tire size

hey guys and gals tried searching a bit but have found little info other than dont go much bigger than 3 percent on diameter increase. I have a 95 660 cc hijet 3 way dump getting loaded on the boat in Tokyo next week but have already picked up a set of 13 inch mags off a 81 rx7 for 100 bucks so i couldn't pass them up even not having the truck yet. Now i am looking at tire options. the stock 145 are like pizza cutters and mismatched and worn out. Found that some weight a 91 Subaru Sambar stock steel 12" rim c/w 6ply 145/R12 LT Yokohama = 21.5 lbs each. the mags came with 215/60r13 bf t/a radials and rim and tire weigh 32 lbs. but i have read on the rx7 forums that the stock rims are 12.5 lbs. i am looking at tires sized 175 to 205. the rx7 ran 5.5"x13" 185/70 HR 13 stock and i have read that they weigh around  26lbs with the rims. That would be only a couple pounds heavier but that weight would be all out at the outer edge of the tire.   In Canada we have less options for 13 inch tires these days and they are not as cheap as in the usa.

i have used an online tire calculator
i am looking at the 185 or 195 60's or 175/70's

                                  145/80-12 175/70-13     Difference
Diameter inches (mm) 21.13 (536. 22.65 (575.2) 1.51 (38.4) 7.2%
Width inches (mm) 5.71 (145)   6.89 (175)        1.18 (30) 20.7%

                       145/80-12        185/60-13          Difference
Diameter inches (mm) 21.13 (536. 21.74 (552.2) 0.61 (15.4) 2.9%
Width inches (mm) 5.71 (145)        7.28 (185)        1.57 (40) 27.6%

                                145/80-12         195/60-13         Difference
Diameter inches (mm) 21.13 (536. 22.21 (564.2) 1.08 (27.4) 5.1%
Width inches (mm) 5.71 (145)         7.68 (195)         1.97 (50) 34.5%

                                 145/80-12            205/60-13   Difference
Diameter inches (mm) 21.13 (536. 22.69 (576.2) 1.55 (39.4) 7.3%
Width inches (mm) 5.71 (145)         8.07 (205)         2.36 (60) 41.4%

i know these numbers may not hold true between different tire manufactures. I am curious to know the average weight of all 3 of them. As i don't want to heavy of a tire as i am worried the little 660 will not be able to keep spinning them on the top end. i know that the issue is the weight of the tire is farther out giving it more of a moment arm and requiring more torque to turn. Most times the truck may have to get on a highway for 5-10 minutes at a time on my trip to work and yes i will be passed a lot. rest of the times we will be driving on roads that the speed limit is 60-80 kph. how will the the wider tire affect the weight in the steering wheel? there is no power steering on it and it will be used by my wife when we go off the pavement. she will have our 3 year old and I will be riding my f650gs. we also have 56 acres of land also that is only 1km from our house on pavement and the rest is gravel so i am looking at putting atv tires on the stock 12 inch steelies down the road for when we go there to clear lands. i was looking at the ALL TRAIL & ALL TRAIL II 23/8/12's. what is the difference between the all trail and the all trail II??

175/70/13's will rub on the front, mine's did, I now run 165/70's no clue as to weight, sorry.

i plan on putting springs under it to help with bottoming out and fit closer to the strut to give more clearance there lift it 2 inches total, no more as i dont want to bind the cv joints. Did you notice much change in handling, acceleration and top speed once going to the 165/70r13's ?? as the caculator says that they are 4.5% taller than the stock 145's

145/80-12 165/70-13 Difference
Diameter inches (mm) 21.13 (536. 22.09 (561.2) 0.96 (24.4) 4.5%
Width inches (mm) 5.71 (145) 6.5 (165) 0.79 (20) 13.8%

oh and thanks for the reply

Don't know about your type of Hijet but the largest width fitted to European Hijets seems to be 165.

The 993cc SE version came with 165/70R13 tyres and is a passenger vehicle with three rows of seats. Fitted with car tyres as standard it handles pretty much the same as a normal car and is very good at catching up with more modern cars on twisty roads. However, I somehow don't think you will be going that far!

Unsure about the offset but I think it is 45. More information on www.hijet.de where he has gone into it in some detail.

its a jdm inport and the rx7 rims are 50mm offset so it will make the wheel base a bit wider over the stock for sure plus the added contact patch.