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captainfly
Joined: 01 Apr 2009
Posts: 230
Location: NWUK
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 Posted Sun Nov 8, 2009 2:05 am |
| JamesBrckmn wrote: | | We have so many gears, compared to a car, for example, because humans aren't as powerful as cars, so we have to be as efficient as possible, by having lots of different gear ratios. |
It is a lot to do with powerbands, most HGV have at least 16 gears as they only have about 500rpm to play with most humans have less than 120rpm to play with. The gears just allow differences in terrain and allow better chainline.
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Mongoose Teocali Comp |
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Northwind
Joined: 06 Sep 2008
Posts: 4560
Location: Edinburgh
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Posted Sun Nov 8, 2009 4:19 pm |
| JamesBrckmn wrote: | | We have so many gears, compared to a car, for example, because humans aren't as powerful as cars, so we have to be as efficient as possible, by having lots of different gear ratios. |
But we have a lot of overlap. Which can be useful, sure, but of the 27 ratios in a standard bike, how many do you need? I just took off 9 of them and put them in a box... And of the 18 that remain there's how many unique (or significantly different) ratios?
We still do it because we're forever chasing what we've already found |
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Captain Turok
Joined: 06 Apr 2008
Posts: 594
Location: The mountains, between London and Kent.
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bigchazrocks
Joined: 04 Jan 2009
Posts: 2155
Location: Bristol / Salisbury-ish / Leicester
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Northwind
Joined: 06 Sep 2008
Posts: 4560
Location: Edinburgh
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Posted Sun Nov 8, 2009 8:12 pm |
| Captain Turok wrote: | | As said previously I believe its just about minimising the differences between the individual gears, so there isn't too much of a step up or down between them. |
But that's not really what happens, with a standard ratio triple and block you mainly get loads of duplication. XX has only 20 gears but covers most of the useful ratios.
We still do it because we're forever chasing what we've already found |
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supersonicLives Here
Joined: 25 Nov 2005
Posts: 48007
Location: Chapeltown, Sheffield
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Posted Sun Nov 8, 2009 8:35 pm |
Duplication is not always a bad thing, and there are a few reasons why it happens.
Firstly if you run a 44tooth chainring with a 11-34 cassette, in order to not duplicate any of these gears you need a second chainring of 15 teeth. Deraillers cannot handle that jump, and even if it could the jump is massive - you would have to change right back through the cassette to get the next gear (of course you do this to an extent with any front meched set up if you want sequental gearing, but many want the larger jump. But not that big).
People do like a large range of gears ie the 44/11 and 22/34, so to not have the big step as above the middle ring is added. Also have better chainlines in the most common gears.
SRAMs 10 speed groupo has a 36 (optional 32) toothed rear cog with a dual chainset (though of course you could fit a triple) choice of 26 & 39, 28 & 42 or 30 & 45 tooth chainrings. I think with a 36, ten speed makes some sense. Note a max of 15t jump at the front. However using that double would not give me any of the range of gearing I want.
I am quite happy to run a triple for the extra weight of 50g or so for another chainring, especially as you have already added the weight of a front mech, cabling and shifter!
Shimano do have a cassette called the Capreo that has a 9t small cog. Not sure of the practicalities of it with MTBs (is on leisure bikes at the minute) and requires of course specific freehub and cassette. But if implemented on MTBs it would expand the range of a double front set up and allow a smaller front cog (ie 36) which would be useful with a double and bash and work well with an 11-34 set up with a 22t front cog.
Zaskar LE 1996
Zaskar Carbon Team
MYSPACE |
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Northwind
Joined: 06 Sep 2008
Posts: 4560
Location: Edinburgh
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Posted Sun Nov 8, 2009 10:18 pm |
| supersonic wrote: | | SRAMs 10 speed groupo has a 36 (optional 32) toothed rear cog with a dual chainset (though of course you could fit a triple) choice of 26 & 39, 28 & 42 or 30 & 45 tooth chainrings. I think with a 36, ten speed makes some sense. Note a max of 15t jump at the front. However using that double would not give me any of the range of gearing I want. |
36/26 gets you fairly close to a 34/22. Thing is, that doesn't have to be an exclusively 10-speed thing, in fact it doesn't seem like any of the main aspects of XX- the 50% step-up between rings, and the big rear cassette- should have to be 10-speed. You'd get wider gearing on the rear which isn't so good, but 22/32 with a 34T block on the back works pretty well for me so 24/36 with a 36-11 block could probably do the business, on an 18-speed.
(maybe I'm just getting carried away with my latest change, but so far the only place I've missed my big ring is on the road, and even then it's not that big a deal, even with the 32T front. So I'm looking at triples with a bit of a new eye, I didn't really expect this.
We still do it because we're forever chasing what we've already found |
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supersonicLives Here
Joined: 25 Nov 2005
Posts: 48007
Location: Chapeltown, Sheffield
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Northwind
Joined: 06 Sep 2008
Posts: 4560
Location: Edinburgh
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captainfly
Joined: 01 Apr 2009
Posts: 230
Location: NWUK
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bomberesque
Joined: 18 Jul 2008
Posts: 1142
Location: Belgium, where rain is typical
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Northwind
Joined: 06 Sep 2008
Posts: 4560
Location: Edinburgh
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I never seem to use my granny ring though 