I've always liked the term pedal-induced bob (dual suspension bike lingo). I used it as a log-in name for some biking sites back in the day. Vance, aka Pedal-Induced Bob. Well, the subject for today is (in part) planetary gear-induced drag.
A seat-of-the-pants observation (made by me) is, that when shifting down to a lower gear for climbing, the amount of energy it takes to keep turning the pedals = the amount it took before shifting. Or at least, a big part of it. There doesn't seem to be an easing of the strain, at least momentarily (maybe more). It really does help to downshift on the hills, but each time I have made the transition, it feels like I've hit molasses for a few seconds.
Again, I haven't got much experience in the lower gears, but it does take noticeably more energy to turn the pedals than a standard derailleur transmission does when going up a few cogs. This is planetary gear-induced drag. There's a bit of friction happening when the planetaries are engaged.
Second guessing the designers, I think maybe a better method of doing this would have been a direct-drive 2nd gear instead of the top gear. Then, the machine would be ridden mainly in the mid-range instead of top gear. This would allow for a top gear of high 80 to 90-ish gear inches, and a more moderate low gear. I don't think running in the planetary gears full time would be good, due to the drag and the wear on the system. I don't know if I wish this yet, though. Maybe I'll find I need the low gear it has now in order to do my climbing, and will just live with spinning on the flats and downhill. We'll see.
Speaking of the spinning, this setup is an improvement on the single speed fixed ratio I was running (50/17, 77.6" vs 82.4") . I am able to get a few more MPH out of it on the flats and downhills, which I appreciate, without losing the ability to climb the ordinary stuff.
The other thing I noticed is the weight. This is no lightweight setup. The wheel weighs in the 1500 grams ballpark. However, I only really notice it when lifting it up and down from the roof rack. It is definitely more porky than before.
My gear-inch specs: 82.4, 61.8, 51.5 based on 50T, 170mm crank, 700c wheel, 25mm tire, 16T cog.
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The losses on "2" are minimal when the hub is run in, and there is no problem with wear - the planets are turning all the time anyway, just not under load in top gear. The losses (and noise) in "1" are more significant, and I'm told this is due to poor gear tooth shape. The teeth are optimised for the small sun used in "2" but not for the larger diameter sun used in "1". The old 5-speed was the same.
ReplyDeleteThe hub does improve a lot over the first 100 miles, and a little bit more by 200 miles, but then it's about as good as it gets.