has been “boring…in a good way”. I like the idea of Quarq and/or Rotor NG power meters, but am giving some thought to the human error element around the BB conversion which appears somewhat magnified with the BB90.
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@averageroadie I really appreciate your thoughts on the crank length. Realistically, when I look at the difference of 5mm vs 7.5mm, yeah, I might as well go the 165mm route. As for the being “locked in” to a specific power meter, I’m not worried about that consideration. I’ll probably hold on to my bike forever and when I do get a new bike, given the trends, a power meter may be standard on higher end bikes three years from now based on the trends within existing Shimano group sets.
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Spider based power meters also have compatibilities issues with chain rings (4 bolt 110, 5 bolt 110, …).
I’ve got a Power2max NGeco ALDHU 3D+ with 30 mm BB and 150 mm cranks. I was curious about going extremely short as a test and these were on stock from Power2max.
I previously had a 24 mm BB that I replaced. It was my first time. I watched a Park tools video on youtube and read the manuals that came with the parts. I bought the tools and torqued the parts to specs.
I had some minor issues :
- It was hard to understand if I needed to use the included spacer (it was not required).
- The part on the rotor cranks that needs to be adjusted to take up the slack (needs to be tight enough but not too tight) was hard to adjust (it would jam, it felt not sturdy). I was worried that I might break the threads during installation or use but it has held up so far after hundreds of km.
- At first, I thought the parts did not fit the frame because the shaft would not enter deep enough by hand. It turned out fine once I torqued the parts to spec.
My thoughts were not articulated properly.
I meant to say that if you wanted to use a SRAM style crank or a Cannondale style spider rings and crank, you won’t be able to carry over your Quarq if it’s the Shimano 4 bolt style Quarq. You’d be “stuck” with Shimano 4 bolt forever.