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General Category => General Discussion => Topic started by: mtiberio on April 28, 2016, 10:44:47 AM

Title: ever hook a tach up to a speedo cable?
Post by: mtiberio on April 28, 2016, 10:44:47 AM

Was wondering how they compare in terms inner cable revolutions per full face sweep...

Yes, I want to use a tach as a speedo. I think it would look neat...

Title: Re: ever hook a tach up to a speedo cable?
Post by: oldbike54 on April 28, 2016, 10:47:19 AM

 Tell the truth Mike , you just want to claim you went 8,000 MPH  :laugh:

 Dusty

Title: Re: ever hook a tach up to a speedo cable?
Post by: mtiberio on April 28, 2016, 10:48:22 AM

Quote from: oldbike54 on April 28, 2016, 10:47:19 AM

Tell the truth Mike , you just want to claim you went 8,000 MPH  :laugh:

 Dusty

or 8... the older I get the faster I was...

Title: Re: ever hook a tach up to a speedo cable?
Post by: oldbike54 on April 28, 2016, 10:51:47 AM

Quote from: mtiberio on April 28, 2016, 10:48:22 AM

or 8... the older I get the faster I was...

 A common affliction  :laugh: Maybe an old Smiths Chronometric tach , watch it jump in 2 MPH increments  :shocked:

 Dusty

Title: Re: ever hook a tach up to a speedo cable?
Post by: Kiwi_Roy on April 28, 2016, 11:52:57 AM

I read somewhere a standard Nth American speedo cable revolves 1,000 revs per mile so at 100mph its doing 1666 RPM
I think tachs are normally driven from the cam shaft 4000 RPM @ 8.000 RPM or is there a gearbox in between?

Or you could go to Speedhut and design one any way you want, try it out.
http://www.speedhut.com/gauges/
Not cable driven of course
 

Title: Re: ever hook a tach up to a speedo cable?
Post by: mtiberio on April 28, 2016, 12:42:45 PM

Quote from: Kiwi_Roy on April 28, 2016, 11:52:57 AM

I read somewhere a standard Nth American speedo cable revolves 1,000 revs per mile so at 100mph its doing 1666 RPM
I think tachs are normally driven from the cam shaft 4000 RPM @ 8.000 RPM or is there a gearbox in between?

Or you could go to Speedhut and design one any way you want, try it out.
http://www.speedhut.com/gauges/
Not cable driven of course
 

Guzzi tach drives go through a set of worm gears, same principle, but different drive gear for the speedo. Also the driven gears are available in different # of teeth for different rear drives. Could all be calculated from first principles, if I had all the parts and numbers in front of me, which I don't.

Title: Re: ever hook a tach up to a speedo cable?
Post by: Mike Tashjian on April 28, 2016, 05:01:12 PM

To get in the ballpark run a speedo with a drill of known speed and then the tach.  I think my cordless on low is like 500rpm and high is 1500 or so.  Mike

Title: Re: ever hook a tach up to a speedo cable?
Post by: Idontwantapickle on April 28, 2016, 05:22:24 PM

All my loose guzzi speedos read 1610 revs per mile. So that's 1 meter per rev or so. The tachs all have the same cryptic numbers 1 - 4 on them, I think that might mean reads 4K at 1K cable speed. So I checked them with my drill that claims 750 rpm.
Results:
Speedo reads 27, pretty close for an old Italian gauge.
Tach reads just shy of 3K. Pretty close again!
So 60 MPH on the tach will read 6440 RPM.
YSMV
Hope that helps.
Hunter

Title: Re: ever hook a tach up to a speedo cable?
Post by: mtiberio on April 28, 2016, 05:46:40 PM

Quote from: Idontwantapickle on April 28, 2016, 05:22:24 PM

All my loose guzzi speedos read 1610 revs per mile. So that's 1 meter per rev or so. The tachs all have the same cryptic numbers 1 - 4 on them, I think that might mean reads 4K at 1K cable speed. So I checked them with my drill that claims 750 rpm.
Results:
Speedo reads 27, pretty close for an old Italian gauge.
Tach reads just shy of 3K. Pretty close again!
So 60 MPH on the tach will read 6440 RPM.
YSMV
Hope that helps.
Hunter

Thank you so much, in other words it would work with a full scale , 8000 rpm, being 70+ mph.