74 XL Speedo selection and connection
#1
06-04-2009, 08:14 PM
Join Date: May 2009
Location: Long Island, NY
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74 XL Speedo selection and connection
I have a 1974 XL Sporster which does not have a tach or speedo. I am looking to pick up a mini handlebar mount speedo. From an earlier post I know the connection is made under the Kick start plate and have found an "inexpensive" mechanical gauge.
http://shopmotorcycleonlinestore.com/productdetail.htm?productId=7725662&browse=236259& shopBy=9158&catalogId=1570
My first question is do I want a 2:1 ratio or 1:1? I am assuming the 2:1 gauges are not transmission driven? I am a bit confused because the only the top 2 mention transmission driven.
Second, is there anything else to purchase/do other than getting a cable and the gauge and plugging them in?
Thanks guys
Danny
http://shopmotorcycleonlinestore.com/productdetail.htm?productId=7725662&browse=236259& shopBy=9158&catalogId=1570
My first question is do I want a 2:1 ratio or 1:1? I am assuming the 2:1 gauges are not transmission driven? I am a bit confused because the only the top 2 mention transmission driven.
Second, is there anything else to purchase/do other than getting a cable and the gauge and plugging them in?
Thanks guys
Danny
#2
06-04-2009, 08:31 PM
Outstanding HDF Member
The last year the Sportster had the front drum brake was 1972. This and earlier years had a speedo drive coming out of the transmission.
The 1973 and later had front disk brake and the speedo drive ran off the front wheel.
That is good in a way for you because you will have to get yourself a drive unit to mount on the front hub.
Then you can turn the wheel 1 revolution while watching the drive to see how many turns it makes in the single wheel revolution. That will give you the answer of what head you will need, 1:1 or 2:1.
The business of speedos and tachs has always been the last thing in the manual and there is almost no information about either, other than the fact you need a cable on both instruments.
I suggest you just get on the phone to J&P and tell them what you want. Chances are good that they will have the drive, the cables (inner and outer) and the head. One stop shopping if you get lucky..... pg
PS: You are not going to like those Drag Specialities handlebar clamps. The things are alwawys going to loosen up leaving the speedo head flopping to one side or the other. You need a much better way of holding the head in position than the 'bicycle' clamp they use.
The 1973 and later had front disk brake and the speedo drive ran off the front wheel.
That is good in a way for you because you will have to get yourself a drive unit to mount on the front hub.
Then you can turn the wheel 1 revolution while watching the drive to see how many turns it makes in the single wheel revolution. That will give you the answer of what head you will need, 1:1 or 2:1.
The business of speedos and tachs has always been the last thing in the manual and there is almost no information about either, other than the fact you need a cable on both instruments.
I suggest you just get on the phone to J&P and tell them what you want. Chances are good that they will have the drive, the cables (inner and outer) and the head. One stop shopping if you get lucky..... pg
PS: You are not going to like those Drag Specialities handlebar clamps. The things are alwawys going to loosen up leaving the speedo head flopping to one side or the other. You need a much better way of holding the head in position than the 'bicycle' clamp they use.
Last edited by piniongear; 06-04-2009 at 08:36 PM. Reason: Added the PS
#4
06-05-2009, 09:46 PM
Really all you need to do is go to any catalog company [J&P Cycles, etc] or any HD shop or any indie motorcycle shop and get the speedo drive unit that goes into the front wheel of any sportster from about 1973 or so to well past 1980. 199x? Whatever. They are all the same. Nothing special for a 19 or 21 front tire - same speedo drive.
#5
06-05-2009, 10:33 PM
Outstanding HDF Member
The 19 inch wheel is a smaller nominal size than a 21 inch wheel, so one turn of a 21 inch wheel is going to cover a greater distance than one turn of a 19 inch wheel. (You would think anyway, but that is not the case. See second paragraph.)
That means you need a different drive ratio to compensate for the difference and thus to enable the speedo head to give an accurate reading in mph.
However, in actual fact, we have to go down to where the rubber meets the road.........(Bad pun was intended).
If you measure the outside diameter of a 19 inch mounted tire, you will find that the outside diameter of a mounted 21 inch tire is almost exactly the same. Different rim sizes, but also different tire sizes and it all totals up to the same measurement.
End result is you can use the same speedo drive for a 19 or a 21 and the reading will be correct. The normal Sportster speedo head is a 2:1 ratio head. The tach head is likewise.......... pg
That means you need a different drive ratio to compensate for the difference and thus to enable the speedo head to give an accurate reading in mph.
However, in actual fact, we have to go down to where the rubber meets the road.........(Bad pun was intended).
If you measure the outside diameter of a 19 inch mounted tire, you will find that the outside diameter of a mounted 21 inch tire is almost exactly the same. Different rim sizes, but also different tire sizes and it all totals up to the same measurement.
End result is you can use the same speedo drive for a 19 or a 21 and the reading will be correct. The normal Sportster speedo head is a 2:1 ratio head. The tach head is likewise.......... pg
#6
06-06-2009, 07:19 AM
#7
09-23-2012, 08:34 PM
However, in actual fact, we have to go down to where the rubber meets the road.........(Bad pun was intended).
If you measure the outside diameter of a 19 inch mounted tire, you will find that the outside diameter of a mounted 21 inch tire is almost exactly the same. Different rim sizes, but also different tire sizes and it all totals up to the same measurement.
End result is you can use the same speedo drive for a 19 or a 21 and the reading will be correct. The normal Sportster speedo head is a 2:1 ratio head. The tach head is likewise.......... pg
If you measure the outside diameter of a 19 inch mounted tire, you will find that the outside diameter of a mounted 21 inch tire is almost exactly the same. Different rim sizes, but also different tire sizes and it all totals up to the same measurement.
End result is you can use the same speedo drive for a 19 or a 21 and the reading will be correct. The normal Sportster speedo head is a 2:1 ratio head. The tach head is likewise.......... pg
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