How do you find out how accurate your speedo is?

[MadzBiker1]

The other night i was on the way to somebody's birthday party on the RS, i was leading 2 other cars aswell there since they didn't know the way. When we got there they mentioned i was doing 10 -15mph over the speed limit, but it shew i was doing the speed limit on my bike so i'm kind of worried now because there's alot of speed camera's near me. ( I saw no flash so i'm hoping it's all good )

It seems fine when i'm at 30 and it's doing a steady pace with the other traffic which are doing the limit so i don't know if it's there's at fault or mine?!

Do you just take it to a garage or something to get it tested?

 

[AZZ3R]

You have a tank bag?

Stick a Sat Nav in the bag get to a nice straight road get to 30 & check the speed against the Sat Nav.

I've had 120 on my SV, but my Garmin read' 115 - Top Speed.

Speedo's are usually out by around 3 or 4mph. But if your still not statsified with the results of a Sat Nav, have it dynoed'. They will measure everything & can check the speed/ speedo reading.

 

[SqueakyBrakes12]

Is the cable going into your speedo loose?
I was riding along happily and suddenly my speedo needle just started dancing about then just stopped and told me i was doing 0mph! I was doing atleast 40-50mph. When I got home I checked the cable and noticed the vibration has loosend it, I took it out, gave it a clean and put it back in, had no problems since.

I'm not that much of a technical guy, but thats my suggestion.

 

[Trinith]

90% chance it's off by about 10%. Due to the way gear ratios and speedometers work it's impossible for a speedo to be off by 5mph. Unless ofcourse the needle has been removed and improperly installed, but that's kinda unlikely.

Check it against a GPS at multiple speeds. I usually do the ones that involve easy math. 10mph, 50mph, 100mph, etc. They're a little easier to figure out sometimes, but really so long as it ends in a 0 and you're not a complete moron it shouldn't be too hard.

Something else you can do is find a spot where you can mark off a mile. Then get going at a given and steady speed and time how long it takes to cross the mile. Again, do this at varying speeds, and a little math, and presto, you can figure your actual speed and compare it to your speedometer reading. There's no real need to pay anyone for anything.

 

[matth1138]

There's no real need to pay anyone for anything.

I shall remember this forever.

 

[Trinith]

There's no real need to pay anyone for anything.

I shall remember this forever.

Just don't forget that I know where you live.

 

[Bloke]

Speedos will only ever legally over read by 10% and never under-read unless you have modified something.

So your problem can't be accounted for within the in-built inaccuracy.

10% of 70 is still only 7mph so to be 15mph can't even be accounted for over-reads in your mates speedos.

Are you sure you haven't changed sprockets or fiddled with the speedo cable?

Sent from my GT-I9000 using Tapatalk

 

[MadzBiker1]

You have a tank bag?

Stick a Sat Nav in the bag get to a nice straight road get to 30 & check the speed against the Sat Nav.

I've had 120 on my SV, but my Garmin read' 115 - Top Speed.

Speedo's are usually out by around 3 or 4mph. But if your still not statsified with the results of a Sat Nav, have it dynoed'. They will measure everything & can check the speed/ speedo reading.

Sorry for the late reply's, I'll try find my sat nav later and try it while i'm out!, got a 30 mile trip so perfect to test (Y)!
I was looking at dyno's because a family member works in a motorcycle tuning garage so they have one there. Only problem
i'd have is i'd want to get the numbers up!

 

[MadzBiker1]

Speedos will only ever legally over read by 10% and never under-read unless you have modified something.

So your problem can't be accounted for within the in-built inaccuracy.

10% of 70 is still only 7mph so to be 15mph can't even be accounted for over-reads in your mates speedos.

Are you sure you haven't changed sprockets or fiddled with the speedo cable?

Sent from my GT-I9000 using Tapatalk

I haven't touched my speedo cable but the previous owner did change the sprocket sizes but then he had an MOT + Service on it so wouldn't they of bought it up?, I was going past a speed warning sign the other day ( one which doesn't flash or gets you in trouble ), and i only activated it at 35mph and it was a 30.

 

[MadzBiker1]

Is the cable going into your speedo loose?
I was riding along happily and suddenly my speedo needle just started dancing about then just stopped and told me i was doing 0mph! I was doing atleast 40-50mph. When I got home I checked the cable and noticed the vibration has loosend it, I took it out, gave it a clean and put it back in, had no problems since.

I'm not that much of a technical guy, but thats my suggestion.

I haven't touched my speedo cable but i checked it over after the message and it was in place fine. All suggestions are welcome ;P, I'd of been panicking trying to get it working if that happend to me!

 

[MadzBiker1]

90% chance it's off by about 10%. Due to the way gear ratios and speedometers work it's impossible for a speedo to be off by 5mph. Unless ofcourse the needle has been removed and improperly installed, but that's kinda unlikely.

Check it against a GPS at multiple speeds. I usually do the ones that involve easy math. 10mph, 50mph, 100mph, etc. They're a little easier to figure out sometimes, but really so long as it ends in a 0 and you're not a complete moron it shouldn't be too hard.

Something else you can do is find a spot where you can mark off a mile. Then get going at a given and steady speed and time how long it takes to cross the mile. Again, do this at varying speeds, and a little math, and presto, you can figure your actual speed and compare it to your speedometer reading. There's no real need to pay anyone for anything.

I'm trying the GPS later BUT i'm also going to have a go at the mile mark. Seems intrested & i feel like trying something new, cheers : )

 

[bc65925]

Simple check without GPS, 60mph = 1 mile per minute

 

[Trinith]

I haven't touched my speedo cable but the previous owner did change the sprocket sizes but then he had an MOT + Service on it so wouldn't they of bought it up?, I was going past a speed warning sign the other day ( one which doesn't flash or gets you in trouble ), and i only activated it at 35mph and it was a 30.

I dont know what the MOT checks, but changing the sprockets WILL change the speedo on almost all bikes. If you change them to add acceleration it will read too high. It'll be high by the same percentage of the gear ratio change. Same for a smaller sprocket in the back (to make the bike accelerate slower but gives better highway gas mileage) only then it would read low.

I would check the odometer too, since you mentioned the gearing change. The odo generally reads off the speed sensor, so if one is thrown off by the gearing change then the other will be too. However the odo is correct from the factory (whereas the speedo isn't) so you can never get the two to be dead on together.