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#319705 - 06/22/10 5:41 pm speedo drive  
Joined: Oct 2004
Posts: 44
crash1292 Offline
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crash1292  Offline
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milwaukee
what ratio am I to use with a A65 19in rear wheel?.
have a 2/1 now and the speedo reads very fast like 20 mph over
smiths speedo ssm 5001/05

Last edited by crash1292; 06/22/10 5:44 pm.
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#319741 - 06/22/10 8:46 pm Re: speedo drive [Re: crash1292]  
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LarryLebel Offline
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LarryLebel  Offline
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Canada
Out only 20% seems pretty good to me for a Smiths speedo. It also seems to me there are only 2 speedo drive gear ratios 2:1 and 15:12 that correspond to 1600 turns/mile and 1000 turns/mile speedos, respectively maybe based on 18" wheels. The 1000 turns/mile speedo on my B44 was way out. I worked out that I needed a 1587 turns/mile unit with a 2:1 drive and 18" wheel but when I got a 1600 speedo the speed is still way off. If your 19" wheel is not stock you are hooped unless you get the speedo recalibrated.

#319804 - 06/23/10 6:48 am Re: speedo drive [Re: LarryLebel]  
Joined: Oct 2007
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Ignoramus Online content
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Ignoramus  Online Content
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Posts: 1,512
Auckland NZ
Smiths made some weird ratio speedo gear boxes....things like 21/10 and 19/10 amoungst others (no idea what they were for) ...good luck finding one to try.

Like Larry says probably best to get the speedo calibrated to suit a more common drive with the 19inch wheel, its not a tricky job


"There's the way it ought to be and there's the way it is" (Sgt Barnes)
#319984 - 06/24/10 5:20 am Re: speedo drive [Re: Ignoramus]  
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DavidP Online content
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DavidP  Online Content

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Gnashville
You didn't say what year your bike is, but that's a grey-face gauge, so I'm guessing late 60's unless the 19" is original.

In any case, my 71 has a 15:12 drive and reads about 5mph high. Maybe if I put a 19" rear wheel on it the gauge would be accurate.


Stepping on others doesn't make you stand tall.

71 A65L "Zelda"
92 BMW K100rs "Gustav"
#319988 - 06/24/10 6:12 am Re: speedo drive [Re: DavidP]  
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Wilfred Offline
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Wilfred  Offline
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Nanaimo, B.C. Canada
crash 1292.....20 mph over at what speed? And then there's the rear tire that can make a substantial difference. On my 86 Volvos, the mag wheels mean I read high by 10 plus percent and the steel wheels with the different tires are pretty close, according to the " your speed " devices that are often seen. Cheers, Wilf.


"It's about the ride..."
#320021 - 06/24/10 12:58 pm Re: speedo drive [Re: Wilfred]  
Joined: Sep 2002
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Alex Offline
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Alex  Offline

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Seattle
I recommend getting this book:
http://www.lulu.com/product/paperback/magnetic-speedometer-repair/5092561

much cheaper than another drive, which isn't gonna have the right ratio anyway. I don't know of any A65 that drove the speedo off a 19" wheel, but Rocket III's ran a 15:12 with the same speedo head as a lightning but probably a different rev/mile number.


A smattering:
'53 Gold Flash
'67 Royal Star
'71 Rickman Metisse
'40 Silver Star
'37 Rudge Special
sixtyseventy Lightboltrocket road racer...and many more.
#320081 - 06/24/10 9:23 pm Re: speedo drive [Re: Alex]  
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crash1292 Offline
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crash1292  Offline
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milwaukee
I have 3 stock 19in BSA rear wheels (WM3 Jones rims,quick change,straight nail spokes) they must have been used on some model

#320084 - 06/24/10 9:51 pm Re: speedo drive [Re: crash1292]  
Joined: Sep 2002
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Alex Offline
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Alex  Offline

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Seattle
Do they all have speedometer drives? Generally, some unit twins up to '65 (Lightning Rocket, Cyclone, maybe others with QD rear wheel)came with 19" rear wheels but, like all the pre-unit QD rear wheels (which were also 19")they do not have the slotted steel tube as a bearing retainer for the speedo drive. The parts books after '65 show only 18" rear wheels for unit twins. But after your pointed this out, crash, I did some more rifling and found that some east coast Lightnings and thunderbolts were supplied with 19" rear wheels as well and here's the clincher: these were apparently equipped with a 21:10 speedo drive. So, maybe that's what you have? I've never seen a drive with that ratio, but I guess they made 'em...


A smattering:
'53 Gold Flash
'67 Royal Star
'71 Rickman Metisse
'40 Silver Star
'37 Rudge Special
sixtyseventy Lightboltrocket road racer...and many more.
#320091 - 06/24/10 10:34 pm Re: speedo drive [Re: Alex]  
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crash1292 Offline
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crash1292  Offline
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Posts: 44
milwaukee
thanks Alex....and yes they all have the speedo drive bearing retainer

#320328 - 06/26/10 3:37 pm Re: speedo drive [Re: crash1292]  
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crash1292 Offline
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crash1292  Offline
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Posts: 44
milwaukee
a 15/12 ratio did the trick

#320346 - 06/26/10 6:00 pm Re: speedo drive [Re: Alex]  
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Rickman Online content
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Rickman  Online Content
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Posts: 2,884
Ohio
Alex,
It's funny your observation is this way, mine has been almost exactly opposite.
Almost Every A65 I've ever owned [ '66 who knows what ( it was my first BSA owned, got it in '73? ), '67 Hornet, '69 Lightening [ Gone now ], and then I graduated to A10's, which all have 19" rears.
Then I acquired this early version A65 Star/Rocket/Thunderbolt Rocket jigsaw puzzle, and the correct fenders ONLY allow an 18" wheel to fit, which is a good thing, as some time ago, I bought a set of beautiful wheels, without rubber on 'em, that 19" tires flew by the rim beads, I thought they were A10 wheels, turns out to be early A65 18" wheels!
I still think I paid too much for 'em when I bought 'em....

Now my other, last? A65 project, is a '69 Fire Bird. I know of a few people here, and through the OVBSAOC, who own Fire Birds. I can ask an actual owner what is correct.
Then, I'll have to try to find them....

Thank You Brit Bike.

Alex, I am a SoCal native. No longer there though.... Thank Goodness!

I'd LIKE to find a speedo driveless rear 19" wheel for the Hornet... It has a MONSTROUS 19" chunk knobbie I can't wait to see the trench it digs with!
I may have to 'rob' a 19" rear wheel off of some Gold Star, or other pre-unit bike....
Brett
P.S. I purposly laced a set of Borrani 18" rims to my A10 twin carb "Rocker" project, so's I could get modern rubber on the bike.... 20 years ago now...

#320352 - 06/26/10 6:40 pm Re: speedo drive [Re: Rickman]  
Joined: Oct 2004
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crash1292 Offline
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crash1292  Offline
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Posts: 44
milwaukee
how many driveless rear wheels do you want?
I have 2 19in and 1 18in
shoot mee a email
crash1292@hotmail.com

#320498 - 06/27/10 9:08 pm Re: speedo drive [Re: crash1292]  
Joined: Aug 2001
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Richard Phillips Offline
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Richard Phillips  Offline
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Posts: 792
San Luis Obispo, CA
For what its worth
My 66 East Coast Thunderbolt has a 19 inch rear wheel and a different ratio drive than an 18 inch rear wheel for a West Coast Model ( cannot remember the ratio )
My 64 Lightning Rocket has a 19 inch rear wheel, but the speedo drive is off the transmission.
Richard


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