The XRR's front wheel/tire is 335/30 R19 and rear is 335/35 R18 (if you look carefully in-game, you can also see the front/rear wheel diameter difference). I believe it is the only LFS car with a larger front wheel than rear (though the tire widths are the same). This type of wheel setup seems to appear occasionally in real life, too. Is there a performance reason for this difference in wheel size? Any setup/physics experts care to elucidate? :juggle:

Here is the original post that listed wheel/tire sizes for LFS cars: (message body posted below)
http://www.lfsforum.net/showthread.php?p=45278#post45278

Quote from StewartFisher :

I did all the cars a while ago after Bob told me where to find the numbers...here's what I got:

UF1000: 160/50 R12
XF GTi: 185/50 R15
XR GT: 185/55 R16 front, 220/50 R16 rear.
XR GT Turbo: 225/45 R17 front, 245/40 R17 rear
RB4 GT: 215/40 R17
FXO Turbo: 240/35 R17
LX 4: 195/60 R13 front, 215/55 R13 rear
LX 6: 205/50 R15 front, 245/40 R15 rear
RaceAbout: 205/45 R17 front, 225/45 R17 rear
FZ50: 235/40 R18 front, 295/30 R18 rear
MRT5: 165/55 R13
XF GTR: 215/35 R16
UF GTR: 215/45 R11
Formula XR: 225/50 R13 front, 285/45 R13 rear
Formula V8: 275/55 R13 front, 390/40 R13 rear
FXO GTR: 335/35 R18
XR GTR: 335/30 R19 front, 335/35 R18 rear
FZ50 GTR: 300/35 R18 front, 370/30 R18 rear

Sizes are given as width/profile and rim diameter in millimetres percent of section and inches respectively.

At a guess, I'd go with lower profile tyres giving more bite and precision, useful at the front, while the higher profile tyres have more give on the limit.

In real life I'm pretty certain most race cars would run as larger wheel diameter as possible so they can fit bigger brakes. Normally the technical regulations tell the teams what the maximum width and diameter is and that is what is used by all teams in most cases. I don't see why one car is allowed 19" rims.

The only thing I can think of is that the XRR is front engined and rear wheel drive so needs bigger brakes at the front than the 4WD FXR (engine aids braking on front wheels) or the rear engined FZR.

Dirt bikes typically have a large front wheel and smaller rear wheel (21" in front and 18 or 19" in rear), although I think this has more to do with being able to roll over rough surfaces more easily. Honda's 250cc and 450cc 4-stroke motocross racers have an 80/100 R21 up front and a 100/90 R19 in the rear.

Short of accommodating big brakes and cooling them the only advantage I can see on running big rims on a RWD car is possibly getting better cooling because more rubber isn't contacting the ground, not that tire temps are an issue for road cars in short runs really (well they are but it's usually because they're too cold). Running smaller wheels allows a big reduction in kerb weight.

I could also see a tire with more inner volume (as a result of a higher profile) having more temperature "capacitance" (to use an EE term). More air in the tire means it takes more energy to heat it, so it's possible to push for a few laps and then settle back down without the tires overheating too much. Of course that also means they take longer to warm up.

It's the same principle as using tire pressure to control tire temps (disregarding the change in grip).

The need for bigger front mag would be to put larger brakes... Anyway I dont know examples of cars doing that.

Having more of the wheel diameter as rubber helps get the power down, IRL at least: http://www.youtube.com/watch?v=9O0b90G8Yhg

I don't know how LFS works out those physics, so I couldn't say what it does for the game.