Speedo is way out.

[Guest]

Hi,

I have a 1982 Suzuki GSX 1100 EZ. The speedo is way out ie when showing 128kph you are only doing 110kph so there's a 18 kph difference. I don't think the difference is as bad at lower speeds possibly only 10 km out.. My question is what's the likely cause? The only three things it could be are the speedo drive at the front wheel, speedo cable or the speedo unit itself. any help or suggestions appreciated.

Thanks

Richard

[jimb12]

Motorcycle speedometers generally read high. That's just the way that the manufacturers set them up. Some examples, my Bandit would typically read around 20mph high compared to timing lights on the dragstrip. Friend's Kawasaki read 24mph high compared to the timing lights.

[carvan40]

I can accept manufacturers setting their speedos a little high to allow for a bit of tolerance but not as much as 20mph, other bikes i have owned have had reasonably accurate speedos. I think the problem lies elsewhere. Has anyone else experienced this problem with this model bike or other model suzuki's.

[bwringer]

Yes, pretty much every motorcycle ever made has this problem.

Yours is certainly on the high side, though. 10% error is common, but your error is worse.

On modern bikes, electronic widgets or recalibrated gauge faces are the most common ways to deal with this.

On bikes with mechanical speedos, you have to adjust either the needle position or the magnetic field strength, or fabricate a new gauge face.


Here's how some folks have tweaked their KLR650 speedos -- KLRs have very similar mechanical speedo innards, they're easy to access, there are zillions of them around, and they tend to be owned by cheapo tinkerers. So there's more information available.

New gauge face

http://www.advrider.com/forums/showthread.php?t=347660

Tweaking the needle. Not sure whether this would be workable on a GS:
http://www.watt-man.com/uploads/SpeedoCal.doc (No idea why the hell this is in a Word doc...)

http://www.thumpertalk.com/topic/905280-mechanical-speedometer-re-calibration-10-error-fixed/

Recalibrating the magnets. Not for the faint-hearted or unsteady:

http://www.klr650.net/forums/showthread.php?t=8635

http://www.klr650.net/forums/showthread.php?t=55564

In most cases, it's harder to get inside GS gauges without damaging them. And IIRC, the magnetic parts may not be as accessible if you wanted to try that route.

[GSX1000E]

Have you tried running a 100/90-19 front tire yet?

[Gorminrider]

given that everything is original, if the odometer is also high, (not low) a different tire/rim size would seem to be the first question. a 19" wheel rim vs an 18" rim will be +5% difference due to rim size alone.The smaller rim would read higher... difference in Tires might make this up to 6%.

If the odo is ok, and the OEM speedo dial is reading High you might as well turn the dial needle up a bit on it's stem...

I've been fussing with this "reading high" too, swapping gauges from a 19" wheel bike to an 18" wheel bike.They are not the same in detail... The Original speedo was spot on, but I am really trying to get a tach replaced and can't get all the idiot lights I love without swapping both speedo and tach together from the 19" T to an 18" E. In my case, error is about 5% so I believe it's the tire size at issue

I wonder if something similar might have happened in your bike's history?

adding per 16% "over" read I wonder even about your dial gauge spring being somehow broken or stretched ?

[lemonshindig]

Bending the needle is the wrong approach. It sounds like your speedometer is off by a certain percentage of speed, not by a fixed amount through the range. Your needle should read zero when you're not moving.

Being off by a constant percentage is normal because it's a geared system. The solution is to change the diameter of the front tire, or change the speedometer gearing. On a bike, changing the gear ratio of the speedometer may not be as easy as it is on a car, but I'm not sure because I've never tried it. I do know that there are universal gearboxes that you can splice into your speedometer cable to account for the inaccuracy.

Mine also reads high by about 10%. It's annoying, but I can't complain too much because I know everything that would cause it, and I know the solution, yet I haven't taken the time to look at it. So it's my fault it's that way.

[carvan40]

I'm running a Michellin 100/90 x 19 tyre whats the signifigance.

[Gorminrider]

I'm running a Michellin 100/90 x 19 tyre whats the signifigance.

I don't have that bike but 19" is a big tire so I'm guessing tire size is NOT the issue. You have to have a "smaller-than-OEM tire to get an overspeed from it.
Between 18" and 19" there is a 5-6% difference per just rim size. (19*22/7)/(18*22/7)=1.05555556. But tire diameter is the better way .

Bending the needle is the wrong approach.

Yes, it is a last resort but I have turned the needle on it's shaft on a Honda and it works very well.

[Gorminrider]

IF you really get into it,the spring on the needle determines how the speedo reads. There is a bent/crushed tab over the spring end ...if you can loosen it, you could adjust the spring. Tightening it (pulling some spring through) will make the speedo dial read lower

[carvan40]

Thanks for the replies, i'm not any the wiser. I might look into the GPS speedo's and thoughts

[Jim R]

Just got my restored '82 GS110G on the road last fall. (100% stock including tire sizes) I could tell the speedo was off just by feel. Finally had the chance to use one of my townships radar speed detectors. It is way off. Shows 40 when I'm doing 34. and shows 60 when I'm doing 50. My biggest concern is that this means it is also tacking the miles on the odometer faster than reality. ie: every actual 10,000 miles will show approx. 12,000 miles. Wondering if anyone has had success adjusting the spring in the speedo. If so, any tips?

[greg78gs750]

who looks at the speedo? heh.

[Footy.]

Just got my restored '82 GS110G on the road last fall. (100% stock including tire sizes) I could tell the speedo was off just by feel. Finally had the chance to use one of my townships radar speed detectors. It is way off. Shows 40 when I'm doing 34. and shows 60 when I'm doing 50. My biggest concern is that this means it is also tacking the miles on the odometer faster than reality. ie: every actual 10,000 miles will show approx. 12,000 miles. Wondering if anyone has had success adjusting the spring in the speedo. If so, any tips?

Just noticed this thread, and I would like to raise a point about the mileage recording aspect of this.

It is annoying, my 78 GS760E reads around 5-8 mph high in the 30-40mph range (where we really need to know for speed restrictions in England). But if Suzuki got the gearing right, and the tyres are STD diameter, this should not affect the mileage recording should it?

The mileage trip mechanism is directly geared so should be accurate, but the speedo needle is dragged around by a magnet resisted by a spring. I think its strong/weak spring or magnet that makes the differences in speed reading's.

[rustybronco]

If the odometer indicates correctly, I think your supposition of the root cause being either the magnet becoming weaker over time, or the spring weakening is correct. Shortening the hair spring should help correct the percentage of error on a mechanical gauge..