Topic: CB750 rpm @ 60mph?

[Gustlock]

For my Café Racer project I found a nice small speedometer. The advert says it indicates 60mph at 2400 rpm.
Does this match the CB750 speedometer? My CB750 has no engine in it at the moment so I can't test it

[BobbyR]

With stock gearing it should be around 4K.

[domer]

if they are advertising a ratio of 2240:60 you found the right speedo... tach is 4:1

[srook]

It is not the tach that is spinning at 2400 rpm it is the speedo drive or more accurately the cable.  It is telling you the ratio of 2400:60, which is close to the stock 2240:60.
Scott

[Gustlock]

Thanks all for the reply's! I will mail the seller if the speedo ratio is 2240:60.

In the meantime somebody told me I could find the ratio on the back of the original speedo:
x400rpm=60kp/h it says (can't read the first number but I believe it says 1).

In the Honda manual I found this:


This shows engine RPM and not cable RPM.

[Gordon]

You're confusing the engine speed with the speed that the speedometer cable is spinning.  When looking at specs of a speedometer, the "rpm to displayed speed" ratio is referring to the speed that the input side of the speedometer is being spun, which has nothing to do with how fast the engine is running.   

[Gustlock]

Mandic explained this to me in a post above Under the image I wrote that the image shows engine RPM and not cable RPM
Thanks for your reply Gordon

[Gordon]

Mandic explained this to me in a post above Under the image I wrote that the image shows engine RPM and not cable RPM
Thanks for your reply Gordon

I thought it had been explained, too, but by posting a graph that shows engine performance curves which have no direct correlation to speedometer gearing it seemed to me like there was still some confusion.

[Gustlock]

Haha no just a small bonus