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Message started by paulmarshall on 12/02/12 at 10:22:32

Title: Sprocket Ratios
Post by paulmarshall on 12/02/12 at 10:22:32

I am currently running a 17/45 at about 2.6. I want to run a 38 on the back, so to keep around a 2.5-2.6 what size tooth would I need on the front? I have looked at other posts and wondered is their a sprocket between 43 and 38?

Title: Re: Sprocket Ratios
Post by paulmarshall on 12/02/12 at 10:26:47

Why you might ask well 1 its for cosmetics and 2 I need to drop chain for more clearance due to modifying left side cover.

All good I found this site. :)
http://www.jtsprockets.com/fileadmin/files/jtgearratio.pdf

Title: Re: Sprocket Ratios
Post by Serowbot on 12/02/12 at 10:55:04

You can play here, too... ;)...

http://www.gearingcommander.com/

Title: Re: Sprocket Ratios
Post by 360k+ on 12/02/12 at 11:27:51

The formula is gear ratio = driven sprocket / driving sprocket. So for instance 45 / 17 = 2.647 Now, substituting terms, you get driving sprocket = driven sprocket / desired ratio. So for instance, 38/2.6 = 14.61. Obviously, you can't buy a sprocket with fractional teeth, so you chose one that is evenly divided but relatively close (15 & 38 tooth = 2.53). This problem is a great candidate for a spreadsheet that would give you a range of sprockets and a nice graph for any combination in mere seconds.

Title: Re: Sprocket Ratios
Post by paulmarshall on 12/02/12 at 11:33:06

Thanks Serowbot that Gear Commander is great.
360k+ I have entered the 15/38 Ratio into the Gear Commander software and its very close to what I am running now. 17/45. A little bit higher geared but not much.
Its just what Im looking for. Thanks

Title: Re: Sprocket Ratios
Post by paulmarshall on 12/06/12 at 21:25:13

I couldnt find a 38 rear sprocket so put a 41 rear sprocket instead. I havent had a chance to put it through its paces yet. Anyone used a 17/41 setup?

Title: Re: Sprocket Ratios
Post by thumperclone on 12/06/12 at 21:59:09

if i remember correctly 1 tooth difference in the drive = 3 tooth difference in the rear
clearances are an issue on the ls one could incorporate a slider like on mx bikes o even an idler sprocket

Title: Re: Sprocket Ratios
Post by Cavi Mike on 12/07/12 at 01:18:09

A 38? You talk to the XS650 guys too much.