freeway rpms?

[slingshot]

on the freeway, at about 65, my 89 gs5 is doing 6000 rpms. does this sound about right?

[mwdbruno]

I run on the interstate at an indicated 75-80 at around 5-6K for reference...though my tach bounces while at highway speed (something else I was going to ask about on the board).

[Jace009]

that's about right....in 6th gear the tach reads about one number less than the speed-o [eg: 60mph=5k rpm's] 5th gear is dead even [eg: 50mph will be 5k rpm's]

You go to remember that the redline is 11k rpm's...most motors at highway speeds are doing 2/3 of their limit for fuel efficency.

[MarkusN]

Your speedos read km/h as well, don't they? In 6th speed in km/h is pretty much rpm x 2 / 100. So 120 km/h (roughly 75 mph) is at 6000 rpm

[JeffD]

Yup,  Your tire wear will also affect your rpm/speed ratio (as well as sprocket choices)

but with my stock '96 I was running at a little under 6k for 70mph when I first rode it on new tires,  Then 1.5yrs later and 17000 miles, my tach was at about 6,500 at 70mph (my tire was worn down...Alot),  anyway I got a new tire (same one as before) and my rpms dropped back down just below 6k for 70mph.

[Kerry]

With the stock Exedra tires, my speedo and tach needles tracked each other exactly in 5th gear.  (40 mph = 4000 rpm, 50 mph = 5000 rpm, 60 mph = 6000 rpm, etc.)

When the rear tire wore out I mounted a taller Cheng Shin 130/90-17 Hi-Max tire and all of a sudden the needles tracked each other in 4th gear.  (In 5th gear I would go 60 mph at 5000 rpm, in 6th gear I would go 60 mph at around 4000 rpm.)

My next rear tire was a Bridgestone BT45 in the stock size (130/70-10) and it registered somewhere in the middle.

============
General Principles
============
The speedometer measures the rotations of your front tire.  It will read a little higher (at a given actual ground speed) as the tire wears out.

The tachometer measures the rotations of your engine.  At a given speedometer reading, the tachometer reading is governed by 3 aspects of your drive train:

1) The number of teeth on your front sprocket

(fewer teeth = higher rpms),
2) The number of teeth on your rear sprocket (fewer teeth = lower rpms) and
3) The circumference of your rear tire (smaller tire = higher rpms).[/list:u]

[cozy]

Kerry,nice breakdown.  Good stuff to know.
I am usually at about 5500 rpm s on the highway at about an indicated 75 mph, yeah i'm a slowpoke but there's lots of traffic around here.