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T120 1969 speedo ratio
#372148 05/08/11 6:48 pm
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Hi guys

I bought my Bonnie a little present, a replica speedo and tach.
They both work fine, but the speedo shows much more than what I´m actually driving.
I´m figuring they gave me the wrong ratio.
The label on the box says

"1966-70 km/t
WW26675K
58-43643
SPEEDOMETER GREY
KMH FACIAS EARLY 1:1 RATIO + 58-43630"

Is it the wrong ratio for my bike or do I have the wrong speedo drive/gear at the rear wheel?


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Re: T120 1969 speedo ratio
Ducknaldo #372159 05/08/11 8:37 pm
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Originally Posted by Ducknaldo
The label on the box says

"1966-70 km/t
WW26675K
58-43643
SPEEDOMETER GREY
KMH FACIAS EARLY 1:1 RATIO + 58-43630"




The speedo should be 1.25:1 to match a 1.25:1 drive box, not 1:1?
The original '69 T120 drive ratio would have been 1.25:1 (15/12)

WW26675K= 1.25:1
http://sahkourakka.com/kauppa/index.php?language=en&main_page=product_info&products_id=319


Originally Posted by Ducknaldo
Is it the wrong ratio for my bike or do I have the wrong speedo drive/gear at the rear wheel?


Check the drive box ratio? = How many cable turns are there in exactly one rear wheel revolution?
If, 1 wheel turn = 1.25 cable turns, then the drive ratio is 1.25:1

Re: T120 1969 speedo ratio
Ducknaldo #372171 05/08/11 9:33 pm
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I´m confused now.

The model # WW26675K should always be a 1,25:1?
If so, the label on the box is wrong, it shows the correct ratio for the speedo inside (1:1), but wrong model # and the speedo is the correct one, but with a wrong internal ratio?

I havent checked the drivebox yet.
Does 1:1 drive boxes for Triumph qd wheels exist at all?


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Re: T120 1969 speedo ratio
Ducknaldo #372329 05/09/11 7:40 pm
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Originally Posted by Ducknaldo

Does 1:1 drive boxes for Triumph qd wheels exist at all?

I don't think so, Smith's made some odd drives (10:21,11:13??), but 2:1 and 1.25:1 are the most common.I have a complete spare Triumph 650 QD wheel with a 2:1 drive on it, perhaps your wheel is also so equipped. That would make your speedometer read about 60% high (assuming your speedo is set up for a 1.25:1 drive).

Eric


1971 T120RV (R.I.P.)
1973 T140V/TR7
1993 Ducati 900 SS
Re: T120 1969 speedo ratio
Ducknaldo #372330 05/09/11 7:45 pm
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Hi Eric

That´s interesting, I guess I should check the rear wheel drive then.
But the speedometer would still be wrong for the bike, since the label says 1:1.
It seems that even in such a relatively simple design, Triumph managed to complicate things beyond reason.


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Re: T120 1969 speedo ratio
Ducknaldo #372333 05/09/11 8:00 pm
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Do you still have the original speedo? and was it ever accurate? If so, the 4 digit number after the part # on the face of the unit indirectly tells you which drive you have. The number is the revolutions per mile. A 4.00x18 wheel rotates about 800 times to cover a mile, so if your old speedo reads 1600 after the part #, you probably have a 2:1 drive.

Eric

P.S. I just noticed you're in Denmark, I'm not sure if the info above is true for odd foreign units of measurement, like the meter.


1971 T120RV (R.I.P.)
1973 T140V/TR7
1993 Ducati 900 SS
Re: T120 1969 speedo ratio
Ducknaldo #372338 05/09/11 8:19 pm
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Ahhh, brilliant.

I´m not sure I understand your calculation though.
My original speedo was never accurate and fluttering all over the place. I recall it being closer to real than this replica though. The old (original?) speedo says 1000 after the part #, what does this tell me then?
Full text from the face is "SSM5001/01A 1000 Made in UK L"


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Re: T120 1969 speedo ratio
Ducknaldo #372344 05/09/11 8:41 pm
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I take it your old speedo read in miles then. If your old speedo requires 1000 cable revolutions for the odometer to indicate 1 mile traveled, and your rear wheel rotates 800 times in that mile, then your drive ratio, as L.A.B. said, should be 1000/800 or 1.25:1. May I ask if the odometer on your new instrument is accurate? If it is, and the speed isn't, you have a defective unit.

Eric


1971 T120RV (R.I.P.)
1973 T140V/TR7
1993 Ducati 900 SS
Re: T120 1969 speedo ratio
Ducknaldo #372347 05/09/11 8:52 pm
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The old speedo is in km/h also.
As I said earlier the new replica speedo says 1:1 (on the label on the box).
I´m quite sure this is the culprit and I need the correct 1,25:1 and everything will be fine then.

Thank you for your help guys.
I think the shop will take this speedo back and give me the correct 1,25:1 and if this is still off, I´ll change the drive instead, so everything is correct for this bike.


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Re: T120 1969 speedo ratio
Ducknaldo #372348 05/09/11 8:53 pm
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Oh and by the way, the odometer is also incorrect, as far as I can tell.


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Re: T120 1969 speedo ratio
Ducknaldo #372350 05/09/11 8:55 pm
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Originally Posted by Ducknaldo
Full text from the face is "SSM5001/01A 1000 Made in UK L"


If it is a Kilometres per hour speedo (which I think the SSM5001/01 unit is) and it is marked "1000" that is 1000 cable turns per Km so the drive box is probably a 2:1 unit? (a 2:1 MPH unit would be marked "1600" (cable turns per mile)

A 1.25:1 ratio Km/h Smiths speedo would be marked "600" and a MPH 1.25:1 is "1000"

So what is the speedo box drive ratio (1 wheel turn = ?? cable turns)?

Originally Posted by Ducknaldo
Oh and by the way, the odometer is also incorrect, as far as I can tell.


If the drive box ratio is wrong then the odo. reading will also be inaccurate by the same percentage as the speedo.


Moderated by  John Healy 

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