Cars Tyre sizes into Assetto Corsa

[ltcars]

If I search tyre sizes at Google, I usually get a result like this:
245/45R12 98

However, AC asks for this:
WIDTH=0.245 I know what to do for this but the rest...
RADIUS=0.330
RIM_RADIUS=0.254

 

[garyjpaterson]

Just a bit of maths, should be easy enough.

245 - tread width (mm)
45 - profile height (as a percentage of the above tread width)
R12 - rim diameter (inches)

You know the rim radius, thats 12 inches divided by 2, then converted to meters (google will do that for you). Though make that 13/2, because AC suggests adding 1 inch...

Overall radius is rim radius plus 45% of 245.

Or you can set up a wee formula in excel to do it for you

WIDTH=0.245
RADIUS=0.26265
RIM_RADIUS=0.1651

 

[ltcars]

Thanks a lot

 

[Stereo]

You know the rim radius, thats 12 inches divided by 2, then converted to meters (google will do that for you). Though make that 13/2, because AC suggests adding 1 inch...

Overall radius is rim radius plus 45% of 245.

You shouldn't include the extra inch in the overall radius though, since it represents the lip of the rim that extends out past the bead. I know your numbers don't, just worth being clear. The rim radius is used for popped tires to say where the car'll ride on its rims.

 

[Willy Wale]

Not sure if it matters in AC but the geometric radius of the wheel/tyre is different to the dynamic (wheel centre to ground) radius because the weight of the car squashes the tyre.

 

[Stereo]

Use the geometric radius in RADIUS=, then adjust the spring rate and spring rate change w/ pressure until the dynamic radius is ok.

 

[garyjpaterson]

You shouldn't include the extra inch in the overall radius though, since it represents the lip of the rim that extends out past the bead. I know your numbers don't, just worth being clear. The rim radius is used for popped tires to say where the car'll ride on its rims.

Yep I should've clarified that, i never even thought about it.

 

[FakeThinkpad]

Could someone help me out with this because Content Manager gives me a size that I don't agree with.

I have a wheel size of 265/35/18

Rim radius
((18+1) / 2) * 0,0254 = 0,2413

Total Radius
(18 / 2) * 0,0254 = 0,2286
(265*0,35) / 1000 = 0,09275
0,2286 + 0,09275 = 0,32185

Yet when looking inside Content Manager it gives me 265/25/18?

 

[ltcars]

Could someone help me out with this because Content Manager gives me a size that I don't agree with.

I have a wheel size of 265/35/18

Rim radius
((18+1) / 2) * 0,0254 = 0,2413

Total Radius
(18 / 2) * 0,0254 = 0,2286
(265*0,35) / 1000 = 0,09275
0,2286 + 0,09275 = 0,32185

Yet when looking inside Content Manager it gives me 265/25/18?

View attachment 226981

I think I had these too in the past, probably just a bug. I'm no expert though

 

[aphidgod]

For tire sizes, I cheat and go to tirerack.com and check the actual manufacturer spec on the tires in question. It's usually very close to, but not quite equal to, the mathematical result posted above.

On the CM thing... I reported that as a bug a year ago. Was told it's working perfectly, even though it's not, so...

 

[FakeThinkpad]

Thanks for the quick reply, sounds like I can disregard this as a bug of Content Manager then and not a formula error.

Thanks again

 

[John Brandow]

Sorry to bring back a super old thread but where do I see the actual model diameter? If I cannot trust CM. It is way off. CM says a 205/30/17 is 30.5cm but in reality it is over 50cm Its really hard to scale tires or get gearing correct without the proper diameter.

 

[aphidgod]

Well, for one you'll want to work with radius in AC, not diameter. All of the speed and gearing math works fine in the game.

I still wouldn't trust CM working with tires, unless it's been fixed recently that whole bit never worked properly. Might be easiest to just edit tyres.ini manually - RADIUS=0.xxx is where you'd make your changes.

 

[Dirk Steffen]

Here is another small tip re. tire radius, loaded tire radius, tire damper value and tire spring rates:

Using the ACTI Motec plugin you can read out directly the two available tire data channels re. radius (static and loaded).
Given those and knowing your other relevant vehicle data and effective forces as available in Motec (direct channels and math channels as needed) you can now go completely bananas and create relevant math channels to plot say tire compression velocity graphs, .... ;-)

The static tire radius channel plots the static set tire radius you have defined in your tyres.ini file.
The loaded radius data channel is the one you want to use to investigate if your used "DAMP" and "RATE" definition make sense.

It is an additional, useful tool to analyse a tire you have built.

 

[Neichello]

WIDTH=0.245
RADIUS=0.26265
RIM_RADIUS=0.1651

Em yo gary im a little confused, you say radius is rim radius + 45% of 245, but that equals 0.27535, not 0.26265?

 

[Stereo]

The nominal radius of the rim (ie. for a 17" wheel, 17 inches) not RIM_RADIUS

 

[John Brandow]

Thank you all so much.