Bicycle Mechanics - Front Cassette?
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01-18-08, 12:01 PM
Rear gear arrangements have evolved nicely. Why haven't we seen similar advances in front gear systems? One would think that narrow chains suitable for nine or ten speed rear cassettes would enable smooth, broad four or five speed gear clusters on the front. As a tourist with a heavy bike, trying to make the most of momentum on highway hills, I appreciate very broad options - from 28 X 34 on the uphill to 54 X 11 on the downhill. A smoother, broader front shifter would be a great thing. What are the obstacles to getting such an option to market?
01-18-08, 12:06 PM
It already happened in the early 80s. See Sheldon (http://www.sheldonbrown.com/shimano.html#ffs)
But that's not really what you're talking about. I think it might be possible, but cross chaining would be a b*tch. I already hate adjusting triple front derailleurs; imagine quad or quint!
In case you haven't noticed, bicycle people are usally tinkerers (after all, the Wright brothers ran a bicycle shop!).
I am totally confident that this has been tried numerous times in numerous ways, and the only thing that kept it from coming to market is that it did not work better (or as well?) as what's already available.
01-18-08, 01:44 PM
That's an interesting thought, but probably not practical.
The width of the crank would likely be affect your stroke.
And as with the rear cassette, it's not the number of gears you have, it's the range that matters.
Finally, is there any gear we're missing that would be needed? We really have all the gears we can push.
01-21-08, 07:51 PM
I've been running 28-40-52 (or 28-38-52 on a bike with wide chain stay), which is as much as any front dérailleur I've found can handle. I'd like to go to a 54 to have a little higher downhill speed, but even if I can find a dérailleur that can span that, the jumps are too big to cross comfortably. My skinny chain fits in between my chain rings. Why not fill that space with a gear?
Of course we don't need every combination of gears. Crossover positions are to be avoided anyway. A smooth shifting front cassette could make shifting smoother with very broad range.
01-21-08, 11:07 PM
Its funny you say that, check out the da Vinci web-site. Our tandem uses 4 cogs up-front which is more or less a cassette, works like it should and it provides enough gears with nice spacing especially on a tandem.
01-22-08, 12:46 AM
Short answer: The cost of developing and marketing is greater than the expected demand/revenue for that product.
Adding a fourth or fifth chainring at current spacing would either 1. Increase tread (Q-factor) 2. Require skinny or offset seat tube (tough sell with carbon bikes -and would likely not work with fatter tires).
This is not desirable.
Closer spaced chainrings would require a narrower cage on the front derailleur, which would increase the chances of getting chainrub from even slight cross-chaining. This is not desirable.
Perhaps an arrangement could be made involving a new type of front derailleur. Except that the pros are already only using 2 chainrings, so a company would be spending money developing somethign that may be toughr to sell or require proprietary frame configurations that aren't racing-derived.
This is undesirable.
Why don't you get a Schlumpf 2-speed bottom bracket and combine that with a SRAM dual-drive hub? BAM! 120 gearing options! (2speed BB x 2 chainrings x 10s cassette x 3speed hub)
PS if your skinny chain fits between your chainrihgs you've got a compatibility issue somewhere.
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