New bandit 12 owner, speedo way off.

[Red01]

Nice theory, Bazza, but a couple of flaws.
1) If it was due to tire wear, the % of error would be constant.  I don't believe the tire's diameter changes that much with increases in speed, and if anything, it would grow from heat increasing the air pressure, putting the error in the other direction.  Ever watch the tires grow on a dragster's slicks when they warm up their tires in the "bleach box?"
2) Why is the odo so much more accurate?

Rumor has it the reason they make them optomistic is for the lawsuit reason... and it seems the most logical to me.

[stormi]

Hmmm... you add 9mph to 45, but only 7 to 70?

About the time I hit the post button I knew that was confusing.... I really didn't explain it right and I'm not going to even try.  Best used in the speed zones that end in zero - that's for sure....       

How about 4.5 to 45?  equals about 49.5mph.. or really close to the 49mph that he stated.  (which is only 4mph over. :)

[stormi]

On the ride home on my new to me bike I notice that at 80mph my wife following in my 07 impala said I was only going 70.

I (03 Bandit) was riding with my friend (85 Maxim) today and a few times I signaled him to take stock of our speed according to his speedo.

Heres the results....
Maxim 110KPH - Bandit 120KPH
Maxim 120KPH - Bandit 130KPH
Maxim 130KPH - Bandit 137KPH
Maxim 137KPH - Bandit 142KPH

This would explain why I've never received a ticket!

Hmm,.. I wonder how accurate that is compared to the 919.  I know I was hauling my @ss to work one day and was doing about 140 when I spotted the cop on coming.  I thought "ahhhh crap" and let go of the throttle, got ready to brake so he could pull me over.  

He didn't even do so much as to signal for me to slow it down.  

I figure either I was -way- off speedo wise, or he saw the front end of the bike dive and decided to leave me alone.  

That said, I have a GPS, if you wanna test your accuracy vs mine, and see if your bike or the other one is more accurate.  It's possible he has non-stock sprockets, or front tire (depending on where his speedo is read from) affecting him too, and you're somewhere in the middle.

I just haven't mounted the GPS on the bars yet.  The mount is on the KTM at the moment.

[Jester]

My '07 Bandit suffers from this as well. I've got a GPS mounted on the bike and use that.

100km on the GPS is 96km on the Speedo
118km on the GPS is 110km on the Speedo

It's out far less at lower speeds so it's a percentage.

[Bazza]

Nice theory, Bazza, but a couple of flaws.
1) If it was due to tire wear, the % of error would be constant.  I don't believe the tire's diameter changes that much with increases in speed, and if anything, it would grow from heat increasing the air pressure, putting the error in the other direction.  Ever watch the tires grow on a dragster's slicks when they warm up their tires in the "bleach box?"
2) Why is the odo so much more accurate?

Rumor has it the reason they make them optomistic is for the lawsuit reason... and it seems the most logical to me.

Red:

This is not my theory, I actually read a very good article on it once which had a whole bunch of Engineering math formulation to back it up. (I was not able to locate it and it was torture to read).

A bike tire from new to finish changes a great deal of overall circumferance. (many mm).

But someone has a pretty good explaination on wkipedia here.
http://en.wikipedia.org/wiki/Speedometer

I have a GPS on my FJR and can assure you that your odometer is also off!

[Red01]

Yes, my odo is off, but it is not off by anywhere near as much as the speedo, so it seems the "calibration" of the two are separate issues.

And after reading the wiki artilce's bit on tire differences...

For example, a standard tire is "185/70R14" with diameter = 185x70/1270 + 14 = 24.20 in. Another is "195/50R15" with 195x50/1270 + 15 = 22.68 in. Replacing the first tire (and wheels) with the second (on 15" wheels), a speedometer reads 24.19/22.68 = 1.0670 times the correct speed or 6.7% too high.

My point about a worn tire getting more accuate as it gets shorter is reinforced.

Let's say you have 5mm worth of tread life.  Using the formula from the wiki for a 180/55R17 you get a diameter of 24.80 (rounded to the nearest 1/100th).  5mm later, your diameter is 24.58.  Less than 1%... which (coincidentently?) is about the same as my odo measured off by.

The important thing we agree on is the OEM speedos are not accurate and this is typical, not something some of us suffer and some don't. 

[China Greg]

My 1998 B12 (mechanical) speedo started jumping around about a year ago. It SUUURGES up at highway speeds; at 65 it wavers wildly, upwards as much as 15 or 20 mph over what is probably correct. I even tried taking the speedo apart (and actually reassembled it), but found nothing visibly wrong.
Time for a new unit.... $175 new, online.

[stormi]

My 1998 B12 (mechanical) speedo started jumping around about a year ago.

You know, I had a similar problem with my old firebird.  It was about a month after I installed cruise control on it.  The CC servo managed to seize and on it's way out, stripped the bullet gear at the transmission.  While it was doing its damage, my speedo would jump all over the place, and I had no idea how fast I was going.  I'd be doing 0, then 30 over, then bang on, then 20 under.  It was making me nuts!  Til finally it just stopped altogether.  Visibly, it was barely possible to tell that the gear had stripped out.  The cable was barely wider than it was long, and the hole wasn't really round looking,... more of a slightly rounded square.  This would be similar if a cable were sticking, or getting hung up from time to time...

Any chance that this is similar to what's happening?  I'd hate to see you put $175 into the head unit, then find out it was the cable or a bullet gear or similar...

[billincentraljersey]

Nice theory, Bazza, but a couple of flaws.
1) If it was due to tire wear, the % of error would be constant.  I don't believe the tire's diameter changes that much with increases in speed, and if anything, it would grow from heat increasing the air pressure, putting the error in the other direction.  Ever watch the tires grow on a dragster's slicks when they warm up their tires in the "bleach box?"
2) Why is the odo so much more accurate?

Rumor has it the reason they make them optomistic is for the lawsuit reason... and it seems the most logical to me.

Red:

This is not my theory, I actually read a very good article on it once which had a whole bunch of Engineering math formulation to back it up. (I was not able to locate it and it was torture to read).

A bike tire from new to finish changes a great deal of overall circumferance. (many mm).

But someone has a pretty good explaination on wkipedia here.
http://en.wikipedia.org/wiki/Speedometer

I have a GPS on my FJR and can assure you that your odometer is also off!

Humm, I have to respectfully disagree.  If I am to increase the gearing ratio of my sprockets, -3 teeth in the rear for example, it will correct the speedo to the true road speed.  If the tire wears, the diameter is smaller, making the total gear ratio go DOWN.  So, wearing down the tire would only make the speed error get worst, not better.

[billincentraljersey]

A cheap solution to the problem, cheaper than a GPS, is to spend $12 on a bicycle speedo.  Find one with a large readout so you don't have to squint.  The speed gets the info from a wired sensor, mounted to the fork, to pick up a magnet signal attached to the wheel.

Someone at the Kawasaki Concours forum chaecked it against a GPS and said it was very accurate.  You actually put a chalk line on the ground and the wheel, roll the bike forward some distance and measure a distance to a second chalk line.  The distance info is entered into the bicycle speedo.

[Bazza]

Humm, I have to respectfully disagree.  If I am to increase the gearing ratio of my sprockets, -3 teeth in the rear for example, it will correct the speedo to the true road speed.  If the tire wears, the diameter is smaller, making the total gear ratio go DOWN.  So, wearing down the tire would only make the speed error get worst, not better.

Bill is correct. If you go to a one tooth larger sprocket on the front of the Bandit, (same as going down 3 teeth on the rear, the speedometer will almost read perfect. (The faster the back wheel spins, the further off your speedometer will be, as it will believe you are going faster than you are) Increase the teeth on your rear sprocket and your speedometer will be off even more.

Tire wear.

A new tires total outside circumferance is much larger than one that is used. (Remember MC tires wear the most in the center. So when you measure your tire wear lets say you have worn 3mm of tread off, well that actually changes the total circumferance of your tire a great deal. (Your tire actually increases RPM the more it wears).

Here is something that explains what I am trying to say. (Warning) you may want to start drinking before actually working your way through this with your calculator. Do the calculations with one fictional tire circumferance, then reduce the circumferance by 20% to account for tire wear.

If you actually do this calculation, you need to find a girlfriend or something.

 
http://www.splitdorfreg.com/Blancard/corbin.html

[Snubnose]

Bill is correct. If you go to a one tooth larger sprocket on the front of the Bandit, (same as going down 3 teeth on the rear, the speedometer will almost read perfect. (The faster the back wheel spins, the further off your speedometer will be, as it will believe you are going faster than you are) Increase the teeth on your rear sprocket and your speedometer will be off even more.

My Brains hurts...its way too hot to think that stuff through!

[LowRyter]

You know, I wish there was a way to get the glass & face off the speedo, get new face printed in the right MPH increments and put it all back together.  If the speedo topped out at 150 rather than 170, it would just about spot on.

I'm told it's not a practical or feasible to get the glass off.   

[Red01]

I think that could be done.  I recall back on one of this boards earlier iterations, there were a few people interested in getting one of those fancy gauge face sets like you see advertised in the back of moto mags for the 2G B12, but they never got enough interested folks to commit to order so the outfit would make some up.  They had to get something like 10 or 12 commited folks, IIRC

[aussiebandit]

In the land of Oz, the ADR (Australian design Regulations) allow for a 10% variance in speedo reading to actual speed. 

In the past the state police forces have allowed the same 10% variance before booking you. The may well pull you over and have a little chat, but wouldn't book you.

But, in one state (Vic), the Government is enforcing a zero tolerance policy and have made a statutory ruling that only allows for 5% variance.

In NSW the government have amended the law relating to demerit points, which indicates a similar policy to Vic. 

1 to 10kmh over the speed limit will attract one demerit point and an $84 fine;
11 to 20kmh over the speed limit will attract three demerit points and a $197 fine;
21 to 30kmh over the speed limit will attract four demerit points and a $338 fine;
31 to 45kmh will result in a three month suspension, five demerit points and a $647 fine;
Over 45kmh will result in a six month suspension, six demerit points and a $1,744 fine.

For the record if you loose 12 demerit points you loose you licence.