At the mo, I have a 46Tx18T gear combo. It's a magic gear. Now, given that dark art called the 'Rule Of Four', if I want to use a 16T cog in the rear, what's that mean to the chainring size I need to go to? 48T chainring? 44T chainring?
I never fully grasped the concept of the rule, so I figure here's my chance to dive right in.
At the mo, I have a 46Tx18T gear combo. It's a magic gear. Now, given that dark art called the 'Rule Of Four', if I want to use a 16T cog in the rear, what's that mean to the chainring size I need to go to? 48T chainring? 44T chainring?
I never fully grasped the concept of the rule, so I figure here's my chance to dive right in.
Des, what the 'ell are you doing running that bigga gear anyways??? The heck with your knees, you're gonna have one a them cardiac episodes or sumthin'.
I'm an idiot for running 38/18 up here in hilly Preskit!
SpinWheelz said:
Cheers, fellas. If you'll excuse me, I'm off to set things on motion to completely wreck my knees now...
This gearing isn't for off-road use, mind you. At the mo, I've got a very nice setup with the 46x18 gear combo on my road-going MTB. I can handle most of the flats and mild ascends with ease with that gearing. But I know I can go faster and I know that I can try and build up a bit more strength if I tweak the gearing a bit, hence the tougher gearing. Granted, that's a helluva tweak, but what the hell, let's see where this goes.
The "rule of 4" isn't 100% foolproof when running "magic gears" on bikes with vertical dropouts. For example, 36/20, 34/18, and 32/16 all run really well on my bike, which has vert drops. That is just as the rule of 4 would predict. But the "rule of 4" also says I could do 36/16 and 32/20, without any chainlength change. Well, there is soem change, I know because 36/16 is really snug (doable with a "stretched" chain), and 32/20 is very loose and would require a tensioner for any real riding.
If you really want to get into just which ones will REALLY work (and why) you need to check out fixed inovatons / fixmeup. http://www.peak.org/~fixin/personal/fmu/php/fmu1_1_big.php
Fixemeup indicates that 44x16 will work exactly as 46x18 would (and is a good bit higher ratio) but that 48x16 requires a signifigantly shorter chainstay- IE, it would be very loose, and likely require a tensioner. There also a lot of gears lower than 46x18 that would work for yah, but not to many ones that are higher, at least not with practical chainring sizes.
It's both the total teeth and the difference between the 2 that need to match. Rule of 4, or with halflink, 2, applies to the total, the difference can't be overcome, chainlength differences are tiny but significant.
If you are running 36/20, how could you run 36/16 without a change in chainlength? You have an extra couple of links hanging around. Remember that the total amount of teeth has to be equal. Using the rule of 4 you actually get 36/20, 34/22, and 32/24 not 36/20, 34/18, and 32/16.
"]The "rule of 4" isn't 100% foolproof when running "magic gears" on bikes with vertical dropouts. For example, 36/20, 34/18, and 32/16 all run really well on my bike, which has vert drops. That is just as the rule of 4 would predict. But the "rule of 4" also says I could do 36/16 and 32/20, without any chainlength change. "
At the mo, I have a 46Tx18T gear combo. It's a magic gear. Now, given that dark art called the 'Rule Of Four', if I want to use a 16T cog in the rear, what's that mean to the chainring size I need to go to? 48T chainring? 44T chainring?
I never fully grasped the concept of the rule, so I figure here's my chance to dive right in.
I meant "chainstay length"- In other words, no need for horizontal droopouts.
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