John,The Rotor instructions
John,
The Rotor instructions are interesting in their approach. The rings are considered to have 5 possible positions of rotational offset for mounting. Two are on one side of the ring and three are 180 degree opposite. Positiosl 1,3 and 5 are on one side and 2 and 4 are on the other opposing side. They want you to start at position 2 and then adjust based on your performance goals after some riding.
Rather than have you work with angles to do the install they just walk you thorough a physical process that gets you to the desired angles. That approach should help the non engineers do the install. The instructional PDF is convoluted the first time you read it then it starts to make sense as you work through. If you just follow it carefully; it does just work and you really don't have to understand what is going on; just follow along and you get the right answer for each unique rider and bike setup. (I admit to doing it wrong the first time and on re-reading the instructions I found my error.)
The process they use is basically: (a) figure out the crank position that is your dead spot; (b) then psychically align the ring on the crank so that the high point is just engaging that chain when the crank is at the dead spot. (c) They have you mark that as position #2; and you subsequently calculate positions 1,3,4 and 5 relative to that one. (d) Then mount the rings with the bolts.
Interestingly; Robert and I have our Vendetta Booms (from the look of his picture) set about exactly the same and we look to be about the same height. Our independent separate physical setup gave us the same exact orientations. It does seem logical. For me I find it rides really nice. I'll do as rotor suggests and ride it a good 200 miles to acclimate before I decide if I want to move it to higher numbered position.
The pdf notes the following about the mounting hold you select, which they call the "OCP"
A higher OCP regulation number is better for acceleration, and a lower regulation number should give a slightly higher top speed. If you would like to be able to transfer power earlier in the stroke or get a feeling of more resistance (often for mashers), rotate the chainring to a lower OCP number. If you would like to transfer power later on in the stroke or have the feeling of less resistance, rotate the chainring to a higher OCP number.
Now that I have it mount, it makes a lot of sense. They do instruct you to mark the holes in question for reference against a fixed spider bolt. In Robert's case and mine the factory etchings nicely line up at different spider bolt and we can just use that as our reference point; as it really doesn't matter which bolt you use as long as that's the one you always use after the initial setup. Him and I are simply lucky due to our boom Position choice and height.
For comparison, on my Wife's Silvo the BB is higher from her shorter legs. When I do the physical mounting process her alignment turns out one hole position counter clockwise from mine. That position results in the same exact angle and position for the ring relative to her dead spot. Her's does not yield the convenient alignment of the etched markings. That is easy enough for me to track correctly by using the Vendetta as a reference since it's only 1 position off; otherwise I would probably have to mark the holes as per the instructions.
I will take some close up photos and add them to the thread. They should show how the angles wind up the same from slight different mounting points. In the end it's a function of the boom height; and then the riders personal preference for positions 1 thru 5 for power uptake. I think that final choice of position 1 thru 5 will likely tie back to your question about whether that preference is different for riders that lay flat and those that sit up. I think lying flat does at times encourage us to be a little more of a masher. but will we prefer a masher friendly alignment; or the one that encourages use to spin more. That should be very interesting to figure out in the coming miles.
Interesting on Round Round 52/36 was good for me, so that's the Qrings I used; I can already tell that 53/39 would have probably had a near equal low end thanks to the ellipticals. Both bikes just gained more low end; and in the wife case we stepped up to a 52 from a 50 and she gained a lot of range.
Lots to like so far, it makes the Vendetta really smooth to pedal; just like a Quest.
