This is what I know and think about on the above subject, it’s not a lot so does anyone have anything additional to add?
PSI when tyres are hot should be between 30-34. 32 is said to be the best when hot.
Rear Tyres wider than Front will lower oversteer/increase understeer. In some cases you can lose a lot of cornering speed though even though the car may feel better.
Test each compound to see what your car can handle.
If using stock or street compounds it’s usually best to upgrade to max tyre widths.
Larger rims can increase turn in ability in front. They can reduce tyre rolling over but your tyres will lose heat easier.
Lighter rims will decrease rotational inertia and improve handling especially in Low class cars.
Larger rim size will lower the tires sidewall and increase tire rigidity but too much will add unnecessary weight. 1" is about 1 lbs per rim - PsychoSasuke
Lighter rim choice is usually best as it reduces Unsprung weight - Dust2Death
When running different PSI’s each end - Stay within ideal hot psi ranges (mentioned above as 30-34psi) whichever end you tune to have more PSI will usually get a bit more grip. To get better turning increase front psi, to stabilise the car increase the rear psi or reduce the front.
There is a point though where if you go too high you start to lose grip. I now aim for max of 33.5 front and 33 rear when hot - SatNiteEduardo
I think he found that it didn’t really matter that much in previous forza’s and in fact heavier was better but in 5 it does make a difference. I’m sure it was Rosny, it was defo a respected tuner that I read said that anyway. I’d have to check but I’m 99% sure.
There is really no ideal cold PSI. The most important number is the PSI when the tires are warm (3-4 Laps as if you where hot-lapping) and that number is 32 PSI. But as long as you are between 30-34 PSI in race it’s OK.
Also, the tire pressure is related to the balance of the car suspension/ Aero … So you can start with your personal favorite PSI and tune everything around that initial PSI .
The higher the PSI, the more responsive the car will be, but too much will provoke a sudden loss of traction. Another thing is you can tweak front PSI or rear PSI ±0.5 to improve turn-in response.
Lighter rims will decrease rotational inertia and improve handling especially in Low class cars.
Larger rim size will lower the tires sidewall and increase tire rigidity but too much will add unnecessary weight. 1" is about 1 lbs per rim
As far as tire widths and compound, that’s very difficult to determine and it’s related to the car, the track, the build, and the driver.
The lightest rims were better in every Forza vs having heavier. In FM3 heavy rims were only better because of the PI penalty, that lessened in FM4 to where many cars used the lightest rim possible. It’s always a balancing act and always will be. Power vs Weight vs PI meaning test it, every situation is different.
To be fair to everyone that does make absolute sense but when has Forza ever made absolute sense. Apologies to Rosny if I misquoted him and thanks to you and Death for confirming that lighter is ALWAYS better if you look at rim choice on its own.
I don t recall having stated such. Its ok Sketchy, no need to apologize. Thank you for the respectable tuner though. We are reading so much about tuning that even i forgot who posted what at some point lol.
I will have to agree with Worm’s statement about the rims.
If i may add the following and its my preference when i tuned, one of the last part that i will install is the rims. I will try to squeeze all the power i can up to 1 -3 pi from the limit and then install the lightest rims possible. I may try to play with the build to shave some weight at the end. Yet again, sometimes you may have to install heavier rims just to shave one pi points in order to get to the max pi you re aiming for.
In conclusion, testing is what matter the most. If you don t try it, you ll never know the results you could possibly achieve.
If you are still within ideal hot psi ranges (mentioned above as 30-34psi) then whichever end has more psi usually gets a bit more grip. To get better turning increase front psi, to stabilise the car increase the rear psi or reduce the front.
There is a point though where if you go too high you start to lose grip. I now aim for max of 33.5 front and 33 rear when hot.
Also another thing I would like to add is ALL of this is VERY TRACK SPECIFIC! So if You are tuning on one track then take the car to another track the telemetry readings will be very different! And that’s why tuning has to be track specific. Otherwise you will have to compromise and that means that you are not maximizing the full potential of the build. Everything you do on one track you have to do it all over again with another one. And most times you will end up with different numbers! The best example for this is the Lotus E21 Open source tunes uploaded by SPxUMADBROYOLO and BryceMW (Big Thanks to them) it’s the same car but every track has a different tune!
I agree with most of what i have already read here. Lightest build usually is the best,weight effects everything. but this is not set in stone,It depends alot on car and the track your running. some cars run faster with a roll cage for example,adding 150lbs. some cars are best with stock rim size,some perform better with maxed rim size ie… mini 97civic 22b 05subaru ect ect. my first 05 scoob had light rims,i did a rebuild adding heavier rims and replacing race brakes with sport,but this allowed me a added front tire width. the fatter build was faster for me,all my lighter build times were killed. So yeah i agree with most of this,but nothing is set in stone,its always worth messing around with the builds and testing them.
In terms of linear acceleration, lighter is better.
For rotational acceleration (rim+tire), lighter is generally better BUT it’s the angular moment of inertia (which varies squarely with the distance away from the centre). i.e. given same 18" rims, a lighter wheel will likely be faster though not always true. And a heavier 17" rims CAN be faster than 18" rims depending on the mass distribution on the rim. But in general, lighter is faster and it is also dependent on how T10 has coded the wheel mass distribution + angular moment of inertia. Only practical way to tell is to test.
Lighter rims will accelerate AND decelerate faster therefore the benefit is twofold > significant impact.
Lighter rims will also ride the fast bumps better > minor impact.
As for cornering performance, I think the rim sizes and tire profile has more to do with cornering than the weight of the rims.
There is no rule other than test the dang car. The only thing hard about tuning for anyone that grasps the basic concepts is being flat out lazy and not testing the cars on whatever track they want.
If you enter a tuning comp and someone beats your tail in the same comp look how he built the car. Go watch a replay of a #1 or an odd ball car with a decent time. Look at the rim size, the brakes, the tire compound, what rims, etc. It isn’t hard unless you make it more difficult by trying to make little absolutes out of everything.
Not trying to be an ass here but it’s just not as difficult as 99% of people make it out to be.
Given the wisdom in the last two posts I wonder if the OP be changed to say that the advice provided that mention specific figures relates to starting points from which to test variations.