Changing gearing -- front vs rear
zv30 at sbcglobal.net
Sat Jun 21 00:11:04 PDT 2008
fyi.sv400 has 14 stock.
Twin Works Factory
----- Original Message -----
From: "Jim Stewart" <js at strappe.com>
To: "Suzuki SV650 Mailing List" <sv650 at micapeak.com>
Sent: Friday, June 20, 2008 10:44 PM
Subject: Re: Changing gearing -- front vs rear
> This won't matter at the track, but I have some observations re: 14 tooth
> countershaft sprocket on the street.
> About 5 years ago I replaced the chain and both sprockets - 14 tooth c/s
> and 44 tooth rear (44 is stock on my SV-S).
> I had fun with the throttle - front end comes up very nicely with that
> ratio, thank you. (The ratio 44/14 is pi to four significant figures.
> Nature is mysterious. Shrug.)
> But after about 10K miles the drive train developed a resonance - at 41
> mph, plus or minus 1 mph, the chain would - ummm - "thrum". It was
> obvious, repeatable, and coincided with the beginning of rather rapid
> chain wear. I continued with this situation for another 2K miles.
> At 12K or so I replaced the whole kit - c/s sprocket, rear sprocket,
> chain - once again with the 14/44 combination.
> After 8 or 9 K the resonance began again.
> I replaced the c/s with the original 15 tooth sprocket and all the
> strangeness vanished. I ran the 15/44 with the same chain and rear
> sprocket for another 10K or so.
> I think this is the same phenomenon that happens with gears, where a
> simple ratio between drive and driven gear will let the teeth wear
> unevenly. This is well understood by mechanical engineers, so I've been
> told, and the choice for mating gears is a ratio that's not evenly
> divisible. Even/even (14/44) is even worse.
> Yes, the stock 15/45 is a nice round 1:3 ratio, but (now we're talking
> about sprockets) it's not a problem, it seems. I've run 15/45 for the last
> 4 years with no problems. I gather 1:3 would never be used in a gear pair.
> I don't know what the mechanism is here, but (as a longtime (50 year) RF
> and audio guy) I can assure you I recognize resonance when I feel it, see
> it, or smell it. Or get a nasty burn from it. (RF is tricky.)
> Thoughts, anyone?
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