Do they get slower with age? funny observation.

[SangreDeDios]

Or maybe its the oposite?
I was just looking at the speedo for my 83 and it only goes up to 80. So I decided to check my 79, 120. And the 76 goes to 140.

I wonder why that is?

 

[gggGary]

That's when the federally mandated 85 mph speedometer law took effect more or less. It was later dropped.

 

[gggGary]

The 85 is closer to the max level ground speed of a stock xs650 than the 140 was.

 

[pamcopete]

Well, here is an Excel spreadsheet that shows RPM vs MPH vs Sprocket ratio for any gear, including Mikes overdrive 5th gear. The RPM's turn red at 7500, which is the nominal red line, if you believe in those things. You will hit red line at 110 MPH with an 18 inch rear wheel and 17/34 sprockets in 5th gear. 120 is 8233 RPM and 140 MPH is 9605 RPM!

Just click on the yellow cells for sprocket teeth, rolling distance and MPH to reveal a pull down with a selection of values. Rolling distance is the distance that the bike moves with one revolution of the rear wheel. It's more accurate than a calculated or even measured diameter or circumference.


XS650 REVS vs MPH


Plug in some values for sprocket teeth or tire size for a given speed, like 120 MPH to see what will work and still stay below red line.