Secondary reduction ratio 850GD

[Pete8092]

Hi

A short intro' I am a GS resource 50 year old virgin, enough about me so on with the question.
I have a stock 850 GD and I cover @ 300 - 500 miles a week however this has changed I am now covering about 800 motorway miles a week.
I am thinking of changing the Secondary reduction ratio from 17/16 to 17/15 or 16/15' too much?

REspect!

[bwringer]

Two questions:

1) Why?
The engine is perfectly fine spinning along at 80mph and 6,000 rpm for days on end. That's what it's made to do. It is common for people to complain that their 850 is turning too many RPMs, but I've never seen anyone give a rational reason why they think so or why they feel it's a problem.

2) How?
Are you going to machine new gears for the secondary drive? If so, I believe you'll be the first, and your machine shop skills and resources are far beyond anything we've seen so far.

[Nessism]

Installing an 1983+ GS1100 shaft final drive unit is the easiest way to drop cruising rpm's.

[Pete8092]

To answer your questions;

1) Fual consumption' I may only save @ 10 -15% a week but this will add up over the year and vibration little as it is it does become tedious.

2) I have asked a number of people including friends who work in machine shops who can machine new gears.

The question is; 17/15 or 16/15?

[Nessism]

Do the math on the cruising rpm's and decide for yourself on the gear ratio.

You will not increase fuel consumption by 10-15%. You will be doing very well if you hit 5%

[bwringer]

Agreed -- on a given motorcycle, fuel consumption is mostly a function of air resistance (jetting plays into it as well). Changing RPM a bit will make little to no measurable difference in fuel consumption.


Based on the numbers you gave:

17/16 = 1.0625 (stock)

17/15 = 1.1333 (about a 6.6% difference, or you'd theoretically go from about 6,000 rpm at about 80mph to about 5,600 rpm at that speed. Even less of a difference at lower speeds.)

16/15 = 1.0666 (Right back where you started...)


Overall it looks like a LOT of effort for not much gain.

But if you do end up going down this path, please keep us updated.