Compact rotor rings actually worth it?

Coach Patrick

So...I am building up a new P5. Turns out one of the seatpost bolts on my P3 was "pulling out" and as such, I had the option for a warranty frame replacement. I have upgraded that to the P5 (don't tell Coach Rich on his 2003 P3!!!) and am building it out to stay sane during the recovery period. 

I am planning on DI2 so I can catch up with (apparently) everyone else I know who owns a bike. And I am still thinking about what bars I want (it's a P5-3, not a -6)...but I had a question about the crank.

After 6 years of hearing Coach Rich talk about compact cranks, I am strongly considering them. Of course, I live in Rhode Island where total elevation gain is 650 FEET in the average EIGHTY MILE ride.

Background

I ride about 85rpms and try to stay aero on all terrain unless it's like 10%. I have a 53/39 Rotor Ring on the front set to TT style (so it's like a 56 tooth ring at the power phase of the pedal stroke and like a 51 at the dead spots) with a 12/25 on the rear. 

Options

#1 - Regular Compact Crank.

#2 - Rotor Compact Crank: A 50T Q-Ring, around the upper dead-spot is equivalent to a 48T, but as the pedal goes down and more strength is applied, the equivalent chainring tooth size reaches 52T.  More on the Rotor website here.

#3 - Stick with the same cranks that have been working (Rotor 53/39).

Other Info

I plan on racing flat courses for the forseeable future (FL, TX, etc and don't really consider Tremblant or Placid that hilly - I can ride Placid in the big ring).  I do plan on trying to lay claim to the fastest EN IM bike split again (while still running well...I might have that combo title, not sure), so there is a lot of TT in my future. 

I guess I can't really tell if I will be gaining or losing anything by going compact. Maybe this is a switch I make for my road bike going forward given that sees a lot more vertical?

Thanks in advance for your help!!

new2703

I'm not expert so not sure qualified to answer. I rode last year and first part of this year on Roto standard cranks. Recently switched to new Dura Ace 9000? crank and love it. I find it to be stiff and what feels like more responsive. Another advantage is that it was designed to be able to switch out the rings. To answer question standard or compact,I would stick with standard especially given your plans for riding.

tim cronk

I have compact gearing with rotor cranks and Q-rings on my DA2 Felt which is a Di 2 bike......

First off... Get the Di2 without a doubt!!!.... You will not be dissappointed...

My take on Q-rings are take em or leave em , I can't tell the difference, I get on my old bike with standard round gears and I'm just as fast or slow NO difference.... But what I can say is round rings shift better , even with Di2 round rings shift better..... I have dropped a chain a few times .....I'm actually considering switching back to round .... I vote round rings I think you will like the smoother shifting better.

Compact vs Standard ..... I have never really run out of gears with an 11-28 in the back and compact in the front but there has been a few times I wish I had more like on a flat with a good tailwind... My natural cadence is closer to 90 and I'll go over 100 without coasting till 33-34mph .... Since your used to standard and know you can ride hills or flats with it my guess for you would be Standard! I could see you spinning out at IMFL in a tailwind with compact.

new2703

x2 on the shifting problems with the roto cranks with q rings.

Dino Sarti

P5-Three or P5-Six both use the Anduro bars. The UCI doesn't certify the bars. The difference in the P5-3 and the P5-6 is the fork. The P5-6 has a more aero fork and the "beard" that covers the front brake. The Anduro bar and seat post come with the frame set, not sure on a warranty tho. The Anduro is great bar~

What brakes are you gonna run? If you go Hydro, you will need to hack Di2. It will take cable brakes tho and then you can use the Di2 bull horn shifter.

Great bike, coach....

William Jenks

Patric, it's time to do some math. 53/11 is a smaller gear (ratio = 4.45) than 50/11 (ratio = 4.54). Go with 50/34 and 11-23 in the flats or 11-26 on a hilly course and you get the best of all worlds. You don't have to worry about not having enough gears. (Although yes, 53/11 is that much faster a gear, you're evidently not finding a need for it now, so why worry about it!)

Use the link below and you'll see you have an extra choice in the 20-27 mph range (fewer cadence gaps) using 50/34 and 11-23 than you do at 53/39 and 12-25. Even with that, the easiest gear is easier and the hardest gear is faster with the compact. It's just math. You'll have a bigger cadence gap at the high end, but you don't ride THAT FAST THAT MUCH.

http://public.tableausoftware.com/views/bikegears/CompareBicycleGearing

This is a simple choice unless you're worried about cadence gaps in the 30+ mph range. (And it will be marginally lighter, to boot.)

tim cronk

@William... I'm with ya and makes sense and for the most part have never needed more than a 50 - 11 combo , BUT I did have a few times at IMTX , IMCOZ , and a Rev3 Venice (all 3 flat courses with wind) where I would have liked another gear.... This may or may not come into play because like you say it hardly occurs....But if your gunning for a slot then every single second counts! 99% of the time my 50/34 11/28 combo is all I need!

TerryO

If you can ride Placid in the big ring, seem stupid to go compact. That being said, if you're going Di2, you have options. I'm assuming 11 speed 9070 Di2, like mine. If you are using powertap, stick with 53/39, or go with the 52/36. With 11 speed cassettes, you have options. If you go Quarq and 9070 11 speed Di2, you only have the SRAM 50/34 or 53/39 option, unless you order chainrings separately like the Stronglight 52/36 which is what I did. In Minnesota, 52/36 is perfect for me with my 12/28 11 speed cassette. But since I went Quarq, I had a set of 50/34 SRAM rings which are on the bike now for Wisconsin. Options. You are a very strong cyclist, so you could stick with 53/39. That being said, Rich is a strong cyclist that lives with the 50/34, but does a shit ton of climbing. Again, if you are going 11 speed 9070 Di2, you have options.

William Jenks

@Tim - If the choice were about top end speed, then it's clear that our fearless leader has been neglecting the cheap option all along and by not having an 11 on his rear cassette. I take that as prima facie evidence that he's not concerned about having higer end gears. Or at least no so concerned taht the 50/11 combo won't be fine. :-)

Again, this is not an ego question or a "you're big" or "you're small" or "your're good at hills" or whatever question...it's pretty simple math and priorities. Pick a combo that gets you pretty tight gear choices in the range that you're going to ride the most and consider secondarily what you will do in rarer circumstances. Plot out the gear graphs and pick. A big advantage of compact is that it makes the "hilly" race much easier to gear properly. If you can live with the gearing near 30 mph, it's what I would choose. But only Patrick knows his realistic speeds that he needs to be best geared around, and that iis a primary driver of the choice. This is a much more analytical choice than messing with crank length...there's no need for speculation on how it will work out at all.

I did read in a recent forum thread recently, though, that there is a new crankset out there with a bolt pattern that will accept both "standard" and "compact" chain rings. (I'm sure you'd have to buy their chain rings, but....) If so, this would make the choice no more costsly than changing cassettes, something most of us are willing to do without much thought. I can't remember the brand, but I am alsmost certain Trevor Garson was knowledgeable about it. He'd be worth asking.

tgarson

I resisted my urge to comment on this thread earlier for fear of derailing it somewhat, but in the interests of spirited discussion, is it worth it to consider whether Q-rings are worth it at all? Not just in the context of compact versus standard, but more specifically we can easily dispel claims made by manufacturers of asymmetric chain rings that demonstrate an increase in power when measured in a crank-based power meter.



The short version is that power is calculated in cycling applications as torque x angular velocity, *averaged* over a complete crank rotation. This only works assuming that the angular velocity of the crank does not vary dramatically over the course of a single rotation. We of course vary our cadence, but on a per-stroke basis on round rings the angular velocity tends to be fairly constant.



For assymetric rings however, well let me defer back to Tom A. who is a whole lot smarter than I am:

However, with a non-round ring that means that, by design, the rotational velocity of the crank is being manipulated such that the rotational speed of the crank is slowed during the downstroke (and upstroke portions as well due to symmetry) to a value below the average



So, what does that mean? In short, it means that during those times that the largest torques are being applied, the rotational velocity is lower than the average over the complete pedal revolution. Since the majority of the power is produced in the downstroke portion of the pedal cycle, this means that power reported will tend to be over-reported, hence the term "artificial power inflation". Get it?

A more thorough analysis can be found here:

http://bikeblather.blogspot.com/2013/01/whats-up-with-those-funky-rings.html

Now, am I saying asymmetric rings don't work? Not quite, although there is certainly a lot of skepticism in those claims from people who know are far more knowledgeable than I am in this subject. However, the simple claim of "slap these rings on and watch your power increase" as proof of their effectiveness is easily debunked.