rpms at 70mph

[Sandy]

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.

I checked my GS1000 with a GPS and it read +5% up to 60 mph and then gradually changed to -4% at at 125 mph with 100 mph being bang on and according to specs and calculations the tach seemed pretty close at all GPS speeds. So until you figure out where your speedos at it will be hard figure out where your tachs at.

[1948man]

Mine was off 1.5 mph at 30 mph and 3mph at 60 mph. both times reading conservative. That's as near as I could tell with my handheld GPS, holding steady for 15-29 seconds. For my purposes, I'll just subtract roughly 5% from my indicated speed. I don't visit the over 85mph range often.

[Steve]

Mine was off 1.5 mph at 30 mph and 3mph at 60 mph. both times reading conservative.

How close is the odometer?

What size front tire do you have on your bike?

If you go to the next larger size tire, you can slow down the speedo so it's accurate, but it will also slow down the odometer.

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[chuck hahn]

the odometer is only reading a distance as calibrated to a constant.This constant being the turning of the speedometer. So if you put a larger tire on and the speed on the speedo is verified to be reading correctly by a radar gun or whatever the odometer will read correctly. Changing a tire to a larger or smaller size has nothing to do with the odometer..It all boils down to how fast the speedo cable is spinning.

[chuck hahn]

I guess i should say it like this::

Smaller tire than what the speedo was ORIGANALLY calibrated to = faster rotation of the speedo cable..the speedo may say you went 1 mile when in fact you only went 8/10 because of the varience

Larger tire than what the speedo was ORIGANALLY calibrated to = slower turning of the speedo cable. The speedo may say you went 1 mile when in fact you went 1and 2/10 miles therefore in either case the SPEED will read incorrectly...either your going faster than it says or your going slower..

[1948man]

I have the stock 19" tire. I'm okay with things and was really just wondering about the final drive but I will check the odometer just to know. My rpms at an actual speed of 70 mimic the '83 1100GK and my manual says I have a .961 5th gear so that with a 3.09 final should explain things. It's cool, I'm done obsessing.

[Steve]

Changing a tire to a larger or smaller size has nothing to do with the odometer..It all boils down to how fast the speedo cable is spinning.

Well, ..., yes and no. The odometer is strictly gear-driven off the cable coming up from the wheel and the speedometer is driven off of that. In fact, it is possible for the speedometer to break and the odometer still works. If you change the front tire size, you will affect the accuracy of both, the odometer and the speedometer. Following your line of thought reinforces that. A larger tire will slow down the speedometer, therefore, it also slows down the odometer.

Unfortunately, the odometer starts out reasonably accurate, while the speedometer is rather optimistic. By changing to a larger tire to slow down the cable, you also change the odometer to a lower reading. The change is only in the 3-5% range and most of us are not too worried about violating any warranties, so it's not much of a problem. However, we do have to worry about maintaining a proper (legal) speed every time we ride, so I feel that speedometer accuracy trumps odometer accuracy.

Just in case you like numbers as much as I do, on a trip a few years ago my wife's bike and my Wing went everywhere together. One bike did not even do an extra trip down a driveway unless the other one went, too. The GPS trip meter was also on for every inch of the trip. My Wing odometer showed that we traveled 1193 miles. Her bike showed 1184 miles. The GPS showed 1175 miles. 1.53% error for my bike, 0.76% for hers. Speedo accuracy: at an indicated 70 mph on my Wing, the GPS shows about 70.5. Her bike shows 68.7. Not sure I would want them any closer than that.

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