[eXphoid]

Hey,

Riding yesterday with my friend on his ninja and i flew well ahead of him on the highways.. he thought I was speeding but I was dead on the speed limit + cars overtaking me.

What are the best ways to check how accurate your speedo is on your bike..? i'd use my GPS but that be difficult to mount for one.

I've ridden alongside my rents at set speeds to check but I was only getting used to the bike so never got an accurate reading.

Any mechanics or engineer suggestions .. ? I want to be sure before I get caught.

 

[Drew]

Well, there are two ways, one is to tape the GPS to the tank, the other is to use the mile markers on the freeways, just time yourself over a distance, in 6 minutes you should see 10 go by at 100km/h

 

[dayeve]

There are quite a few ways to test it but the gps is going to the the easiest. You could time yourself between two points of a set distance, but that would probably be more difficult then reading a gps.
It could possibly be that your bike is fine and its your mates bike who's speedo that reads incorrectly. Try matching your speed with a friends cars or bikes.
Also make sure you match your speed with them at different speeds like 40km, 60km and 100kmph because a reading of 1-2kmph over at 60kmph will be more at 100kmph depending on the percentage on how far your speedo is out.

 

[Drew]

The mile markers I'm referring to are on the way into every city on the freeway and they're more or less 1km apart. Time over distance is a lot easier like that.

 

[eXphoid]

True, I forgot about the markers.

Not sure where but heading up to ballarat way there's the speed checkpoints.. bikes will be picked up on that right?
Guess i'm gonna have to tape up the gps and see how that goes..

 

[Drew]

lol I remember my dad had an interesting conversation with some police about one of those speed points, it reported him to be doing 100km/h exactly, so he set his cruise control on that and got booked for 103 by the police. There was some interesting BS about who calibrates what and all that, but in the end he wrote a letter and had the fine cleared. The moral of the story though is that they're a sort of a big joke really.

If you go for a long run with the GPS though you should be able to get your speed within a few points of a km though, so it won't be a big deal really.

 

[aj26]

GPS does have satellite lag and due to weather conditions as well it can affect what "determined speed" you are getting. When I'm driving my GPS will say I'm doing 75 when my speedo says 80-82.

My mobile GPS that I use is very very slow and will say I'm doing 0 when I'm already doing about 30, or even saying that my mobile will say I'm doing 10km lower than the actual.

Normally when I'm going past a speed camera I will look down and drop my speed at 10km (60 zone I'll do 50), Just incase if the thing decides to book me I can say no I was doing 50 at the time.
What can speed checkpoints do? Because I remember when heading down to Wagga Wagga there was a couple and people were doing 130-150 in a 110 zones.

 

[rudeney]

Those speed checkpoints are bullshit as drew has pointed out. They have one on the gateway at the moment with the roadworks going on, they are incredibly inaccurate and rarely even pick up my bike.

 

[Drew]

GPS does have satellite lag and due to weather conditions as well it can affect what "determined speed" you are getting. When I'm driving my GPS will say I'm doing 75 when my speedo says 80-82.

My mobile GPS that I use is very very slow and will say I'm doing 0 when I'm already doing about 30, or even saying that my mobile will say I'm doing 10km lower than the actual.

Normally when I'm going past a speed camera I will look down and drop my speed at 10km (60 zone I'll do 50), Just incase if the thing decides to book me I can say no I was doing 50 at the time.
What can speed checkpoints do? Because I remember when heading down to Wagga Wagga there was a couple and people were doing 130-150 in a 110 zones.

Theres no such thing as satellite lag, the GPS works by making a number of extremely precise calculations which are quite power intensive, so most devices which aren't linked to a vehicles power systems (like dataloggers) will only do the calculation a few times a second, if that. Mobile phones, not being dedicated GPS devices will update a lot less freqently than that even, sometimes waiting over a second between updates. Thats what you're seeing when your phone doesn't update frequently, not "satellite lag".

Its a good idea due to the rate of updating to wait a good number of seconds before relying on the data provided and (obviously) don't expect to get usable data while riding through a corner, because your bikes tyre diameter is lower, so your speedo will be indicating higher and on top of that the GPS won't see you as taking a bend it will just see the points where it does a calculation. As far as a GPS is concerned you're not taking a corner, you're turning out some sort of interesting polygon.

 

[muzza]

or you could chuck it on a dyno?
that would definately be the easiest if your speed is measured in the gearbox/back wheel.

 

[dayeve]

Just ride around until you get booked and then ask how fast you were going. Tell them not to let you off easy and they should give you a fine letting you know how many km you were over.

 

[Drew]

or you could chuck it on a dyno?
that would definately be the easiest if your speed is measured in the gearbox/back wheel.

The dyno isn't going to be awesomely accurate because the tyre is compressed onto the roller, giving you a different rolling radius and also the tyre will tend to give you a different slip on the roller because of the whacky contact patch.