so... a couple of things. you can switch crank arm length for some cranks, but not all. for this you need a design that does not have a captive spider. for example, specialized and hollowgram (cannondale) crank arms come to mind; shimano and FSA cannot.

once you've got a design where the arms are separate from the spider, you then need to worry about calibration. the electronics are contained in the spider. in theory, swapping a spider should not require recalibration.

in my experience, quarq designs (despite the marketing material) have always required a recalibration of slope during any ring change -- not only from one size to another but from one brand to another. the arm change length is another area that should not require the recalibration...but i would not trust a quarq that has not been slope-checked. whether you send that in or do it yourself (it's easy) is another matter.

SRM tends to be less affected by changes in rings. (i always check, but i'm obsessive -- a change from 53/39 -> 56/44 results in a 0.5% change for me...essentially nothing.) arm length never requires recalibration (i swap hollow gram and specialized cranks often for myself and friends/customers).

just my experience, but with quarq there is no way i would change anything about the system without checking slope.

can't speak to P2M as while i've seen them i just haven't used/serviced them extensively. power2max does not allow the end user to check slope, so it's a non-starter for me. i'm also not a fan of the way it handles zero offset and the temperature issues it had in the past. in theory it's good, but i've got some scenarios where i believe it provides data that may be​ problematic.

Thanks a lot, tetonrider! That's a lot of good info.

I didn't know about the P2M's inability for the end user to check slope. It's also good to know about the quarqs' ability to be able to change crank arms at home. I guess I'll mostly wait and see if I can get a good deal on a quarq.

just to be clear, quraq now claim that "omnical" means a chainring change does not require recalibration; my experience suggests that it does.

a friend is selling a quarq w/ specialized (172.5) arms and shimano rings (53/39). not certain of his asking price but think it is around a grand. he recently got an SRM. not sure if that works but if so i can connect you.

that sounds like a nice deal but ideally i'd like a 50/34 and 170mm with a gxp bb. specialized arms will need bb30 right?

edit: did a little bit of reading and found out that they will be compatible with bb30/pf30/osbb. my frame has a pf30 which has an adapter for gxp (i believe) and I use gxp cranks. i would like to try native bb30 stuff some day but i'm just (possibly irrationally) scared of screwing up 1) the pf30-gxp adapter uninstallation and 2) the bb30 installation and dealing with a creaking bb.

For my next frame (still deciding, lots of looking) i'll maybe get a native bb30 crankset. let's see.

specialized arms have a 30mm axle, yes.

in brief, you can run cranks with 24mm axles (shimano, sram GXP) in frames whose bottom brackets are bb30 variants (bb30, pf30, OSBB). bb30 just means that the bearings are pressed directly into the frame. pf30 was a way for manufacturers to reduce costs; you press the bearings into cups which are pressed into the frame. OSBB is specialized's take on bb30. strictly speaking, bb30's spec stipulates 68mm bottom bracket width; specialized frames were slightly narrower and thus used slightly wider than standard cups to make up the difference.

[things could have changed for 2015 frames, but the above was true for all 2014 & earlier frames that i've owned/seen/worked on.]

a gxp or shimano-style crank is probably your best bet for a long-term investment. i think we're a loooong way away before you see anyone make a frame that is not compatible or cannot be adapted to fit a shimano crank. for instance, twice in the past week i've installed shimano cranks (SRM) on cervelo bikes with "BBright" bottom brackets. in that case, the buyers wanted a 24mm axle crank in a larger BB. rather than use bearings with 30mm ID and adapters (reducers), we used a rotor bottom bracket that eliminated the adapters.

check rotor part # 4624--i believe that works to reduce any pf30 bottom bracket to accept a 20mm axle. (for the cervelo, i had to use 4624L for BBright->24mm.)

praxis also has some good setups.

other than weight, shimano cranksets are among the finest out there. (i know you're not necessarily looking at shimano, but i offer it because there is nothing inherently wrong with a 24mm axle.) the specialized and cannondale units (30mm) are lighter when using the same chainrings -- but there is no benefit for the average user in terms of power transfer. i suggest people think about future-proofing a purchase, as well as Q-factor, resale, aesthetics and chainrings moreso than any attributes of the arms.

don't be afraid of bb30 if you've gone with a reputable brand--i've ridden 7 bb30 frames for tons of miles...no creaks. sure, they can happen, but careful installation tends to eliminate this.

looks like shimano beefed-up the carbon carrier on their new MTB 11s cassettes. just got one friday, a bit early. was a bit worried/curious to see what they'd done, esp with the low cadence/high torque that characterizes typical mountain biking. picked up a DA cassette (revised model) to go on my wife's bike. they added a 2nd set of rivets to the 2nd-largest carrier. we'll see if it develops any play or creak.

thanks a lot for the info and advice. really appreciate it!

Hmmm...good thing I asked.

Some facts bearing on the problem: I weigh ~185. The tires I'm using (Specialized Espoir tubulars) are marketed as training tires and have butyl tubes; I wanted something relatively cheap but decent so if I screwed them up mounting them I wouldn't be out that much money. My boss, from whom I bought the wheels, helped me mount the tires using Tufo tape and they came out fine. I would've preferred 700x25s, but they're out of stock until November. Racing tires will go on in March.

There's no way I can do an apples-to-apples comparison on ride feel. The tubulars are mounted on Reynolds 66s, while most of my riding has been done on Open Pros with 700x25s which measure 27mm wide. Based on the duelling theories above, I'm going to run them at the same pressure I run my one wheelset with 23s at for a start and modify from there if necessary.

Road surfaces where I live in the sticks are decent or better, with railroad tracks being the only square edges. I often ride from where I work in a small city, and the roads there are concrete with expansion joints, so there are square edges there.

ETA: Rode for two hours on the new (to me) wheels and tires. I was singularly unmotivated to ride this morning due to having slept really poorly last night. I ended up running the tires at 105f/115r. I rode too slowly to feel any aero benefit, average speed was 17.9 mph. My average HR was only two bpm above my recovery HR range. Predictably, I felt road imperfections more than I usually do, what with the 66mm rims and 23mm tires vs. the 19mm rims and 27mm tires I'm used to. I don't know how much the training tire with a butyl tube contributed to that. No judgement yet. I'll probably do the Tuesday Worlds to see how they feel at speed.

I'm thinking of getting a Ridley Noah (the ISP version). The geometry is perfect for me but I was only concerned a bit about the ISP. Are there any not so obvious pain points with an ISP bike, esp. adjustability-wise? I won't travel with this bike and I'm also not concerned about it's resale value.

I think [MENTION=197606]Creatre[/MENTION] just bought that exact bike.

I'm not sure I agree 100%; there is a point where lower pressure will be slower due to deformation. The crazy-low pressures we run in 'cross tubulars (example: I am 125 lbs and depending on the course will run as low as ~20f/22r in 32mm tires, plenty go even lower than that) are faster because they keep the tire in better contact with the ground, and because surface irregularities means the tire is doing a lot more work and softer makes for less work to deform it. It's just a completely different environment for the tire than you have on the road, where most of the deflection in a tire is from the weight on it, or from cornering forces. On the road, folding more rubber than you need to in order to keep the tire on the road is just wasting energy.

The other issue with lower pressure is the effect of cornering forces on tire shape. Lower pressure means the tire can't resist lateral forces as effectively, so it could fold a bit. In theory, this hurts cornering precision. In practice, I'm not sure how much of an issue it really is on the road. It's a real thing in cyclocross, where those sub-30 PSI pressures make tire folding a fact of life. But in cyclocross we deal with it because we basically have no choice, not because flopping around on soft tires feels great.

Overall, I agree that most people ride on much higher pressures than necessary. Over the years I've come down to something 80f/85 r for racing on 23mm clinchers and have not found that it slows me down at all. Even keeping in mind that I am light, I'm running tires at well below the pressures they are designed for, and could probably get another 5-10 PSI out of them before they started feeling too squishy. But then pinch flats become a risky. Eh. Tire pressure is an arcane subject. But I think the conventional wisdom of running road tubulars at slightly higher pressures than clinchers is basically sound.

many good points. i think we're tossing around slower and faster. i was referring to rolling resistance, but when we talk about "faster" overall, the performance of a tire in corners as you note could come into play. a tire that rolls faster is not faster overall it if folds underneath the rider and causes a crash.

a few years ago i tested pressure on real-world roads. i'd done testing Crr testing on rollers (before and since) to compare rolling resistance of various tires and tubes. in theory, the results from smooth rollers translate to roads, but i wanted to see.

for my test i varied pressure while riding similar power (and corrected for it). i was riding up a steep, protected grade to eliminate or at least minimize the effect of wind. i dropped pressure from 120 on down to 80. never went below 80, but as i went lower each run was faster/i went further, adjusted for power. perhaps there is a point where distance traveled would go back down, but i didn't see it or see any evidence of it. (well, surely at zero pressure it would happen...)

your point about cornering is a good one; at a certain point the characteristics of a tire change and this would come out in cornering, so there is a balance. my testing was centered around a hill climb/time trial, so that wasn't so much a factor.

as noted before,

re: the last point (tubulars @ higher pressure than clinchers), i know that sounds right, but two things come to mind:
1) my testing was done on tubulars, and the tubulars had lower Crr for lower pressures.
2) tubulars resist pinch flats better. higher pressure is a way to also reduce pinch flats (for clinchers). tubulars don't need to rely on that.

for similar construction, tubular sidewalls are more supple for the same pressure (better handling)...but this doesn't mean it's got lower rolling resistance. it's really the opposite of conventional thinking.

it's part of the reason why we can run lower pressures for tubulars in CX than we can if we were running tubes or tubeless. pinching/burping a tire (for tubes or tubeless) is more an issue at lower pressure. [of course for tubeless, the sidewall is structural and therefore stiffer, so there's always a difference in feel for a given pressure. this is particularly notable for MTB tubular vs tubeless.]

i appreciate the points in your post.

we're not even getting into differing construction of tires...

If we're talking SRM you can change the arms on Shimano, at least on the 130 BCD series. They stock a variety of arms.

Add Rotor in there as well.

IIRC, he got the Noah RS, the non-ISP version.

Yup, you are correct. I personally stayed away from Ridley ISP. I just don't like the idea of having a static post. Especially if I want to travel, change fits, resale, etc.

Sram arms also can be changed on both Quarq and SRM. Also, you can swap it from GXP to BB30 if needed.

The real-world testing is interesting, and not necessarily the results I would expect! Cool. And the point that sidewall suppleness doesn't necessarily mean lower crr is well-taken. As a real-world example, Jeremy Powers switched from Dugast to FMB cyclocross tubulars for this season because the FMBs were clearly faster. Dugasts use traditional cotton construction for the sidewalls, while FMBs are latex-coated cotton and have stiffer sidewalls. Yet, they are faster, and it's a win-win because the tires hold their shape better in the corners. Pretty interesting stuff - here's the Velonews article on it: Jeremy Powers explains switch to FMB tubular tires for 2015 - VeloNews.com.

I guess the lesson here is that tires are a surpisingly complex subject and their effect on speed at various pressures is often unintuitive.

I've disassembled all but the cranks and the shifters on my old bike. I have to get new tools to finish the job, then time to clean stuff up and put it up for sale.

I was half tempted to put the set on my Cross bike, but I'd like to eventually convert all my stuff to 11 speed. Having to swap out cassettes becomes really old.

does anyone make a cantilever brake hanger with a large "drop?" i'm using the problem solvers one now and the curve between the hanger and the bottom of my stem is very very tight. is it ok to remove the barrel adjuster? i can't even use it because it's too hard to turn.

I've seen setups where they drill the stem and use that as the hanger; at some point too much drop on the hanger and you run out of cable pull.
May or may not be OK to remove the adjuster, see how much float there is and if the cable is going to chafe.

You can remove the adjuster and replace it with a cut down metal 5mm housing ferrule.

What do you mean by cut down? I was just going to remove the adjusted and use a fertile but I'm worried about the cable/housing slipping off the hanger. I've also seen drilled stems but would like to avoid that. Cable pull isn't an issue right now. I've got plenty of room on that end.

I thought you had cable pull issues, as in the bridle was hitting the adjuster at full stop. If not just use a metal ferrule.

Tektro Alloy Cable Hanger

Mikey, if you need one of those hangers I have one I don't need. I use a fork mounted hanger.