I’m a pretty good tuner and have tuned a few top 50 and even a top 10 rivals car… but one aspect that I haven’t wrapped my head around yet is rim size. I understand that larger rims=more weight, but more responsive tires. Is the weight worth the responsiveness? By responsiveness, does that equate to better turn in and/or faster acceleration? Is it best to upgrade rims by a size or two to balance between both aspects?
The tire weight is considered unsprung weight, meaning it does not affect the springs of the car. So it helps hold and keep the car on the ground, but your engine still needs to overcome the additional weight it adds to the overall car to make it move.
I like to always go with the largest rim I can, it makes for a good trade off of unsprung weight vs performance, you usually get a couple PI back for going for the largest. ( that can be used for engine HP stuff) Also large diameter rim means small aspect tire, or better known as side wall. Less side wall, less chance for it to roll on itself. But, that is some real life physics that might only be partially in the game. There is a ton of stuff about tires / tyres out there on the web it is crazy.
So that is my vote, Largest rim, extra PI or free, buy some engine goodies to compensate. One thing to add that I picked up from another thread in FM5. think about adding 1HP for every 3lbs you add to the car,
Thanks for the discussion starter,
Meow
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Thanks for sharing Kitty. Those are some pretty good points.
For me, it depends on the car and how it handles, but I haven’t considered everything in Kitty’s post. Usually for cars that are in a lower class and don’t have the power already, I add the larger wheels so I can get some extra HP. If they have plenty of power but lots of weight, I tend to leave them off because I don’t need more power and I don’t want the extra weight.
Thanks PPIDrive, I always over-think things 
Curiosity and cats you know…
I wouldn’t say it was over thinking. Those are valid points, and they all make sense. Again, we don’t know how much of the real world is modeled into the physics but they have done a pretty darn good job so.
Think about it this way - in my A Class Legacy RS I was able to get in a couple more PI points with 21" rims and it made a huge difference in the power upgrades I could take without lifting the weight too high. In my A Class 2011 STi I have stock rims or one size up and Eduardo’s Evo would always out accelerate me on the same part of a race. By bumping up the rims to max, I am able to change or add some power upgrades which did the trick and I wasn’t out-accelerated anymore.
There is validity to your point. As I said though, unless I’m doing the car to try and be competitive in, I leave it in a mode that is visually pleasing while I play SOLO. Even that way, I do fairly well on the boards so it makes me happy. There isn’t any one way to play the game 
Whenever I increase the rim size, it seems to always increase the PI. Even when I go to the largest size.
In this game incresing rim size on the front almost always results in increased PI.
Increasing rear rim size its a mixed bag - sometimes PI goes up, sometimes down.
I’ve found that sometimes the rear rim size increase will raise the PI and then lower it. It depends on what the size was originally, how far it can go, and what drive type you have.
I usually just go with what looks good haha, but I have found bumping up the size in some cars has helped it feel more responsive both going in to turns as well as holding corners at speed, the roll effect definitely factors in the game, how much? Can’t say but it’s there
Thanks everyone for your responses… great discussion!