It's not too restrictive over here, the cops get tough on young guys who lower their cars to the point where they scrape over cigarette butts (which are frowned on too, the government is trying to tax cigarettes out of existence, which isn't a bad thing, unless you're an addict) but if a car looks reasonably roadworthy, you're pretty safe, so there are a lot of "Sleepers" out there, especially old Toyota's with 500(+) BHP turbo engines under the hood.
Bike-wise, well you can buy a 200(+) BHP hyperbike if you want to go really fast, but if you want to build an unsafe abomination and expect not to grab the attention of the local Gendarmes, you're deluded. Many half arsed Cafe Racers sneaked thru the cheap "Club Permit" system when it was first introduced, before a series of incidents involving poorly modified bikes being involved in horrendous "fails" made the government mandate a proper "Roadworthy Inspection" is conducted prior to obtaining a club plate.
Once it's passed, there is no requirement to have it inspected again until you sell it, and that's (in the case of club permits) the responsibility of the buyer, not the seller, so I see the occasional abomination for sale cheap of Ebay or FB, with "No Roadworthy certificate", which usually means that they've done something horrible like chopping/welding their frames poorly, and the Roadworthy Inspector has told him to bugger off.
On the other hand, if you want to build a well engineered "special", get a licensed welder to do all your welding, and have him give you something in writing to say it was done by a qualified metalsmith, and take it to an engineer to give his approval, fill out a "VASS" form (can't remember what VASS stands for) and you can still get it legally registered. Of course,
if you get your bike registered before you start modifying it, unless you build an absolute abomination, it'd be unusual for the cops to take much interest in you. I like to think that it's all about safety and not bureaucracy, but sometimes there are some overlaps. I see a few Groms around the city and as much as I loved minibikes when I was 10, I can't really see the point now.
