rpms at 70mph

[1948man]

According to the chart in this thread, I should be turning 4186 rpms at 70 mph. At that rpm I am barely over 60mph. I have the standard 16" rear wheel. Any ideas what is out of whack? http://www.thegsresources.com/_forum...l+drive+ratios

[Steve]

One prime suspect would be your speedometer.

Do you have a GPS you can take along for a speed verification run?

.

[SqDancerLynn1]

You could have the 3.09 rear gear

[1948man]

Thanks for the ideas. Steve, I have a little hand held GPS that I checked the speedo on my previous bike. Had to remain steady for 20-30 seconds for it to settle out but I will definitely try that. Lynn, according to the chart, a 3.09 final gear would produce the symptoms I am experiencing and I'm not sure if the history of the bike I got is correct so that could well be it. Jim M

[bwringer]

You can only expect 25 to 30 year old analog instruments to offer vague approximations of actual RPM and speed.

Then again, when I mounted a GPS to my 850G with 110,000 miles, I was shocked to find that the speedo is dead on.

[1948man]

Doh!! I looked in the owner's manual I downloaded from Cliff's site and it confirms Lynn's idea that maybe I have a 3.09 final ratio. I guess I should have looked there before going with what the chart said. This would suggest I should be about 4445 at 70 mph and 3810 at 60 mph.

[Nessism]

Doh!! I looked in the owner's manual I downloaded from Cliff's site and it confirms Lynn's idea that maybe I have a 3.09 final ratio. I guess I should have looked there before going with what the chart said.

If it's an '83 it has the 2.9 gears in back. I put an '83 1100GL rear end in my 850 and can confirm those numbers. The rear end difference is not all that great by the way, only about 300 rpm or so at freeway speeds.

[1948man]

Yeah, I was looking at my cyber manual and it seems kind of generic, like maybe it was printed for the '82 model. Hmmm. The rpms seems to point towards the 3.09, maybe they used some 3.09's and some 2.91's in the '83's or maybe it's my speedo. Or maybe the PO replaced the original.

[twr1776]

When was yours manufactured? I just looked at my 83 and it was 9/82 and I have the 2.91 as near as I can tell. If yours was manufactured earlier it could be you got the 3.09 from the factory. Suzuki tended to use up all of last years parts before going to the next years production run.

[Nessism]

When was yours manufactured? I just looked at my 83 and it was 9/82 and I have the 2.91 as near as I can tell. If yours was manufactured earlier it could be you got the 3.09 from the factory. Suzuki tended to use up all of last years parts before going to the next years production run.

The parts fishe only shows the 2.91 gears, no mention of 3.09's for '83. Also, 9/82 is September, so that's an early 1983 model.

[sscott]

Just a guess here but could the tachometer be off?

Is there someone you can ride along with (safely of course) and compare speeds to? Might help

[1948man]

I'll check with the GPS as close as I can. Just curious, how do you determine the specs of a part from the parts fiche? I looked under "propeller shaft" at Alpha sports and can see how everything goes together but can't figure out what the ratio of the final gear shown is.

[Nessism]

I'll check with the GPS as close as I can. Just curious, how do you determine the specs of a part from the parts fiche? I looked under "propeller shaft" at Alpha sports and can see how everything goes together but can't figure out what the ratio of the final gear shown is.

Calculate the ratio: Driven gear # teeth / Drive gear # teeth

[1948man]

Why didn't I think of that. Checked speedo with gps and gps says 63 mph when speedo says 60mph. Actual speed is 5% higher than indicated speed. Guess that accounts for the bulk of the discrepancy. Seems most newer speedos read 7 to 10% error in the other direction.

[850 Combat]

iI would verify that at more speed vs indicated RPM points to determine that it is linear. Where I have checked this, the tach is linear, but the speedo gets farther and farther out, percentage wise.