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The Street => The Bike Shop => Topic started by: Thepoolman on March 17, 2016, 05:36:35 PM

Title: chain stay length, gear ratio chart...
Post by: Thepoolman on March 17, 2016, 05:36:35 PM

haven't been on here in ages... what happened to the chain stay length/ gear ratio chart...

or what would the  length of  30-9 - 31-9     33-9 33-10 be?

trying to get slammed on a 13.75 frame.   but also need that man gear ratio.     I used to always run 27-9  but i need a much harder ratio.   

 Thanks!

Title: Re: chain stay length, gear ratio chart...
Post by: montymitch on March 17, 2016, 06:03:40 PM

http://www.vitalbmx.com/forums/General-BMX-Talk,2/Gear-Ratios-and-chain-stay-length,1282702

Title: Re: chain stay length, gear ratio chart...
Post by: Thepoolman on March 18, 2016, 08:22:02 PM

I saw that... but the only thing that helps me off that is 30/9.     the old bg chart had 31 and 33.   

Title: Re: chain stay length, gear ratio chart...
Post by: Narcoleptic Insomniac on March 18, 2016, 10:23:32 PM

http://eehouse.org/fixin/formfmu.php

Title: Re: chain stay length, gear ratio chart...
Post by: dersou ousala on March 19, 2016, 05:48:27 PM

31/9 and 33/9 would be good for 13.75. The other would sit at 13.875 or 13.625.
but damn... 33/9 thats a manly gear ratio

Title: Re: chain stay length, gear ratio chart...
Post by: Thepoolman on March 19, 2016, 10:44:13 PM

I'm running 33-10 now and its too easy.  Riding around the city is way way too much work with an easy ratio and I rarely pedal when at skateparks.   Looks like ill be staying with 33-10 or 31-9.   Thanks dudes.

Title: Re: chain stay length, gear ratio chart...
Post by: weedbix on March 19, 2016, 10:57:19 PM

That chart is wrong. The BG chart was wrong too. This one is the most accurate:

http://eehouse.org/fixin/formfmu.php?maxRing=33&minRing=30&maxCog=9&minCog=9&stayLen=13.75&wheelDiam=19.15&isMetric=0&display=table&useHalfLink=1&stretch=0.00&axleAdjust=vert&sortKey=Stay_length

Be aware that the way some frames rear ends' are measured is inconsistent

Title: Re: chain stay length, gear ratio chart...
Post by: montymitch on March 20, 2016, 10:31:46 AM

I think there are simply too many variables to have a 100% accurate chart. They only time I've needed one was to see if changing from a 28t to 25t would require a half link adjustment. Chain stretch, sprocket wear, chain line, and the current moon phase all figure in to the reality of making things work right.

Title: Re: chain stay length, gear ratio chart...
Post by: dude... on March 22, 2016, 12:34:00 AM

yeah, once a new chain stretches it can make your back end at least half a cm longer, even more. so many threads on here about slamming the back end about 8 years ago lolz

Title: Re: chain stay length, gear ratio chart...
Post by: weedbix on March 22, 2016, 04:09:21 AM

True, there is variation. But it's variation from a value we CAN totally predict

Title: Re: chain stay length, gear ratio chart...
Post by: dude... on March 23, 2016, 07:12:07 PM

totally true, people just sometimes forget that there will be a bit of variation over time as things bed in

Title: Re: chain stay length, gear ratio chart...
Post by: Sasha on March 24, 2016, 11:44:20 AM

I'd be surprised if most BMX companies didn't just weld on random length rear ends making this totally useless.