mechanical speedo's off by certain %, so i've heard, true?

[tmc008]

so i've heard (or read) that mechanical speedo's are a certain amount off the faster you go. (suggested fix: electronic bike speedo) but my question is, if you put on a 15t sproket will this 'overfix' that issue? (since i've read that the 15t sprocket throws the speedo off by 6%) or will that set you back even further?

[mjm]

so i've heard (or read) that mechanical speedo's are a certain amount off the faster you go. (suggested fix: electronic bike speedo) but my question is, if you put on a 15t sproket will this 'overfix' that issue? (since i've read that the 15t sprocket throws the speedo off by 6%) or will that set you back even further?

Speedo is driven by the front wheel - gearing changes have no effect on the speedometer.  Tires do.  Installing a taller profile tire - say an 80 series instead of the stock 70 series will reduce the error - a lower series - like a 60 will make it worse - always assuming that the tire is appropriate for the width of the rim.

[chimivee]

The other day I was riding w/ Pkaaso and his buddy Marty who has a fancy GPS computer thingy on his fancy FZ1.  This thing gives super accurate speed readings and he paced us.  At an actual 55mph, our bikes both read 60mph.  So, figure about a 10% error, which seems consistent w/ what others have found.

[KevinC]

It has nothing to do with the fact they are mechanical speedos. All the motorcycle electronic ones read about 10% high also.

It is actually legislated in Britain at least that they have to be calibrated so that the worst case combination of tires and tolerances, they still read high. Plus I think the manufacturers like to go for bragging rights at the pubs...

[Rashad]

Well, i went by one of those highway construction things that tell you your speed.. and it was very very accurate.. i think it may be the 140/80 rear i have.. not sure.

[gsJack]

Well, i went by one of those highway construction things that tell you your speed.. and it was very very accurate.. i think it may be the 140/80 rear i have.. not sure.

Rear tire size doesn't affect speedo reading as stated above.

I've noticed the speedometer on my 02 is much more accurate than the one on my 97.  They are using a different speedo now.  The one from the Bandits.

My 97 was about 4 mph off at 40 mph.  Passing one of those speed indicator radar carts showed 36 mph.  Was off even more at highway speeds.  The new 02 seems to be only about 1 mph off at 40 mph.  Gotta check it at higher speeds when I get a chance.

[KevinC]

Rashad,

The speedo comes off the front tire, so the rear makes no difference. Borrow a GPS, and I'm sure you'll find your's is 10% high too.

[glenn9171]

Using my Garmin GPS III, my speedometer on my '01 model is 10% high as stated above.  At an indicated speed of 40MPH (on the speedometer), the GPS says 36.  Speedo of 80 is actual 72.  Take 10% of the indicated and subtract it.  There is your actual speed.

[rizp]

man, I thought I was pretty awesome doing this on my own, but lo and behold it's already been done. Oh well, I'll just thow my $.02 worth of data on the pile as well.

I have a magellan handheld unit which will log max speed as part of it's nav functions. so I threw it in my backpack and took it up to 80mph indicated. After I stopped, I checked it, and it read 70 mph.

I reset the GPS and tried again on the way home. voila, 80mph indicated = 70mph actual for me.  Guess I'm not the bad-boy racer on the highway I thought I was.  :lol:  :mrgreen:

Anybody else with a GPS do this test, or are you all too busy geocaching?

Regards,
Riz


p.s. I'm running a stock size front tire.

[cay]

Yeah, I ride with a bar-mounted GPS -- my speedo indicates 8-10% high too.

Note that a 10% delta between real and indicated speed translates directly into a 10% delta between real and indicated odometer display / gas mileage calculations.  Your little GS isn't saving you as much on gas money as you thought it was.  

C

[weaselnoze]

Anybody else with a GPS do this test, or are you all too busy geocaching?
.

my dad is obsessed with geocaching.  i go with him sometimes.  its a real hoot

[weaselnoze]

if the indicated speeds are off consistently, why not just have a corrected guage face??? am i the only one who has thought of this, or is there a reason it wouldnt work..?

[JetSwing]

so the bottomline is gs' top speed is only around 100mph??  

[rizp]

hey cay,
thanks for the disheartening news about the fuel economy  :lol:

and to think, I just started feeling good about getting up to 46mpg city after switching out the air filter.  :x

So you have a bar-mounted GPS on your GS?? care to post a pic of your setup? I hate using the GPS in my backpack.

It's an archaic handspring visor springboard that devours AA's, the visor fixed battery is crap,  and ALSO, if I'm doing any nav-logging, the thing is notorious for stopping when something touches the screen. it's great in a car with a cig. adaptor, but not best elsewhere.

Just curious to see what a GPS setup would look like on our humble little commuter.

Regards
Riz

[marc]

Geocaching? (ears up!)
I'm too a geocaching addict!

About my experience on the counter: at 120Km/h my counter is 140Km/h.
Using a 120/80 tire solves the problem.

Do these counters have an adjustable spring?

[stefman722]

I have a digital speedo/tach installed on my bike and yes, the analogue speedo is off starting at 60 kmph. I left my analogue speedo on aswell so i could tell the difference. Same goes for my analogue Tach, it is sometimes off by a few hundred RPMs. I will take pictures of my speedo/tach if you wish.

[mjm]

Yeah, I ride with a bar-mounted GPS -- my speedo indicates 8-10% high too.

Note that a 10% delta between real and indicated speed translates directly into a 10% delta between real and indicated odometer display / gas mileage calculations.  Your little GS isn't saving you as much on gas money as you thought it was.  

C

No, it does not.  Speed is via a magnetic coupling/spring/damping arrangement and the odometer is geared - the DOT types get very angry when the recorded milage is off by any significant amount -

[red_phil]

Agreed.
My odometer said 112 miles and multimap route planner said 111 for a recent trip.
I'm guessing the extra mile came in from the extra little bits into and out of
car parks etc.

[weaselnoze]

since no one answered me before, why not change the guage face to show more realistic speed?  is my thinking off?

[cernunos]

Weasy, just use the speedo to impress your friends..."look, my bike does 130 mph". If it's off a little just go whatever amount it's off by faster than what you want to do. That way you can always feel like you are flyin'. GS is a good bike, Earth is round with small cracks and bumps...slightly wet, and the GStwin forum is pretty cool.

C.........