anotherbrian

I did 50mi+ of 12%+ repeats on a badly (at least by appearance) cross-chained 11spd drivetrain, and while it never broke, looking down at the chainline as I rode was disturbing.

I don't know the actual % loss to efficiencies, but I'd read the larger idler pulleys were very marginal gains, so would think a straight chainline would have to be beneficial.

I think you're right on parallelogram though, at least for road components. A Shimano 1x MTB derailleur (spec'd for 46T but can fit a 50T), can at least clear a 32T sprocket in the 9th gear position (based on Shimano's 11-40, 11-42, and 11-46T cassettes). So if you are satisfied with 32T being your top gear, just put two gears of spacers behind it and set the limit screw (at least for mechanical).

An alternative might be an offset rear derailleur hanger. My Specialized Tarmac disc bike (first gen) had a wonky chainline spacing that required special hubs (135mm SCS) to mimic a traditional road 130mm, however they sold a derailleur hanger that shifted the derailleur outboard to allow regular 135mm hub to be used. It works great, and put the bike back to a traditional 135mm chainline ... add some washers and a longer rear derailleur fixing bolt and it could potentially space it out even further (or have a hanger machined with the extra offset), allowing a regular road derailleur to be used.

Tourist in MSN

Leonard Zinn has written a few articles on friction losses, chain line, etc. I am not going to put together a list of articles, but this one article i found rather insightful.
https://www.velonews.com/gear/gear-issue-friction-differences-between-1x-and-2x-drivetrains/

It is easier to see the graph from that article here.
https://www.velonews.com/wp-content/...5%2C871?w=1080

Even with a cross chained drive train on the larger sprockets, the friction losses in watts were not much higher than with the sprockets that had a better chain line.

For my riding on my bikes, when I think about chainline, my primary concern is not friction loss and whether or not it slowed me down, my concern is reduction in chain life.

I have bar end shifters on two touring bikes. One advantage to that is I can tell from the feel of the lever position about where my chain is on the cassette, that makes it much easier to avoid cross chaining than with a brifter where I have no feedback on where I am on the cassette when I shift until I run out of gears on that chainring and need to change the front derailleur. Thus, I am often cross chaining with a brifter for the rear derailleur, but not when using bar end shifters.

anotherbrian

Cross chained will be less efficient than straight, no matter what the gears used are. But those articles do make very clear that gear selection (i.e. an 80x40 would be more efficient compared to a 20x10 due to the less articulation angle/bend) effects the efficiency.

The stakes are high is this Everesting business and I'm sure future challengers will chase every marginal gain they can get. The oversized idler on Ronan's bike ranges $500-1500 based on options, and eventually people will run out of things to buy.

Another place to look for info on going fast with the least effort is the IHPVA (International Human Powered Vehicle Associations, ihpva.org) journals -- lots of scholarly articles (though dated) if you're trying to build bikes that people can beat the existing speed record of 89.59mph (or just pedal over 60mph+).

Tourist in MSN

One hundred percent agree.

But an 80T chainring might weigh enough with the extra amount of chain you need, that lifting that extra weight up the mountain could negate your reduced friction. I will leave that up to the lab geeks to calculate.