Do you know how fast or how far you are going?

[Steve]

Motorcycle speedometers are like politicians, they only lie when they are working.

So...just when have you seen a politician working? :shock:

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[SqDancerLynn1]

Doing the size conversion, Most of the bigger GS used a 100/90/19 for the front, not a 90/90/19 Unless you have a twin. Switching to a 110/90/19 improves the speedo accuracy

[themess]

Mechanical speedometers are prone to having errors that differ at different speeds. Adding one of those bicycle speedometers/computers should mostly fix that problem, because it works by timing and counting wheel revolutions. It can be adjusted to work with the actual wheel diameter, within a small fraction of a percent. If the air pressure changes greatly, tire diameter will change slightly, reducing its accuracy. If tire pressure is very low, tire squirm would probably make a larger difference. The bicycle speedometer (at least the Sigmas) will also read to any speed that our GSes will reach, overcoming the 85 MPH limitation. It will also show max speed and average speed, and add two more odometers.

Darn, I ought to put one on!

[Killer2600]

Speedometer? what are those? I only go three different speeds: slower than traffic around me, same as traffic around me, and faster than traffic. Usually I'm doing the later of the three unless traffic doesn't permit :-D

[ajf]

'81 GS650G with stock tires: both the speedometer and odometer read 10% high. '04 SV650S: speedo is 7% high, odo is exactly correct. Apparently Suzuki became more sophisticated in it's silly efforts to protect us from ourselves.

[DMPLATT]

I'm not sure about older motorcycles.
However, newer motorcycles do in fact have built in error in the speedo. I don't fully understand why.
However, the ZZR's are well known to have about 10% error. Mine is just about exactly that. At 65MPh, the GPS shows 59MPH.
Many Police Speed guns that I have passed show the same results.
My friend on a 2005 Busa, rode with me to a ZZR rally in Georgia. I had a hand held GPS and his Busa is also right at 10% off.

My GS though, I don't recall that being off much at all.

[bwringer]

Speedos are deliberately built overly optimistic, likely due to a tangled knot of liability issues. The usual 5% - 10% error you see on new bikes is just ridiculous, IMHO, but some nervous Nelly lawyer somewhere thinks it has to be that way. At least on newer bikes with electronics, you can usually buy a little widget to plug in to correct this.

On a bike that's 25 - 30 years old, isn't it enough of a miracle that it's moving? Ancient mechanical devices like GS speedometers and tachometers are only haphazardly accurate. Each one is slightly different and special in its own way, like a snowflake.

[lurch12_2000]

Speedos are deliberately built overly optimistic, likely due to a tangled knot of liability issues. The usual 5% - 10% error you see on new bikes is just ridiculous, IMHO, but some nervous Nelly lawyer somewhere thinks it has to be that way. At least on newer bikes with electronics, you can usually buy a little widget to plug in to correct this.

On a bike that's 25 - 30 years old, isn't it enough of a miracle that it's moving? Ancient mechanical devices like GS speedometers and tachometers are only haphazardly accurate. Each one is slightly different and special in its own way, like a snowflake.

Now..now, I expect my bike to do more than just move. Maybe I shouldn't push my "snowflake" to 100mph, but I was just curious how far off the GS speedos were back then.
There are 2 things I NEED to find out. Locate a speed trap sign that flashes your speed and go through it 10-20 times to get numbers for my speedo variance. The other was to get weighed in at the local recycling plant to clear up the discrepancies in weight specs from manuals, internet sites and original brochures. The stupid things I waste my time on.........I'll report back to the forum as long as I don't get arrested or crushed for scrap in the process!:shock: