Speedo Ratio Explained ? CJ360

TJGM

TJGM

Of Wild Kind...
Hey guys,
Been awhile ! Finally got back to my CJ360 project. A divorce and a couple last minute moves later, I can't find the box that had my speedo & tach in it. My question is, what can I use as a new one, or can I just throw a CB400 ish on there ?

Thanks,
~T
 
2240:60 is the ratio you want.
I am not actually sure what the ratio is relative too, i have heard people say its something like "2240 rpm at 60 mph", but I am not sure how correct that is.
A speedo has a magnet inside of a cup thing that is driven by the cable attached to the front wheel. As the cable increases velocity, so does the magnet, and so does the cup thing (I think it may also have a magnet in it as well...). And as they speed up, the magnet on the cup trys to catch the magnet in the cup due to some physics stuff, and there is a hair spring connected to the cup, which is connected to the dial, so the dial is relative to how fast the cup is moving.. I think.
Someone please correct me if i am wrong.
 
TJGM said:
Thanks. So what can I slap on my CJ360 ?
Click to expand...

ANY speedometer that has a 2240:60 ratio will work. Check out cognito moto, dime city cycles, most 70's honda cb models use 2240:60 ratio (cb360,cb350,cb450,cb550 probably more than that)
 
cb360j said:
2240:60 is the ratio you want.
I am not actually sure what the ratio is relative too, i have heard people say its something like "2240 rpm at 60 mph", but I am not sure how correct that is.
A speedo has a magnet inside of a cup thing that is driven by the cable attached to the front wheel. As the cable increases velocity, so does the magnet, and so does the cup thing (I think it may also have a magnet in it as well...). And as they speed up, the magnet on the cup trys to catch the magnet in the cup due to some physics stuff, and there is a hair spring connected to the cup, which is connected to the dial, so the dial is relative to how fast the cup is moving.. I think.
Someone please correct me if i am wrong.
Click to expand...
That's pretty close. the 'cup' is aluminium and non-magnetic, until magnet is pinning and induces a field then 'drags' the cup around. I always thought it was real simple mechanically but REALLY complicated unless your an engineer who understands that stuff. It's surprising they are even close to accurate at any speed but apparently were max of 5% out at 30mph (then got progressively worse) Yamaha always had the 'best' RTS (race tuned speedo ;D ) They could be as much as 40mph 'fast' when you got to about 85 actual mph
 
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