The speed limit may say one thing, but no one ever drives the speed limit. Where I drive most of the time I know what tolerances are in place. If I drive in a less familiar location, such as when visiting family, I do not know how tightly speed limits are enforced.
What is the best way to establish how fast I can drive without getting a ticket?
While I would advise just simply sticking to the speed limits put in place for yours and others safety, there are a a couple of tricks I've picked up which work at least in the UK!
Speed cameras have tolerances that are in place in order to stop people getting tickets when in fact they're travelling below the speed limit. After all it costs a fair bit for the authorities to distribute tickets and costs them even more if it gets disputed and thrown out, so it's in their interest to have accurate speed cameras!
The tolerance that I have learned to go by is about 10% over the actual speed limit as I've heard that this is the possible error that a speed camera could present when measuring speed.
A second point of interest is that car speedometers aren't actually all that accurate either, displaying slightly higher than you are actually going (this figure I was once told was +2mph) and if you've ever traveled with a sat nav in the car which shows speed, you'll have seen that the cars displayed speed is a fair bit higher than the reading on the sat nav. I have subsequently found out that the sat nav reading is actually the more accurate of the two (which I refused to believe for a long time) so if you're using one of those you can always ignore your own speedo and go with what that is saying.
Even with all these measures I still change my speed depending on the road conditions and situations that I am in. If it's an empty motorway then I'll happily go 90-100mph unless there are speed cameras around at which point I will slow down to just over the speed limit (+5-10 mph) and I'll usually slow down a bit when passing other vehicles (just in case of unmarked police cars) as if you're caught going over 100mph (or twice the speed limit) you'll instantly lose your license and will be taken to court so I save those speeds for solo drives on lonely roads.
After all that I would still just simply advise staying to whatever you're comfortable with, if you're going to break speed limits you've got to be prepared to risk getting a speeding ticket and to be honest sometimes people can just be outright idiots and deserve lose their license.
Anyways, that's the work around a I use and have never got a ticket or anything but as I said, I live in the UK and I'm unaware of it is applicable internationally but it might be of use to you.
The fastest speed you can drive without getting a ticket is the posted speed limit. In the US the cops will not typically mess around with anything under 5 mph over the speed limit. However they will use any amount over the speed limit as reason to pull you over and often just write you a warning. They will do this because they have some reason that they want to know more about you, what your doing, maybe think you might be driving drunk, or you look like you could be transporting drugs etc.
In school zones there are very steep fines for even doing a mile or two over the speed limit. Here in NV they police school zones with a vengeance, and you just do not speed at all in them.
In construction zones they have a zero tolerance and fines are doubled in most states. So you do not speed at all.
Most states I understand from talking to truck drivers have a zero tolerance policy for commercial vehicles on the interstate. You will get pulled over for 76 MPH in a 75 MPH zone and written a speeding ticket if you are in a large semi truck.
Me I just cruise the speed limit, never get tickets, and never get pulled over. Speeding in the city rarely gets you to your destination any faster and greatly increases your chance for an accident. Between drunk drivers and aggressive drivers the huge majority of accidents happen.
