Hi once more!

There's one more mystery I've been unable to reveal which concerns tire wear and dirt on tires. And once more Aston National + the FZR serves me well for demonstrating that which I cannot explain with my limited knowledge of car dynamics.
In the beginning of the straight one usually cuts the chicane to carry more speed on to the straight. In the process, the left front and rear tire get dirty because there's a little sandy area next to the curb. The dirt pickup is uneven (more dirt on the rear compared to the front) but it also seems that the rate at which the front and rear tires become clean again is not balanced.
In the end of the straight the dirtier rear tires are completely clean while the front tires have some more problems shaking off the rest of the dirt.

I was thinking that it might have to do with the weight distribution of the car and thus more weight in the rear of the car would cause more tire scrub. But this doesn't make much sense to me...
It can't be excessive tire spin because there's actually no rear tire spin on the long straight. The rear tires are gradually getting cleaner a lot faster by just going down the straight at 200 Kp/h+.
Now I'd like to know why this happens and I'd be delighted if any of you had some ideas about this

As I love screenshots, I've attached three of those :P

biggie

Dirt is only lost when the tyre is loaded. That means in the LFS-world a tyre that rolls without a car doesn't lose dirt at all and will stay dirty forever, a tyre with an oil-truck on it will have lost all it's dirt with one turn.
And as you can see, the tyre load on the rear is higher, thus the dirt goes off faster.

At least this is my interpretation of what I see in LFS and it'd be one of the first things I wanted to have changed in the near future, if I were allowed to demand anything.

Vain

Also, although the rears arent actually spinning, they will be operating at a much higher slip ratio than the fronts due to the acceleration, which also wears the dirt off.

Actually, if you look at the .raf file in f1perfview, the driven wheels do spin a little bit at high speed, up to about 5 mph faster than the overall vehicle speed. This effect is even more pronounced on motorcycles, and I think I recall someone (I believe it was Colin Edwards) stating that the rear wheel spins something like 15 mph faster than the front (when the front wheel is on the ground... smartass ).

EDIT: Alright, 5 mph seems to be a bit of an exageration, at least with the FO8 at medium downforce. The image attached shows an FO8 approaching T1 at AS Historic with medium downforce at 280 kmh with the rear wheels spinning at 283 kmh.

Yep, i'd go with that too. The FZR tends to understeer until you wear the
rears from powerdrifting, which is what the FZR does. That means that the
front tires get little load on acceleration and that the rear tires, on top of
getting the load the front aren't getting, tend to wear faster bacause they
are the driven wheels. All this points to more 'scrubing' on the rear tires
which would remove dirt. Test out the opposite, a UFR should provide the
opposite situation where the front tires usually get worned out fast while the
rear could go on forever if driven properly. Driving the same course, you should
see the dirt come off the front tires first. That would show if we are indeed
interpreting LFS correctly.

Couldn't this just be related to the toe settings for the wheels? I can only assume more toe-in or toe-out is going to give more scrub and so quicker cleaning of dirt and higher temps from just driving in a straight line.

Maybe try setting the toe to 0 front and rear, and see if the same thing happens.

Well, yes, anything that generates 'scrub' will clean the tires.
Setting the toe to 0 would be a good way to verify indeed.

Yeah, but the scrub caused by a 500hp engine trying to rotate the rear wheels is vastly greater than the scrub caused by a fraction of a degree of toe, so I dont think you'd see much difference.

A clearer test might be to jump in the FXR, and do the same test three times, one with all the power to the rear, one with it all to the fronts (euch) and one with 50-50, and see what difference it makes.