Here's what I've said before on this topic:
https://www.gtplanet.net/forum/showthread.php?p=5235419#post5235419
I wish there was a pinned topic in the online section explaining this about pp restricted races for newbies.
That you might as well just go back to aspec if you don't have full suspension, full LSD, & full transmission on all cars you might expect to want to use in an online race.
There's no way to force restrict tuning parts out of a race. So unless you play in an organized race with ALL people being trustworthy for the honour system, you should just assume everyone's adding the best items... even if they SAY it's "street legal" or "road cars". This generally does NOT mean everyone's sticking to sports suspension & whatnot.
Basically, unless you're playing in an organized race where there's strict rules about tuning, tires, car choice, etc..
You should assume the following:
If it's a one make race - everyone gets their cars all hopped up as much as possible, with all the best parts. Then power-limits down (and/or ballasts up) just to fit into whatever restriction is on the race.
If it's class race - ie: any car of a particular class, whether it be sports cars, hatch, saloon, sedan, or coupe or even kei cars... Everyone gets out either the most hopped up car they have in that category, or the most high end car they have in the category.
If it's a purely pp restricted race...
They don't get a car that's ballpark that pp or just mod it up to the pp with a few upgrades. They FULLY modify it, and then limit it down into the pp restriction.
And that makes a big difference in some lower-performance cars. A racing flywheel, fully adjustable LSD can make some crappy cars very drivable.
Or, they just even skip that and just take a car that, out of the box, is superior, and power limit that down to the pp restriction.
I'm not saying this is ALWAYS the case. As there are some people you'll find not doing all of this all the time. But you can just guarantee that at some point or another, there's going to be at least one person in the room that does this, and then everyone else will follow suit not to be left in the dust.
Here are some very good threads about the issues involved:
https://www.gtplanet.net/forum/showthread.php?t=196351&highlight=pp+fails
https://www.gtplanet.net/forum/showthread.php?t=200752&highlight=pp+upgrade+online
https://www.gtplanet.net/forum/showthread.php?t=201041
https://www.gtplanet.net/forum/showthread.php?t=201278&highlight=pp+upgrade+online
I've found that most of the time it pays to join a room with a PP limit as then no individual is going to have a massive advantage when it comes to the vehicles performance.
Well that's not necessarily true!!
Differences of quality, handling & power can vary WILDLY at the same PP number.