Why is there so much gear overlap between the two front chain rings?
Here is what I mean:
If I start in my lowest gear (with the front and rear derailers) and go all of the way to the highest gear with my rear derailer, why is it that when I switch to the larger ring in the front and then find the equivalent gear in the back, then I only have a couple of more (higher) gears to go. It seems like a bike could be made to have the two front rings so much different in size that there would be no overlap, then we’d have higher and lower gears.
the basic reas is that it’s impractical/impossible to have a very large difference in size between your front chainrings. You simply can’t shift between them–going down the chain will fall off, and going up it’ll grind and fail to move up cleanly.
Cross-chaining is inefficient and puts extra strain on the parts, so a little overlap means you can spend more time in the more efficient positions.
And they do make compact chainrings, which have a 16 tooth difference in front rather than the usual 13 or 14. Beyond that and front shifting degrades quite a bit, but if you need more than you can get with a compact crankset and wide range rear cassette you can just get a triple.
the basic reas is that it’s impractical/impossible to have a very large difference in size between your front chainrings. You simply can’t shift between them–going down the chain will fall off, and going up it’ll grind and fail to move up cleanly.
And, if the big ring diameter sticks out too far past the small ring, it’ll also get in the way of the chain angling from the small ring to the small end of the cassette… so beyond cross-chaining simply being less efficient and increasing wear on the cogs/chain, it can even get blocked completely in the small/small direction if it’s sharp enough.