Jerry cans can currently fit into the hunting bag (taking up all of it's space) as well as the mountain bag (leaving 5 slots left in the backpack). Tires are still pretty huge, but you wouldn't realistically be able to fit the tires into a backpack in real life.

You are totally correct. However, in the end Dayz is a game and I personally felt first time that I was "wasting time" while looking/carrying tires for several hours (eventhough in dayz I have been just running around for hours and hours before quitting without anything "exciting" happening.) Sacrificing backpack slots for a tire is in my opinion a pretty fair trade. Alternate opinions/ideas about this mechanic are most certainly welcome.

DayZ is a hardcore game thats the key difference. Its about realism and its part of what makes DayZ exciting and unique. Doing anything in the game takes a lot of time so when you are faced with a PvP situation its intensity is much higher than any other game.

The tire or jerry can sizes should not decrease. It is realistic, no way would you be able to fit a tire into any backpack. If the Devs really wanted to assist in this situation then maybe they can add a craftable tire carrying kit with rope or something. Hang 1 around your back (although this would be pretty uncomfortable in reality) or perhaps make a sled to be able to lug more than 1 tire around. But I doubt the latter would happen.

As it is now is not too bad. Getting a vehicle working is very much so an "end-game" thing. Its another task that you can decide to do and it shouldn't be easy.

Just Changed to winter tires this morning at my OWN car. I took two tires, one in the left and one in the right hand and brought them to the vehicle.

In dayz you can ony carry one tire? Lacking realism at this end it is as the author mentioned. Took me the whole day to get all truck parts & tires while me running around the world map with only one tire per run. A little frustrating....