inaccurate odo reading + speeding

**middens** · 08-11-2009, 01:36 PM

I just purchased a bike and am trying to determine if my odometre reading is accurate (maybe 10-15km/h). It seems like it may be reading a lower speed than I am actually travelling. I am a new rider and have just brainstormed a few ideas on how to determine my true speed. Maybe I can get a few ideas from people out there? Sorry if this is a noob question!!

I have thought of:
- using a GPS with a speed tracker but I don't know how accuate it is and don't really want to be staring down at a GPS screen while riding.
- being paced by another vehicle tracking their speed (somewhat inaccurate I imagine)

I don't want to get dinged with speeding!

**caboose483** · 08-11-2009, 01:39 PM

Next time you see a cop, ask him to get a reading on you.

Go exactly the speed limit then come back and ask him what he got you at. I've had a few trucks with bigger tires so i've done this a few times.

**KLR-Andy** · 08-11-2009, 02:20 PM

Thats what I did, the police last year was regularly standing on Mavis, stopped by, asked him to measure me, I waited for an opening it traffic and at 70 km I do 65 km.

**tat2** · 08-11-2009, 06:14 PM

Originally Posted by middens

I just purchased a bike and am trying to determine if my Speedometer reading is accurate (maybe 10-15km/h). It seems like it may be reading a lower speed than I am actually travelling. I am a new rider and have just brainstormed a few ideas on how to determine my true speed. Maybe I can get a few ideas from people out there? Sorry if this is a noob question!!

I have thought of:
- using a GPS with a speed tracker but I don't know how accuate it is and don't really want to be staring down at a GPS screen while riding.
- being paced by another vehicle tracking their speed (somewhat inaccurate I imagine)

I don't want to get dinged with speeding!

The option of asking a cop is one, the other is to get the GPS, read the documentaion on the acuracy of the speed reading and go with that.

You don't need to be dead on accurate, thats just paranoid.

Every speedo out there is inaccurate most actualy read high, on my KLR as an example if I am doing 115kph, my GPS read 101kph, it is in accurate above 40kph. My 2K Katana was accurate to 100kph and then the speedo would go out.

**Skurj** · 08-11-2009, 06:18 PM

I could be wrong but i think all manufacturers have to build in some error on the high side, so that the indicated speed is higher than actual. It wasn't always this way, but now it protects the manufacturer from liability..

So if you speedo says you are doing the limit you can bet you sure aren't going over it (if you haven't tampered with the bike/speedo/sprockets/whatever)

**01cbr** · 08-11-2009, 06:31 PM

I just ran into this issue.

I recently re programmed my speedo healer and it seemed to be reading low.

On the 400 i confirmed this when 114 km/h would have me passing EVERYONE.

I think im going to try re programming it again before I try to see how accurate it is....but i will probably just tail a friend in a car and ask him to go exactly speed limit.
Though not exactly accurate....at least I know im not going 50 over when the im have in indicated 10 over.

**Torren** · 08-11-2009, 08:35 PM

Go out in your cage and drive out to a spot that has a fairly long continuous stretch of road that you don' that to change lanes in, and one that your not going to run into a whole lot of traffic. Country backroads are great for this..

Stop your car at a specific landmark (road sign, driveway, intersection ect..) and reset your trip meter. Drive down the road for pretty much as long as you can. The longer you can go the more accurate the comparison will be. If you can go 10k that's great.

Jump on your bike and do it again. Compare your trip meter readings. They should be close, within a couple of percent. If they are off by a fair ammount it doesnt really matter, you will now know the average speed that your bike reads as compared to your car.

I know my bike reads about 10 percent over actual speed. So at 40 it reads 44, 80 reads 88.. and so on..

It's not a perfect method, but it's easy and it's close enough to keep you out of trouble.

**Brian P** · 08-11-2009, 10:34 PM

^ The above, will check the odometer (distance), not the speedometer. The error in the odometer is not necessarily (and in virtually all cases IS NOT) the same as the error in the speedometer. Your odometer could be accurate but the speedo could be 7% high, or 10% high, or 2% high, you don't know.

But ... a variation of the above procedure can be used. Establish a known, preferably long distance (several kilometers is best - the kilometer markers on the 400 series highways can be considered accurate). Then, get a stopwatch that's easy to click the button to start/stop. Get up to the speedometer reading at which you want to check the speedometer, and start timing the moment you pass the first marker, go at an absolutely constant speed and click it the moment you pass the next marker the known distance away. From knowing the distance and the time, calculate the actual speed, compare it to speedo reading.

**Torren** · 08-12-2009, 09:17 PM

The error in the speedo should always be equal to error of the odometer. They both get their input from the same source. If one is not matching the other, one of the units is malfunctioning. If your machine is still in warranty, get it taken care of.

If you do both methods and find out your speedo error, and you still manage to get a ticket.. you earned it.

- Torren

**KLR-Andy** · 08-12-2009, 09:52 PM

The speedo meter, is accurate or optimistic by up to 10% (normally engineered in and it is by car/bike model).
The ODO meter normally is accurate, unless you made tire or sprocket changes.
Unless you have certain Hondas.
Honda had to settle a class action suit for severly optimistic odometers and people were out of warrenty far before they actually hit the limit. (only manufacturer ever to be caught doing this, not saying the rest are innocent.

**Brian P** · 08-12-2009, 10:20 PM

Originally Posted by Torren

The error in the speedo should always be equal to error of the odometer.

Wrong.

Although there is a precise mathematical relationship between *actual* distance, speed, and time ... your instrument displays do not necessarily follow it. In fact, due to the way the motor vehicle standards are written, I guarantee that they do not follow it.

If you have digital LCD instruments ... they are all just numerical displays. They will display whatever number that the underlying programming tells them to display. If the underlying programming tells the speedometer to display a number that is (say) 7% higher than what the mathematically correct speed is ... that's what it does, with digital precision.

If you have a mechanical speedo, you can very easily make up a new background for the speedo that results in a different scale from the mathematically correct one ... and so can the speedometer's original manufacturer.