Well, I never. All these years I've been riding a bike, and I didn't realise that I was breaking one particular road rule pretty much every time I mounted up.
And if you've ever ridden a bike, it's extremely likely you've done what I've been doing, too.
After all, it's a common practice. If you're climbing a hill, or accelerating away from a set of lights, or wanting to increase your speed on the flat, what better method than to lift your bum off the saddle and use your bodyweight to power down on the pedals?
But then I heard of road rule 245:
"The rider of a bicycle must (a) sit astride the rider's seat facing forwards …"
Sit astride? Always? What about the time-honoured technique of "getting out of the saddle"?
Road rule 245
Rules is rules, sure, but have you ever tried tackling such famous hills as Yarra Street in the Melbourne suburb of Kew, or the vertiginous Awaba Street in Sydney's Balmoral? Not to mention the long and grinding climbs many of us love to tackle in national parks across Australia.
Even with a compact crank and a 28 on the back there's no way I'm getting up hills like that in the seated position without tweaking a knee tendon. Surely the law can't be serious?
I confess I only heard about the unnerving road rule 245 when the NSW government announced last month it had just changed.
In a list of amendments to various road rules, Transport for NSW said it was changing number 245 in order to clarify "that bicycle riders are allowed to stand on the pedals facing forward, for example while riding uphill".
It now reads that a rider must "be astride the rider's seat facing forwards", in what a Transport for NSW spokesperson told me was "a common sense change designed to make the rule clearer for riders".
It turns out that the changes are in line with amendments to the model Australian Road Rules, and other states, such as Victoria and Queensland, are considering them too.
Delving into these matters, I couldn't help but notice a few other things. For example, the rule also says a rider must be "facing forwards", which reminded me of a point of national pride - an Australian is the current holder of the Guinness World Record for riding a bicycle backwards.
Queenslander Andrew Hellinga covered an astonishing 337.6 kilometres in 24 hours riding a bicycle backwards in October 2013. That's an average of just over 14km/h if you don't factor in the stops, and he almost doubled the old record of 180 kilometres in the process.
Wisely, he did it on a test track.
Meanwhile, part C of rule 245 says that if your bike has a seat, you're not allowed to ride "seated in any other position on the bicycle".
Which made me think of Chris Froome's style when he went on a downhill solo breakaway to claim the yellow jersey in last month's Tour de France – although it could be argued that at times he was not so much sitting on the top tube as lying on the handlebars.
This was quite an amazing descent last night by @chrisfroome .. RT if you want to see that again tonight. #sbstdf pic.twitter.com/9ovLmPnv53— SBS Radio Sport (@SBSRadioSport) July 10, 2016
So, NSW is sorted on the seated issue (as is WA, with its own nicely worded regulation 211), but what about jurisdictions that aren't?
A spokesperson for VicRoads told me that the change to road rule 245 "was agreed nationally through the National Transport Commission road rule maintenance process and will be adopted by VicRoads. The amendment will align the road rules with current cycling practices."
The change is expected to be made in 2017, but in the meantime, the wording remains "sit astride".
What are the chances?
But what are the chances of being fined for disobeying that edict?
Recently, ran an article on ways you could get fined that you might not know about.
These included a $298 fine in NSW for waving at a friend out of a car window, while leaving your car unlocked when you are more than three metres away from the vehicle could cost you $99.
But of course, road rules often come down to discretion on the part of the authorities.
And indeed, a Victoria Police spokesperson told me: "A cyclist could be fined for riding improperly by standing on their pedals but police are able to use their discretion and this rule is only enforced if the rider is creating a risk to themselves or other road users."
So there you have it. A law you probably never knew about is busy being amended to better reflect the way bikes are ridden. I guess we can put this down as a win for common sense and for cyclists – and perhaps our knees.
Fairfax journalist Michael O'Reilly has written the On Your Bike blog since 2011.
Follow Michael on Twitter or Facebook, email him or read more of his blogs.