Speedo WAY off....

coreyoreo · October 23, 2011, 05:40:14 PM

Hi all.. finally got my '89 all tuned up but the speedo is way off. I'm talking probably 15-20mph over the flow of traffic at freeway speeds.

I was only traveling city streets until the tune-up, so I wasn't aware of the speedo issue until I ran the freeway.

Any ideas on what to check out first and/or how to correct it?

Thanks in advance for any help.

Corey

RichBaker · October 23, 2011, 07:42:21 PM

It indicates slower than actual speed? Wierd, if so..... most Jap speedos are typically fast by 10% or so. Mine is....... There is a post giving an address of a place that repairs them in here somewhere. Found it......

Creative Audio

702 Towson Ave
Fort Smith, AR 72901
(479) 782-0336

Assuming the front tire isn't WAY too big in circumference, it's most likely the speedo, itself.

coreyoreo · October 23, 2011, 09:16:39 PM

No no, Rich, I'm sorry.. I guess I wasn't clear enough.

I meant to say that If I'm traveling w/ the general flow of traffic, say, 70-75, +/-, my speedo says I'm doing near 85-90mph... Can't give an accurate speed check til I test it w/ someone.

Definitely is off though...

RichBaker · October 23, 2011, 10:54:33 PM

OK.... as I said, that's pretty much normal. I checked mine against a GPS, one of those "YOUR SPEED IS" carts (made a bunch of passes at it one night) and did time/distance computations to determine the error after I got a couple speeding tickets on her. Turns out the cops were/are lying bastarards......

My speedo indicates ~9.5% fast, I was doing within 3-4 MPH of the limit, indicated, for every ticket.... in a 45MPH zone.

coreyoreo · October 23, 2011, 11:41:12 PM

Aye.. ok, Rich, thanks.. I won't worry about it then.

Thanks for the help!

Corey

moparman70 · October 24, 2011, 12:12:44 PM

I find that they are low - both my 86 and 90 are low -- pretty close though on the slower speeds but 80mph is more like 75 actual -- 100mph is more like 90 and it gets worse as you past the century mark. Only true high speed readings can be taken via GPS. I mounted mine right on the triple clamp - some foam etc -- works well be creative.

stevecc

1tinindian · October 24, 2011, 12:55:02 PM

My 91 is pretty close, but still off.
At my indicated 60 MPH, GPS is at 57 MPH.
I can live with that!

Leon

Sideburns · October 24, 2011, 01:33:58 PM

What tyre size do you have? 120/70 17 or 120/60 17?

Running a 60 tyre means having a smaller diameter. (correct me if I'm wrong)

craigo · October 24, 2011, 06:36:43 PM

My speedo is optimistic, as in it says I am going faster than I really am. According to the GPS, it's 10% off. If I am going an indicated 70mph, I am going closer to 63mph. This is also not good as the odometer is also ticking off the miles at the same 10% rate. So, my bike has almost 40k miles, it's really closer to 36k.

It does not matter which tire I use also. I had a Michelin Pilot Power on then I bought it and now have a Dunlop Roadsmart. Same 10% error.

CraigO

Flying Scotsman · October 24, 2011, 07:52:36 PM

I got used to the speedometer being off and I also have a small hand held GPS I use.A solution would be to make up a new face for the spedometer that fits over the oem face.Then send me a couple lol.

coreyoreo · October 24, 2011, 10:26:49 PM

Quote from: Sideburns on October 24, 2011, 01:33:58 PM
What tyre size do you have? 120/70 17 or 120/60 17?

Running a 60 tyre means having a smaller diameter. (correct me if I'm wrong)

It's a 120/70 17.

That's why I'm thinking the cable may be off another bike, the gearing could be different?

andyb · October 25, 2011, 08:14:33 AM

The speedo cable will spin at the same speed on both ends if it's still intact!

A different sized tire will change the speedo's reading (if 120/70-17 is the basline, a 120/60-17 will read 4.16% higher, a 110/80-17 will read 1.3% higher), and as they wear down that will increase slightly (a 120/70-17 worn down 1mm all around will be 0.3% higher, but it's not linear with wear).

That said, don't be sure that it's a linear error. It's not uncommon for the error to be 5% at 50mph and 9% at 150mph (numbers pulled from ass for illustration). Tachometers also share this behavior, some being increasingly wrong linearly if that makes sense, and some having a dual-zone error (FZR600 tach's change just over 6000rpm to a higher error, why do I know this crap?!)

Only really matters when there's cops or cameras around though. Easy to handle if you're in traffic, but a little scary if you're the only one on the road and know where the speedtrap is!

coreyoreo · October 25, 2011, 09:09:32 AM

Got it, Andy, & thanks for the advice everyone. Looks like I'll just do a neanderthal speedo check-- riding next to a friend who I know is doing 70 mph & see what the speedo says & go from there..

This is why this site is the best!!!

Arnie · October 26, 2011, 07:48:38 PM

Quote from: coreyoreo on October 25, 2011, 09:09:32 AM
Got it, Andy, & thanks for the advice everyone. Looks like I'll just do a neanderthal speedo check-- riding next to a friend who I know is doing 70 mph & see what the speedo says & go from there..

How will you KNOW that your friend is doing 70mph ? Does he have a GPS or has his speedo been calibrated? Most car speedos are almost as inaccurate as bike speedos.

Arnie

FJTillDeath · October 27, 2011, 03:26:10 AM

Just to butt in quickly but once when I had a problem with my speedo(it would hover around 120km) Arnie told me to clean some of the parts, now the general notion is the stock speedo wont be entirely accurate, but would cleaning the cables etc make the window of error any smaller? i have always wondered about my true speed sometimes...

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Speedo WAY off....