Bike chain formula

Well, this is partly about the bike chain formula, and partly about the nifty titanium road bike frames for not-a-lot-of-money at Habanero Cycles. The Team Issue Nuevo frame comes in my size (not made-to-order, but close enough for the $300 difference). I’ve been in correspondence with Mark (see the “who’s who” at the bottom of the page), and I can “part out” my current bike onto their frame. Then I could just replace parts as they wear, and I’d never have to buy a new bike again; Mark wrote, “Your grandchildren will be riding it.”

However, there’s a difference in the chainstay length between this frame and my current frame, so I’d have to shorten a chain to the right length (you knew I’d get to the title of this post eventually, didn’t you?) (…and the chainstay is one of those two pieces of tubing that run from the pedal-crank housing to the rear axle; most bicycles have two of ’em). So how long of a chain would you need? Well, Park Tool to the rescue. They’ve got a page for figuring chain lengths, with the “use the old chain as a guide” method, the “wrap it around and figure it out” method, the “this formula is close enough for most purposes” formula, and the “this is the real formula, but it’s so complicated, we hoped we wouldn’t have to put it here” formula (check out the page, and see if I’m kidding).

Well, this is a challenge to which I must rise… and it’s what spreadsheets are made for. I made a spreadsheet in OpenOffice.Org Calc, where if you know the three variables (chainstay length, number of teeth on largest front gear, number of teeth on largest rear gear), you plug the values into the greyed-out cells in the spreadsheet, and you get the chain length in inches. And I added tabs so that you can use the chainstay length in inches, centimeters, or millimeters. Get it here (right-click & “save as”).

(No, I won’t do it as an Excel file. First of all, I refuse to participate in Microsoft’s monopoly of the office desktop. Second, if you go get Openoffice.Org – it’s a free [as in free beer] office software suite, and it runs on most of the operating systems of any readers of this deservedly-neglected blog – you can save it as an Excel file, because in many ways, Openoffice.Org is more robust than MS Office. And, of course, if you go get Openoffice.Org, eventually, you might find that you don’t have to spend hundreds of dollars enriching Microsoft, because the free program does everything you want it to do.)


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