this is something that is bugging me for a long time already, so though i will write it here hoping some of you will take this advice.
When you do a texture ("skin") for any model in mxs (rider, track object, etc....including norm/spec maps) please make sure you save it in 8bit mode. There is hardly any visible change and the files size can be reduced about 40%. That means the game needs less memory to load all the textures and the textures takes less hdd space as well.

More info here if you are interested
For example the team trucks that are placed on the outdoors tracks currently are in 16bit mode. I had problems with some of the FAMmx series tracks and when i resaved the textures in 8 bit problems were gone.
Same goes for gear set, lots of them lately are saved in 16bit color mode...and when i get a pack of textures for a render of one single rider that is 70 Mb its just ridiculous
I really hope some of you will read this and follow it.
Thanks for all the great creations you guys do for this game!