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Title: speedo drive ratio... ??? Post by: JonnoSkye83 on March 06, 2011, 01:47:08 AM hi all,
just wondering... my trike has yamaha front forks and wheel (xt600 if i remember correctly) it also has its original speedo drive unit. ive seen a few aftermarket speedos on fleabay that state... "60mph = 2240rpm" on them, does anyone know if i were to buy one if it would show my correct speed? (90/90-21 front wheel/tyre) Title: Re: speedo drive ratio... ??? Post by: brock on March 06, 2011, 02:19:05 AM I reckon that if you spin that front tyre/wheel combination at 2240rpm you'll be doing 153mph :o
533.4mm dia wheel 90x.9 = 81 (tyre profile ) x 2 = 162 = 695.4 overall dia. , x 3.142 = 2185mm circ , distnce travelled per rev x 2240 = 4894400mm per min , = 4894.4m per min x 60 = 293664 m per hour / 1.09 ( metres to yards ) = 269416.5 yds per hour / 1760 = 153.07 mph it's late , someone check it Title: Re: speedo drive ratio... ??? Post by: Manky Monkey on March 06, 2011, 07:32:50 AM I checked it -made absolutely no sense at all to me. :P
I assume the rpm is referrring to engine revs, not wheel ones. For those without a rev counter, it gives a rough guide to how hard the engine's working? Title: Re: speedo drive ratio... ??? Post by: JonnoSkye83 on March 06, 2011, 08:43:39 AM i was wondering if it was something to do with the speed the speedo drive is turning the cable... cable spinning at 2240rpm = 60mph... if i knew the ratio the speedo drive reduces to i could probably work it out... thats if 2240rpm is indeed cable speed...
??? >:( ??? :-\ Title: Re: speedo drive ratio... ??? Post by: Manky Monkey on March 07, 2011, 12:14:18 AM The chrome mini speedos have been around for years & are notoriously innacurate -the needle bounces around so much they usually read plus or minus about 30mph. More for show, to keep the boys in blue happy, than for any serious use.
Title: Re: speedo drive ratio... ??? Post by: brock on March 08, 2011, 08:53:01 PM "I assume the rpm is referrring to engine revs, not wheel ones"
I thought that the Yamaha units were driven from the little round thingie with a sticky out bit that goes on the side of the wheel and gets held by a bumpy bit on the bottom of the fork leg. I thought I had one in the shed to check he ratio , I'm guessing there's a little bevel or worm drive box in there, however , can't find it. This from an American Yamaha site :- "All Japanese Motorcycles are equipped with mechanical speedometers of 2240 RPM= 60mph! This will work on all Japanese bikes with cable driven Speedo! Universal on all Japanese Bikes - Honda, Kawasaki, Yamaha, Suzuki." trust it if you will Title: Re: speedo drive ratio... ??? Post by: Cabman77 on March 08, 2011, 10:32:52 PM It`s late for me and I`ve had a hard day but the mini speedos are one of two ratios just can`t remember what they are( 2.1to1 keeps coming into my head but I wouldn`t trust that) but the lower of the two suits most jap bikes. I had one on my last triumph/cycle haven chop with a jap front end and it was deadly accurate and steady. I`ve ridden with others that were unreadable but that one was spot on.
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